22. Carboxylic Acid Derivatives: NAS

Which of the following best describes the first step in the acid-catalyzed transesterification mechanism of an ester with an alcohol?

Starting with methyl acetate, what neutral nucleophile would you use to synthesize each of the following compounds? a. ethyl acetate

1,4-Diazabicyclo[2.2.2]octane (abbreviated DABCO) is a tertiary amine that catalyzes transesterification reactions. Explain how it does this.

What reagents would you use to convert methyl propanoate to the following compounds?

a. isopropyl propanoate

b. sodium propanoate

What products are obtained from the following reactions? b. phenyl acetate + excess ethanol + HCl

Write the mechanism for the acid-catalyzed transesterification of ethyl acetate with methanol.

Show how you would use anhydrides to synthesize the following compounds. In each case, explain why an anhydride might be preferable to an acid chloride.

(a) n-octyl formate

(b) n-octyl acetate

Propose a mechanism for the following ring-opening transesterification. Use the mechanism in Problem 21-13 as a model.

a. Draw the mechanism for the following reaction if it involves specific-base catalysis.

Grignard reagents add to carbonate esters as they add to other esters.

(c) Diethyl carbonate is a liquid reagent that is easy to handle. In contrast, phosgene is a highly toxic and corrosive gas. Show how you might use diethyl carbonate instead of phosgene to make Lexan®.

Acid-catalyzed transesterification and Fischer esterification take place by nearly identical mechanisms. Transesterification can also take place by a base-catalyzed mechanism, but all attempts at base-catalyzed Fischer esterification (using –OR″, for example) seem doomed to failure. Explain why Fischer esterification cannot be catalyzed by base.

Predict the products of the following reactions.

(g)

Acid-catalyzed transesterification:

Complete the mechanism for this acid-catalyzed transesterification by drawing out all the individual steps. Draw the important resonance contributors for each resonance-stabilized intermediate.