22. Carboxylic Acid Derivatives: NAS

D. N. Kursanov, a Russian chemist, proved that the bond that is broken in the hydroxide-ion-promoted ­hydrolysis of an ester is the acyl C—O bond, rather than the alkyl C—O bond, by studying the hydrolysis of the following ester under basic conditions:

a. What products contained the ¹⁸O label?

b. What product would have contained the ¹⁸O label if the alkyl C—O bond had broken?

The intermediate shown here is formed during the hydroxide-ion-promoted hydrolysis of the ester group. Propose a mechanism for the reaction.

Predict the products and propose mechanisms for the following reactions.

(b)

Suppose we have some optically pure (R)-2-butyl acetate that has been 'labeled' with the heavy ¹⁸O isotope at one oxygen atom as shown.

(a) Draw a mechanism for the hydrolysis of this compound under basic conditions. Predict which of the products will contain the ¹⁸O label. Also predict whether the butan-2-ol product will be pure (R), pure (S), or racemized.

Propose a mechanism for the base-promoted hydrolysis of γ-butyrolactone:

Explain why we speak of acidic hydrolysis of an ester as acid-catalyzed, but of basic hydrolysis as base-promoted.

Soap manufacturers always use base to hydrolyze fats, and never acid. Suggest two reasons that basic hydrolysis is preferred.

Predict the products of saponification of the following esters.

(a)

Predict the products of saponification of the following esters.

(b)

Predict the products of saponification of the following esters.

(c)

Predict the products of saponification of the following esters.

(d)

Methyl p-nitrobenzoate has been found to undergo saponification faster than methyl benzoate.

(a) Consider the mechanism of saponification, and explain the reasons for this rate enhancement.

Methyl p-nitrobenzoate has been found to undergo saponification faster than methyl benzoate.

(b) Would you expect methyl p-methoxybenzoate to undergo saponification faster or slower than methyl benzoate?

What are the products of the following reactions?

i.

j.