Phthalic anhydride is an organic compound with the formula C₈H₄O₃. It's the anhydride of phthalic acid. This substance appears as white, shiny, crystalline needles with a strong, choking smell. It dissolves in hot water, benzene, carbon disulphide, and alcohol but is only slightly soluble in water and ether.
Phthalic anhydride is produced by the catalytic oxidation of ortho-xylene or naphthalene. When separating it from by-products like o-xylene in water or maleic anhydride, a system of "switch condensers" is used. It can also be made from phthalic acid.
Phthalic anhydride is widely used in manufacturing plasticisers, polyester, and alkyd resins. It is also used to make phthaleins, phthalates, benzoic acid, synthetic indigo, artificial resins, synthetic fibers, dyes, pigments, pharmaceuticals, and chlorinated products.
In the plastics industry, phthalic anhydride is crucial for producing phthalate esters, which are plasticisers for synthetic resins. It also serves as a building block for synthetic resins like glyptal, alkyd resins, and polyester resins. Additionally, it is a precursor for various dyes and in the synthesis of primary amines, agricultural fungicides, and certain medicines like thalidomide.
Phthalic anhydride is released into the environment mainly from chemical plants during the production of plastics and resins. The primary sources are off-gases and industrial effluents, but catalytic oxidation has reduced pollutant releases.
Phthalic anhydride has been detected in U.S. drinking water and baked potatoes' flavor components but not quantified. In moist soil, it hydrolyses to phthalic acid, minimizing significant leaching unless there is a large spill. It is not expected to bioaccumulate in aquatic organisms.
Exposure can occur during the manufacturing of phthalate-derived products or from leaching of phthalate plasticisers in certain medical plastics like blood bags, syringes, and tubing. Phthalate esters are environmental pollutants.
The main ways people are exposed to phthalic anhydride are:
Phthalic anhydride can irritate the eyes, respiratory tract, and skin. It doesn't affect dry skin but burns wet skin, likely due to forming phthalic acid. Animal tests show moderate acute toxicity.
Long-term exposure can lead to conjunctivitis, rhinitis, bronchitis, skin and respiratory tract irritation, and occasional bloody sputum. Workers have experienced lower blood pressure and mild CNS effects. In animals, exposure led to lung and kidney issues, weight loss, and other organ effects.
The EPA's provisional Reference Concentration (RfC) for phthalic anhydride is 0.12 mg/m³, and the Reference Dose (RfD) is 2.0 mg/kg/day.
No human studies are available, but in mice, phthalic anhydride was teratogenic when injected. Male rats exposed through inhalation had reduced sperm motility.
There are no human studies on cancer risk. Animal studies showed no clear link between phthalic anhydride exposure and tumor development. The EPA has not classified its carcinogenicity.
Use enclosures, ventilation, or other methods to keep airborne levels below limits. If dust or mist forms, use proper ventilation.
For handling phthalic anhydride, use:
For large spills, use:
Always consult a specialist for proper protective clothing before handling phthalic anhydride.
NIOSH: The National Institute for Occupational Safety and Health has set a recommended exposure limit (REL) for phthalic anhydride of 6 mg/m3 and 1 ppm TWA
OSHA: The Occupational Safety & Health Administration has set a permissible exposure limit (PEL) for phthalic anhydride of 12 mg/m3 and 2 ppm TWA
Safe Work Australia: Safe Work Australia has established a time weighted average concentration (TWA) for phthalic anhydride of 6.1 mg/m3 and 1 ppm for a 40-hour work week.
