Phthalic anhydride

Phthalic anhydride (CAS 85-44-9), commonly abbreviated as PA, is a white crystalline solid produced by the catalytic oxidation of naphthalene or o-xylene. It functions as a foundational chemical intermediate. This material supplies reactive anhydride groups for the synthesis of resins, plasticizers, dyes, and specialty esters across multiple industrial sectors. PA is the primary building block for alkyd resins.

These resins are used in architectural and industrial coatings, where it controls resin hardness, drying behavior, and film durability. In plastics processing, it reacts with alcohols to produce phthalate plasticizers. These plasticizers modify flexibility in PVC compounds for cables, flooring, and packaging films. Unsaturated polyester resins for composites and laminates rely on PA as a key monomer for production.

It determines the crosslink density and mechanical performance of the cured material. It also serves as a precursor to phthalocyanine pigments and to synthetic musks and fragrance intermediates. These intermediates are used in personal care formulations. Phthalic anhydride is supplied as white flakes or molten liquid, with flake form being the standard for bulk and bagged shipments.

Technical grade is the predominant commercial specification, with purity typically at 99.5% or higher. It is available in bulk tankers, bulk bags, and 25 kg bags depending on application requirements.