EXERCISE 9 ACYL COMPOUNDS: SOAPS AND DETERGENTS
I.
INTRODUCTION A. Acyl Compounds
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Acyl compounds compounds are are of the type
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,where G is a halogen halogen
G
bonded bonded to the carbonyl carbonyl group group through through oxygen oxygen or nitrogen. nitrogen. The most widely distributed acyl 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: $ #
# & al'yl or aryl
%$In the carboxyl group, the hydroxyl group is directly attached to the carbonyl group which allows the resonance stabilization of the conugate base formed upon release of a proton: $
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:)ase
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%-)ase
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Thus, carboxylic acids ha!e a greater tendency to release a proton than other organic compound types.
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"sually, carboxylic acid functional deri!ati!es contain the acyl group #
The following types are functional deri!ati!es of carboxylic acids: $
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acid halide
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acid anhydride
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ester
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amide
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%,C
-
%,C
-
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substituted amides -itriles, # * C -, though not acyl compounds, are considered as carboxylic acid functional deri!ati!es because they are readily hydrolyzed to carboxylic acids. ≡
-ucleophilic addition to the carbonyl group is less li'ely in acyl compounds than in aldehydes and 'etones. The characteristic reaction of acyl compounds is nucleophilic acyl substitution:
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( #3
:-u
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%,C
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G
G
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( G* -u
-u
Through this reaction, carboxylic acids may be con!erted to the functional deri!ati!es and in turn, the functional deri!ati!es may be con!erted to carboxylic acids. The acyl compounds differ in their reacti!ities toward nucleophilic acyl substitution and this is e!ident from their hydrolysis reactions. The more reacti!e compounds are hydrolyzed by water alone. The less reacti!e ones either re/uire a strong nucleophile as the hydroxide ion or an acid catalyst to enhance the electron deficiency of the carbonyl carbon, ma'ing it more attracti!e to a nucleophile. Alcohols, phenols, ammonia and amines react with acyl compounds in much the same way as water does.
B. Soaps and Detergents
0sters of long chain carboxylic acids and the trihydric alcohol, glycerol, are 'nown as triacylglycerols or triglycerides. The carboxylic acids attached to glycerol may be identical 1simple triglycerides2, or different 1mixed triglyceride2.
$ % .C
%$% .C
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C # $
%C
%$%C
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C #3 $
% .C
%$% .C
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C
glycerol
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triacylglycerol
Triacylglycerols undergo the same reactions as the low molecular mass esters4 hydrolysis in a basic medium yields long 5 chain carboxylate salts and glycerol. This reaction is called saponification4 the salts produced are called soaps. 6oap produced from triacylglycrols is a mixture of long chain carboxylate salts.
$ %.C
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C $
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C
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-a
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soaps
7etergents on the other hand, are also amphiphatic and are generally characterized by the presence of a sulfate group. They are usually deri!ed from C 3 to C38 alcohols:
$ C%,1C%.2 39C%.
%$lauryl alcohol
II.
%,C1%.C239%.C
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6
$
%$%,C1%.C239%.C
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$
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lauryl hydrogen sulfate
sodium lauryl sulfate 70T0#G0-T
OBJECTIVES
3. To obser!e the general properties of carboxylic acids. . To compare the acidity of carboxylic acids and phenols. . To !erify experimentally the intercon!ersion among acyl compounds.
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. To become familiar with the physical and chemical properties of fats and oils and to understand the chemical basis of these properties. ;. To learn how to prepare soap. <. To compare the properties of soap and synthetic detergents.
III.
PROCEDURE
A. 6olubility and acidity of carboxylic acids 3. =ater silubility >?erform this test with acetic acid, benzoic acid, and sodium benzoate a. b. c. d.
?lace m@ water in a test tube. Add a small amount of the sample 1< drops or a small piece2 6ha'e to mix. 0xamine the mixture. Test with blue litmus paper
. #elati!e acidities of carboxylic acids and phenols >?erform using benzoic acid and phenol a. b. c. d. e.
?lace m@ water in a test tube Add < drops of the sample Add 39 drops of 39 -a$% 0xamine the mixture #epeat using 39 -a%C$ instead of -a
%$). %ydrolysis of acyl compounds ?erform 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
3. . . .
?lace < drops or a spatula tip of sample in a test tube Add m@ water carefully $bser!e for any sign of reaction 1e.g. heat e!ol!ed, bubbles, etc.2 If no change is seen, heat the test tube for minutes without boiling in a hot water bath ;. Cool the mixture <. Test with blue litmus paper C. 6aponification of coconut oil 3. ?lace 39 m@ ethanol in a 99 m@ bea'er . Add 3; m@ < B -a$% . Add 3; m@ coconut oil4 mix by swirling . Add boiling chips and co!er the bea'er with a watch glass
;. %eat the mixture while swirling o!er a small flame. Continue for about 3; minutes or until the mixture is !iscous <. Cool the mixture . Add ;9 m@ saturated -aCl solution while stirring 8. 6uction filter the product D. =ash the soap twice with 3; m@ ice*cold distilled water 39.Allow to dry 7. Comparison of soaps and detergents 7issol!e one spatula tip of soap sample in 9 m@ of warm distilled water. 7o the same with a sample of detergent. "se mixtures formed for the following tests. 3. %ydrolysis Test the mixture with red and blue litmus paper . #eaction with acid a. ?lace ; m@ of the sample in a test tube b. Add 39 m@ 9.; B %Cl c. 6ha'e to mix. $bser!e . #eaction with EsoftF and EhardF water a. ?lace ; m@ of 9.9 B -aCl 1soft water2 in a test tube b. Add 3; drops of the sample c. #epeat with 9.9 B CaCl 1hard water2 . 0mulsifying action a. ?lace 8 drops of 'erosene in a test tube b. Add ; m@ sample c. 6ha'e the tube !igorously for three minutes d. Allow to stand for ; minutes. #un water blan'.
IV.
QUESTIONS
3. 0xplain the difference in the solubility of benzoic acid and sodium benzoate in water. =hich of the two would you predict to be more soluble in C%Cl 0xplain. . )ased on the results in ?art A., what can be said about the relati!e acidities of phenols and carboxylic acids Arrange the following compound types in order of increasing acidity: carboxylic acid, alcohol, phenol and water. . )ased on the results in ?art ), arrange the following compound types in the order of decreasing hydrolysis rate: acid halides, acid
anhydrides, esters, and amides. Gi!e the theoretical explanations for the obser!ed differences in reaction rates. . Is the soap water mixture a true solution Cite examples to support your answer. ;. =hat is a colloidal mixture %ow does a colloidal mixture arise when soap is mixed with water <. $n the basis of the litmus test, are the soap*water and detergent*water mixtures acidic, basic or neutral 0xplain the difference, if any in the reactions of the soap*water and detergent*water mixtures to litmus paper. . =hich would you predict to ha!e a greater emulsifying power in Ehard waterF, soaps or synthetic detergent 0xplain. 8. 0xplain the cleaning property of soaps and detergents based on your obser!ations of their emulsifying action.
