Propose a mechanism for the acid-catalyzed hydrolysis of phenylalanine ethyl ester.

a. When a carboxylic acid is dissolved in isotopically labeled water (H₂O¹⁸) and an acid catalyst is added, the label is incorporated into both oxygens of the acid. Propose a mechanism to account for this.

c. If an ester is dissolved in isotopically labeled water (H₂O¹⁸) and an acid catalyst is added, where will the label reside in the product?

Show how you would accomplish the following syntheses.

c. hexan-1-ol → 2-hydroxyheptanoic acid

Predict the products and propose mechanisms for the following reactions.

(a)

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.

(b) Repeat part (a) for the acid-catalyzed hydrolysis of this compound.

The Reformatsky reaction is an addition reaction in which an organozinc reagent is used instead of a Grignard reagent to add to the carbonyl group of an aldehyde or a ketone. Because the organozinc reagent is less reactive than a Grignard reagent, a nucleophilic addition to the ester group does not occur.

The organozinc reagent is prepared by treating an α-bromo ester with zinc.

Describe how each of the following compounds can be prepared, using a Reformatsky reaction:

c.

Propose mechanisms for the following reactions.

(c)

Propose mechanisms for the following reactions.

(d)

The mechanism for acidic hydrolysis of a nitrile resembles the basic hydrolysis, except that the nitrile is first protonated, activating it toward attack by a weak nucleophile (water). Under acidic conditions, the proton transfer (tautomerism) involves protonation on nitrogen followed by deprotonation on oxygen. Propose a mechanism for the acid-catalyzed hydrolysis of benzonitrile to benzamide.