When acetic acid reacts with ketene , product formed is :

Explanation

To solve the question of what product is formed when acetic acid reacts with ketene, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- Acetic acid (CH₃COOH) is a carboxylic acid with the structure:
\[ \text{CH}_3 - \text{C}(=O) - \text{OH} \]
- Ketene (CH₂=C=O) is an unsaturated compound with the structure:
\[ \text{CH}_2 = \text{C}(=O) \]

2. **Write the Reaction**:
- When acetic acid reacts with ketene, the reaction can be represented as:
\[ \text{CH}_3COOH + \text{CH}_2=C=O \rightarrow \text{Product} \]

3. **Understand the Mechanism**:
- The reaction involves the nucleophilic attack of the acetic acid on the electrophilic carbon of ketene. The hydroxyl (OH) group of acetic acid can attack the carbon of ketene, leading to the formation of an intermediate.

4. **Formation of Acetic Anhydride**:
- The intermediate formed will lose a water molecule (dehydration), resulting in the formation of acetic anhydride. The structure of acetic anhydride is:
\[ \text{CH}_3COO - \text{C}(=O) - \text{CH}_3 \]
- This can also be represented as:
\[ \text{(CH}_3\text{CO)}_2\text{O} \]

5. **Final Product**:
- Therefore, the product formed when acetic acid reacts with ketene is acetic anhydride.

### Final Answer:
The product formed when acetic acid reacts with ketene is **acetic anhydride**.

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