19Perfumes in Detergents

John RamsbothamInternational Flavors and Fragrances, Hilversum, The Netherlands

I. INTRODUCTION

The word "perfume" is derived from the Latin roots "per" and " fumum," which togethermean "through smoke." This is indicative of the practice of burning incenses and spicesto produce odorous smokes in religious festivals. The term "fragrance" is used synony­mously with " perfume" in the detergent industry and this convention is adopted here. Theimplication of the Latin root of fragrance is a " sweetness of smell," which is perhapsmore descriptive of the functional use of perfumes in products than is the term "perfume. "

The importance of fragrance to a detergent product 's commercial success is virtuallybeyond question. If something does not " smell right " or laundered clothes do not smellfresh once washed, a consumer will very likely not repurchase a product no matter howclever the technology which it contains. Many chemists appreciate that something is nec­essary to cover product base (mal)odors but quite how this is achieved remains somethingof a mystery. In fact, a more technical product development often runs the risk that theaspects of (mal)odor are regarded as some sort of irritation which can be put off until amarketing department decides that a launch date is in sight. At this late stage in the day,a perfume house can find itself impossibly short of time to create a fragrance which istechnically stable , does not destabilize the product, successfully masks all base malodorsand is aesthetically acceptable. This review examines all the technical aspects behindperfume creation.

Something of the nature of perfumes and the perfume industry is revealed in the factthat perfumes are complex blends of volati le organic chemicals. A detailed discussion ofthe individual perfume chemicals is outside the scope of this review, but excellent textsare available which itemize the ingredients in common use by perfumers [1] and theirunderlying individual chemistry [2]. At this early stage of the review, suffice it to say thata perfumer can access several hundred ingredients stretching across most classes of organicdetergent chemicals. It goes without saying that these can potentially interact with eachother and with the product base in a variety of chemical reactions. Interactions can beadditionally complicated by a variety of solvent effects. In short, the more " technicallycomplex " a base is in terms of physical structure and/or chemical composition, the morelikely it is to be difficult to perfume. The complexity of this part of the creative processis all too frequently underestimated by outsiders to the industry.

The perfume industry is almost as mysterious to outsiders as is a perfume itself.Many perfume houses are not public companies and, consequently, do not publish annual

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reports for shareholders. The top four companies operating on a transnational basis insupplying perfumes to the detergent industry are International Flavors & Fragrances, IFF(U.S. public company), Givaudan-Roure (part of Hoffman-LaRoche, Switzerland),Firmenich (private company, Switzerland), and Quest (lCI). Of these, only IFF issues anannual report for shareholders from its New York headquarters. P&G, Henkel , Colgate ,and Kao are examples of firms with in-house perfumery groups catering exclusively orvirtually exclusively for the company needs . There are many more national and smallertransnational companies. Readers interested in this aspect of the industry are best advisedto contact the individual companies themselves; comparative publications are few and farbetween and the most recent are those by Unger [3]. However, in recent years, there aresigns of more openness from the companies on their activities and the situation sketchedhere could change.

Key players in the detergent industry are global operators, and once they have in­vested in a fragrance, they need to be able to obtain it reliably around the world in anidentical form on each delivery and in sufficient quantities. This clearly implies that amajor fragrance house also has to have an efficient global operation along with very highstandards of quality control in manufacturing and raw materials. The raw materials ofperfumery extend across natural and synthetic products and it will be appreciated that afragrance house needs to obtain these to a constant high specification, which includes odor.To this extent , the perfume industry has an extra dimension beyond that of the fine­chemical industry. Against the background of these remarks, it can be appreciated that themajor perfume companies also manufacture speciality raw materials used in their creations.Although many of these are manufactured by one company and sold to others, the per­fumers of the company having immediate access to key specialities often have an inherentprice advantage over their competitors. From a customer point of view, an importantimplication of this is that a competitor seeking to imitate a fragrance in a product will notbe able to do this at a price advantage using the same key ingredients as the original andmake a viable return. Invariably, alternatives or cheaper compositions will have inferiorperformance standards to the original perfume. A fragrance created for a customer isnormally the exclusive property of that customer unless otherwise agreed and will not besold to other customers.

It is to the advantage of both the perfume house and client to have a clear modusoperandi. The following discussions will hopefully make it abundantly clear that a situationin which the perfume supplier has full access to both the detergent formulation and detailsof the production process is ideal. Although major companies are coming to recognizethis, there is still a widespread reluctance to reveal more than sketchy details and evensometimes release the base with which the perfume house is to work. Without belaboringthe point, one major reason for this is a failure to realize that a fragrance has a technicaldimension alongside the obvious artistic one. Simply bearing in mind that one is dealingwith a blend of volatile organic chemicals focuses the thoughts in many cases. Some yearsago, discussions in the industry gave rise to a series of articles dealing with the sort ofinformation which should be exchanged in "perfume briefings"; it is still instructive toread through these as a guide to structuring one's own thoughts [4]. Having said all this,revealing information on products and processes involves professional trust which needsto be established. Patents (applications) when available invariably solve most queries oftechnical information.

At least part of the reason for a perfume not being viewed as a technical componentof a detergent formulation is that odor does not lend itself to being quantified by somesort of physical measurement. Moreover, although analytical techniques permit constantlybetter analyses of compositions to be obtained, one should never lose sight of the fact that

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a consumer is indeed purchasing performance in terms of smell and not a weight loss orgas-liquid chromatography trace. Thus, although some fragrance compositions may mod­ify in technical terms during storage as a function of time, it is quite possible that this hasbeen allowed for by the perfumer to achieve a particular organoleptic result. One well­known perfumer in the detergent industry once remarked that a totally stable fragrancewould never win a market test! Perhaps this is going too far, but his sentiment would beunderstood by many perfumers. This fact, coupled with the difficulties in describing odorsonce one gets beyond direct comparisons such as "it smells like oranges," only serves toreinforce the concept of a perfume as being somehow not really a component with "tech­nical properties." The jargon in a fragrance house which enables perfumers and odorevaluators to talk to each other basically draws heavily on analogies with the senses ofsight, touch, and hearing. Universally, volatile components of a fragrance are referred toas top or head notes, whereas increasingly less volatile fractions are typified as middleand base notes-analogies with music . Yet again, alongside more obvious verbal descrip­tors such as "sandalwood," "woody," or "musky," one will come up against expressionssuch as "very green."

The description and classification of perfumes is a study in itself, as is the importantrelationship between odor and color. Most major fragrance houses have their own viewson these important topics, but an excellent book which gives general insights into manyof these creative aspects of perfumery remains that by Wells and Billot [5]; a recent volumefrom Calkin and Jellinek reveals much of modern perfumery [6].

Once you have found a perfume house and decided how to brief it, all that remainsis to select the winning fragrance. Here again, we come up against all the subjective andartistic properties of smell, assuming that any technical problems have been resolved. Mostperfume suppliers will be quick off the mark to convince you that their creative methodsare the ones to go with via a convincing presentation and maybe even glossy literature.The fact remains that it is something of a gamble on which the perfume house does itsbest to shorten the odds! Perfume houses invariably work in competition with other houseson a "no cure, no pay" basis and a poor record is quickly punished. Any attempts to goin for these fabled massive profit margins which perfumes are popularly supposed tocommand will also reap a quick retribution either from competitors anxious to undercutthe price or from the purchasing department of the customer armed with a report from hisanalytical department who will want to know what is going on. Sophisticated analyticalequipment, an experienced analyst, and the actual sample of fragrance oil can reveal manydetergent fragrance formulations to >90% accuracy nowadays. A perfumer creating fordetergent and household products invariably has a maximum amount of money he can"spend" per ton of product. Whereas he needs to meet all the technical and aestheticdemands put upon him, he also needs to remember that manufacturing time and complexitycost money. This almost forces him to create as simple a composition as possible, naturallymaximizing the content of his company's specialities.

Having rather flippantly compared the process of actually selecting a winning per­fume to a game of chance, this should not be interpreted as implying that the creativeprocess itself leaves very much to chance . The actual creative team comprises perfumers,odor evaluators, and applications chemists. It is the job of the chemists together with theperfumers to ensure that a creation is technically sound; these aspects will be discussedin some detail in the following sections. Once a perfumer is clear as to which chemicalshe is free to use, it is up to him to create the fragrance. Most major companies now havea department of odor evaluation experts who are highly trained in monitoring the(comparative) behavior of fragranced products in use. In the case of laundry detergents,for example, they are fully familiar with market trends and tastes in the product categories

694 Ramsbotham

involved. This extends to laundering habits, machines used, the location of the machines,and so forth. It is the job of the odor evaluators to evaluate products under as near actualin-use conditions as possible and provide information to the perfumer on where his creationcould be improved. Very often, perfumers will, in effect, be competing with each other aswell as against leading products from the target market(s). Fragrance performance at allthe so-called "magic moments" of product usage starting when the product is put into awashing machine right through until laundry is stored in the closet are critically evaluated.As if this is not enough, confirmatory market testing will also be conducted in some cases.

While the perfume selection and creation is going on, chemists will be subjectingcandidate submissions to all kinds of (accelerated) stability testing in an effort to ensurethat neither product nor fragrance are unacceptable or incompatible with each other.(Designing and translating information into realistic data is something on which a bookcould be written.) In the light of all this test work, it is clear why fragrance houses canmake demands for large amounts of product base and packaging and will need to knowmarketing plans and product positionings when working optimally.

Fragrances have a long history of safe use and the industry has had the foresight toset voluntary stringent standards for itself in this respect via the Research Institute forFragrance Materials (RIFM) and the International Fragrance Association (IFRA). All themajor fragrance houses are members of these organizations and conform to their standards.Deeper insights into the workings of these international bodies and how they interfacewith national organizations are given in review articles by Schrankel [7], Jackson [8], andStofberg [9]. The success of these bodies in regulating the registration of new fragrancechemicals and acting upon any findings which set existing compounds in an adverse lightis evidenced by the relative lack of controversy around perfumes. In addition to safetyand toxicity issues, IFRA also helps to set professional norms within the industry bydefining guidelines on issues where national legislation is rather vague; a typical case inpoint is a "Statement on Natural Perfumes," Information Letter 325. This effectivelyprevented a potentially unedifying situation whereby all sorts of "nature-identical" andperfumes containing "significant quantities of essential oils" were all offered as "naturalperfumes" within the widely differing norms of different national legislations.

Of the reviews cited in the previous paragraph, that of Schrankel broaches the topicof the environmental fate of perfumes. This very topic was the subject of IFRA InformationLetter 337 issued in 1990. This letter itemizes reasons why perfumes are not likely toaccumulate in the environment or disrupt environmental equilibria under likely conditionsof use. However, in recent years, the qualitative assurances set out in this letter have runinto the quantitative requirements of environmental labeling schemes. Invariably, theseassign some sort of "score" to the ingredients in a product which relate to the speed andextent of the biodegradability of the components in the environment. Although perfumeingredients are fairly simple organic chemicals with molecular weights invariably belowabout 300, there are literally thousands of them. Quantitative data on all their individualbiodegradation characteristic, impact on aquatic organisms, and so forth are simply notavailable and one unfortunate consequence of this is that perfumes are generally given themost pessimistic score possible. This clearly poses a major problem for the industry anda professional unified approach from IFRA is now needed. In 1994, Information Letter444 entitled" Environmental Impact of Perfumes-Cradle to Grave Assessment" probablysignaled some early moves on this issue. It goes without saying that if some satisfactoryagreements/data are not forthcoming to resolve this issue, particularly if eco-labels becomeof significant commercial importance to detergent products, then it could provide theimpetus for the perfume industry to develop in some novel directions. For example, de-

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veloping fragrances and/or ingredients which deliver acceptable organoleptic performanceat much lower concentration in products than is currently the case would be one way tominimize the volumes of fragrance used and thereby obtain more favorable "scores" underthe latest European community eco-label legislation [10].

Environmental questions are as much a topic for debate in modern perfumery as forother branches of the detergent industry. This simply underlines the fact that fragrances,although frequently falling into the category of formulation "minors," can have quitemajor impacts on products. The following sections now explore the technological impli­cations of some of these impacts.

II. CHEMICAL AND PHYSICAL PROPERTIES

As was intimated earlier, a perfume is a blend of volatile organic chemicals which rangeup to molecular weights of about 300. In principle, these chemicals can contain one ormore of the functional groups, which are dealt with in any basic text on organic chemistry,ranging from aliphatic hydrocarbons, alcohols, and aldehydes to terpenes. They also covernatural extracts or "essential oils" which are invariably themselves mixtures. The deter­gent perfumer will generally create a composition using between about 20 and 100 ingre­dients , which is invariably much less complex than the "fine fragrances" in cosmetic uses,which can extend to several hundred components. It will come as no surprise to learn thatsignificant interactions between these components can occur, which can, in turn, haveconsequences for the odor of a fragrance and the way in which it interacts with productand package .

A. Chemical Reactions in Perfume Oils

Anyone who has purchased a fine fragrance or cologne will be aware that as the partlyused bottle stands on the dressing table, the contents darken in color with time. Blakewayand his co-workers have written one of the most comprehensive published studies of thisphenomenon in recent years [11]. This publication quantifies more general comments madeby Conover [12], which contains useful references to earlier work. Most of the data areof general relevance to perfume oils and emphasize the need for protecting some rawmaterials such as terpenes against (auto)oxidation reactions. However, reactions are notlimited to oxidation and the following schematic equations summarize the kinds of inter­actions which proceed to an equilibrium:

RCH2.CHO + R'.OH

OR'/

RCH2·CH

"" OH

hemIacetal

ester exchange

-CHO + NH2 ~ -CH = N- + H20

Schiff's Base

696 Ramsbotham

Any Schiff's base formation in a perfume itself is brought about by the deliberate inclusionof methyl anthranilate in the mixture. Work published almost 50 years ago by Wells [13]reviews some interesting Schiff's compounds of use to the perfumer. For the chemist, itis important to note that the formation of a Schiff's base can be quite slow and thecompounds can be highly colored. Perfume oils delivered to a detergent manufacturer willbe stable and matured, such that the consequences of the reactions reviewed in this sectionshould be somewhat academic. However, autooxidation reactions such as

[0]>

d-Limonene carvone carveol

can become significant if the protective effect of antioxidant is removed by effectivedilution following inclusion in a product. Proctor and Gamble (P&G) has even taken outa patent in this area for adding extra antioxidant to dishwash liquid to stabilize terpene­rich fragrances which otherwise can autooxidize and result in the "necking" or " panel­ing" of flexible plastic containers [15].

B. Chemical Reactions Between Perfumes and Bases

The chemical reactions described in the preceding section can all take place when one ofthe reactive groups is present in the perfume and the other in the product base. Generallyspeaking, the perfumer will do his best to avoid such interactions and it is, therefore ,helpful for him to have a detailed knowledge of the product being perfumed. Problemsmost often arise due to the presence of small amounts of impurities inadvertently intro­duced when compounding the base; this is where a knowledge of product raw materialcomponent specifications and production processes is helpful. For example, discolorationswhich slowly intensify when a perfumed product is stored alongside an unchanging, un­perfumed reference can often be traced back to Schiff's base formation between perfumealdehydes and some -NH2 group present in a base component. Perfume chemists seemto develop a sort of sixth sense for this type of phenomenon and increasingly sophisticatedanalytical techniques prove an invaluable aid to troubleshooting. Some idea of the chem­istry involved can be obtained from a study of perfumes and color reactions in soappublished some years ago by Pickthall [16] which introduces other reactants such as heavymetals . Iron is particularly associated with forming colored complexes with some fra­grances.

Detergent bases themselves naturally have a pH when in aqueous solution. For thepurposes of a perfumer, even powders must be considered as entities which are highlyconcentrated aqueous solutions in their packaging. During storage and in use by the cus­tomer, small amounts of moisture in a powder behave effectively as concentrated solutionsas far as the fragrance is concerned. Having said this, it will be appreciated that productpH is a key property when deciding which perfume ingredients can be used; pH-relatedreactions such as ester hydrolysis, aldehyde condensations, and so forth all come into play.Pragmatically, a product base falling in the pH range 4.5-8.0 will permit a perfumer toutilize practically all the chemicals at his disposal. The choice falls off sharply on goingfrom pH 8.0 to 10.0 and from pH 4.5 to 2.5. This fall accelerates even more sharply from

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pH 10 to 12 and from 2.5 to 1.5 to leave a situation in caustic soda or mineral acid-basedcleaners where only about 25-30 perfume chemicals are left for the perfumer. Consider­ation of these ranges reveals the importance of the pH of the detergent formulation to thecreative flexibility of the perfumer. Modern heavy-duty laundry powders in the pH rangeof about 9.5-11.0 vary quite markedly in their reaction to perfumes but can never offerthe perfumer the creative flexibility possible in fine fabric or some "color care" productsof pH 9 or lower. Similarly, the switch from fabric rinse conditioners of pH 5-6.0 to so­called ester quat formulations of <pH 3 presents perfumers with complex creative prob­lems.

Alongside the acidity or alkalinity of a base come the problems associated withreactive chemicals such as hypochlorite bleach, peroxygen salts with various activators orcatalysts, and even the residual esterase activity of some enzymes. Here again, a knowledgeof the product composition and perfume chemistry help to avoid problems associated withperfume deactivation of the detergent formulation. However, it is fair to say that the pHis the major determinant of which fragrance materials can be used.

Although it is a fact that the perfumer can use computerized databases and theoreticalconsiderations to rule out numbers of chemicals which will definitely not be stable in aparticular formulation, restricting a perfume to only components which are individuallystable in the formulation is widely agreed to run the risk of winning a test with the chemistsbut not with the consumers! For this reason, an important aspect of creating a perfumefor a new detergent formulation involves discovering "synergisms" which permit a per­fumer to utilize chemicals which, although not totally stable when tested alone, are ac­ceptably stable once combined in a perfume composition. Fragrance raw material inter­actions of the type discussed in Sec. ILA offer some explanation for this phenomenon.This particular aspect of fine-tuning a perfume obviously needs great care and evenchanges in tetraacetyl ethylene diamine (TAED)-perborate bleach ratios can influence this.In the same context, the advantage to a perfume house which has a good range of specialitychemicals which are stable in aggressive bases and give odors otherwise unattainable isclear.

Chemists and technologists always do well to remember that consumers are pur­chasing smell and product performance, not technical features such as perfect "weight­loss-as-a-function-of-time" properties. There is an obvious desire on the part of the chem­ists to achieve a degree of technical perfection which a perfumer may find less necessaryprovided he can deliver a certain "smell experience" within the commercial lifetime of aproduct. It goes without saying that the technical performance of the product itself shouldnot suffer by this. In short, a perfumer may decide that a certain quantity of afragrance component can be lost by decomposition due to instability, but that a sufficientamount of the component will remain to deliver the nuance which is key to the perfor­mance. Another variant on this practice involves the deliberate creation of in situ chemicalsin a base. As an example, in the days of hypochlorite bleach liquors with 8 - 10% availablechlorine, some perfumers were known to take the view that a small amount of hypochloritecould be used to deliberately produce chloroform with primary or secondary alcoholsadded as perfume components. This gives a pleasant, characteristic sweetness to the fra­grance note. It goes without saying that such a practice is no longer commercially feasible,not to say environmentally responsible in the light of absorbable organic halides [17]. Inconclusion, the point being made is that an analytical chemist's view of chemical stabilitymay not always coincide exactly with the actual properties of a commercially successfulfragrance.

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C. Physical Chemistry of Perfumes

Reflection on the potential properties of a blend of volatile organic chemicals will quicklylead to the conclusion that one could expect some sort of solvent effect of perfumes indetergent bases. This is indeed the case and one should be on the lookout for viscositychanges and their consequences in liquid formulations . These consequences can be quiteserious in liquids where a degree of structuring is present to hold insoluble componentsin suspension, such as is the case in a cream scouring formulation or a zeolite-built laundryliquid. If a fragrance is simply postdosed to such products, one can encounter phaseseparation, which renders the product unusable without a plaintive " shake well beforeuse" warning. Cooperation between product formulator and perfume chemist is called forto adjust the structurants in liquids to allow for the effects of fragrance.

The expression " perfume oil" also implies a measure of insolubility in water.Whereas some compounds such as phenyl ethyl alcohol (rose odor) and some more polaraldehydes are significantly water soluble, perfume oils are generally hydrophobic in nature.This can become important when fragrancing products with a significant oleophilic phase,such as concentrated dishwash liquids or fabric rinse conditioners with a significantliposorne-like micelle structure [18]. Fragrance tends to migrate out of the aqueous phaseand concentrate in the oil phase. In the case of a simple micellar-type solution such as adishwash liquid , a result of this is that the fragrance note from the bottle seems to weakenas a function of time as the migration process takes place. Components which go to makeup a classic citrus note will exhibit this property to an extreme, being particularly hydro­phobic. If the freedom is present to opt for other odors built up of less hydrophobicmoieties, this phenomenon is less pronounced. It goes without saying that when theseconcentrated formulations are diluted into water, the fragrance does "burst " out. In asense, this is a sor t of inherent microencapsulation process. In the case of the rinse con­ditioner or liquids having liposorne-like structures with alternate oil and aqueous phases,the migration of fragrance can simply break up the structures to such an extent that phaseseparation occurs. The solution to such a situation is often to add the fragrance at the sametime as the structure is being formed, so that an equilibrium situation establishes. In short,fragrance oil is not always best stirred into a product as the final manufacturing step wheneverything has cooled.

The ability of a perfume to partition itself within a structured liquid can be used toincrease product viscosities. The technique here invariably involves incorporating com­pounds which can form hydrogen bonds with each other such as alcohols. Detergentformulators will probably be most familiar with this technique in the form of addingglycols to low-active DTDMAC rinse conditioners. Although similar solvents can be usedwith perfumes, a more elegant illustration of viscosity boosting by fragrance is given bythe use of perfume tertiary alcohols in hypochlorite bleach formulations which are thick­ened by an amine oxide-based surfactant system. Presumably, the alcohol groups enhancehydrogen-bonding between the amine oxide micelles and mention of this is made in thepatent literature [19].

The way in which a perfume partitions itself can also have important effects on itsin-use performance, and although this topic will receive attention in Sec. VI, some generalguidelines are relevant here. If a perfume is required to perform an air-freshening functionin something like a toilet bowl cleaner, care needs to be exercised that fragrance is not soefficiently solubilized by the formulation that the great majority simply washes down thedrain . Analagous rules apply to laundry care products, where affini ty for cloth is paramountto ensuring a good "freshness" after clothes are cleaned. As in many areas of perfumery,

Perfumes in Detergents 699

although a lot of theoretical predictions can be made to approach a desired goal , fragranceoptimization invariably depends on pragmatic in-use evaluations using the formulator'sactual base .

Having dealt with fragrance solvent and partitioning effects, it is salient to examineaspects of fragrance volatility. The evaporation rate of an organic chemical in a mixtureis proportional to its partial vapor pressure, which is expressed by the following equationderived from Raoult 's law:

P, =P?f,ni

where Pi is the partial pressure in the mixture, p? is the vapor pressure of pure product,I', is the activity coefficient of the component, and n, the mole fraction in the mixture.Values of p?are fairly readily available and a knowledge of the composition of the perfumeleads to values for 1I i' Activity coefficients present the first hurdle because they can beenvisaged as correction factors relating to the departure of the behavior of a substance ina blend from its " ideal" behavior when pure. For example, alcohols exhibit a fair degreeof structure forming by virtue of hydrogen-bonding. The extreme example is water, whichcan be envisaged as the first alcohol in a homolous series-s-H: OH, CH30H, CH3 • CH2 '

OH, and so forth. Without hydrogen-bonding, one would expect it to be a gas at ambienttemperatures. When alcohols are blended with other organic chemicals such as hydrocar­bons and esters, the hydrogen-bonded structures are partially broken down, and this isreflected by values of activity coefficients which are higher than 1.0. Some of the mostnonideal blends comprise hydrocarbons and alcohols, and values of r can be as high as5 or more . In practical terms, the implication of this is that the actual volatility of analcohol in a blend with hydrocarbons can be considerably higher than one would expecton the basis of its vapor pressure as a pure substance. It will be appreciated that thecomplex nature of fragrance blends renders any calculations of their actual vapor com­position at any time extremely complex, although the basic ideas are confirmed by analysis.In addition, there is no simple correlation betw een vapor pressure and perceived odorintensity. In short, the design of commercially successful perfumes by computer is a verylong time away. Having said this, attempts have long been made to rationalize physicalchemistry and perfume performance and one of the most comprehensive published reviewsremains that of Louis Appell [20].

Most recently, P&G has incorporated some of the preceding ideas into patent appli­cations relating to fragrance design. They propose, quite logically, that for a fragrance toperform from cloth after a laundry treatment, substantivity of the ingredients on the clothis necessary. Accordingly, they suggest that octanol-water partition coefficients be usedas a measure of hydrophobicity and boiling points as indications of volatility, and thatthese are key arbiters for substantivity in numerous products involving washing and rins­ing, as is the case in detergent applications [21]. So-called "enduring perfume ingredients"are defined as having boiling points in excess of about 250°C and a water insolubilityexpressed in terms of the logarithm to the base 10 of an octanol-water coefficient ex­ceeding 3. The patents contain extensive illustrative data but, unfortunately, do not extendtheir discussions to encompass a consideration of odor thresholds alongside these physical­chemical criteria. In cases where the fragrance is required to " burst" or "bloom " froman aqueous medium, such as in toilet bowl cleaner detergent compositions, the water­insolubility criterion is combined with a boiling-point requirement of less than about 260°C[22] .

Before leaving a consideration of physical properties of perfumes, it is noteworthythat some perfume compounds such as heliotropine or benzophenone are highly viscous

700 Ramsbotham

liquids or even solids in their pure state . Handling is often facilitated by using them insolution and, to this end, odorless solvents such as diethyl phthalate (DEP) or dipropyleneglycol (DPG) are used. Yet again, some compounds such as skatole are only used at verylow concentrations and need dilution with solvents to enable accurate handling and weigh­ing. In short , solvents in modern perfumery have a very functional purpose and are notsimply present as cheap diluents.

D. Microencapsulation and Absorption

In the light of the comments in Sees, II.B and II.C, the attraction of techniques for pro­tecting perfumes in chemically hostile bases and delivering them where and when theyare needed is overwhelming. The fact that there are so few detergent products whichemploy microencapsulated perfumes indicates that achieving these goals by perfume en­capsulation is not as successful practically as we would like. The allure of the encapsu­lation technique is evident from the massive open and patent literature on the topic andthe object of this section is to summarize where perfume microencapsulation in detergentproducts could be applicable.

Fragrance absorbed or contained in a matrix in the form of a microparticle can beprepared in numerous ways, such as spray-drying, spray-chilling, drum-chilling, cryogrind­ing, coacervation, and so forth. These processes naturally put a price premium on thefragrance which has to be justified by some sort of perceivable performance benefit. Fra­grance slowly diffuses out of most microencapsulates during the storage of a product. The"leaked" fragrance is then exposed to any potentially aggressive chemicals in the base,which often negates any major stabilizing effect of the microencapsulate. If a fragrance­impervious encapsulate is used, one then has to consider the question of to what extentthe product needs additional conventional perfuming for "out-of-the-pack aesthetic pur­poses." The slow diffusion of fragrance from microparticles is sometimes claimed topromote perfume longevity or substantivity on a substrate. Practical evaluations of prod­ucts often reveal that the levels of perfume emitted are, unfortunately, too low to be readilyperceivable even though prolonged emission is indeed achieved . Finally, a point which isoften overlooked, is the fact that a skilled perfumer can achieve quite surprising perfor­mance standards using his "conventional" technology.

Observations such as those in the preceding paragraph lead to the conclusion thatmicroencapsulated fragrance in detergent products will probably be employed to addresssituations where the use of a liquid perfume oil is a problem either to the product or theprocess or where some sort of "trigger" releases fragrance at an appropriate stage inproduct usage, thus avoiding premature perfume loss. An example of where a liquid fra­grance could be a problem is to be found in the compact laundry detergents. Bulk densitiesare ever-increasing and this is reflected in considerably less porous products. Moreover,the replacement of compounds such as sodium perborate monohydrate by sodium percar­bonate represents the removal of a relatively efficient absorbent by a nonporous entity.Fragrance conventionally sprayed onto such mixtures will take increasingly longer to soakin and one solution to this manufacturing problem would clearly be to supply the fragrancein a solid form. The problem of handling fluid components (i.e., fragrance and nonionicsurfactants) in this context has recently been reviewed [23]. The basis of the technique isthat fragrance can be readily absorbed on a wide range of inorganic solids, particularlyaerosol silicas and zeolites, as has been described by several authors [24-28]. It goeswithout saying that one would be looking for the minimum retention of fragrance in theabsorbate or encapsulate once the product was used. In this context, the destruction or

Perfumes in Detergents 701

"activation" of the perfume carrier by some sort of "trigger" clearly offers a solution toany problems of retention.

There are basically two triggers for detergent products-moisture and heat. Moisturein the form of sweat has been successfully exploited in deodorant formulations, but thescope is much wider, as Miles has pointed out in an article on the topic of moisture­triggered encapsulation systems for fragrances in household and personal product [29].The same trigger is commercially exploited in tumble drier sheets by P&G and a char­acteristically comprehensive patent series dealing with the use of 13-cyclodextrins as clath­rates in this end use has appeared over recent years [30]. Significant quantities of perfumeare clathrated or "trapped" in the cyclodextrin, which is, in turn, entrapped on cloth[31,32]. Subsequent exposure of a towel to moisture or clothing to sweat is claimed to besufficient to release a burst of fragrance. The concept of using heat as a trigger in tumbledriers where the heat of the drier accelerates perfume release from a wax has been men­tioned by Unilever [33].

Numerous other claims for encapsulated fragrances are found in the literature in arange of detergent formulations. However, the conspicuous lack of products utilizing mi­croencapsulated fragrance is evidence of the difficulty in achieving acceptable cost/performance figures. The concentrated or compact detergent powders probably signal onepossible point of breakthrough for encapsulation technology, particularly where consumersdemand a high level of perfume on cloth. Modern compacts are increasingly less porousand some have reached a stage where conventional perfume dosage is limited to around0.4 wt% if problems of manufacture or in-pack agglomeration are to be avoided. There isat least one major soaper who has addressed this dilemma by spray-drying a portion ofthe fragrance dose in a modified starch. This obviates problems of the type just referred to,as well as sidestepping the dilemma of overintense pack odors. The encapsulated fragranceis released into the wash liquor when water hits the powder and dissolves the starch.

E. Preservative and Antimicrobial Properties of Perfumes

One of the functions of essential oils in plants and herbs is to protect the vegetation againstattack by fungi and bacteria. This biocidal property of essential oils is well documented[34,35] and, not surprisingly, this activity is shared by a large number of synthetic fra­grance ingredients [36]. Efforts to utilize this activity have attracted continued interestover the years, particularly in personal care products, to make products free of proprietarypreservatives and utilizing the so-called "natural protection" of essential oils or perfumes.A recent paper has summarized the salient literature in this area and concludes after de­tailed tests that although it may be theoretically possible to use certain "cocktails" toobtain acceptable product protection, the limitations on perfumer creativity in terms of thechoice and high concentration of ingredients needed render the concept fairly impractical[37]. Generally household detergent products have not attracted the same degree of atten­tion, although Unilever does consider the possibility in a patent [38] which places rathermore stringent constraints on perfume ingredient selection than prior art. The data indicatethat adequate preservative action of aqueous detergents could be obtained although per­fumer flexibility is clearly restricted. Perhaps the future lies in developing synergisticcombinations of fragrance and proprietary preservative [39].

F. Semlochemical Activity of Perfumes

Continuing on the theme of the previous section, essential oils produced by some plantsrepel predatory insects, whereas in other plants, oils attract insects to assist with pollina-

702 Ramsbotham

tion. This behavior-modifying or semiochemical activity of essential oils has long beenrecognized and a comprehensive compilation of the essential oils with an anecdotal historyfor repelling all manner of crawling and flying insects as well as the treatment of anystings and bites with essential oils has been published by WOTWood [41]. The various typesof mosquito represent one of the largest single categories of insect pest for which there isan interest in developing repellents. Citronella and lemongrass oils are widely reportedrepellents, with lavender, pennyroyal, tansy, and sassafras probably less recognized. Al­though there is no doubt that essential oils such as citronella work in the case of mos­quitoes, proprietary repellents such as diethyltoluamide (DEET) are generally considerablymore effect ive [42]. Having said all this, there are undoubted advantages to be had fromsemiochemical fragrances used either alone or as (synergistic) additives alongside chem­icals such as DEET in a range of products.

Reference has been made to individual essential oils and the patent literature extendsthis to combinations of oils which are perfumes in the sense of the technical definition­blends of volatile organic chemicals. Beldock and Beldock describe blends of at least0.01 % terpineol and citronella plus either similar levels of geraniol and/or rhodinol extra[43]. These chemicals can be used as well as a fragrance in insect -repellent lotions orsprays and favorab le comparative data against DEET-based products are presented. Claimsfor repelling mosquitoes and blood-sucking insects are claimed for blends of pennyroyal,anise , and chrysanthemum oils [44]. Emphasis is given to the fact that the combinationshave a pleasant smell in contrast to prior art. Implicit in this type of literature is the factthat some sort of synergy exists in blends . Further study of the literature in the generalarea also reveals that the synergy extends to activity in combination with DEET. Notsurprisingly, activity can be very concentration dependent and can be influenced by theproduct base itself.

Published data extending observations on the semiochemical nature of essential oilsto synthetic perfume ingredients are relatively scarce and are the virtual monopoly ofInternational Flavors & Fragrances. Reference 45 refers to earlier publications in describ­ing the use of some chemicals in soaps, polymers, candles, and detergent bars. At the timeof writing, the only significant detergent use of fragrance as a semiochemical is in hard­surface cleaners and is reviewed in a Lever patent application [46]. The reasoning is thatinsects such as cockroaches can be transporters of germs and, therefore, cleaners whichtend to repel them are desirable. Under sterile conditions with no food present, the patentdemonstrates that a level of more than 0.5 wt% limonene in a cleaner is sufficient to rendera surface totally undesirable to cockroaches relative to a surface not limonene treated . Thewhole picture becomes less clear-cut when food sources are introduced, when flying asopposed to crawling insects are considered, and when proprietary repellents are introducedas target standards.

III. PERFUME MODELS, STRUCTURES, AND JARGON

Consideration of the comments in Sec. II quickly leads to the realization that althoughtechnically helpful generalizations can be made to rationalize the behavior of a perfumein a detergent formulation , one needs to be very cautious when trying to make morespecific predictions based on the known behavior of individual perfume components. De­spite this somewhat pessimistic statement, there are some models used to portray perfumeswhich can be very helpful to the chemist when attempting to rationalize the behavior ofa fragrance. The basic model is that shown in Fig. 1 of a triangle divided into at least

Perfumes in Detergents

general increase inraw material price

j MIDDLE

BACK(substantivity)

rincreasingvolatility

703

Figure 1 Triangle model of perfume.

three parts to represent the major segments of a fragrance. The most volatile componentsused by the perfumer, such as low-molecula r-weight esters and aldehydes, are referred toas "top" or " head notes." These compounds tend to accumulate in the headspace ofproducts and play a major role in determining the initial impact of perfumes when aproduct is freshly smelled from its packaging. Generally speaking, these molecules haverelatively little affinity for substrates such as textiles and do not contribute much to thelong-lasting properties or " substantivity" of the perfume. This latter property is governedby the so-called " back" or " base notes " of the fragrance (represented at the bottom ofthe triangle). The compounds in this segment of the perfume are rather involatile. Theirmolecular weights can extend up to about 300 and, physically, some of them are almostsolid in their pure state. Between the top and base note components comes the body ofthe fragrance in the form of the " middle notes " which determine the character of aperfume. It goes without saying that the perfumer deals with much more detailed subdi­visions than this, but it is sufficient for technical purposes.

The reference to " notes" illustrates the difficulty in talking about odors, as directcomparisons with fairly well-known smells such as those of lemon or lavender are nolonger sufficient. One has to resort to comparisons involving the other senses. The use ofthe word " note" in the context of a perfume " composition" clearly draws analogies withmusic and the sense of hearing. The other common analogy is with colors and artistry­one frequentl y hears that a perfume has very " green" top notes. There is a complexjargon which perfumers use to describe the smells they have created; this jargon is nec­essary for communication with their colleagues when deciding on how modifications needto be made . One needs a common vocabulary to point to the relevant bit of the perfume.Here again , we come up against an area of perfumery which lies outside the scope of atechnical review. However, chemists interested in delving further into this aspect will findthat all the major perfume suppliers have genealogies to describe cosmetic or fine fra­grances, which include descriptors of odors. Some discussion is to be found in the varioustextbooks already cited , and Refs. 47-50 deal with various aspects of this topic in moredetail.

Returning to a consideration of the model shown in Figure 1, the volatility of theingredients increases as one goes from the base to the apex of the triangle, as one wouldexpect. Coupled with this , the less volatile a component is, the more complex its molecular

704 Ramsbotham

structure tends to be. In general terms, back note components cost a lot more energy tosynthesize and move around a perfume compounding plant than do top note chemicalsand this is mirrored in higher costs. The commercial consequence of this is that substan­tivity costs money and modifying perfumes to be more substantive in a very price­competitive product can present the perfumer with a lot of problems. Another aspect ofthis is that fragrances which do not need to be substantive, such as those used in dish­washing applications, are generally cheaper per kilo than those for a fabric rinse condi­tioner, for which "lasting freshness" is a key feature of the product.

Another way in which the simple triangular model can be helpful in anticipatingproblems was illustrated some years ago when a major manufacturer decided that a fra­grance being very successfully used in heavy-duty detergent powders should also be usedto continue the brand image in a new liquid laundry product. The liquid had a more neutralpH than a concentrated solution of the powder and aggressive chemicals such as bleacheswere absent. Quite correctly, it was reasoned that the perfume would be technically stablein the liquid and that a product launch should go ahead. It transpired that the level ofperfume used in the liquid to give acceptable out-of-bottle smells was around three to fourtimes the conventional dose for such a product. The reason for this can be illustrated usingthe triangular model again, as shown in Fig . 2. Traditional laundry detergent powders arepackaged in cardboard boxes which certainly permit fragrance to be lost once opened bythe consumer. Products can be used at high laundry temperatures. Product base malodorsfrom solids are generally easy to cover and so the perfumer would tend to construct afragrance akin to the rather squat triangle in Fig. 2, where the heavier components in theperfume ensure low perfume losses. Laundry liquids, by contrast, tend to be used at lowertemperatures and are stored in sealed bottles such that perfume loss is not such an itemof concern. However, masking base malodors over liquids in sealed bottles is often a keyfeature relative to a powder and this leads to the triangle rather richer in top notes inFig. 2. Using the powder fragrance to achieve the headspace concentration needed in aliquid inevitably leads to high dosing and (unnecessary) high perfume cost. The solutionto this is to let the perfumer rebalance his fragrance .

The emphasis in the discussion so far has been on how a perfume is built up orstructured to achieve performance characteristics. It goes without saying that these char-

LIQUID SOLID

Figure 2 Perfumes for solids and liquids.

Perfumes In Detergents 705

acteristics are influenced by the medium being perfumed. For example, changing the vis­cosity of a fluid modifies the rate at which perfume diffuses out of it and this can bereflected in changes of perceived intensity and even a modification in note. Some solidcomponents such as zeolites and clays can preferentially absorb the smaller moleculesused in top notes and this can modify the perceived balance of a fragrance. For reasonssuch as this, it is important to test even the most apparently conventional base to ensureoptimal perfuming. It is apparent that fragrance substantivity in detergent products is verymuch an operational phenomenon and not something inherent only in the perfume itself[51,52].

The interactions between the fragrance components modified by the base effectsreferred to in the previous paragraph illustrate how skilled the perfumer needs to be toachieve a composition or blend which preserves a particular character of odor. Someattempt was made by Pickthall to discuss the matter scientifically over 40 years ago [14]and the opening words of his paper are as true today as when he wrote them. "It isremarkable that so little has been written on these two important phenomena in perfumery,namely, blending and fixation." Perhaps it is not so remarkable, as the phenomena are socomplex to attempt anything more than generalizations. However the term "fixation" isone we have not yet reviewed and it is important in the context of substantivity.

"Fixing" a perfume implies that one adds something to the composition to renderit longer-lasting. It will be appreciated that this is very closely associated to the processof re-creating a perfume or reblending it to render it more substantive. Nowadays, thedistinction between the two processes is very blurred. However, one still encounters theterm "fixateur" in the context of a specific additive which when put into a perfume(usually the claim is "any" perfume) enhances its long-lastingness. Many claims involvecompounds well known to the perfumer, such as the various "musks," and are reallytargeted at cosmetic perfumes. Nonetheless, simply adding these compounds to a perfumeeffectively reblends it and maybe even ruins its balance, not to say anything about itsactual cost. This situation is invariably even more exacerbated in detergent formulationsand attempts to enhance substantivity by fixateurs are invariably inferior and more costlythan asking the perfumer to try and reblend his composition. Similar remarks apply to so­called "boosters" which are claimed to enhance the impact of a fragrance by enhancingits evaporation rate. In fact, I am inclined to share the view of a colleague who referredto these types of chemicals as "pixie dust" -at least this is kinder than "snake oil"! Inthe context of ingredients which actually prolong perfume perception without impairingthe balance of a fragrance by reducing intensity, the reader is referred to Sec . VI.A. andthe references to highly substantive but essentially odorless perfume alcohol esters whichslowly hydrolyze to release fragrant alcohols.

IV. PERFUME FUNCTIONALITY

A prime object of fragrancing a detergent formulation is to render it aesthetically pleasingto the user. However, many formulation components are inherently malodorous and simplyputting a perfume in among them will just put a pleasant smell alongside the bad ones.Attempting to overpower malodors with high doses of fragrances is also doomed to failure,even if it is commercially feasible. The perfumer has to make his compositions such thatthey mask out any perception of malodors by the user and leave a totally aestheticallypleasing impression. Perfumes which are formulated with this malodor-masking propertyare referred to as "functional" fragrances. In recent years, the idea of extending this

706 Ramsbotham

property of fragrances into detergent formula tions has been evidenced in package claimssuch as "removes dirt and odors" on laundry products. In this context, the perfume whichis substantive on the cloth after the laundering process is called upon to mask any lingeringdomestic malodors and suppress the onset of their perception on the laundered garment.These domestic malodors can vary from stale tobacco smoke and cooking smells to sweat­generated body malodors. It will be appreciated that this aspect of fragrance functionalityis applicable and relevant to virtually all products used in the household and institutionalenvironments.

A. Malodors in Products

Malodors which are inherent in product formulations usually arise from low-molecular­weight impurities which are usually of a polar nature. Examples of these are fatty alcoholsin ethoxylated alcohol nonionic surfactants (fatty malodors) and traces of pyrrolidones inpoly(vinyl pyrrolidone) dye transfer inhibitors (e.g ., 2-pyrrolidone = mouse-like odor).Inadequately preserved products can decay and develop malodors in storage; the mostcommon malodor is the intense fatty odor caused by rancidity usually resulting fromheavy-metal-catalyzed oxidation of unsaturated fatty acids typically found in soaps andsome fabric conditioner actives. Product usage can also generate low-molecular-weightmalodorants. Examples here include the vinegar-like odors arising from (per)acetic acidgenerated in TAED -persalt bleach systems and the butyric acid-like malodors (fat/vomit)associated with lipase enzyme activity on fatty stains on damp cloth.

Malodors which are inherent in product usage often need to be identified using acombination of a good nose and analytical equipment-often a combination of a GLCand a mass spectrometer. Once the malodor has been identified, its source has to be tracedand it helps to have a knowledge of how the ingredients in the formula are made, as wellas what they are. For example, some manufacturers produce an innocent surfactant suchas sodium dodecylbenzene sulfonate by in situ neut ralization of the acid. This can leave"pockets " of extremes of pH in some production processes for a period which is longenough to permit other detergent ingredients to come into contact with them and degrade.In one memorable mystery, persistent malodors were traced to the parts per million ofmercaptans generated from an alkaline reaction of the optical brightener containing tracesof DMF solvent. In short , it is not possible to give general rules for this sort of detectivework, but a knowledge of the product and production process on the part of the applicationchemist and an open dialogue with the manufacturer are vital.

It goes without saying that the best form of malodor control in product formulationis to try and limit it where possible at the source by keeping product specifications tightand modifying production processes. Some commoner sources of product malodor willalso be referred to in Sec. VI. It is often a good idea to let the perfume house evaluateindividual formulation components as well as the final formulation to pinpoint the sourceof troublesome base malodors.

B. Chemical Nature of Malodorants

The chemical identity of many common malodorants is fairly well recognized [53-55].The low-molecular-weight aliphatic carboxylic acids are responsible for rancid malodorsand vomit/sweat/toilet smells. Molecules containing a nitrogen or sulfur atom are alsoinvariably malodorous. Sulfides are associated with bad egg and garlic-like odors. Mer­captans and thioacids account for bathroom-like sme lls and boiled cabbage and are delib-

Perfumes in Detergents 707

erately used as warning signals in domestic gas supplies. Fatty amines are responsible forfishy-urinic malodors. In the context of product bases, one is fortunately faced with iden­tifying either a single substance or usually a very simple mixture. Clearly, any moleculefalling into the chemical categories just summarized should be viewed with suspicion.

Turning to the nature of malodors which account for environmental or domesticproblems such as bathroom, body, or kitchen smells, we are invariably faced with quitecomplex mixtures. Moreover, although the general character of these smells is instantlyrecognizable, there can be considerable variations in their compositions due to differentdiets, cultures, and habits. (We will address the problems associated with this for theperfumer in the following subsections.) However, if we sidestep the problem of variationsin malodor composition for the moment, it is instructive to look at some published malodorcompositions to see how they indeed are made up of blends of the types of chemicalreviewed in the last paragraph. The compositions in Table 1 were published by the U.S.General Services Administration Federal Supply Service as a suggestion for workers in­volved in creating standard malodors

These standard malodors were recommended for use in aerosol formulations whichcould be used to create malodors in test rooms. In all cases except the tobacco malodor(#3), 0.1 pbw of malodor is mixed with 4.9 pbw of dipropylene glycol and put into anaerosol with 95 pbw propellant. The tobacco malodor was used at 0.2% pbw with 4.8

Table 1 Chemical Composition of Some Malodors

Kitchen #1 Isovaleraldehyde 30.0Diacetyl (2,3 butanedione) 3.85 Phenyl acetic acid 3.0Pyridine 3.85 Butyric acid 0.25Diallyl sulfide (Thia allyl ether) 9.23 Indole (0.5 % in DPG) 1.5Dimethyl sulfide 40.00 p-Cresyl isovalerate 1.5Heptaldehyde 3.85 p-Cresyl phenyl acetate 2.75Paraldehyde 1.90 Mecaptoic acid 5.0Propionic acid 36.92 Dipropylene glycol 26.00Acetic acid (glacial) 0040 WC#5

Tobacco #3 Dipropylene glycol 62 .82Furfural 5.0 Skatole 0.91Pyridine 0.1 I3-Thionaphtole (2-napthalenethial) 0.91Methyl ethyl pyridine Mercaptoacetic acid 21.18(5 ethyl 2 methyl pyridine) 12.6 1I-Caproic acid (hexanoic acid) 6.00

Mercaptoacetic acid 0.7 p-Cresyl isovalerate 2.18Beechwood creosote 1.2 1I-Methyl morpholine 6.00Pyroligneous acid 30.6 Hospital #7Dipropylene glycol 49.8 Beechwood creosote 0042

Occupied Space Tetrachloroethane 36.21Tobacco #3 90 Quinoline 8.36Body odor #4 10 Guaiacol 8.36

Bathroom-WC #6 Eugenol 4.18Body odor #4 5.0 Methyl salicylate 4.18WC#5 30.0 Isopropanol 38.29Kitchen #1 7.5 Kitchen #2DPG 57 .5 Kitchen #1 50

Body Odor #4 Tobacco #3 501I-Caproic acid (hexanoic acid) 30.0

708 Ramsbotham

pbw DPG. It goes without saying that many workers will have their own variants on thepreceding formulas , but they are illustrative of how malodors are built up.

The actual compositions of malodors are invariably even more complex thanthose just quoted and one which has received considerable attention is sweat-generatedbody malodor. Quite remarkably, it was only as recently as 1990 that Dr. George Preti ofMonell reported at an American Chemical Society meeting that 3-methyl-2-hexenoic acidis the chief cause of underarm odor. It had previously been widely assumed that combi­nations of isovaleric acid and androstenol were the guilty parties [56]. A subsequent patenttaken out by Monell [57] contains detailed compositions and comprehensive references.

C. Malodo r Counteraction

Malodors, like perfumes, are composed of volatile chemicals. In cases where the sourceof the malodor is limited to principally one or two chemicals, it may be feasible to tackleit chemically. For example, many malodors arise because of organic acids. If these can beinduced to form esters or salts , their malodorous properties will be diminished and eveneliminated. The alkaline action of baking soda to neutralize many acidic malodors is awell-known remedy to keep refrigerators fresh and illustrates this. In the context of mal­odors arising as a result of biological processes such as body odors, there may be waysto interfere with the process so that malodor does not develop [56-58]. For example,armpit malodor develops when bacteria degrade sweat. Therefore, chemicals to kill thebugs or render their life less hospitable by lowering the humidity (antiperspirant) or mod­ifying skin pH will inhibit the malodor development. The existence and feasibility of suchmethods to control malodors should naturally always be considered alongside the use ofperfumes. However, a general point to bear in mind is that many chemical neutralizationprocesses obviously rely on a molecular contact between malodorant and neutralizer. Ifthis cannot be achieved, then, obviously, chemical malodor control will be impaired.

Before considering how and when perfumes can assist in malodor control, it isimportant to have a brief understanding of how we perceive malodors. There are two basicmechanisms. Odor quality and identification proceed via the olfactory nerve, and stimulior " sensations" are a function of the activation of the trigeminal nerve [59] . Many per­fumes offer a relatively low activation of the trigeminal system, whereas some of theclassic malodors are strong trigeminal stimulants. Without having a deep knowledge ofthese two perception mechanisms, it can be appreciated that trying to mask trigeminalstimulation using olfactory nerve stimulation presents the perfumer with a problem. It istherefore necessary to be aware of which malodorants offer significant trigeminal activa­tion; some examples from Ref. 59 are

Sweet: bromoform, chloroform, ethylchloride, iodoform, nitrobenzeneSour: acetic, butyric, propionic, and valerianic acidsPainful/prickly: acetone, acetic acid, ammonia, formic acid, thiophene, bromine

Fortunately, some odorants available to the perfumer also have a significant degree oftrigeminal activity:

Cool sensations: camphor, eucalyptol, menthol, peppermint, and safrole

In addition to the above, other common perfume ingredients are also known to begood trigeminal stimulants and examples are isoamyl, butyl, ethyl, and fenchyl acetateesters , fenchol, menthone, and pulegone. Fina lly, one should not fall into the trap of

Perfumes in Detergents 709

thinking that all malodors are trigeminal in character; skatole and indole, for example, areprimarily olfactory nerve stimulants.

Trigeminal stimulants such as hypochlorite bleach liquors, ammonia, or vinegar ina cleaner or excessive butyric acid evolved by lipase action are virtually impossible tomask using classic perfumes. In Sec. II.B, reference was made to the in situ formation ofchloroform in a hypochlorite bleach liquor. The sweet sensation of this trigeminal stimulantalongside the choking-prickly sensation of the bleach is perhaps one rationalization forthis old technique. In general terms, putting a perfume into a rather strong trigeminalstimulant leaves one with the impression of an odor alongside a sensation. A good exampleof this is the use of perfume in the so-called "apple-vinegar" cleaners in Germany. Thebest one can hope for is to render an (un)pleasant sensation somewhat more bearable orcreate a situation in which the perfume lingers longer in the air than the trigeminal stim­ulation . The psychology of powerful cleaners not smelling particularly pleasant at the timeof use but leaving reassuringly pleasant aftereffects is clearly operative in such cases .

Perfumes have a long anecdotal history of removing the perception of malodors.Exactly how they achieve this is still not fully understood, although our knowledge isincreasing rapidly and a chapter on the "Perception of Odor Mixtures" by Laing in Ref.59 is a good review in this area. From the point of view of the perfumer, recourse to thetriangular model introduced in Sec. III (Fig . 1) provides one qualitative mean of visualizingmalodor masking. The middle and back note components of a fragrance potentially com­prise many odor chemicals which individually can have quite malodorous smells. A pop­ular example in this respect is the chemical civetone which is key in giving classic fra­grances such as "Chanel No.5" important aspects of their performance and character.Civetone itself has an intense fecal note when smelled alone. This sort of fact had led toone way of visualizing malodor masking by perfumes, as is illustrated in Figure 3. Inshort, a perfumer confronted with a malodor(s) attempts to construct a fragrance withsomething of a "hole" in it into which the elements of the smell being masked somehowfit. This method of attempting to visualize the masking technique is clearly highly quali­tative, but it does help to emphasize that a masking fragrance blends with but does notnecessarily chemically destroy malodorants. Moreover, implicit in the concept is that the"hole" is invariably complex and that an appropriate concentration of perfume is requiredto function.

Published literature on masking malodors by perfumes (as opposed to academicstudies) falls into two classes. The Lever group of companies have a long series of patentsand applications which describe techniques used to construct fragrances which fall intothe general "perfume with a hole category. " Recent applications [60,61] describe howfragrance materials, including some having inherently low odor intensities, such as diethylphthalate (DEP) solvent, can be combined to have a deodorant effect in use. Fragrancematerials are divided into six classes in a defined manner (viz. phenolic substances, al­dehydes and ketones, esters, alcohols and ethers, nitrogen-containing substances, and es­sential oils). The deodorant fragrance has to contain at least five different componentsfrom preferably three predefined groups and components from at least four of the sixclasses. The candidates also have defined malodor-reducing values against isovaleric acidsolutions. Although the thrust of the claims is to cover sweat-generated body malodors(underarm patch assessment) in the widest range of products, earlier publications [62] haveclaimed that control of many other malodors can also be achieved against models such asthose proposed by the U.S. Federal Supply Services and given in Sec. IV.B. This latterfeature illustrates the fact that malodor coverage is not necessarily totally specific for onemalodor. Whereas "universal malodor" coverage is rather ambitious, the skilled perfumer

710 Ramsbotham

+

MALODOR

PERFUME

TOTAL PERCEPTION

Figure 3 Malodor masking by blending.

can indeed create fragrances using proprietary techniques such as those described by theLever companies to encompass a wide range of malodors. Having said this , it will beappreciated that some variations in malodor type can often be tolerated and this caters forvariations within a malodor type mentioned in Sec. IV.A.

The second group of published data concerns various malodor-neutralizing chemi­cals . By implication, such chemicals can be used by the perfumer as magic bullets toconfer some sort of deodorizing property to his fragrance. These chemicals have the ad­vantage that they come complete with documentation as to their claimed efficiency, butthis should always be reconfirmed in the actual fragrance which is being used. An excellentearlier review of this area which is still relevant today was prepared by Johnsen [63], whodiscusses many chemicals and their deodorizing mechanisms. Many perfume companieshave access to a proprietary deodorizing cocktail which undoubtedly has some malodor­neutralizing capacity when used appropriately. However, suffice it to say that such chem­icals should really be evaluated once formulated into fragrances in a commercially relevantmanner. Because their neutralizing power is dependent on a molecular contact with themalodor, this may not always be effective in every formulation and very often it limitsthe perfumer in formulating a fragrance which can also potentially react with the neutral ­izer.

Whatever technique is used to create the fragrance, the advantage of having a com­position which blends with a malodor is that this process takes place in the nose . Theimplication of this is that the source of the malodor and the location of the perfume neednot coincide. The operational advantage of this in domestic and laundry products in sit­uations where a malodor unavoidably develops or is present is a clear bonus.

Perfumes in Detergents

V. PERFUME, MOODS, AND SYNESTHESIA

711

Although the importance of having a technically stable perfume along with an aestheticallypleasing odor is obvious, other features of perfume choice such as associations of smellwith product color and emotional feelings (i.e., product positioning) have not yet beenmentioned. The phenomenon of stimulation of one of the senses to influence the others isknown as synesthesia and this can be very important in the selection of fragrances. Manyof the comments made in the following account would have been limited to personalcosmetic fragrances up until a few years ago but are applied increasingly to the full rangeof consumer products.

Jellinek has recently published a comprehensive review of work dealing with theinfluence of perfumes on moods and emotion [64]. Although this area has only relativelyrecently been the focus of intense interest in the perfume industry, aromatherapists willbe quick to point out that the ability of essential oils to modify mood states has beenknown for hundreds of years [65]. In the context of consumer products, aromatherapy­type claims are the ones invariably encountered in the marketplace. The 5000 years ofaccumulated largely anecdotal evidence on the way in which the 30 or so aromatherapy(eessential) oils influence mood states is sufficient to satisfy advertising authorities whena manufacturer makes a soft marketing claim for a product. For example, references to asensual foam bath formulation along with references to jasmine and sandalwood or claimsfor refreshing or relaxing feelings are taken as being relatively harmless marketing andnot misleading. However, there is a much more serious side even to this example and alot of research is going on to understand topics such as human pheromones [66]. Thearomatherapy oils are IFRA-approved fragrance ingredients and a perfumer will generallyconstruct a fragrance around ones having the appropriate anecdotal mood associations sothat the appropriate marketing claim can be made for products. More general perspectiveson fragrance as a "silent persuader" have been reviewed in a recent book by Dor­land [67].

In the context of soft marketing claims, simply taking essential oils as part of afragrance and ignoring any interactions both with other fragrance ingredients and theproduct base odor is scientifically suspect. Moreover, limiting the choice of fragranceingredients to 30 or so essential oils while obviously restricting perfumer creatively mayalso not be feasible in some bases for technical/stability reasons . Considerations such asthese render it imperative to understand how fragrances, in general, influence people'sfeelings and this has given rise to studies under the general umbrella terms of aroma­chology or aroma science [64]. Generally speaking, it seems that psychological responsesto smell can be classified into eight mood states which are in general line with emotionalresponses following stimulation of the other senses. These moods are qualitatively sum­marized in Fig. 4 [68]. The mood states fall into four positive states on the right-handside of the figure and four negative ones on the left. Those at the top of the diagram arehigh-arousal states, whereas those at the bottom are low-arousal states. Emotional responseto an odor invariably involves modifications in several mood states and this applies bothto fragrance ingredients as well as perfumes [68].

Although Fig. 4 is a clear oversimplification of matters and the mood states, in reality,overlap each other, certain general statements can be made. The most important of theseis that selecting a fragrance on aesthetic grounds really only reliably correlates with afeeling of happiness or euphoria. Correlations with states of sensuality, relaxation, andstimulation are not reliably present, although it goes without saying that experienced per­fumers and odor selectors will have a fair idea of the suitability of a fragrance for use in

712 Ramsbotham

sensuality

relaxation

IIIhappiness

apathy

stress

depression~~IIII

Figure 4 Olfactively influenced mood states.

these contexts. However, personal and cultural experiences will also influence these mattersand cannot be ignored when trying to develop creative rules for widely different geograph­ical locations. The techniques used by perfume companies to build these mood statespredictively into perfumes are obviously proprietary secrets!

Something of the hidden depths of these techniques can be appreciated when it isrealized that unpleasant smells generally correlate with an enhancement of negative moodstates at the expense of positive ones. In this context, the efficient masking of any basemalodors is of relevance. Moreover, we have also seen that many important fragranceingredients are individually rather malodorous and, therefore, individually also tend tohave negative mood associations. These elements have to be incorporated into a fragrancewith positive psychological associations by the perfumer; again, proprietary techniquesexist to achieve this.

The obvious applications of these sorts of studies is to create fragrances which areboth aesthetically and psychologically appropriate for a chosen product positioning.Whereas this is almost self-evident in personal care type products such as the "relaxing"bath product referred to earlier, some household products have much more tenuous claimsto an emotional positioning. A cleaner needs to leave something smelling "fresh," forexample, and the actual meaning of this attribute needs to be defined in terms of moodstates. Having said all this, one needs to emphasize that we are not talking about mind­bending drugs but more about creating odors which are compatible with mood states; thisaspect of creative perfumery is only just starting to be exploited, although its commercialpotential has long been recognized [69].

One expects a lemon smell to come from something yellow and not a pronouncedblackcurrent or strawberry note. Synesthesia tells us quite simply that lemons are yellow,blackcurrent is black, and strawberries are red. As soon as the odor begins to have lessclear associations with well-known objects, color associations are less self-evident. Likeperfumes, colors are also associated with emotions and, not surprisingly, with fragrances.In a study on color associations, Jellinek puts the matter quite succinctly as "certain colorsgo with a perfume, others do not" [70]. On this note, suffice it to say that it always pays

Perfumes in Detergents 713

to let the perfume supplier see the pack and product presentation package at an early stagein the creative process to ensure that the perfume does indeed "go with the product."

VI. PERFUMES IN FORMULATIONS

It is clear that creating a winning fragrance for a detergent product is very much a mul­tidisciplinary team effort which demands a clear technical insight, on the one hand, withthe realization that the artistic element of the perfume is being purchased by the consumer,on the other. It is the object of this final section to review more specific technical featuresof categories of detergent products which give problems in perfumery. It will be imme­diately apparent that some problems such as malodors from free alcohol in alcohol ethox­ylates will be common to several categories of products. To avoid tiresome repetition,such phenomena are not repeatedly referred to in the following account.

A. Heavy-Duty Laundry Powders

Problems arising from surfactant systems are twofold. The more serious one involvesbase malodors which often can be traced to very low levels of (low-molecular-weight)fatty acids or alcohols. Intense fatty notes from free alcohol in ethoxylated fatty alcoholscan be very troublesome. The second feature is that improvements to the fat-solubilizingpower of the surfactant system will tend to result in higher levels of perfume solubilizationwith resulting lower cloth deposition. Base malodors are always best tackled at the sourceand a perfumer can readily advise which malodor he can more easily cope with whenasked. Suppliers of surfactants can sometimes modify their process or product specificationto accommodate matters; the narrow-cut ethoxylates and the processes of "topping andtailing" nonionic ethoxylates are examples of this. In situ neutralization of acids to formanionics such as sodium dodecylbenzene sulfonate and the consequent possibility of (lo­calized products) extreme pH were referred to in Sec. IV.A.

The presence of oxidizing agents or bleaches in powders presents an obvious limi­tation to the perfumer. One has to view powders as being subject to moisture during partof their life and the packaging obviously plays a role here; thus, appropriate stability testingis always advisable. Any change in the formulation which has a bearing on the bleachingpower could influence the perfume stability. The limitation on fragrance raw materialchoice increases in the order sodium perborate, sodium percarbonate, perborate + TAED,percarbonate + TAED. In addition to this, changing the ratio of the persalt to activatorneeds to be monitored. Clearly, the utilization of other bleach systems demands similarprecautions.

Enzymes manufactured for use in modern detergent formulations often have an un­pleasant odor when delivered in bulk, but covering any traces of this in fully formulatedproduct rarely presents a problem for the experienced perfumer. However, it is theoreticallypossible that problems could arise from some of the carrier materials used. For example,PVP could conceivably introduce traces of pyrrolidone malodors, whereas clays such asKaolin and bentonite can introduce heavy metals and/or selectively absorb some fragrancecomponents. Some sulfur-containing chemicals used in production processes can besources of malodor, although this is rare. Of all the enzymes currently used, only the lipaseor fat-splitting enzymes are a regular source of problems, in that their activity is primarilyon damp cloth rather than in the wash liquor itself. In cases of heavy staining, short-chainfatty acids such as butyric acid can be evolved , and because they have trigeminal activity,

714 Ramsbotham

they are all but impossible to mask using perfume. Generally, one has to arrive at acompromise as to the maximum level of lipase which can be used without incurringexcessive malodor. One ingenious exploitation of this damp cloth activity is revealed byFirmenich [71] whose proposal was to use fatty esters of fragrant alcohols in either de­tergent s or fabric softeners. The ester is decomposed by esterase activity to release thealcohol. P&G have a similar but more specific application involving geranyl succinate[72], which is used in some of their fabric softeners, but which makes no direct referenceto lipase but rather to slow decomposition by hydrolysis and thereby improved fragrancesubstantivity. A similar idea using sulfonates of specified perfume alcohols is also claimedby P&G [73].

Builders and sequestrants generally pose no unexpected problems for the perfumein terms of chemical stabilities. However, it is possible that changes in the porosity of abuilder can influence the distribution of fragrance onto a powder base such that the topnotes tend to be more absorbed into the pores. This can influence out-of-the-pack perfor­mance and dictate a certain rebalancing of the fragrance. Reformulating from sodiumtripolyphosphate to a zeolite builder would clearly be a common situation where this wouldbe expected. Analogous phenomena could occur with components such as layer and dis­i1icates and some clays which have an absorptive capacity. A less immediately obviousfeature of changes in builder component could involve the moisture content of the base .For example, switching from phosphate to zeolite builders invariably raises the hygro­scopic character of a base which can clearly induce a higher" activity " of the bleach inthe pack. This will , in turn, provide a more aggressive environment for "minors" such asthe perfume and enzymes. In a similar vein, an inadequately powerful sequestrant systemwill tend to permit heavy-metal-catalyzed decomposition of the bleach, which can beresponsible for unexpected instabilities in fragrance.

The increasing use of polymeric additives in detergent formulations generally posesno problems. Increasingly rarely, one does detect an accumulation of "plastic-related"odors in the headspace of newly opened containers and one source can be due to tracesof monomers from the polymer. One of the more notoriously difficult odors is that remi­niscent of a mouse cage ; this is related to pyrrolidone in PVP.

The general pH of the powder can influence the freedom of material choice of theperfumer. In-pack pH generally lies anywhere from 9 to 11 and a shift of even half a unitin this critical area can tip the balance between stability and instability. Finally, the porosityof the base and the application of perfume has been referred to in Sec. II.D.

B. Fabric Conditioner

The prime feature of liquid rinse additives playing a role in perfumery is their pH. Ingeneral terms, actives containing ester linkages in their structures need to be formulatedat quite acidic pH and this does limit a free ingredient choice. Product base malodors areoften related to decomposition of the side chains by in-pack hydrolysis (too high productpH) and/or rancidity reactions when unsaturation is present. This latter reaction is partic­ularly troublesome because it cannot be predictably reproduced and is autocatalytic. Per­fumery can do little to mask it and all the standard techniques familiar to the soap producerare worth trying (viz. addition of sequestrants, antioxidants, or even borohydride treat­ment) . Equally troublesome and irreproducible is the bacterial attack of some bases. The" dirty" smell characteristic of this evil can be prevented by adequately preserving theproduct.

Perfumes in Detergents 715

Liquid rinse conditioners which contain above about 8 wt% active matter can exhibitall sorts of viscosity behavior once fragrance is added. In cases where there is a well­defined micellar structure such as in distearyl dimethyl ammonium moieties [18], the artof adding perfume is to ensure that it is distributed in an equilibrium manner within thestructure by adding it as the liquid structure is formed. By implication, this means that itcan be added at elevated temperatures and not necessarily as the final production step. Incases where the liquid structure is not well defined and/or the base comprises a mixtureof active substances, each formulation requires an individual treatment. Pragmatically, oneneeds to establish if particular classes of compound are going to have extreme effects onviscosity. Finally, a commonsense rule but one which is very valid is simply, "If anadditive/perfume gives a physico-chemical problem, use as small a quantity of it as pos­sible." Admittedly, this might be easier said than done, but it does illustrate one of theadvantages of concentrating a fragrance.

Solid rinse additives are invariably encountered in the form of tumble drier sheets.The major problem here is one of avoiding premature fragrance loss and this is maybeone instance where some form of heat-triggered fragrance encapsulation is warranted; thishas been extensively patented by Procter and Gamble (Sec. 11.0). Solid or powder rinseconditioners, although they are frequently a topic for the patent literature, have never beena real commercial success because of rather poor cold-water dispersability characteristics.Perfume problems would probably be primarily associated with fatty base odor coverage.

C. Light-Duty Laundry Liquids and Powders/Booster Products

Most of the features in the preceding two sections come back in the other areas of laundrycare. Light-duty laundry products tend to have milder pH's than heavy duties and areinvariably free of an oxidizing bleach and permit a higher degree of perfumer flexibility.Laundry liquids, in general, have a fatty acid or soap component and this can be a sourceof inherent base malodor. Booster products often involve a bleach component and thisprovides obvious limitations.

D. Hard-Surface Cleaners

The presence of trigeminal stimulants such as acetic acid (vinegar) and ammonia is afeature of some products, but this is not a problem because the odor is very much aperceived signal of "activity." Other product (mal)odors which are peculiar to cleanersbut are not perceived positively can often be traced back to the various solvents. In thiscontext, glycol ethers can be troublesome, although they are generally excellent solventsfor fragrances in formulations [74]. Although alternative chemicals without the odor havebeen proposed [75], toxicological considerations are producing a move to using propyleneglycol ether analogs. Whereas these latter do not present technical difficulties as such [76],their solubilizing power for perfumes is significantly inferior to that of traditional glycolethers and this is sometimes a problem in formulations such as window cleaners, whichoften contain insufficient solubilizing surfactants.

Many of the lemon- and pine-type fragrances used in cleaners depend on terpenechemicals. These chemicals have characteristic odors and are generally good grease-cuttingsolvents. However, they are highly water insoluble. In the early eighties, Procter andGamble started to issue a series of patents [77] which basically claim cleaners which areclear and comprise 1-20 wt% surfactant, 0.5-10 wt% mono- or sesquiterpenes, and

716 Ramsbotham

0.2-to wt% of a polar solvent (benzyl alcohol or glycol ether). Whereas a discussion ofcleaner technology is outside the scope of this review, suffice it to say that the perfumerneeds to be aware that he could quite easily cause a formulation to infringe these patentsby using a very terpene-rich fragrance. Products of the P&G technology are invariablymicroemulsions and Colgate has recently claimed that the grease-cutting power of cleaners,in general, is significantly higher than would be expected when the perfume oil is presentas the oil phase of a microemulsion [78].

Finally, the formulator and perfumer both need to be aware of the fact that when afragrance is being used in a cleaner, its oil-like character can contribute to streaking insome formulations. This may need checking in some compositions; generally, the problemis related to the water insolubility of the perfume.

E. Manual Dishwash Liquids

Generally, perfuming these products is fairly straightforward. The major barrier in termsof base-related malodors can often be traced to low levels of free-acid impurities. Besidesexperimenting with fragrance, it is sometimes feasible to raise the pH of the formulationslightly and observe a significant alleviation of the problem. Having said this, citrus-likeor terpene-rich fragrances are very commonly used and the phenomenon of autooxidationand the possible resulting paneling of bottles needs to be adequately protected against[15].

A more unexpected phenomenon can occur when concentrated formulations are pre­pared. Highly water-insoluble perfume moieties such as the terpenes tend to diffuse intothe oil phase of the surfactant micelles. The more significant this becomes, the more onecan be confronted with a phenomenon that the smell of perfume from the product becomesless intense in spite of a proportionately higher perfume dose . If this is accompanied byan explosive release of the perfume in water when using the product, micelle diffusion isindeed a likely cause. Short of changing either the perfume or the surfactants, there is noviable remedy for this.

In Sec. IV, product base odors and their control were discussed at some length andthe difficulty of masking trigeminal malodorants using conventional perfumes was ex­plained. Lamberti [79] provides an ingenious method for masking the odor of ammoniaderived from urea hydrotrope hydrolysis in manual dishwash liquids. His solution is toinclude esters such as methyl or ethyl lactates which hydrolyze at comparable rates to thatof the urea to liberate lactic acid, which subsequently forms ammonium salts. An alter­native mechanism of ammonolysis involves direct interaction between the ammonia andthe esters. The removal of acidic or basic malodors by reacting them with either bases oracids is sometimes useful as a quick diagnostic tool. In the case of a dishwash liquid, forexample, if a malodor is diminished by raising the pH and then returns or is intensifiedby lowering the pH, there is a high chance that acids are responsible for the malodor. Thissort of knowledge plus insights into formulation and ingredients can sometimes help intransforming a problem into one of manageable proportions.

Finally, one still comes across fragrance discoloration on storage. The culprit hereis invariably a Schiff's base (see Sec. II.B) formed between a perfume aldehyde and atrace of the -NH2 group coming from alkanolamide foam booster or even urea hydrotope.More subtle is the discoloration of water-white dishwash liquids, where care has to begiven to formulating fragrances with minimal or no inherent color.

Perfumes in Detergents 717

F. Hypochlorite-Containing Products

These products range from sodium hypochlorite bleach liquors themselves to substancessuch as the chlorinated isocyanurates which generate hypochlorite in contact with waterand are used in machine dishwash powders. As we have seen earlier, these products areamong the most restricting to the perfumer because of the combination of an extremelyhigh pH and the oxidizing power of the hypochlorite ion. There is, in practice, a littlemore creative freedom with the dishwash powders just referred to and multisurface clean­ers containing a maximum of 1% available chlorine. However, this clearly needs to bedetermined from base to base . There is one class of dry bleach which should never befragranced and that is calcium hypochlorite, which can ignite in the heat of exothermicoxidation of fragrance addition.

Hypochlorite bleach liquors fall into two classes; the thickened cleaner-sanitizersand preparations with minimal additives for laundry usage. Starting with the latter for­mulations, one needs to remembe r that even when technically stable perfume chemicalsare used [80], they will need solubilizing. Whenever an organic chemical is added to ahypochlorite bleach liquor, the rate of the inherent breakdown of sodium hypochlorite tooxygen and sodium chloride (the " gassing reaction ") is increased . This can be limited byensuring that the solubilizer requirement of the fragrance is minimized. Moreover, anyaddition to a bleach liquor effectively consumes alkaline buffer and it is expedient toensure that free alkali equivalent to about 1 wt% sodium hydroxide is present once theperfuming process is complete. In spite of all precautions, additions to the bleach liquorwill accelerate its loss of available chlorine and an agreement needs to be reached betweenthe perfumer and bleach manufacturer as to what can be tolerated. Generally speaking,one must be prepared for an increase of between 5% and 10% in the rate of loss ofavailable chlorine on going from unfragranced to fragranced bleach liquor. Some ideasabout stability tolerances can be obtained from the patent literature [81]. The thickenedhypochlorite bleaches share all the characteristics detailed above, but the solubilizingpower of the detergent thickeners invariably renders the solubility of fragrance as only arelatively minor problem. However, as we have seen in Sec. II.C, fragrance can enhancethe viscosity of some thickening systems.

A general caution applicable to both the manufacture and bottling of bleach whichcontains solubilized fragrance is that one must be prepared for more failures arising fromstress-cracking. Although this seems most serious for PVC piping, it is not limited to thisplastic, and the only totally certain cure in a plant is to use titanium piping. The problemseems related to the presence of the detergent (solubilizer/thickener), which enhances thewetting of the plastic by the bleach liquor. This same phenomenon presumably facilitatesany penetration of the plastic by fragrance and this is most likely in the case of PVc.Fortunately, the problems with packaging are relatively rare but have attracted the attentionof major bleach producers [82].

G. Soap and Syndet Bars

The largest categories by far are for personal cleansing and for laundry usage. The tradi­tional fatty acid based soap bars have a pH of around 9-9.5 and contain between 1.0 and1.5 wt% perfume. Once unwrapped in a bathroom, they can function almost as air fresh­eners in some cases. The traditional " pan process" for soap preparation presents the veryreal possibility that sometimes quite considerable quantities of heavy metals, principallyiron, are introduced into the soap and these can present the perfumer with a variety of

718 Ramsbotham

color reactions we related in Sec. II.B [16]. Besides metal contents, the quality of tallow,palm , or coconut oils clearly influences the base odor of the soap-poor odor and poorcolor invariably go hand-in-hand. The prime cause of actual base malodor is rancidity andthe autocatalytic nature of this dictates that sequestrants and antioxidants are actuallypresent in the feedstock used by the soap manufacturer if this is not used totally fresh[83]. The results of rancidity are readily apparent and the trigeminal stimulation of thefatty acids renders malodors all but impossible to mask completely. In recent years, theuse of soaps prepared from distilled fatty acids (DFA soaps) has improved base quality,although the pH problem remains for the perfumer.

Laundry bars introduce the use of fillers and builders which are not present in barsused for personal cleansing. On the one hand, these can introduce heavy metals; on theother, they can " absorb" certain fragrance top notes as we discussed in Sec. IV.A and theextent to which they do this and the degree of perfume rebalancing which is needed isdictated by testing.

Syndet bars for personal cleansing are predominantly of approximately neutral pHand present no special problems to the perfumer as a rule.

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