1 Chapter 16 Carboxylic Acids and Esters 16.1 Carboxylic Acids Copyright © 2007 by Pearson...

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Chapter 16 Carboxylic Acids and Esters

16.1

Carboxylic Acids

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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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

CH3 — C—OH hydroxyl group or CH3COOH

carboxyl group

Carboxylic Acids

3

Models of Carboxylic Acids

The three-dimensional models show the geometry of atoms in carboxylic acid molecules.


4

The IUPAC names of carboxylic acids

Replace the -e in the alkane name with -oic acid.

CH4 methane HCOOH methanoic acid

CH3—CH3 ethane CH3—COOH ethanoic acid

Number substituents from the carboxyl carbon 1.

CH3 O | ║

CH3—CH—CH2—C—OH 4 3 2 1

3-methylbutanoic acid

IUPAC Names

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The common names of simple carboxylic acids Are formic acid (1C), acetic acid (2C), propionic acid

(3C), and butyric acid (4C). HCOOH formic acidCH3—COOH acetic acid

Locate substituents using , , γ for the carbon atoms adjacent to the carboxyl carbon.

CH3

γ | CH3—CH—CH2—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.


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Names and Sources of Some Carboxylic Acids

TABLE 16.1


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Common Carboxylic Acids

Methanoic acid (formic acid)

O

║

H─C─OH

ethanoic acid (acetic acid)

O

║

CH3─C─OH


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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.

ortho 1, 2 location

meta 1, 3 location

para 1, 4 location

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Aromatic Carboxylic Acids

OHC

O

OHC

O

OHC

O

ClNH2

benzoic acid 3-chlorobenzoic acid 4-aminobenzoic acid m-chlorobenzoic acid p-aminobenzoic acid

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Give the IUPAC and common names:

A. CH3—COOH

CH3

|B. CH3—CH—COOH

C.

Learning Check

COOH

Br

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A. CH3—COOH ethanoic acid (acetic acid) CH3

|B. CH3—CH—COOH 2-methylpropanoic acid

(-methylpropionic acid)

C. 2-bromobenzoic acid(o-bromobenzoic acid)

Solution

COOH

Br

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Learning Check

Give the IUPAC and common names for the following:

A. CH3─CH2─COOH

CH3

|B. CH3─CH─CH2─COOHC.

OHC

O

Br

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Solution

A. CH3─CH2─COOH propanoic acid (propionic acid)

CH3

|

B. CH3─CH─CH2─COOH 3-methylbutanoic acid (β-methylbutyric acid)

C. 3-bromobenzoic acid (m-bromobenzoic

acid)

OHC

O

Br

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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] ||CH3—CH2 CH3—C—H CH3—C—OH

ethanol ethanal ethanoic acid(ethyl alcohol) (acetaldehyde) (acetic acid)

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Learning Check

What alcohol could be used to prepare the following:

1. butanoic acid

2. propanoic acid

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Solution

What alcohol could be used to prepare the following:

[O] [O]

1. butanol butanal butanoic acid

[O] [O]

2. 1-propanol propanal propanoic acid

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16.2 Properties of Carboxylic Acids



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Polarity of Carboxylic Acids

Carboxylic acids Are strongly polar. Have two polar groups:

hydroxyl (−OH) and carbonyl (C=O).

δ-

O ║δ+ δ- δ+

CH3CO H

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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 || |

CH3—C C—CH3

| ||

O—H O A dimer of acetic acid

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Comparison of Boiling Points

Compound Molar Mass Boiling Point

O

║

CH3−CH2−C−H 58 49°C

CH3−CH2−CH2−OH 60 97°C

O

║

CH3−C−OH 60 118°C

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Solubility in Water

Carboxylic acids Form hydrogen

bonds with many water molecules.

With 1-4 carbon atoms are very soluble in water.

Water molecules


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Boiling Points and Solubility

TABLE 16.2

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Acidity of Carboxylic Acids

Carboxylic acids Are weak acids. Ionize in water to produce carboxylate ions

and hydronium ions.

O O ║ ║

CH3−C−OH + H2O CH3−C−O– + H3O+


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Acid Dissociation Constants

Carboxylic acids Have small Ka values. Exist mostly as molecules

and a few ions in aqueous solutions.

TABLE 16.3

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Neutralization of Carboxylic Acids

Carboxylic acid salts Are a product of the neutralization of a carboxylic acid

with a strong base. CH3—COOH + NaOH CH3—COO– Na+ + H2O

acetic acid sodium acetate (carboxylic acid salt) Are used as preservatives and flavor enhancers.


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Learning Check

Write the equation for the reaction of propanoic acid with

A. water

B. KOH

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Solution

Write the equation for the reaction of propanoic acid with

A. waterCH3—CH2—COOH + H2O CH3—CH2—COO– + H3O+

B. KOH CH3—CH2—COOH + KOH CH3—CH2—COO– K+ + H2O

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16.3 Esters

16.4 Naming Esters


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Esters

In an ester, The H in the carboxyl group is replaced

with an alkyl group.

O

CH3 — C—O—CH3

ester group


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Esterification is The reaction of a carboxylic acid and alcohol in the

presence of an acid catalyst to produce an ester. O

H+

CH3—C—OH + H—O—CH2—CH3

O

CH3—C—O—CH2—CH3 + H2O ethyl acetate (an ester)

Esterification

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

Learning Check

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Write the equation for the reaction of propanoic acid

and methanol in the presence of an acid catalyst. O H+

CH3—CH2—C—OH + H—O—CH3

propanoic acid methanol O

CH3—CH2—C—O—CH3 + H2O

Solution

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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 alcohol from acid O

methyl CH3— O—C —CH3

ethanoate (acetate)

IUPAC: methyl ethanoate

common: methyl acetate

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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.

CH3

O

CO

OH

O

C

OH

CH3O

O

C

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Esters in Plants

Esters give flowers andfruits theirpleasant fragrances and flavors.

TABLE 16.4


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Learning Check

Give the IUPAC and common names of the following compound, which is responsible for the flavor and odor of pears.

O

CH3—C—O—CH2—CH2—CH3

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Give the IUPAC and common names of the following compound, which is responsible for the flavor and odor of pears.

from 1-propanol O CH3—C—O—CH2—CH2—CH3

Propyl ethanoate (IUPAC)Propyl acetate (common)

Solution

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Learning Check

Name the following esters: O ║A. CH3—CH2—CH2—C—O—CH3

O

B. CH3—CH2 —C—O—CH2—CH3

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Solution

A. Methyl butanoate (methyl butyrate)

B. Ethyl propanoate (methyl propionate)

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Learning Check

Write the structure of the following esters:

A. Ethyl pentanoate

B. Propyl butyrate

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Solution

A. Ethyl pentanoate O ║

CH3—CH2—CH2—CH2—C—O—CH2—CH3

B. Propyl butyrate

O ║

CH3—CH2—CH2—C—O—CH2—CH2—CH3

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16.5

Properties of Esters


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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—CH2—CH3 + H2O

O H—C—OH + H—O—CH2—CH3

Acid Hydrolysis of Esters

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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 ||

CH3—C—O—CH2—CH3 + NaOH O

CH3—C—O– Na+ + HO—CH2—CH3

salt of carboxylic acid alcohol

Base Hydrolysis (Saponification)

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“Soaps”

The base hydrolysis of long chain fatty acids produces acid salts called “soaps”.


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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.


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Write the organic products when methyl acetate reacts withA. Water and an acid catalyst

B. KOH

Learning Check

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Write the organic products when methyl acetate reacts with:A. Water and an acid catalyst

O CH3—C—OH + HO—CH3

B. KOH O

CH3—C—O– K+ + HO—CH3

Solution

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