EXERCISE 9 ACYL COMPOUNDS: SOAPS AND DETERGENTS

I. INTRODUCTION

A. Acyl Compounds Acyl compounds are of the type ,where G is a halogen

bonded to the carbonyl group through oxygen or nitrogen. The most widely distributed acyl compunds ar the carboxylic acids. Carboxylic acids are the most important of the acidic organic compounds. They contain the carboxyl group as their functional hroup:

In the carboxyl group, the hydroxyl group is directly attached to the

carbonyl group which allows the resonance stabilization of the conjugate base formed upon release of a proton:

Thus, carboxylic acids have a greater tendency to release a proton

than other organic compound types. Usually, carboxylic acid functional derivatives contain the acyl group The following types are functional derivatives of carboxylic acids:

R

O

G

R

O

OH

R = alkyl or aryl

R

O

OH

+ :Base

R

O

O- R

O-

O

+ H-Base

R

O

R

O

X R

O

O

O

R R

OH

OR

CH3

O

NH2

acid halide acid anhydride ester amide

Nitriles, R - CN, though not acyl compounds, are considered as carboxylic acid functional derivatives because they are readily hydrolyzed to carboxylic acids.

Nucleophilic addition to the carbonyl group is less likely in acyl compounds than in aldehydes and ketones. The characteristic reaction of acyl compounds is nucleophilic acyl substitution:

Through this reaction, carboxylic acids may be converted to the functional derivatives and in turn, the functional derivatives may be converted to carboxylic acids.

The acyl compounds differ in their reactivities toward nucleophilic

acyl substitution and this is evident from their hydrolysis reactions. The more reactive compounds are hydrolyzed by water alone. The less reactive ones either require a strong nucleophile as the hydroxide ion or an acid catalyst to enhance the electron deficiency of the carbonyl carbon, making it more attractive to a nucleophile. Alcohols, phenols, ammonia and amines react with acyl compounds in much the same way as water does. B. Soaps and Detergents Esters of long chain carboxylic acids and the trihydric alcohol,

glycerol, are known as triacylglycerols or triglycerides. The carboxylic acids attached to glycerol may be identical (simple triglycerides), or different (mixed triglyceride).

CH3

O

NH

R

CH3

O

NR1

R

substituted amides

R1

O

G

+ :Nu CH3

O-

G

Nu

CH3

O

Nu

+ G-

glycerol triacylglycerol

Triacylglycerols undergo the same reactions as the low molecular mass esters; hydrolysis in a basic medium yields long – chain carboxylate salts and glycerol. This reaction is called saponification; the salts produced are called soaps. Soap produced from triacylglycrols is a mixture of long chain carboxylate salts.

Detergents on the other hand, are also amphiphatic and are

generally characterized by the presence of a sulfate group. They are usually derived from C12 to C18 alcohols:

II. OBJECTIVES 1. To observe the general properties of carboxylic acids. 2. To compare the acidity of carboxylic acids and phenols. 3. To verify experimentally the interconversion among acyl compounds.

HC

H2C

H2C O

O

O

C

C

C

O

O

O

R

R1

R2

HC

H2C

H2C OH

OH

OH

HC

H2C

H2C O

O

O

C

C

C

O

O

O

R

R1

R2

+ 3NaOH HC

H2C

H2C OH

OH

OH

+ R

O

O-Na R1

O

O-Na R2

O

O-Na

soaps

CH3(CH2)10CH2OH H3C(H2C)10H2C O S

O

O

OH H3C(H2C)10H2C O S

O

O

O-

Na+

lauryl alcohol lauryl hydrogen sulfate sodium lauryl sulfate DETERGENT

4. To become familiar with the physical and chemical properties of fats and oils and to understand the chemical basis of these properties.

5. To learn how to prepare soap. 6. To compare the properties of soap and synthetic detergents.

III. PROCEDURE A. Solubility and acidity of carboxylic acids

1. Water silubility *Perform this test with acetic acid, benzoic acid, and sodium benzoate a. Place 2 mL water in a test tube. b. Add a small amount of the sample (6 drops or a small piece) c. Shake to mix. d. Examine the mixture. Test with blue litmus paper

2. Relative acidities of carboxylic acids and phenols

*Perform using benzoic acid and phenol a. Place 2 mL water in a test tube b. Add 6 drops of the sample c. Add 10 drops of 10% NaOH d. Examine the mixture e. Repeat using 10% NaHCO3 instead of NaOH

B. Hydrolysis of acyl compounds

Perform this test with acetyl chloride, acetic anhydride, ethyl benzoate and benzamide as samples CAUTION: ACETYL CHLORIDE AND ACETIC ANHYDRIDE MUST BE HANDLED IN THE FUME HOOD 1. Place 6 drops or a spatula tip of sample in a test tube 2. Add 3 mL water carefully 3. Observe for any sign of reaction (e.g. heat evolved, bubbles, etc.) 4. If no change is seen, heat the test tube for 2 minutes without boiling in

a hot water bath 5. Cool the mixture 6. Test with blue litmus paper

C. Saponification of coconut oil

1. Place 10 mL ethanol in a 400 mL beaker 2. Add 15 mL 6 M NaOH 3. Add 15 mL coconut oil; mix by swirling 4. Add boiling chips and cover the beaker with a watch glass

5. Heat the mixture while swirling over a small flame. Continue for about 15 minutes or until the mixture is viscous

6. Cool the mixture 7. Add 50 mL saturated NaCl solution while stirring 8. Suction filter the product 9. Wash the soap twice with 15 mL ice-cold distilled water 10. Allow to dry

D. Comparison of soaps and detergents

Dissolve one spatula tip of soap sample in 30 mL of warm distilled water. Do the same with a sample of detergent. Use mixtures formed for the following tests.

1. Hydrolysis Test the mixture with red and blue litmus paper

2. Reaction with acid

a. Place 5 mL of the sample in a test tube b. Add 10 mL 0.5 M HCl c. Shake to mix. Observe

3. Reaction with “soft” and “hard” water

a. Place 5 mL of 0.02 M NaCl (soft water) in a test tube b. Add 15 drops of the sample c. Repeat with 0.02 M CaCl2 (hard water)

4. Emulsifying action

a. Place 8 drops of kerosene in a test tube b. Add 5 mL sample c. Shake the tube vigorously for three minutes d. Allow to stand for 5 minutes. Run water blank.

IV. QUESTIONS

1. Explain the difference in the solubility of benzoic acid and sodium benzoate in water. Which of the two would you predict to be more soluble in CHCl3? Explain.

2. Based on the results in Part A.2, what can be said about the relative

acidities of phenols and carboxylic acids? Arrange the following compound types in order of increasing acidity: carboxylic acid, alcohol, phenol and water.

3. Based on the results in Part B, arrange the following compound types

in the order of decreasing hydrolysis rate: acid halides, acid

anhydrides, esters, and amides. Give the theoretical explanations for the observed differences in reaction rates.

4. Is the soap water mixture a true solution? Cite examples to support

your answer.

5. What is a colloidal mixture? How does a colloidal mixture arise when soap is mixed with water?

6. On the basis of the litmus test, are the soap-water and detergent-water

mixtures acidic, basic or neutral? Explain the difference, if any in the reactions of the soap-water and detergent-water mixtures to litmus paper.

7. Which would you predict to have a greater emulsifying power in “hard

water”, soaps or synthetic detergent? Explain.

8. Explain the cleaning property of soaps and detergents based on your observations of their emulsifying action.