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Phthalic anhydride

Phthalic anhydride
IUPAC name 1,2-benzenedicarboxylic anhydride
Other names Isobenzofuran-1,3-dione
CAS number 85-44-9
RTECS number TI3150000
Molecular formula C8H4O3
Molar mass 148.1 g/mol
Appearance white Flakes
Density 1.53 g/cm3, solid
Melting point

131 °C

Boiling point

295 °C subl.

Solubility in water 0.62g/100g reacts slowly
R-phrases R22, R37/38, R41, R42/43
S-phrases (S2), S23, S24/25, S26, S37/39, S46
Flash point 152 °C
Related Compounds
Related compounds Phthalic acid
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Phthalic anhydride is the anhydride of phthalic acid. It dissolves in alcohol and some other organic solvents.

Phthalic anhydride is obtained either by catalytic oxidation of ortho-xylene with O2 (oxygen) or by catalytic oxidation of naphthalene (called the Gibbs phthalic anhydride process 1918). The byproducts of the naphthalene reaction are carbon dioxide and water.

It is hydrolyzed by hot water, forming ortho-phthalic acid. This process is reversible, with phthalic anhydride being re-formed from the acid above 180 °C.[1]

When separating the phthalic anhydride from byproducts such as o-xylene in water, or maleic anhydride, a series of switch condensers is required, rather than a complicated setup of distillation columns that never converge in many industrial process simulation programs such as AspenTech.

Phthalic anhydride is widely used in industry in the production of dyes (rhodamine, anthraquinone derivatives), insecticides, plasticizers and pharmaceuticals. It also finds use in analytical chemistry.


  1. ^ Noller, Carl R. (1965). Chemistry of Organic Compounds, 3rd ed.. Philadelphia: W. B. Saunders, 602. 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Phthalic_anhydride". A list of authors is available in Wikipedia.
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