Phthalic anhydride was first reported in 1836 by Laurent.

OSHA PEL: TWA 1 ppm
ACGIH TLV: TWA 1 ppm (skin, sensitizer) Not Classifiable as a Human Carcinogen
DFG MAK: 1 mg/m³ as total dust
DOT Classification:  8; Label: Corrosive

Phthalic anhydride, also called as Isobenzofuran-1,3-dione, has the CAS registry number 85-44-9. In addition, its EINECS registry number is 201-607-5. This chemical has the IUPAC name of 2-benzofuran-1,3-dione which is a white crystalline solid with choking odour. Phthalic anhydride is the organic compound with the formula C₆H₄(CO)₂O. It is moisture sensitive, that is somewhat soluble in water. This chemical is stable but combustible, and incompatible with strong oxidizing agents, strong bases, moisture, strong acids.Phthalic anhydride usually reacts slowly with water to form phthalic acid and heat. It can undergoe exothmeric nitration with fuming nitric acid-sulfuric acid and may give mixtures of the potentially explosive phthaloyl nitrates or nitrites or their nitro derivatives. The substance is easily to sublime below its boiling point. What's more, its dust may form an explosive mixture with air.

Physical properties about Phthalic anhydride are: (1)ACD/LogP: 1.194; (2)ACD/LogD (pH 5.5): 1.19; (3)ACD/LogD (pH 7.4): 1.19; (4)ACD/BCF (pH 5.5): 4.76; (5)ACD/BCF (pH 7.4): 4.76; (6)ACD/KOC (pH 5.5): 106.31; (7)ACD/KOC (pH 7.4): 106.31; (8)#H bond acceptors: 3; (9)Index of Refraction: 1.613; (10)Molar Refractivity: 35.682 cm³; (11)Molar Volume: 102.563 cm³; (12)Polarizability: 14.145 10-24cm³; (13)Surface Tension: 58.0709991455078 dyne/cm; (14)Density: 1.444 g/cm³; (15)Flash Point: 139.655 °C; (16)Enthalpy of Vaporization: 53.468 kJ/mol; (17)Boiling Point: 294.999 °C at 760 mmHg; (18)Vapour Pressure: 0.0020000000949949 mmHg at 25°C

Preparation of Phthalic anhydride: In industry, there are two kinds of preparation methods of Phthalic anhydride, o-xylene and naphthalene. Phthalic anhydride can be made from the reaction of o-xylene with air and also from naphthalene, also called as Gibbs phthalic anhydride process, which is isolated from coal tar and from petroleum.

C₆H₄(CH₃)₂ + [O] → HOOCC₆H₄COOH
HOOCC₆H₄COOH → C₆H₄(CO)₂O + H₂O
C₁₀H₈ + 4.5 O₂ → C₆H₄(CO)₂O + 2 H₂O + 2 CO₂

Phthalic anhydride can also be prepared from phthalic acid. It reacts with acetic anhydride in the presence of microscale phosphoric acid.

C₆H₄(COOH)₂ → C₆H₄(CO)₂O

Uses of Phthalic anhydride: Phthalic anhydride is used in the manufacture of materials such as artificial resins. It is an important industrial chemical, especially for the large-scale production of plasticizers for plastics. Phthalic anhydride is a precursor to a variety of reagents useful in organic synthesis. Phthalic anhydride is widely used in industry for the production of certain dyes which is well-known in the preparation of the anthroquinone dye quinizarin by reaction with para-chlorophenol followed by hydrolysis of the chloride. Phthalic anhydride is a versatile intermediate in organic chemistry. It undergoes hydrolysis and alcoholysis.

When you are using Phthalic anhydride, you should be very cautious. This chemical is harmful if swallowed and irritating to respiratory system and skin. There will be a risk of serious damage to eyes. The substance may cause sensitisation by inhalation and skin contact. You should not breathe its dust and avoid contact with skin and eyes. In case of contact with eyes, you need rinse immediately with plenty of water and seek medical advice. Whenever you will contact or use it, you should wear suitable gloves and eye/face protection.

You can still convert the following datas into molecular structure:
(1)Canonical SMILES: C1=CC=C2C(=C1)C(=O)OC2=O
(2)InChI: InChI=1S/C8H4O3/c9-7-5-3-1-2-4-6(5)8(10)11-7/h1-4H
(3)InChIKey: LGRFSURHDFAFJT-UHFFFAOYSA-N

Toxicity of Phthalic anhydride: