Abstract

There are 11 benzenepolycarboxylic acids, some of which are sold as the anhydride or the methyl ester. Two of these substances, terephthalic acid and phthalic anhydride, are principal chemical products. Two others, isophthalic acid and trimellitic anhydride, have substantial commercial sales. The rest have low volume specialized applications or are not available commercially. This is a review of the basic physical properties, manufacturing methods, production volumes and prices, toxicological aspects, and uses of these compounds.

Terephthalic acid and its dimethyl ester rank about tenth in tonnage for all organic chemicals, and production is expanding substantially. They are used to make poly(ethylene terephthalate) for fibers, film, and containers. The principle mode of commercial manufacture is direct liquid-phase oxidation of p-xylene using a homogeneous heavy metal–bromine catalyst system. Isophthalic acid and trimellitic anhydride are made from m-xylene and pseudocumene respectively using the same process.

Phthalic anhydride is made primarily by gas-phase oxidation of o-xylene over a fixed catalyst containing vanadium and titanium oxides. It is used as a raw material for plasticizers, unsaturated polyesters, and other resins.