Phthalic anhydride

 

Phthalic anhydride

Chemical formula	C8H4O3
OTP appearance	white, acrid smelling crystals
Molar Mass(g/mol)	148.1
Density(g/cc)	1.53
Melting Point(°C)	131.6
Boiling Point(°C)	295
Solubility in water(g/L)	6.2
NFPA 704	1 3 0

Uses

Other

• Key chemical reagent

Production

Synthesis

Phthalic anhydride is synthesized by the oxygenation of 1,2-dimethylbenzene (o-xylene). The process differs in the oxidant. Both processes produce maleic anhydride as well, so they must be separated by fractional distillation.

Air

Vaporize 1,2-dimethylbenzene and mix with air (1:300) over a vanadium pentoxide catalyst at elevated temperature

C₆H₄(CH₃)₂ + 3 O₂

{V₂O₅

→

525°C}

C₈H₄O₃ + 3 H₂O

Sodium dichromate

Reflux an aqueous solution of sodium dichromate and 1,2-dimethylbenzene for a prolonged period

C₆H₄(CH₃)₂ + 4 Na₂Cr₂O₇ → 4 Na₂CrO₄ + 2 Cr₂O₃ + C₈H₄O₃ + 3 H₂O