Phthalic Anhydride (99,8%) - India

Brief Overview
Phthalic anhydride, represented by the formula C6H4(CO)2O, serves as the anhydride of phthalic acid and is a significant commercial form of the acid. It marked the pioneering use of a dicarboxylic acid anhydride on a large scale, with this white solid playing a crucial role in industrial chemistry, particularly in the extensive production of plasticizers for plastics. The estimated global production volume in 2000 reached about 3 million tonnes annually.


Manufacturing Process:
Discovered by Auguste Laurent in 1836, phthalic anhydride is currently synthesized through various methods, including the oxidation of naphthalene or ortho-xylene. In these processes, vanadium pentoxide (V2O5) serves as the active oxidant, playing a key role in multiple steps and being regenerated by molecular oxygen. Starting from o-xylene, the oxidation reaction is run at about 320–400 °C and has the following stoichiometry:
C6H4(CH3)2 + 3 O2 → C6H4(CO)2O + 3 H2O
The reaction proceeds with about 70% selectivity. About 10% of maleic anhydride is also produced: C6H4(CH3)2 + 7.5 O2 → C4H2O3 +4 H2O + 4 CO2
Phthalic anhydride and maleic anhydride are recovered by distillation by a series of switch condensers.
The naphthalene route (the Gibbs phthalic anhydride process or the Gibbs–Wohg naphthalene oxidation reaction), a process whose use has declined in compared to the o-xylene route, has the following mechanism:

Phthalic anhydride can also be prepared from phthalic acid by simple dehydration.