Overview
Phthalic anhydride is an organic compound belonging to the class of cyclic dicarboxylic anhydrides. First synthesized in the 19th century, it became industrially significant in the 1920s with the development of phthalate plasticizers. Today, it serves as a foundational chemical for polyester resins, accounting for approximately 60% of global consumption. Manufactured primarily via catalytic oxidation of ortho-xylene, modern production processes achieve yields exceeding 95%. The compound's reactivity stems from its strained anhydride ring, which readily opens to form esters and amides. Global production exceeds 5 million metric tons annually, with major manufacturers concentrated in Asia, North America, and Europe.
Physical and Chemical Properties
As a white crystalline solid, phthalic anhydride sublimes at temperatures above 100°C without melting—a property utilized in purification processes. Its vapor pressure reaches 1 mmHg at 96.3°C, requiring careful handling to prevent airborne exposure in industrial settings. The compound hydrolyzes slowly in cold water but rapidly in hot water to form phthalic acid. In alkaline solutions, this reaction occurs instantaneously. Characteristic IR absorption at 1850 and 1780 cm⁻¹ confirms the anhydride functional group. Its reactivity with alcohols forms phthalate esters, while reactions with amines produce imides—key intermediates for high-performance polymers.
Main Applications
The largest application (60-70% of production) involves plasticizer synthesis, particularly dioctyl phthalate (DOP) for PVC products. These plasticizers impart flexibility to vinyl flooring, cables, and medical tubing. Unsaturated polyester resins (UPRs) consume 15-20%, serving in fiberglass-reinforced composites for marine and automotive parts. In coatings, phthalic anhydride-modified alkyd resins enhance drying time and durability for industrial paints. Smaller applications include anthraquinone dyes for textiles, flame retardants like resorcinol bis(diphenyl phosphate), and pharmaceutical intermediates such as phenolphthalein. Emerging uses include bio-based plasticizers and epoxy curing agents.
Safety and Storage
Classified as a Category 2 skin/eye irritant under GHS, phthalic anhydride requires NIOSH-approved respirators with P100 filters during handling. Dust explosions are possible (LEL 1.7% in air), necessitating explosion-proof equipment in processing areas. Storage recommendations include double-walled containers with desiccants to prevent moisture absorption. Bulk storage silos should maintain temperatures below 40°C with nitrogen blanketing. Spills should be neutralized with sodium carbonate solution, never water, to avoid exothermic hydrolysis. First aid measures include flushing eyes/skin with water for 15 minutes and seeking immediate medical attention for inhalation exposure.
B2B Procurement Guide
Industrial buyers should specify technical grade (≥99.5%) or refined grade (≥99.8%) depending on application requirements. Key quality parameters include maleic anhydride content (<0.1%), iron content (<3 ppm), and color (APHA <30). Major shipping options include ISO tank containers for molten product (140-150°C) or multi-layer paper bags for solid form. Price fluctuations correlate with ortho-xylene feedstock costs—typically 0.65-0.75 metric tons of o-xylene yields 1 ton of phthalic anhydride. Evaluate suppliers for ISO 9001 certification, on-site phosgene monitoring (byproduct risk), and capacity for just-in-time delivery to minimize inventory costs.
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