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History of phthalic anhydride:
Auguste Laurent first reported phthalic anhydride in 1836. More contemporary
routes include catalytic oxidation of ortho-xylene and naphthalene ("Gibbs phthalic
anhydride process"), although use of naphthalene has declined. Starting from o-
xylene, the oxidation follows the following stoichiometry:
C6H4(CH3)2 + 3 O2 C6H4(CO)2O +3 H2O
Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is
the anhydride of phthalic acid. Phthalic anhydride is a principal commercial form
of phthalic acid. It was the first anhydride of a dicarboxylic acid to be usedcommercially. This colorless solid is an important industrial chemical, especially
for the large-scale production of plasticizers for plastics. In 2000, the world wide
production volume was estimated to be about 3M tones per year.
A modified vanadium pentoxide (V2O5) serves as the catalysts, being active in the
range 320 - 400 C. The phthalic anhydride is separated from byproducts by a a
series of switch condensers. Phthalic anhydride and maleic anhydride are
recovered by distillation. Phthalic anhydride can also be prepared from
phthalicacid
Uses:The primary use of Phthalic Anhydride is as a chemical intermediate in the
production of plastics from vinyl chloride. Phthalate esters, which function as
plasticizers, are derived from Phthalic Anhydride. Phthalate plasticizers are usedfor the production of flexible PVC products such as cables, pipes and hoses, leather
cloth, shoes, film for packaging etc. Phthalic Anhydride has another major use in
the production of polyester resins and other minor uses in the production of alkyd
resins used in paints and lacquers; certain dyes (anthraquinone, phthalein,
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rhodamine, phthalocyanine, fluorescin, and xanthene dyes); insect repellents; and
polyester polyols for polyurethanes. Besides, it is also utilized as a rubber scorch
inhibitor and retarder