1 Lecture 6: Carboxylic Acids and Esters 16.1 Carboxylic Acids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 A carboxylic acid  Contains a carboxyl group, which is a carbonyl group (C=O) attached to a hydroxyl group (—OH).  Has the carboxyl group on carbon 1. carbonyl group O  CH 3 — C—OHhydroxyl group or CH 3 COOH carboxyl group Carboxylic Acids

3 Models of Carboxylic Acids  The three-dimensional models show the geometry of atoms in carboxylic acid molecules. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

4 The IUPAC names of carboxylic acids  Replace the -e in the alkane name with -oic acid. CH 4 methane HCOOH methanoic acid CH 3 —CH 3 ethane CH 3 —COOH ethanoic acid  Number substituents from the carboxyl carbon 1. CH 3 O | ║ CH 3 —CH—CH 2 —C—OH methylbutanoic acid IUPAC Names

5 The common names of simple carboxylic acids  Are formic acid (1C), acetic acid (2C), propionic acid (3C), and butyric acid (4C). HCOOH formic acid CH 3 —COOHacetic acid  Locate substituents using , , γ for the carbon atoms adjacent to the carboxyl carbon. CH 3 γ  |  CH 3 —CH—CH 2 —COOH 3-methylbutanoic acid (  -methylbutryic acid) Common Names

6 Alpha Hydroxy Acids Alpha hydroxy acids (AHAs)  Occur naturally in fruit, milk, and sugarcane.  Are used in skin care products. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

7 Names and Sources of Some Carboxylic Acids TABLE 16.1 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

8 Common Carboxylic Acids Methanoic acid (formic acid) O ║ H─C─OH ethanoic acid (acetic acid) O ║ CH 3 ─C─OH Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

9 Aromatic Carboxylic Acids Benzoic acid  Is the aromatic carboxylic acid.  Locates substituents by assigning 1 to the carbon attached to the carboxyl group.  Has common names that assign prefixes ortho, meta, and para for 2 substituents. ortho1, 2 location meta 1, 3 location para1, 4 location

10 Aromatic Carboxylic Acids benzoic acid 3-chlorobenzoic acid 4-aminobenzoic acid m-chlorobenzoic acid p-aminobenzoic acid

11 Give the IUPAC and common names: A. CH 3 —COOH CH 3 | B. CH 3 —CH—COOH C. Learning Check

12 Learning Check Give the IUPAC and common names for the following: A. CH 3 ─CH 2 ─COOH CH 3 | B. CH 3 ─CH─CH 2 ─COOH C.

13 Preparation of Carboxylic Acids  Carboxylic acids can be prepared by oxidizing primary alcohols or aldehydes.  The oxidation of ethanol produces ethanoic acid (acetic acid). OH O O | [O] || [O] || CH 3 —CH 2 CH 3 —C—H CH 3 —C—OH ethanol ethanal ethanoic acid (ethyl alcohol) (acetaldehyde) (acetic acid)

14 Learning Check What alcohol could be used to prepare the following: 1. butanoic acid 2.propanoic acid

Properties of Carboxylic Acids Lecture 6: Carboxylic Acids and Esters Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

16 Polarity of Carboxylic Acids Carboxylic acids  Are strongly polar.  Have two polar groups: hydroxyl ( − OH) and carbonyl (C=O). δ - O ║ δ + δ - δ + CH 3  C  O  H

17 Boiling Points of Carboxylic Acids The boiling points of carboxylic acids  Are higher than alcohols, ketones, and aldehydes of similar mass.  Are high because they form dimers in which hydrogen bonds form between the polar groups in the two carboxyl groups. O H—O || | CH 3 —C C—CH 3 | || O—H O A dimer of acetic acid

18 Comparison of Boiling Points CompoundMolar MassBoiling Point O ║ CH 3 −CH 2 −C−H5849°C CH 3 −CH 2 −CH 2 −OH6097°C O ║ CH 3 −C−OH60118°C

19 Solubility in Water Carboxylic acids  Form hydrogen bonds with many water molecules.  With 1-4 carbon atoms are very soluble in water. Water molecules Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

20 Boiling Points and Solubility TABLE 16.2 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

21 Acidity of Carboxylic Acids Carboxylic acids  Are weak acids.  Ionize in water to produce carboxylate ions and hydronium ions. O O ║ ║ CH 3 − C − OH + H 2 O CH 3 − C − O – + H 3 O + Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

22 Acid Dissociation Constants Carboxylic acids  Have small K a values.  Exist mostly as molecules and a few ions in aqueous solutions. TABLE 16.3

23 Neutralization of Carboxylic Acids Carboxylic acid salts  Are a product of the neutralization of a carboxylic acid with a strong base. CH 3 —COOH + NaOH CH 3 —COO – Na + + H 2 O acetic acid sodium acetate (carboxylic acid salt)  Are used as preservatives and flavor enhancers. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

24 Learning Check Write the equation for the reaction of propanoic acid with A. water B.KOH

25 Lecture 6: Carboxylic Acids and Esters 16.3 Esters 16.4 Naming Esters Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

26 Esters In an ester,  The H in the carboxyl group is replaced with an alkyl group. O  CH 3 — C—O—CH 3 ester group Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

27 Esterification is  The reaction of a carboxylic acid and alcohol in the presence of an acid catalyst to produce an ester. O  H + CH 3 —C—OH + H—O—CH 2 —CH 3 O  CH 3 —C—O—CH 2 —CH 3 + H 2 O ethyl acetate (an ester) Esterification

28 Write the equation for the reaction of propanoic acid and methanol in the presence of an acid catalyst. Learning Check

29 Naming Esters The name of an ester contains the names of  The alkyl group from the alcohol.  The carbon chain from the acid with –ate ending. from alcoholfrom acid O methyl  CH 3 — O—C —CH 3 ethanoate (acetate) IUPAC: methyl ethanoate common: methyl acetate

30 Ester Products Aspirin  Is used to relieve pain and reduce inflammation.  Is an ester of salicylic acid and acetic acid. Oil of wintergreen  Is used to soothe sore muscles.  Is an ester of salicylic acid and methanol.

31 Esters in Plants Esters give flowers and fruits their pleasant fragrances and flavors. TABLE 16.4 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

32 Learning Check Give the IUPAC and common names of the following compound, which is responsible for the flavor and odor of pears. O  CH 3 —C—O—CH 2 —CH 2 —CH 3

33 Learning Check Name the following esters: O ║ A. CH 3 —CH 2 —CH 2 —C—O—CH 3 O  B.CH 3 —CH 2 —C—O—CH 2 —CH 3

34 Learning Check Write the structure of the following esters: A. Ethyl pentanoate B. Propyl butyrate

35 Solution A. Ethyl pentanoate O ║ CH 3 —CH 2 —CH 2 —CH 2 —C—O—CH 2 —CH 3 B. Propyl butyrate O ║ CH 3 —CH 2 —CH 2 —C—O—CH 2 —CH 2 —CH 3

36 Lecture 6: Carboxylic Acids and Esters 16.5 Properties of Esters Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

37 In acid hydrolysis  An ester reacts with water to produce a carboxylic acid and an alcohol.  An acid catalyst is required. O  H + H—C—O—CH 2 —CH 3 + H 2 O O  H—C—OH + H—O—CH 2 —CH 3 Acid Hydrolysis of Esters

38 Base hydrolysis (also called saponification)  Is the reaction of an ester with a strong base.  Produces the salt of the carboxylic acid and an alcohol. O || CH 3 —C—O—CH 2 —CH 3 + NaOH O  CH 3 —C—O – Na + + HO—CH 2 —CH 3 salt of carboxylic acid alcohol Base Hydrolysis (Saponification)

39 “Soaps” The base hydrolysis of long chain fatty acids produces acid salts called “soaps”. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

40 Cleaning Action of Soap A soap  Contains a nonpolar end that dissolves in nonpolar fats and oils, and a polar end that dissolves in water.  Forms groups of soap molecules called micelles that dissolve in water and are washed away. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

41 Write the organic products when methyl acetate reacts with A. Water and an acid catalyst B. KOH Learning Check

42 Write the organic products when methyl acetate reacts with: A. Water and an acid catalyst O  CH 3 —C—OH + HO—CH 3 B. KOH O  CH 3 —C—O – K + + HO—CH 3 Solution