Question

How do chemists synthesize anhydrides?

Answer 1

They use one of two common methods.

Explanation:

You might think that you could form an anhydride by heating a carboxylic acid.

`"RCOOH" + "HOCOR" stackrelcolor(blue)(Δcolor(white)(m))(→) "RCO-O-COR" + "H"_2"O"`

However, carboxylic acids do not usually lose water by heating.

Chemists therefore use two other methods to synthesize anhydrides.

1. Reaction of carboxylate salts with acyl chlorides

`"CH"_3"COONa" + "CH"_3"COCl" stackrelcolor(blue)(Δ)(→) "CH"_3"CO-O-COCH"_3 + "NaCl"`

2. Using a dehydrating agent

Chemists can also use dehydrating agents to remove the water from carboxylic acids.

Common dehydrating agents are acetic anhydride, trifluoroacetic anhydride, `"PCl"_5`, `"P"_4"O"_10`, and dicyclohexylcarbodiimide (DCC).

`"2CH"_3"COOH" + "P"_4"O"_10 → "CH"_3"CO-O-COCH"_3 + "P"_4"O"_9("OH")_2"`