Organic Chemistry

760 CHAPTER 18 Carbonyl Compounds II

An amino group can be protected by being converted into an amide (Section 17.8).

The acetyl group can subsequently be removed by acid-catalyzed hydrolysis.

Protecting groups should be used only when absolutely necessary, because each

time a protecting group is used, it must be attached and then taken off. This adds two

steps to the synthesis, which decreases the overall yield of the target compound (the

desired product).

PROBLEM 31

What products would be formed from the preceding reaction if aniline’s amino group were

not protected?

PROBLEM 32

a. In a six-step synthesis, what will be the yield of the target compound if each of the

reactions employed gives an 80% yield? (An 80% yield is a relatively high labora-

tory yield.)

b. What would be the yield if two more steps were added to the synthesis?

PROBLEM 33

Show how each of the following compounds can be prepared from the given starting mate-

rial. In each case, you will need to use a protecting group.

a.

b.

O

C

H

Br

O

C

H

COOH

HO CH 2 CH 2 CH 2 Br HO CH 2 CH 2 CH 2 CHCH 3

OH

O

CH 3 CHCH 2 COCH 2 CH 3

OH

O

CH 3 CHCH 2 COCH 2 CH 3

Cl

CH 3 CHCH 2 COH

OH

O

HCl

CH 3 CH 2 OH

excess

+

O

CH 3 CHCH 2 COH

COOH

O

CH 3 CHCH 2 COCH 2 CH 3

CN

CH 3 CH 2 OH

HCl

H 2 O

∆

−CN

SOCl 2

aniline

NH 2

O

O

acetanilide

HNCCH 3

O

p-nitroacetanilide

HNCCH 3

NO 2

p-nitroaniline

NH 2

+ CH 3 CO−

NO 2

CH 3 CCl HNO 3

H 2 SO 4

1. HCl, H 2 O, ∆


2. HO−

O