Phthalic anhydride is a versatile intermediate in organic chemistry, in part because it is bifunctional and cheaply available. Hydrolysis by hot water forms ortho-phthalic acid.[5]
Hydrolysis of anhydrides is not typically a reversible process.
Phthalic acid is however easily dehydrated to form phthalic anhydride.
Above 180 °C, phthalic anhydride re-forms
