Phthalic Anhydride, abbreviated as PA, is an important aromatic cyclic anhydride and a key intermediate in the organic chemical industry. It is a white crystalline solid with a pungent odor, widely used in the production of plasticizers, resins, dyes, and other specialty chemicals.

1.Chemical Identity

Chemical Name: Phthalic Anhydride; 1,3-Isobenzofurandione
Abbreviation: PA
Chemical Formula: C8H4O3
Molecular Weight: 148.12 g/mol
CAS Registry Number: 85-44-9
UN Number 2214 (Class 8 Corrosive Substance)
Structural Feature: A cyclic anhydride formed by the dehydration of phthalic acid, with a benzene ring fused to a five-membered anhydride ring

2 . Core Industrial Applications

PA is a versatile intermediate with extensive applications across multiple industries:
Plasticizer Production (Largest Application)Reacted with alcohols (e.g., 2-ethylhexanol, butanol) to produce phthalate esters, the most widely used plasticizers for polyvinyl chloride (PVC). Key products include DOP (dioctyl phthalate), DBP (dibutyl phthalate), and DINP (diisononyl phthalate), which improve PVC flexibility and processability.
Polymer Resins
Unsaturated Polyester Resins (UPR): Copolymerized with glycols and unsaturated acids to produce UPR, used in fiberglass-reinforced plastics (FRP) for boats, pipes, and construction materials.
Alkyd Resins: Reacted with polyols and fatty acids to form alkyd resins, the base component of industrial coatings, paints, and varnishes.
Dyes and Pigments
Serves as a precursor for phthalocyanine dyes and pigments, which are widely used in textile dyeing, printing inks, and plastic coloring.
Specialty ChemicalsUsed in the synthesis of pharmaceutical intermediates, insecticides, surfactants, and flame retardants. It also acts as a curing agent for epoxy resins.