[5] The modern industrial variant process instead uses vanadium pentoxide (V2O5) as the catalyst in a gas-phase reaction with naphthalene using molecular oxygen.

[4] The primary use of phthalic anhydride is a precursor to phthalate esters, used as plasticizers in vinyl chloride.

[4] In the 1980s, approximately 6.5 million tonnes of these esters were produced annually, and the scale of production was increasing each year, all from phthalic anhydride.

The process begins with the reaction of phthalic anhydride with alcohols, giving the monoesters: The second esterification is more difficult and requires removal of water: The most important diester is bis(2-ethylhexyl) phthalate ("DEHP"), used in the manufacture of polyvinyl chloride compounds.

A well-known application of this reactivity is the preparation of the anthraquinone dye quinizarin by reaction with para-chlorophenol followed by hydrolysis of the chloride.

[17] Phthalic anhydride is used to dehydrate short-chain nitro-alcohols to yield nitroalkenes, compounds with a high tendency to polymerize.

Studies show that exposure to phthalic anhydride can cause rhinitis, chronic bronchitis, and asthma.