Which of the following is the major product formed by acid-catalyzed hydrolysis of a thioester lactone?

• A. A $\mathrm{carboxylic} \mathrm{acid}$ and a $\mathrm{thiol}$
• B. An $\mathrm{ester}$ and a $\mathrm{thiol}$
• C. A $\mathrm{carboxylic} \mathrm{acid}$ and an $\mathrm{alcohol}$
• D. An $\mathrm{alcohol}$ and a $\mathrm{thiol}$

Answer: (A)

Verified step by step guidance

1. Recognize that a thioester lactone is a cyclic thioester, meaning it contains a sulfur atom bonded to a carbonyl carbon within a ring structure.
2. Understand that acid-catalyzed hydrolysis involves protonation of the carbonyl oxygen, increasing the electrophilicity of the carbonyl carbon and making it more susceptible to nucleophilic attack by water.
3. Identify that water acts as the nucleophile, attacking the protonated carbonyl carbon, leading to ring opening and formation of a tetrahedral intermediate.
4. Realize that the tetrahedral intermediate collapses, breaking the C–S bond (the thioester bond), which results in the formation of a carboxylic acid and a thiol as the products.
5. Conclude that the major products of acid-catalyzed hydrolysis of a thioester lactone are a carboxylic acid and a thiol, because the thioester bond is cleaved and the ring is opened.