Organic Chemistry

acetyl chloride

686 CHAPTER 17 Carbonyl Compounds I

PROBLEM 9

What will be the product of a nucleophilic acyl substitution reaction—a new carboxylic

acid derivative, a mixture of two carboxylic acid derivatives, or no reaction—if the new

group in the tetrahedral intermediate is the following?

a. a stronger base than the group that was already there

b. a weaker base than the group that was already there

c. similar in basicity to the group that was already there

17.8 Reactions of Acyl Halides

Acyl halides react with carboxylate ions to form anhydrides, with alcohols to form es-

ters, with water to form carboxylic acids, and with amines to form amides because in

each case the incoming nucleophile is a stronger base than the departing halide ion

(Table 17.1). Notice that both alcohols and phenols can be used to prepare esters.

All the reactions follow the general mechanism described in Section 17.7. In the

conversion of an acyl chloride into an acid anhydride, the nucleophilic carboxylate ion

attacks the carbonyl carbon of the acyl chloride. Because the resulting tetrahedral inter-

mediate is unstable, the double bond is immediately reformed, expelling chloride ion

because it is a weaker base than the carboxylate ion. The final product is an anhydride.

+ OH +

phenyl propionate

+ H 2 O +

butyryl chloride butyric acid

+ 2 CH 3 NH 2 + CH 3 NH 3 Cl−

+

cyclohexanecarbonyl N-methylcyclohexanecarboxamide

chloride

NHCH 3

H+ + Cl−

H+ + Cl−

propionyl chloride

CH 3 CH 2 Cl

Cl

C

O

CH 3 CH 2 O

C

O

CH 3 CH 2 CH 2 OH

C

O

CH 3 CH 2 CH 2 Cl

C

O

C

O

C

O

++Cl−

H+ + Cl−

acetyl chloride acetic anhydride

+ CH 3 OH +

benzoyl chloride methyl benzoate

OCH 3

CH 3 Cl

Cl

C

O

CH 3 O

C

O

CH 3

C

O

CH 3 O−

C

O

C

O

C

O

3-D Molecule:

Benzoyl chloride