Phthalic anhydride

Phthalic anhydride is the cyclic anhydride of phthalic acid, an aromatic compound used chiefly as a feedstock for plasticizers, resins, dyes, and other chemicals.

o-Xylene oxidation: An industrial process that oxidizes o-xylene to phthalic anhydride using air and a catalyst. This is the principal modern route from a petroleum-derived feedstock to phthalic anhydride.
Diethylhexyl phthalate: A phthalate ester used as a plasticizer, especially in flexible polyvinyl chloride. Phthalic anhydride is a starting material for this widely used plasticizer.
Friedel–Crafts reaction: A class of reactions that uses a Lewis acid to attach alkyl or acyl groups to aromatic rings. Early phthalic anhydride synthesis used Friedel–Crafts chemistry to build an aromatic precursor.
Maleic anhydride: A cyclic anhydride derived from maleic acid, widely used to make resins and chemical intermediates. It is a major industrial anhydride, but its ring is unsaturated and nonaromatic.
Naphthalene oxidation: The catalytic oxidation of naphthalene, used industrially to produce phthalic anhydride. This older production route established phthalic anhydride manufacture before o-xylene became dominant.
Alkyd resin: A polyester resin modified with fatty acids or oils, used in paints and coatings. Phthalic anhydride supplies aromatic acid units for many alkyd resins.
Coal tar: A complex mixture of chemicals produced during the destructive distillation of coal. Naphthalene recovered from coal tar historically supplied feedstock for phthalic anhydride.
Succinic anhydride: A five-membered cyclic anhydride derived from succinic acid. It shares the cyclic anhydride structure but lacks phthalic anhydride's fused benzene ring.
Phthalate ester: An ester derived from phthalic acid, commonly made by reacting an alcohol with phthalic anhydride. Alcohol ring-opening converts the anhydride into commercially important phthalate esters.
Unsaturated polyester resin: A thermosetting resin formed from unsaturated polyesters and typically cured with a reactive monomer. Phthalic anhydride can provide the aromatic component of these resins.

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PhenolphthaleinRelated: It is a starting material in the classic synthesis of phenolphthalein.