Phthalic Anhydride

Phthalic anhydride is the organic compound with the molecular formula C8H4O3. It is the anhydride of phthalic acid. [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][1] Phthalic anhydride occurs as white, lustrous crystalline needles, and has a characteristic pungent choking odour. It is soluble in hot water, benzene, carbon disulfide, and alcohol and is slightly soluble in water and ether. [2] Phthalic anhydride is obtained by catalytic oxidation of ortho–xylene or naphthalene. When separating the phthalic anhydride from production by products such as o–xylene in water, or maleic anhydride, a series of “switch condensers” is required. It can also be prepared from phthalic acid. [3]

Uses [2,4]

Phthalic anhydride is used in the manufacture of plasticisers, polyester and alkyd resins. It is also used in the manufacture of phthaleins, phthalates, benzoic acid, synthetic indigo, artificial resins, synthetic fibres, dyes, pigments, pharmaceuticals, and chlorinated products.

Phthalic anhydride is an important chemical intermediate in the plastics industry from which are derived numerous phthalate esters that function as plasticisers in synthetic resins. Phthalic anhydride itself is used as a monomer for synthetic resins such as glyptal, the alkyd resins, and the polyester resins. It is also used as a precursor of anthraquinone, phthalein, rhodamine, phthalocyanine, fluorescein, and xanthene dyes.

Phthalic anhydride is used in the synthesis of primary amines, the agricultural fungicide phaltan, and thalidomide. Other reactions with phthalic anhydride yield phenolphthalein, benzoic acid, phthalylsulfathiazole (an intestinal antimicrobial agent), and orthophthalic acid.

Environmental Effects [4]

Phthalic anhydride is released to the environment from chemical plants, mainly those that manufacture the chemical or use it in the production of plastics and resins. The major sources of these releases are process off-gases and industrial effluents; however, the use of catalytic oxidation now reduces the release of pollutants in off-gases. Phthalic anhydride has been identified but not quantified in U.S. drinking water and in the volatile flavour components of baked Idaho potatoes. No information was found for the transport of phthalic anhydride in the environment or in soil. However, in moist soil, the chemical will hydrolyse to phthalic acid and significant leaching is not expected to occur, other than in the case of a large spill. Phthalic anhydride is not expected to bioaccumulate in aquatic organisms. Plants and animals exposed to radiolabelled di-2-ethylhexyl phthalate (DEHP) in a microecosystem contained, but did not accumulate to any great extent, phthalic anhydride, a metabolite of DEHP.

Sources & Routes of Exposure

Sources of Exposure [5]

  • Exposure to phthalic anhydride may occur during the manufacture of phthalate-derived products.
  • It has been suggested that exposure to phthalic anhydride may occur from the use of plastics from which phthalate plasticisers are leached, specifically certain medical plastics such as blood bags, plastic syringes, and plastic tubing.
  • Phthalate esters have been identified as environmental pollutants.

Routes of Exposure [2]

The probable routes of exposure to phthalic hydride are:

  • inhalation;
  • ingestion; and
  • skin and/or eye contact

Health Effects [5]

Acute Effects

  • Phthalic anhydride is irritating to the eyes, respiratory tract, and the skin in humans, but no permanent injury is observed. Since phthalic anhydride has no effect on dry skin, but burns wet skin, it has been suggested that the actual irritant is phthalic acid, which is formed on contact with water.
  • Tests involving acute exposure of rats have shown phthalic anhydride to have moderate acute toxicity.

Chronic Effects

  • Conjunctivitis, rhinitis, rhinoconjunctivitis, bronchitis, and irritation of the skin and mucous membranes of the respiratory tract have been observed in workers exposed to phthalic anhydride. Other effects observed in workers chronically exposed to phthalic anhydride were occasional bloody sputum, emphysema, lower blood pressure, and minor signs of central nervous system (CNS) excitation.
  • Animals exposed to heated phthalic anhydride experienced congestion, irritation, and injury of lung cells.
  • Hypersensitivity of guinea pigs to phthalic anhydride dust has been reported, with bronchoconstriction, transiently increased respiratory rate, and elevated IgG antibodies observed following an inhalation challenge.
  • Decreased body weight, increased incidence of lung and kidney lymphocytosis, bile duct inflammation, adrenal atrophy, and mineralization of the thalmus were reported in mice exposed to phthalic anhydride in the diet.
  • EPA has calculated a provisional Reference Concentration (RfC) of 0.12 milligrams per cubic metre (mg/m3) for phthalic anhydride based on respiratory effects in humans.
  • EPA has established a Reference Dose (RfD) of 2.0 milligrams per kilogram body weight per day (mg/kg/d) for phthalic anhydride based on lung and kidney effects in mice.

Reproductive/Developmental Effects

  • No studies regarding reproductive or developmental effects in humans were available.
  • Phthalic anhydride was reported to be teratogenic in mice following intraperitoneal injection.
  • Decreased spermatozoa motility time was reported in one study in which male rats were exposed via inhalation.

Cancer Risk

  • No studies were available on the carcinogenic effects of phthalic anhydride in humans.
  • A bioassay of phthalic anhydride for possible carcinogenicity was conducted by administering phthalic anhydride in feed to groups of male and female rats and mice. It was observed that no tumours occurred in the rats or mice of either sex at incidences that could be clearly related to the administration of phthalic anhydride.
  • EPA has not classified phthalic anhydride regarding carcinogenicity.

Safety [6]

First Aid Measures

  • Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Cold water may be used. WARM water MUST be used. Get medical attention immediately.
  • Skin Contact: In case of contact, immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Cover the irritated skin with an emollient. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention immediately.
  • Serious Skin Contact: Wash with a disinfectant soap and cover the contaminated skin with an anti-bacterial cream. Seek immediate medical attention.
  • Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention immediately.
  • Serious Inhalation: Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such as a collar, tie, belt or waistband. If breathing is difficult, administer oxygen. If the victim is not breathing, perform mouth-to-mouth resuscitation. WARNING: It may be hazardous to the person providing aid to give mouth-to-mouth resuscitation when the inhaled material is toxic, infectious or corrosive. Seek immediate medical attention.
  • Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. If large quantities of this material are swallowed, call a physician immediately. Loosen tight clothing such as a collar, tie, belt or waistband.

Fire Information

  • Phthalic anhydride may be combustible at high temperature.
  • Auto-ignition temperature is 570°C
  • Phthalic anhydride is slightly flammable to flammable in presence of heat and non-flammable in presence of shocks.
  • For fighting small phthalic anhydride fires, use dry chemical powder.
  • For fighting large fires, water spray, fog or foam should be used. Do not use water jet.

Exposure Controls & Personal Protection

Engineering Controls

  • Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommended exposure limits.
  • If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.

Personal Protective Equipment

The following personal protective equipment is recommended when handling phthalic anhydride:

  • Splash goggles;
  • Synthetic apron;
  • Vapour and dust respirator (be sure to use an approved/certified respirator or equivalent);
  • Gloves.

Personal Protective Equipment in Case of a Large Spill:

  • Splash goggles;
  • Full suit;
  • Vapour and dust respirator;
  • Boots;
  • Gloves;
  • A self-contained breathing apparatus should be used to avoid inhalation of the product.
  • Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.


United States [7]

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

Australia [8]

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.


Phthalic Anhydride