Phthalic anhydride
[CAS# 85-44-9]

Identification

• Classification: Pharmaceutical intermediate >> Heterocyclic compound intermediate >> Pyrimidine compound >> Amine
• Name: Phthalic anhydride
• Synonyms: 2,5-Isobenzofurandione
• Molecular Formula: C₈H₄O₃
• Molecular Weight: 148.12
• CAS Registry Number: 85-44-9
• EC Number: 201-607-5
• SMILES: C1=CC=C2C(=C1)C(=O)OC2=O

Properties

• Density: 1.4±0.1 g/cm³ Calc.^*, 1.53 g/mL (Expl.)
• Melting point: 131 - 134 °C (Expl.)
• Boiling point: 295.0 °C 760 mmHg (Calc.)^*, 295 °C (Sublimes) (Expl.)
• Flash point: 139.7±15.9 °C (Calc.)^*, 152 °C (Expl.)
• Solubility: 0.50-0.70 g/100g (Expl.)
• Index of refraction: 1.613 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS05;GHS07;GHS08 Danger
• Risk Statements: H302-H315-H317-H318-H334-H335
• Safety Statements: P233-P260-P261-P264-P264+P265-P270-P271-P272-P280-P284-P301+P317-P302+P352-P304+P340-P305+P354+P338-P317-P319-P321-P330-P332+P317-P333+P317-P342+P316-P362+P364-P403-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Respiratory sensitization	Resp. Sens.	1	H334
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H302
Serious eye damage	Eye Dam.	1	H318
Skin sensitization	Skin Sens.	1	H317
Specific target organ toxicity - single exposure	STOT SE	3	H335
Specific target organ toxicity - single exposure	STOT SE	3	H370
Skin sensitization	Skin Sens.	1A	H317
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H312
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412

Discovery and Applications

Phthalic anhydride is a white crystalline organic compound that serves as an important industrial chemical intermediate. It is the anhydride form of phthalic acid and is produced primarily by the catalytic oxidation of ortho-xylene or naphthalene. This compound was first synthesized in the 19th century and has since become a key raw material in the chemical industry due to its reactivity and versatility.

The production of phthalic anhydride is carried out on a large scale using vapor-phase catalytic oxidation processes. Ortho-xylene or naphthalene is passed over a vanadium pentoxide catalyst at elevated temperatures, resulting in the formation of phthalic anhydride with high yield and purity. This manufacturing route is favored because it is efficient and cost-effective.

Phthalic anhydride is primarily used as a precursor to produce plasticizers, especially phthalate esters, which are added to polymers such as polyvinyl chloride (PVC) to increase flexibility and durability. These plasticizers improve the physical properties of plastics, making them suitable for applications in cables, flooring, automotive parts, and consumer goods.

Beyond plasticizers, phthalic anhydride is utilized in the synthesis of alkyd resins, which are widely employed in paints, coatings, and varnishes. These resins provide desirable properties such as gloss, adhesion, and chemical resistance, contributing to the durability and appearance of coated surfaces.

Phthalic anhydride is also involved in the manufacture of dyes, pigments, and pharmaceuticals. It acts as a building block for various chemical compounds, including isobenzofuranones and certain herbicides. In the pharmaceutical industry, derivatives of phthalic anhydride have been used as intermediates for producing drugs with anti-inflammatory and other therapeutic properties.

Due to its reactive anhydride group, phthalic anhydride readily undergoes hydrolysis to form phthalic acid and reacts with alcohols to produce phthalate esters. It can also react with amines to form imides, which are valuable in polymer chemistry and material science for their thermal stability and mechanical strength.

Safety and environmental considerations are important in the handling and use of phthalic anhydride. It is a respiratory irritant and can cause skin and eye irritation upon contact. Industrial processes are designed to minimize exposure and environmental release. The compound is also subject to regulations regarding its use and disposal to reduce potential health and ecological impacts.

In summary, phthalic anhydride is a white crystalline compound obtained by catalytic oxidation of ortho-xylene or naphthalene. It serves as a fundamental chemical intermediate in producing plasticizers, alkyd resins, dyes, pharmaceuticals, and other materials. Its chemical reactivity and versatility underpin its widespread industrial applications, while safety and environmental measures are integral to its production and use.

References

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DOI: 10.1007/s00204-016-1714-y

2000. Exposure assessment and sensitisation in workers exposed to organic acid anhydrides. International Archives of Occupational and Environmental Health. 73(3), 163-170.
DOI: 10.1007/s004200050422

2008. Nickel-Catalyzed Decarbonylative Addition of Anhydrides to Alkynes. Journal of the American Chemical Society. 130(48), 16486-16487.
DOI: 10.1021/ja806569h