Phthalic anhydride

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Phthalic anhydride
Phthalic anhydride purified by anewsoul.jpg
Fluffy phthalic anhydride
Phthalic anhydride structural formula.png
IUPAC name
Other names
Phthalic anhydride
Jmol-3D images Image
Molar mass 148.1 g/mol
Appearance White solid
Odor Acrid
Density 1.53 g/cm3 (20 °C)
1.2 g/cm3 (135 °C)
Melting point 131.6 °C (268.9 °F; 404.8 K)
Boiling point 295 °C (563 °F; 568 K)
0.62 g/100 g (20 °C)
19.0 g/100 g (100 °C)
Slow hydrolysis
Solubility Dissolves and slowly reacts with alcohols, amines
Soluble in acetone, benzene
Slightly soluble in carbon disulfide, diethyl ether
Vapor pressure 0.0015 mmHg (20 °C)
Safety data sheet Sigma-Aldrich
Flash point 152 °C (305.6 °F; 425 K)
Lethal dose or concentration (LD, LC):
4,020 mg/kg (oral, rat)
1,520 mg/kg (oral, mouse)
800 mg/kg (oral, cat)
800-1,600 mg/kg (oral, rat)
2,210 mg/kg (oral, mouse)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Phthalic anhydride is an organic compound, the anhydride of phthalic acid. It is an important industrial chemical used in the production of plasticizers, dyestuffs, and pharmaceuticals.



Phthalic anhydride hydrolyzes in water to phthalic acid.


Phthalic anhydride is a white solid, which slowly reacts with water.


Phthalic anhydride is sold by various chemical suppliers and it's quite cheap. It can also be purchased online.


Phthalic anhydride can be prepared from diethylhexyl phthalate, which can be easily found in vinyl gloves, available in most pharmacies and medical supply stores. Look on the box label for gloves that are made with PVC. Grind about 50 g of gloves to flakes in a beaker. Add isopropanol and reflux the mixture for an hour to extract the diethylhexyl phthalate. Filter the resulting alcoholic solution and then boil off half of its volume. A solution of 10 g of sodium hydroxide is then added to the alcoholic solution of diethylhexyl phthalate and reflux the mixture for another hour, to hydrolyze it to disodium phthalate. Turn off the heating and let it cool. The reaction mixture will separate into two layers, the upper layer is the alcoholic layer, while the bottom is the aqueous layer, containing the disodium phthalate. Remove the alcohol layer and collect the disodium phthalate aqueous solution. To the aqueous solution, add 25 ml of fuming hydrochloric acid (12 M) to convert it to phthalic acid. Cool the solution to precipitate the phthalic acid and decant off the water. Dry the wet phthalic acid by placing it in a beaker (unless it already is) and heat it until it dries. Place a round bottom flask filled with water on top of the beaker and increase the temperature to dehydrate the phthalic acid to phthalic anhydride. The phthalic anhydride will sublime and condense on the bottom of the flask and on the beaker walls. The crystals appear as cotton candy. When a sufficient amount of the anhydride has deposited, take the beaker off the hotplate, let it cool, and collect the crystals. Do not wait too much, as the anhydride crystals will get too heavy and will fall back in the phthalic acid melt. Repeat until no more phthalic anhydride condenses.[1]

Another route involves the oxidation of naphthalene with nitric acid or vanadium pentoxide. Mercury(II) sulfate and sulfuric acid can also be used.

The modern industrial route is the vapor-phase oxidation of ortho-xylene by air over a catalyst.




Phthalic anhydride is a skin irritant. Phthalates are endocrine disruptors. Avoid breathing dust and vapors of phthalic anhydride.


Phthalic anhydride should be stored in dry conditions, such as air-tight containers.


Can be neutralized with an aqueous alkaline solution to disodium phthalate.

Complete destruction can be achieved with a strong oxidizing solution, such as chromic acid, Fenton's reagent, piranha solution.




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