Organic Chemistry

Section 17.21 Dicarboxylic Acids and Their Derivatives 717

COH

COH

HOCOH

O

HOC COH

O

HOCCH 2 COH

O O

HOCCH 2 CH 2 COH

O O

HOCCH 2 CH 2 CH 2 COH

O O

HOCCH 2 CH 2 CH 2 CH 2 COH

Phthalic acid

Carbonic acid

Oxalic acid

Malonic acid

Succinic acid

Glutaric acid

Adipic acid

2.95

3.58

1.27

2.86

4.21

4.34

4.41

5.41

6.35

4.27

5.70

5.64

5.27

5.28

O O

O

O

O

Table 17.2 Structures, Names, and pKa Values of Some Simple Dicarboxylic

Acids

Dicarboxylic acid Common name pKa1 pKa2

show that the acid-strengthening effect of the COOH group decreases as the separation
between the two carboxyl groups increases.
Dicarboxylic acids readily lose water when heated if they can form a cyclic anhydride
with a five- or a six-membered ring.

Cyclic anhydrides are more easily prepared if the dicarboxylic acid is heated in the
presence of acetyl chloride or acetic anhydride or if it is treated with a strong dehy-
drating agent such as P 2 O 5.

CH 2

CH 2

∆

C OH

O

O

O

glutaric anhydride

phthalic anhydride

OH+ 2 O

CH 2 C OH

O

glutaric acid

∆

C OH

O

COH

O

phthalic acid

+ H 2 O

O

O

O