The compound that gives a lactone on heating is

Options

A. pentanedioic acid
B. 4-hydroxypentanoic acid
C. 4-aminopentanoic acid
D. 2-hydroxypentanoic acid

Answer

To determine which compound gives a lactone upon heating, we need to analyze the four options provided. A lactone is a cyclic ester formed from the reaction of a hydroxy acid, where the hydroxyl group (-OH) reacts with the carboxylic acid group (-COOH) to form a ring structure.

### Step-by-Step Solution:

1. **Understanding Lactones**:
- A lactone is formed when a hydroxy acid loses a molecule of water (H2O) during heating, resulting in a cyclic structure. The general structure of a lactone includes a carbonyl group (C=O) and an ether linkage (C-O) in a ring.

2. **Analyzing the First Compound: Pentane-1,2-dioic acid**:
- Structure: This compound has five carbon atoms with two carboxylic acid groups at positions 1 and 2.
- Upon heating, water is eliminated between the two carboxylic acid groups, forming a six-membered ring. However, this structure does not fit the definition of a lactone as it contains two carboxylic acid groups and does not form a cyclic ester.
- **Conclusion**: Not a lactone.

3. **Analyzing the Second Compound: 4-Hydroxypentane-1,2-dioic acid**:
- Structure: This compound has five carbon atoms, with a hydroxyl group at position 4 and two carboxylic acid groups at positions 1 and 2.
- Upon heating, the hydroxyl group at position 4 can react with one of the carboxylic acid groups, leading to the formation of a five-membered lactone. The structure will include a carbonyl group and an ether linkage, fitting the definition of a lactone.
- **Conclusion**: This compound forms a lactone.

4. **Analyzing the Third Compound: 2-Aminopentanoic acid**:
- Structure: This compound has five carbon atoms, with an amino group at position 2 and a carboxylic acid group at position 1.
- Upon heating, the amino group does not facilitate the formation of a lactone. Instead, it can lead to the formation of an amide, which does not fit the lactone criteria.
- **Conclusion**: Not a lactone.

5. **Analyzing the Fourth Compound: 2-Hydroxy-pentanoic acid**:
- Structure: This compound has five carbon atoms, with a hydroxyl group at position 2 and a carboxylic acid group at position 1.
- Upon heating, the hydroxyl group can react with the carboxylic acid group to form a cyclic structure. However, this structure is highly strained and unstable, leading to the formation of an epoxy compound rather than a stable lactone.
- **Conclusion**: Not a lactone.

### Final Answer:
The compound that gives a lactone upon heating is **4-Hydroxy-pentane-1,2-dioic acid**.