What is the result when phthalic acid amhydridr is heated?

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