Organic Chemistry

854 CHAPTER 20 More About Oxidation–Reduction Reactions

the oxidation of cyclohexyl methyl ketone form methyl cyclohexanecarboxylate or cy-

clohexyl acetate?

To answer this question, we must look at the mechanism of the reaction. The ketone

and the peroxyacid react to form an unstable tetrahedral intermediate with a very weak

bond. As the bond breaks heterolytically, one of the alkyl groups

migrates to an oxygen. This rearrangement is similar to the 1,2-shifts that occur when

carbocations rearrange (Section 4.6).

Several studies have established the following order of group migration tendencies:

Therefore, the product of the Baeyer–Villiger oxidation of cyclohexyl methyl ketone

will be cyclohexyl acetate because a secondary alkyl group (the cyclohexyl group) is

more likely to migrate than a methyl group. Aldehydes are always oxidized to car-

boxylic acids, since H has the greatest tendency to migrate.

PROBLEM 11

Give the products of the following reactions:

a. d.

b. e.

c. f.

O

CH 3 CH 2 CH 2 CCH 3

1. Ag 2 O, NH 3


2. H 3 O+

O

CH (^3) RCOOH
O
O
CH 3 CH 2 CH 2 CH

1. Ag 2 O, NH 3


2. H 3 O+

O

CH

RCOOH

O

O

CH 3 CH C

CH 3 CH 3

CH 3

CCH 3

RCOOH

O O

CCH 2 CH 3

RCOOH

O

O¬O O¬O

RCOOH

O

or

?

cyclohexyl methyl

ketone

methyl

cyclohexanecarboxylate cyclohexyl

acetate

CH 3 OCH 3

C

O

C

O

O CH 3

C

O

OCCH 3

C CH 3 COOH

OO

B

+ + CH 3 CO−

O

RC

O−

O

HO

R′

OCCH 3

RC

O−

O

O

R′

+ HB+

an unstable

intermediate

R′ OR

mechanism of the Baeyer–Villiger oxidation

C

O

RR′

H tert-alkyl sec-alkyl = phenyl primary alkyl > methyl

relative migration tendencies

most likelyto migrate >>> least likelyto migrate

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