Chapter 9

Derivatives of Ethylene

Over 100 billion Ib of chemicals and polymers per year are made fromethylene, by far the most important organic chemical. Over 40% of allorganic chemicals by volume are derived from ethylene. Unfortunately, wecannot describe the interesting chemistry and uses for all the importantderivatives of ethylene. We will limit our detailed discussion to thosechemicals made from ethylene that appear in the top 50, which amount to 8important organic chemicals. These are listed in Table 9.1.

Again we are faced with the question of what order to treat thesechemicals: by rank, alphabetically, and so on. Some of these chemicals canbe grouped by manufacturing process, since one may be made from another,and both originally from ethylene, in a multistep synthetic sequence. Wetake advantage of this manufacturing relationship in our choice of ordersince it groups these chemicals together in one important feature that wewish to emphasize: their chemistry of manufacture. The discussions ofthese chemicals will be different from that for inorganics. For inorganics the

Table 9.1 Ethylene Derivatives in the Top 50

Ethylene dichlorideVinyl chlorideAcetic acidVinyl acetateEthylbenzeneStyreneEthylene oxideEthylene glycol

ethylene

ethylenedichloride

vinylchloride

acetaldehyde acetic acid

vinyl acetate

ethy !benzene styrene

ethylene glycolethylene oxide

Figure 9.1 Synthesis of ethylene derivatives in the top 50 chemicals.

emphasis was on the simple reaction, the engineering aspects of thechemical's manufacture, uses, and economics. Because there are moreorganics than inorganics in the top 50, we must sacrifice some details inengineering and economics but still stress the chemistry of manufacture(including mechanism when known) and uses of the chemicals. Let us recallat this point that nearly half of all ethylene is polymerized to polyethylene.This process and the polymer will be discussed in a later chapter. Other thanthis the main large-scale industrial reactions of ethylene are summarized inthis chapter. Fig. 9.1 gives an outline of this chemistry with the order thatwe will use to consider these chemicals. They are in four pairs, since vinylchloride is made from ethylene dichloride, vinyl acetate is made from aceticacid, styrene is processed from ethylbenzene, and ethylene glycol ismanufactured from ethylene oxide.

1. ETHYLENE DICHLORIDE (EDC)

Cl-CH2-CH2-Cl

Ethylene dichloride is one of the highest-ranked derived organicchemicals and is made in excess of 20 billion Ib/yr. There are two majormanufacturing methods for this chemical, each of which contributes about50% to the total production of EDC. The classical method for EDCmanufacture is the electrophilic addition of chlorine to the double bond ofethylene. The yield is good (96-98%); it can be done in vapor or liquidphase at 40-5O0C using ethylene dibromide as a solvent, and the product iseasily purified by fractional distillation. The mechanism is well understoodand is a good example of the very general addition of an electrophile to adouble bond. Here the intermediate is the bridged chloronium ion, since inthis structure all atoms have a complete octet. A primary carbocation is lessstable. Polarization of the chlorine-chlorine bond occurs as it approaches theTC cloud of the double bond. Backside attack of chloride ion on the bridgedion completes the process.

Reaction:

Mechanism:

slow

In contrast to this direct chlorination there is the oxychlorination ofethylene using hydrogen chloride and oxygen, the other major method nowused. Since the chlorine supply is sometimes short and it is difficult tobalance the caustic soda and chlorine demand (both are made by theelectrolysis of brine), hydrogen chloride provides a cheap alternate sourcefor the chlorine atom. Most of the ethylene dichloride manufactured isconverted into vinyl chloride by eliminating a mole of HCl, which can thenbe recycled and used to make more EDC by oxychlorination. EDC andvinyl chloride plants usually are physically linked. Most plants are 50:50direct chlorinationroxychlorination to balance the output of HCl.

50% CH2=CH2 + 2HCl + 1X2O2 ^ Cl-CH2-CH2-Cl + H2O

Cl-CH2-CH2-Cl +> CH2=: CH-Cl + HCl (recycle)

50% CH2=CH2 + Cl2 ^ Cl-CH2-CH2-Cl

Cl-CH2-CH2-Cl *• CH2=CH-Cl + HCl (recycle)

What probably happens in the oxychlorination process is that chlorine isformed in situ. The reaction of hydrogen chloride and oxygen to givechlorine and water was discovered by Deacon in 1858. Once the chlorine isformed, it then adds to ethylene as in the direct chlorination mechanism.Cu+2 is the catalyst and helps to more rapidly react HCl and O2 because of itsability to undergo reduction to Cu+1 and reoxidation to Cu+2. KCl is presentto reduce the volatility OfCuCl2.

2HCl + 2Cu+2 >• Cl2 + 2Cu+ + 2H+

2Cu+ + V2O2 + 2H+ ^ 2Cu+2 + H2O

Ethylene dichloride is a colorless liquid with a bp of 840C. As with manychlorinated hydrocarbons, it is quite toxic and has a TLV value of 10 ppm(TWA). It is on the list of "Reasonably Anticipated to Be HumanCarcinogens."

Nearly all ethylene dichloride is made into vinyl chloride, which ispolymerized to the important plastic poly(vinyl chloride) (PVC).Perchloroethylene (perc) is used as a dry cleaning agent (55%), a chemicalintermediate (29%), and a metal cleaning agent (11%). Perc has a 75% shareof the dry cleaning business. Methyl chloroform is one of a few chlorinatedcompounds that has low toxicity, but it is being phased out because of itsozone depleting potential. Sometimes called "1,1,1," it is used as a chemicalintermediate (60%), a metal cleaning agent (25%), and as an ingredient in

adhesives, coatings, and inks (8%). Vinylidene chloride is polymerized to aplastic (Saran®). The ethylenediamines are used as chelating agents, themost important being ethylenediaminetetracetic acid (EDTA).

vinyl chloride perchloroethylene methyl chloroform

vinylidene chloride ethyleneamines

Despite these minor uses, the economics of EDC is linked to the demandfor PVC plastic.

2. VINYL CHLORIDE (VINYL CHLORIDEMONOMER, VCM)

CH2=CH-Cl

Although there are two manufacturing methods for ethylene dichloride,all the vinyl chloride is made by a single process, thermal dehydro-chlorination of EDC. This takes place at temperatures of 480-51O0C under apressure of 50 psi with a charcoal catalyst to give a 99% yield. Vinylchloride is a gas at ambient pressure with a bp of -13 0C. It is separated fromethylene dichloride by fractional distillation. Vinyl chloride readilypolymerizes so it is stabilized with inhibitors to prevent polymerizationduring storage. The mechanism of formation is a free-radical chain processas shown below. Although the conversion is low, 50-60%, recycling theEDC allows an overall 99% yield.

Reaction:

The largest use of vinyl chloride is in the manufacture of poly(vinylchloride) plastic, which finds diverse applications in the building andconstruction industry as well as in the electrical, apparel, and packagingindustries. Poly(vinyl chloride) does degrade relatively fast for a polymer,but various heat, ozone, and ultraviolet stabilizers make it a useful polymer.A wide variety of desirable properties can be obtained by using variousamounts of plasticizers, such that both rigid and plasticized PVC have largemarkets. PVC takes up 98% of all vinyl chloride with only 2% being usedfor chlorinated solvents and poly(vinylidene chloride).

After some tough years in the 1970s vinyl chloride had a good economicgain in the 1980s. The 1997 production of approximately 15 billion Ib isexpected to increase by about 3% per year in the near future. At a price of210/lb that gives a total commercial value of $3.2 billion. One of thereasons vinyl chloride has had some bad years is the recent findings oftoxicity. It causes liver cancer and is on the list of chemicals that are"Known to Be Human Carcinogens." In 1973 its TLV was 200 ppm. Thiswas reduced in 1974 to 50 ppm and in 1980 the TWA was 5 ppm. In 2000 itis 1 ppm. However, apparently this causes no health problems for poly(vinylchloride) uses. Only the monomer is a health hazard. As a result, theeconomic situation looks good.

3. ACETIC ACID (ETHANOIC ACID, GLACIALACETIC ACID)

Mechanism:

If there is a prime example of an organic chemical that is in a state of fluxand turnover in regards to the manufacturing method, it is probably aceticacid. There are now three industrial processes for making acetic acid.Domestic capacity in 1978 was almost equal among acetaldehyde oxidation,

«-butane oxidation, and methanol carbonylation. In 1980 methanolcarbonylation exceeded 40% of the capacity and will continue to increase inits share of capacity because of economic advantages. In 1998 methanolcarbonylation was 64% of capacity. Acetic acid will also be covered in thederivatives of methane chapter, but it is appropriate to cover it here sinceboth it and vinyl acetate are still made from ethylene.

Ethylene is the exclusive organic raw material for making acetaldehyde,70% of which is further oxidized to acetic acid or acetic anhydride. TheWacker process, named after a German company, for making acetaldehydeinvolves cupric chloride and a small amount of palladium chloride inaqueous solution as a catalyst. The inorganic chemistry of this reaction isunderstood: (1) A TC complex between ethylene and palladium chloride isformed and decomposes to acetaldehyde and palladium metal; (2) thepalladium is reoxidized to palladium chloride by the cupric chloride; and (3)the cuprous chloride thus formed is reoxidized to the cupric state by oxygenfed to the system. The three equations that follow indicate the series ofredox reactions that occur. When added together they give the overallreaction. The yield is 95%.

(1)

(2)

(3)

overall:

The details of the organic chemistry of the reaction of ethylene withPdCl2 (equation (1) above) are also known and are shown in Fig. 9.2. Thepalladium ion complexes with ethylene and water molecules and the wateradds across the bond while still complexed to palladium. The palladiumthen serves as a hydrogen acceptor while the double bond reforms. Keto-enol tautomerism takes place, followed by release of an acetaldehydemolecule from the palladium.

When it was a major source for acetic acid, acetaldehyde was in the top50 at about 1.5 billion Ib. Now it is under a billion pounds but it is still usedto manufacture acetic acid by further oxidation. Here a manganese or cobaltacetate catalyst is used with air as the oxidizing agent. Temperatures rangefrom 55-8O0C and pressures are 15-75 psi. The yield is 95%.

Figure 9.2 Mechanism of the Wacker reaction. (Source: White)

Although the oxidation reaction is simple, the mechanism is quitecomplex and involves the formation of peracetic acid first.

Some of the peracetic acid decomposes with the help of the catalyst andthe catalyst is regenerated by this process.

Most of the peracetic acid decomposes via a cyclic reaction withacetaldehyde to form two moles of acetic acid.

A second manufacturing method for acetic acid utilizes butane from the€4 petroleum stream rather than ethylene. It is a very complex oxidationwith a variety of products formed, but conditions can be controlled to allowa large percentage of acetic acid to be formed. Cobalt (best), manganese, orchromium acetates are catalysts with temperatures of 50-25O0C and apressure of 800 psi.

The mechanism of this reaction involves free radical oxidation of butaneto butane hydroperoxide, which decomposes to acetaldehyde via p scissions.It is similar to the oxidation of cyclohexane to cyclohexanol andcyclohexanone, which will be discussed in Chapter 11, Section 4.

The third and now preferred method of acetic acid manufacture is thecarbonylation of methanol (Monsanto process), involving reaction ofmethanol and carbon monoxide (both derived from methane). This isdiscussed in Chapter 12, Section 3.

Table 9.2 Uses of Acetic Acid

Vinyl acetate 60%

Cellulose acetate 10

Acetic esters 10

Solvent for TA/DMT 10

Miscellaneous 10

Source: Chemical Profiles

Although we have included acetic acid manufacture under ethylenederivatives, as you can see it is made from three of the seven basic organics:ethylene, C4 hydrocarbons, and methane, with the most important methodbeing from methane. Pure 100% acetic acid is sometimes called glacialacetic because when cold it will solidify into layered crystals similar inappearance to a glacier. It is a colorless liquid with a pungent, vinegar odorand sharp acid taste, bp 1180C, and mp 170C.

Table 9.2 summarizes the uses of acetic acid. Vinyl acetate is anothertop 50 chemical. Acetic anhydride is used to make cellulose acetate and attimes has been in the top 50 chemicals itself. Cellulose acetate is a polymerused mainly as a fiber in clothing and cigarette filters. Ethyl acetate is acommon organic solvent. Acetic acid is used as a solvent in the manufactureof terephthalic acid (TA) and dimethyl terephthalate (DMT), which aremonomers for the synthesis of poly(ethylene terephthalate), the "polyester"of the textile industry. A minor household use of acetic acid is as a 3-5%aqueous solution, which is called vinegar.

4. VINYL ACETATE

Vinyl acetate is one of many compounds where classical organicchemistry has been replaced by a catalytic process. It is also an example ofolder acetylene chemistry becoming outdated by newer processes involvingother basic organic building blocks. Up to 1975 the preferred manufactureof this important monomer was based on the addition of acetic acid to thetriple bond of acetylene using zinc amalgam as the catalyst, a universalreaction of alkynes.

In 1969, 90% of vinyl acetate was manufactured by this process. By1975 only 10% was made from acetylene, and in 1980 it was obsolete.Instead, a newer method based on ethylene replaced this old acetylenechemistry. A Wacker catalyst is used in this process similar to that for aceticacid. Since the acetic acid can also be made from ethylene, the basic rawmaterial is solely ethylene, in recent years very economically advantageousas compared to acetylene chemistry. An older liquid-phase process has beenreplaced by a vapor-phase reaction run at 70-140 psi and 175-20O0C.Catalysts may be (1) C-PdCl2-CuCl2, (2) PdCl2-Al2O3, or (3) Pd-C,KOAc. The product is distilled; water, acetaldehyde, and some polymer are

separated. The acetaldehyde can be recycled to acetic acid. The purecolorless vinyl acetate is collected at 720C. It is a lachrymator (eye irritant).The yield is 95%. The mechanism of this reaction is the same as the Wackerprocess for ethylene to acetic acid, except that acetic acid attacks rather thanwater. You should develop this mechanism similar to Fig. 9.2, subtitutingacetic acid for water.

Table 9.3 gives the uses of vinyl acetate. Poly(vinyl acetate) is usedprimarily in adhesives, coatings, and paints, especially those that are water-based. This percentage of use has increased dramatically in recent years.The shift to water-based coatings has certainly helped vinyl acetateproduction. Copolymers of poly(vinyl acetate) with poly(vinyl chloride) areased in flooring and PVC pipe. Poly(vinyl alcohol) is used in textile sizing,adhesives, emulsifiers, and paper coatings. Poly(vinyl butyral) is the plasticinner liner of most safety glass.

Table 9.3 Uses of Vinyl Acetate

Poly(vinyl acetate) 55%Poly(vinyl alcohol) 19Poly(vinyl butyral) 12Copolymers 8Miscellaneous 6

Source: Chemical Profiles

Vinyl acetate is a good example of an ethylene chemical with a highpercentage of exports, sometimes near 30%. The United States now has acost advantage in ethylene production and many ethylene derivatives havehigh export percentages.

5. ETHYLBENZENE

Despite the use of new catalyses for manufacturing some industrialorganic chemicals, many well-known classical reactions still abound. TheFriedel-Crafts alkylation is one of the first reactions studied in electrophilicaromatic substitution. It is used on a large scale for making ethy!benzene.

or zeolites

Note that ethylbenzene is a derivative of two basic organic chemicals,ethylene and benzene. A vapor-phase method with boron trifluoride,phosphoric acid, or alumina-silica as catalysts has given away to a liquid-phase reaction with aluminum chloride at 9O0C and atmospheric pressure. Anew Mobil-Badger zeolite catalyst at 42O0C and 175-300 psi in the gasphase may be the method of choice for future plants to avoid corrosionproblems. The mechanism of the reaction involves complexation of the

ethylene with the Lewis acid catalyst, attack of the electrophilic carbon onthe aromatic ring, loss of the proton to rearomatize, and desorption of thecatalyst with subsequent protonation in the side chain.

Excess benzene must be used. A common benzene:ethylene ratio is1.0:0.6. This avoids the formation of di- and triethylbenzenes. The firstethyl group, being electron donating inductively as compared to hydrogen,will activate the benzene ring toward electrophilic attack by stabilizing theintermediate carbocation. The benzene when in excess prevents this since it

+ ortho (predominant isomer)

increases the probability of the attack on benzene rather than onethylbenzene, but some polyethylbenzenes are formed, and these can beseparated in the distillation process and burned for fuel. Alternatively,disubstituted isomers can be transalkylated with benzene to give two molesof monosubstituted product. The benzene is recycled.

Ethylbenzene is a colorless liquid, bp 1360C. Despite the elaborateseparations required, including washing with caustic and water and threedistillation columns, the overall yield of ethylbenzene is economicallyfeasible at 98%.

Almost all ethylbenzene (99%) is used to manufacture styrene. Only 1%is used as a solvent.

6. STYRENE (VINYLBENZENE, PHENYLETHENE)

Approximately 79% of the styrene produced in the United States is madefrom ethylbenzene by dehydrogenation. This is a high-temperature reaction(63O0C) with various metal oxides as catalysts, including zinc, chromium,iron, or magnesium oxides coated on activated carbon, alumina, or bauxite.Iron oxide on potassium carbonate is also used. Most dehydrogenations donot occur readily even at high temperatures. The driving force for thisreaction is the extension in conjugation that results, since the double bond onthe side chain is in conjugation with the ring. Conditions must be controlledto avoid polymerization of the styrene. Sulfur is added to preventpolymerization. The crude product has only 37% styrene but contains 61%ethylbenzene. A costly vacuum distillation through a 70-plate column at9O0C and 35 torr is needed to separate the two. The ethylbenzene isrecycled. Usually a styrene plant is combined with an ethylbenzene plantwhen designed. The yield is 90%.

metal oxide

Because styrene readily polymerizes it is immediately treated with anantioxidant such as/>-/-butylcatechol at 10 ppm.

Many phenols, especially "hindered phenols" such as butylated hydroxytoluene (BHT), are good antioxidants. They act as radical scavengers byreadily reacting with stray radicals to give very stable radicals via resonance.

The alkyl radicals then cannot initiate the polymerization of substances suchas styrene.

This happens:

Instead of:

A new alternate method for the manufacture of styrene, called the oxiraneprocess, now accounting for 21% of production, uses ethylbenzene. It isoxidized to the hydroperoxide and reacts with propylene to givephenylmethylcarbinol (or methyl benzyl alcohol, MBA) and propyleneoxide, the latter being a top 50 chemical itself. The alcohol is thendehydrated at relatively low temperatures (180-40O0C) using an acidic silicagel or titanium dioxide catalyst, a much cleaner and less energy-dependentreaction than the dehydrogenation. Other olefins besides propylene could beused in the epoxidation reaction, but it is chosen because of the high demandfor the epoxide. Some acetophenone is separated and hydrogenated back toMBA.

Table 9.4 Uses of Styrene

Polystyrene 62%

ABS resins 11

SB latex 8

Unsaturated polyester resins 7

SBR 6Miscellaneous 6

Source: Chemical Profiles

Table 9.4 shows the uses of styrene. These are dominated by polymerchemistry and involve polystyrene and its copolymers. We will study thesein detail later, but the primary uses of polystyrene are in various moldedarticles such as toys, bottles, and jars, and foam for insulation andcushioning. Styrene manufacture is a large business. With a production of11.4 billion Ib and a price of 300/lb styrene has a commercial value ofapproximately $3.4 billion.

7. ETHYLENE OXIDE

Another example of a famous organic chemical reaction being replacedby a catalytic process is furnished by the manufacture of ethylene oxide. Formany years it was made by chlorohydrin formation followed bydehydrochlorination to the epoxide. Although the chlorohydrin route is stillused to convert propylene to propylene oxide, a more efficient airepoxidation of ethylene is used and the chlorohydrin process for ethyleneoxide manufacture has not been used since 1972.

Old method:

The higher yields (85%) in the chlorohydrin method are not enough tooutweigh the waste of chlorine inherent in the process. Although the yieldsin the direct oxidation method (75%) are lower, the cheap oxidantatmospheric oxygen is hard to beat for economy. Some overoxidation tocarbon dioxide and water occurs. Good temperature control at 270-29O0Cand pressures of 120-300 psi with a 1 sec contact time on the catalyst arenecessary. Tubular reactors containing several thousand tubes of 20-50 mmdiameter are used. Even though metallic silver is placed in the reactor, theactual catalyst is silver oxide under the conditions of the reaction. Ethyleneoxide is a gas at room temperature with a bp of 140C.

Table 9.5 lists the uses of ethylene oxide. Ethylene glycol is eventuallyused in two primary types of end products: polyesters and antifreeze. Abouthalf the ethylene glycol is used for each end product. Poly(ethyleneterephthalate) is the leading synthetic fiber and has other importantapplications in plastic film and bottles. Ethylene glycol is a commonantifreezing agent especially in automobile radiators.

As a hospital sterilant for plastic materials, ethylene oxide was ideal sinceradiation or steam cannot be used. It is in this application that evidence ofhigh miscarriage rates (3x normal) of women on hospital sterilizing staffscaused a lowering of the TLV to 1 ppm. The chemical was most often usedin closed systems but in this application incidental exposures were said to goas high as 250 ppm. Since 1984 ethylene oxide is no longer used as ahospital sterilant. It is now on the "Known to Be Human Carcinogens" list.Ethylene oxide is important in the manufacture of many nonionic detergentsto be discussed in a later chapter. It is a feedstock for synthesizing glycolethers (solvents for paints, brake fluids) and ethanolamines (surfactants and

Table 9.5 Uses of Ethylene Oxide

Ethylene glycol 58%

Ethoxylate surfactants 12

Ethanolamines 10

Di, tri, & polyethylene glycols 9

Glycol ethers 6

Polyether polyols 3

Miscellaneous 2

Source: Chemical Profiles

New method:

gas scrubbing of refineries to remove acids). The manufacturing chemistryof these two materials is given below.

Diethylene and triethylene glycol (DEG and TEG) are produced as by-products of ethylene glycol. DEG and TEG are used in polyurethane andunsaturated polyester resins and in the drying of natural gas. DEG is alsoused in antifreeze and in the synthesis of morpholine, a solvent, corrosioninhibitor, antioxidant, and pharmaceutical intermediate.

diethylene glycol (DEG)

triethylene glycol (TEG)

morpholine

8. ETHYLENE GLYCOL (ETHAN-1,2-DIOL)

HO-CH2-CH2-OH

The primary manufacturing method of making ethylene glycol is fromacid- or thermal-catalyzed hydration and ring opening of the oxide. Nearlyall the glycol is made by this process. Either a 0.5-1.0% H2SO4 catalyst isused at 50-7O0C for 30 min or, in the absence of the acid, a temperature of1950C and 185 psi for 1 hr will form the diol. A 90% yield is realized when

the ethylene oxideiwater molar ratio is 1:5-8. The advantage of the acid-catalyzed reaction is no high pressure; the thermal reaction however needsno corrosion resistance and no acid separation step.

The ethylene glycol, bp 1980C, is readily vacuum distilled and separatedfrom the DEG, bp 2460C5 and TEG, bp 2880C. The mechanism of thereaction follows the general scheme for acid-catalyzed ring openings ofepoxides.

Research is being conducted on the direct synthesis of ethylene glycolfrom synthesis gas. In one process very high pressures of 5,000 psi withvery expensive catalysts Rhx (CO) are being studied. An annual loss ofrhodium catalyst of only 0.000001% must be realized before this processwill compete economically. At least five other alternate syntheses ofethylene glycol that bypass toxic ethylene oxide are being researched.

Table 9.6 shows the use profile for ethylene glycol. In 1950 only 48% ofantifreeze was ethylene glycol, whereas in 1962 it accounted for 95% of all

Table 9.6 Uses of Ethylene Glycol

Antifreeze 30%Polyester fiber 27Polyester bottles 25Industrial uses 10Polyester film 4Miscellaneous 4

Source: Chemical Profiles

antifreeze. Its ideal properties of low melting point, high boiling point, andunlimited water solubility make it a good material for this application. Thepolyester bottle market is rising rapidly. Ten years ago it was a smallpercentage of ethylene glycol use. Now one fourth of all glycol goes to thistype of polyester market. The polyester bottle market is expected to increase>8% per year in the near future, while fiber grows only at 3-4% per year. Aproduction of 6.5 billion Ib and a price of 290/lb for ethylene glycol gives acommercial value of $1.8 billion.

Suggested Readings

Chemical Profiles in Chemical Marketing Reporter, 2-9-98, 2-16-98, 4-20-98, 11-2-98, and 11-9-98.

Kent, Riegel's Handbook of Industrial Chemistry, pp. 809-830.Szmant, Organic Building Blocks of the Chemical Industry, pp. 188-264.White, Introduction to Industrial Chemistry, pp. 62-79.Wiseman, Petrochemicals, pp. 43-63, 102-103, 151-152, and 163-164.Wittcoff and Reuben, Industrial Organic Chemicals, pp. 88-148.