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Phthalic anhydride

Phthalic anhydride


IUPAC name	1,2-benzenedicarboxylic anhydride
Other names	Isobenzofuran-1,3-dione
Identifiers
CAS number	85-44-9
RTECS number	TI3150000
SMILES	C1=CC=C2C(=C1)C(=O)OC2=O
Properties
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
Hazards
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 Phthalimide
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.

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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.