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.

Where is Phthalic anhydride used?

• Alkyd resins: primary building block controlling resin hardness, drying behavior, and film durability in architectural and industrial coatings
• Plastics processing: reacts with alcohols to produce phthalate plasticizers that modify flexibility in PVC compounds for cables, flooring, and packaging films
• Unsaturated polyester resins: key monomer determining crosslink density and mechanical performance of composites and laminates
• Precursor to phthalocyanine pigments and synthetic musks and fragrance intermediates used in personal care formulations
• It supplies reactive anhydride groups for the synthesis of resins, plasticizers, dyes, and specialty esters.
• Used worldwide for the production of polyester polyols.
• Used as a hardener and crosslinker for polymers.

Formulation notes

• Can react violently with alcohols, amines (including 1,2-diaminoethane, 1,3-diphenyltriazene, ethanolamine, ammonia), amides, inorganic hydroxides, barium peroxide, calcium permanganate, peroxyacetic acid, sodium dichromate, sodium peroxide, aniline, and hypochlorous acid.
• Attacks certain plastics, rubber, and coatings.
• Decomposes on contact with hot water, forming phthalic acid.
• Reacts with strong oxidants, strong acids, strong bases, and reducing agents.

Typical specification

• Purity is at least 99.8 wt% as determined by titration.
• Maleic anhydride content is at most 0.10 wt% as determined by GC.
• Colour is at most 10 Hazen/APHA as determined by visual or colorimeter.
• Moisture content is at most 0.10 wt% as determined by Karl Fischer.
• Supplied in white crystal or flake form.

Regulatory status

• Causes skin irritation (H315) under the harmonised CLP classification.
• The occupational exposure limit (INSST 2021) is 1 ppm (6 mg/m³) as an 8-hour time-weighted average, with a sensitizer notation.
• With more than 0.05% maleic anhydride, classified for transport as UN 2214, hazard class 8, packing group III.

Storage, packaging and handling

• Should not be allowed to contact moisture.
• Store separated from combustible substances, reducing agents, strong oxidants, strong bases, strong acids, and food and feed.
• Store with ventilation along the floor, dry, well closed, and only in the original packaging.
• Can be transported in molten form.

Frequently asked questions about Phthalic anhydride

In which applications is phthalic anhydride used beyond resins and plasticizers?

It is used in the production of rubber accelerators and various chemical intermediates.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.