Carboxylic Acids and Carboxylic Acid Derivatives

Chapter 15

Pages 408-438

Structure of Carboxylic Acids

R C OHO

The carboxyl group is shown in red and may be written in the condensed form: -COOH.The term carboxylic is taken from the terms carbonyl and hydroxyl, the two structures that make up the carboxyl group.

Properties of Carboxylic Acids

• Very polar compounds• Can hydrogen bond to one another and to water• Boil at higher temperatures than aldehydes,

ketones, or alcohols• Smaller carboxylic acids are soluble in water• Lower molecular weight acids have sharp, sour

tastes and unpleasant aromas• Longer chain carboxylic acids are called fatty

acids and are important components of biological membranes

Naming Carboxylic Acids - IUPAC

• Determine the name of the parent compound, the longest continuous chain containing the carboxyl group.

• Replace the –e ending with the suffix –oic acid. If there are two carboxyl groups, the suffix is –dioic acid.

• Number the chain so the carboxyl carbon is number 1.

• Name and number substituents.

Naming carboxylic acids of cycloalkanes

• Add the suffix carboxylic acid to the name of the cycloalkane or substituted cycloalkane.

• The carboxyl group is always numbered 1.

• Other substituents are named and numbered as usual.

C

O

OHCyclopentanecarboxylic acid

Name the following.

CH3CHCH2CHCOOH

CH3 CH3

CH2CH2CHCOOH

Cl Cl

COOH

CH3

COOH

CH2CH3

Name the following.

CH3CHCH2CHCOOH

CH3 CH3

CH2CH2CHCOOH

Cl Cl

COOH

CH3

COOH

CH2CH3

2,4-dimethylpentanoic acid

3-methylcyclohexanecarboxylic acid

2-ethylcyclopentanecarboxylic acid

2,4-dichlorobutanoic acid

Common Carboxylic Acids

Name Structure Source

Formic acid HCOOH Ants

Acetic acid CH3COOH Vinegar

Propionic acid CH3CH2COOH Swiss Cheese

Butyric acid CH3(CH2)2COOH Rancid butter

Stearic acid CH3(CH2)16COOH Beef fat

Draw structures for the following.

• 2,3-dihydroxybutanoic acid

• 2-bromo-3-chloro-4-methylhexanoic acid

• 1,4-cyclohexanedicarboxylic acid

• 4-hydroxycyclohexanecarboxylic acid

• Formic acid

• Acetic acid

Naming Aromatic Carboxylic Acids

• These are usually named as derivatives of benzoic acid.

• Generally, the –oic acid or –ic acid suffix is attached to the appropriate prefix.

C OH

O

Bro-bromobenzoic acid

Naming Aromatic Carboxylic Acids

• Often, the phenyl group is treated as a substituent.

H2C C

O

OH HC

CH3

H2C

H2C C

O

H

2-phenylethanoic acid 4-phenylpentanoic acid

Draw structures for the following.

• 2,4,6-tribromobenzoic acid

• 2,2,2-triphenylethanoic acid

• 3-phenylhexanoic acid

• 3-phenylcyclohexanecarboxylic acid

Preparation of Carboxylic Acids

• As discussed in Ch 14, carboxylic acids can be prepared from the oxidation of primary alcohols and/or aldehydes.

1º alcohol Aldehyde Carboxylic acid

Examples:

a)1-propanol

b)2-methylbutanal

[O ]

[O ]

Carboxylic acid - ACID

• Carboxylic acids act as acids because they are proton (H+) donors. They are weak acids that dissociate to form a carboxylate ion and a hydrogen ion as shown:

carboxylic acid carboxylate anion hydrogen ion

R

O

OH

R

O

O-

+ H+

Acid/Base Reaction

• Since a carboxylic acid acts as an acid, it will neutralize a strong base like NaOH or KOH to form water and the salt of the carboxylic acid.

R

O

OH

+ NaOH R

O

O-

Na+

+ OH2

Examples

Write a balanced equation and name the products that are formed.

Acetic acid + sodium hydroxide

Benzoic acid + potassium hydroxide

YOU TRY THESE!

• Propanoic acid + potassium hydroxide

• Ethanol

• Butanedial

• Hexanoic acid + sodium hydroxide

[O ]

[O ]

Structure of Esters

R C ORO

•Esters are carboxylic acid derivatives.•They are formed from the reaction of a carboxylic acid with an alcohol.

Formation of an Ester

R1 C OH

O

+ R2 OH R1 C O R2

O

+ H2O

Carboxylic acid alcohol Ester WaterEXAMPLE

H3C C OH

OH2C OH

H3C C O CH2CH3

O

+ H2O

H3C+

Ethanoic acid ethanol(Acetic Acid)

Ethyl ethanoate(Ethyl acetate)

H+, heat

H+, heat

Properties of Esters

• Mildly polar• Have pleasant aromas• Found in natural foodstuffs (banana oil,

pineapples, raspberries, etc.)• Boil at approximately the same

temperature as aldehydes or ketones of similar molecular weights

• Simpler ones are somewhat soluble in water

Naming Esters

• Use the alkyl portion of the alcohol as the first name.

• Remove the –ic acid ending of the carboxylic acid and replace it with –ate.

• The same naming rules apply if the common name of the carboxylic acid is used.

Examples of Ester Names

H3C C O CH3

O

H3C C O CH2CH2CH3

O

C O CH3

O

C O CH3

O

Br

Methyl ethanoate (methyl acetate)

Propyl ethanoate (propyl acetate)

Methyl benzoate Methyl m-bromobenzoate

You Try These!

H3C C O

O

H2C C O CH3

O

C O CH3

O

C O CH2CH3

O

NO2

H2CH3C

Answers to You Try These!

• Cyclopentyl ethanoate

– (cyclopentyl acetate)

• Ethyl cyclohexanecarboxylate

• Methyl p-nitrobenzoate

• Methyl butanoate

Formation of Soap - Esterification

• Fats and oils are triesters of the alcohol glycerol.

3 CH3(CH2)14COOH

3 Palmitic acid+

H2C

HC

H2C

OH

OH

OH

Glycerol

H2C O C(CH2)14CH3

O

HC

H2C

O

O

C(CH2)14CH3

C(CH2)14CH3

O

O

TriglycerideTripalmitoylglyceride

Formation of Soap - Saponification

• When they are hydrolyzed by saponification, the products are soaps.

H2C O C(CH2)14CH3

O

HC

H2C

O

O

C(CH2)14CH3

C(CH2)14CH3

O

O

NaOH

H2O, heat

+Na-O C(CH2)14CH3

O

+Na-O C(CH2)14CH3

O

+Na-O C(CH2)14CH3

O

Acid Chlorides

R C ClO

IUPAC name - Replace the –oic acid ending of the IUPAC name with –oyl chloride.Common name – Replace the –ic acid ending of the common name with –yl chloride.

Examples of Acid Chlorides

H3C C Cl

O

H2CH2C C Cl

O

Br

C ClCl

O

Ethanoyl chloride(acetyl chloride)

3-bromopropanoyl chloride

p-chlorobenzoyl chloride(4-chlorobenzoyl chloride)

Properties of Acid Chlorides

• Noxious, irritating chemicals

• Slightly polar

• Boil at approximately the same temperature as aldehydes or ketones of similar molecular weights

• React violently with water

Formation of Acid Chlorides

R C OH

O PCl3, PCl5, or SOCl2

R C Cl

O

Carboxylic acid Acid Chloride

H3C C O H

O

H3C C Cl

OPCl5

Ethanoic acid Ethanoyl chloride(acetic acid) (acetyl chloride)

Hydrolysis of Acid Chlorides

R C Cl

O

R C OH

O+ H2O

+ HCl

Acid chloride water Carboxylic acid Hydrochloric acid

H3C C Cl

O

H3C C OH

O+ H2O

+ HCl

Ethanoyl chloride ethanoic acid

(acetyl chloride) (acetic acid)

Acid Anhydrides

R C OO

C RO

An acid anhydride is two carboxylic acids with a water molecule removed.“Anhydride” means without water.

Formation of Acid Anhydrides

R C O C R

O O

R C OH

O

+ R C OH

O

Carboxylic acid Carboxylic acid

Acid anhydride

+ H OH

Water