Concept:Acid anhydrides are literally formed by removing a water molecule (dehydration) from two molecules of a carboxylic acid. This requires a powerful, specialized dehydrating agent.
Formula:$$ 2\text{R-COOH} \xrightarrow{\text{P}_2\text{O}_5, \Delta} (\text{R-CO})_2\text{O} + \text{H}_2\text{O} $$
Solution:- Phosphorus pentoxide (\( \text{P}_2\text{O}_5 \)) is one of the strongest dehydrating agents known in chemistry.
- When heated with a carboxylic acid, it forcefully extracts \( \text{H}_2\text{O} \), chemically locking the two acid remnants into an anhydride linkage.
Why other options are incorrect:\( \text{H}_2\text{SO}_4 \) is a dehydrating agent, but it is typically used for esterification or dehydrating alcohols to alkenes. \( \text{P}_2\text{O}_5 \) is required for the much more difficult dehydration of acids to anhydrides.
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