Organic Chemistry

The hydrolysis of methyl trifluoroacetate has two slow steps. increases the
rate of the first slow step by providing metal-bound hydroxide ion, a better nucleophile
than water. increases the rate of the second slow step by decreasing the basicity
of the group that is eliminated from the tetrahedral intermediate.

PROBLEM 7

The rate constant for the uncatalyzed reaction of two molecules of glycine ethyl ester to form

glycylglycine ethyl ester is In the presence of the

rate constant is What rate enhancement does the catalyst provide?

PROBLEM 8

Although metal ions increase the rate of decarboxylation of dimethyloxaloacetate, they

have no effect on the rate of decarboxylation either of the monoethyl ester of dimethylox-

aloacetate or of acetoacetate. Explain why this is so.

PROBLEM 9

The hydrolysis of glycinamide is catalyzed by Propose a mech-

anism for this reaction.

Co^2 +

H 2 NCH 2 CNH 2 +

O

H 2 O H 2 NCH 2 CO− + +

O

NH 4

[Co(ethylenediamine) 2 ]^2 +.

dimethyloxaloacetate

acetoacetate

monoethyl ester of

dimethyloxaloacetate

O

C

O

C

CH 3

CH 3

C

O

−O C O− O−

O

C CH 2

O

CH 3 C O−

O

C

O

C

O

C C

CH 3

CH 3

CH 3 CH 2 O

1.5* 106 s-^1 M-^1.

0.6 s-^1 M-^1. [Co(ethylenediamine) 2 ]^2 +,

Zn^2 +

Zn^2 +

O

C +

O

OO

−O

C

CH 3

CH 3

C C

Cu Cu

O

O

−O

C

CH 3

CH 3

CCOC 2

+ − −

+ +

Section 24.5 Metal-Ion Catalysis 1009

Zn

Zn

Zn

Zn

Zn

Zn

OH 2

OH + H+

slow

slow

CF 3 OCH 3

H 2 O

C

O

CF 3 OH

C

O

CF 3 C OCH 3

OH

O−

CF 3 C OCH 3

OH

O−

CF 3 C OCH 3

OH

O

OH 2 + OCH 3

−

metal-bound

hydroxide ion

decreases the

basicity of the

leaving group

+

+

+

−

−

+

+

+

+ +

+

+