Phthalic Anhydride, Anhydride Phtalique, Anhydrid Kyseliny Ftalove, 85-44-9

PHTHALIC ANHYDRIDE

Phthalic Anhydride / Anhydride Phtalique / Anhydrid Kyseliny Ftalove
CAS Number: 85-44-9
EC Number: 201-607-5

1. IDENTIFICATION INFORMATION

Phthalic anhydride is one of the most important organic chemical intermediates. This aromatic dicarboxylic acid anhydride has an internal anhydride structure formed by the dehydration of two carboxyl groups attached to a benzene ring. The anhydride group in its molecular structure provides high reactivity, making it an indispensable raw material in the synthesis of plasticizers, resins, dyes, and pharmaceutical products. As the most widely used aromatic anhydride in industry, phthalic anhydride holds a significant position in the global chemical industry with millions of tons of annual production capacity.

2. PHYSICAL PROPERTIES

Phthalic anhydride is a white, needle-like crystalline solid at room temperature. It is commercially available primarily in flake form, which provides convenience for storage, transportation, and dosing. The melting point is 131.6°C and serves as the most critical quality control parameter for product purity; impurities cause a depression in the melting point and broadening of the melting range. The boiling point ranges from 284-295°C, but sublimation begins at approximately 150°C before reaching this temperature. This property necessitates vacuum operation during purification by distillation. The vapor density of 5.1 (air=1) indicates that its vapor is approximately 5 times heavier than air; therefore, in the event of a leak, vapor accumulates near the ground, creating explosion or toxic exposure risks in enclosed spaces. Water solubility at 20°C is 6 g/L, with slow hydrolysis occurring during dissolution to form phthalic acid, which lowers the solution pH to approximately 2.

3. CHEMICAL PROPERTIES

Phthalic anhydride undergoes a wide variety of chemical reactions due to the high reactivity of its anhydride group. It slowly reacts with water to hydrolyze to phthalic acid; this reaction is exothermic, and contact with large quantities of water can cause heat release and pressure increase in closed containers. It reacts with alcohols to form mono- and di-esters (plasticizer precursors), which represents the most important industrial reaction of phthalic anhydride. It reacts with amines to form phthalimide derivatives. It forms phthalate salts with strong bases. Under normal storage conditions, the compound is chemically stable, but reactivity increases with strong oxidizing agents, strong bases, and moisture, potentially leading to violent reactions or decomposition. Dust concentrations in air can form explosive mixtures.

Molecular Structure:

        O
        ||
    C---C
   /     \
  O       O
   \     /
    C---C
    ||   ||
    O    O
         |
    (Benzene Ring)

4. PRODUCTION PROCESS

Phthalic anhydride is produced industrially by two main methods. In the naphthalene oxidation method, molten naphthalene mixed with air is oxidized in a fluidized or fixed-bed reactor using vanadium pentoxide (V₂O₅) catalyst; the resulting phthalic anhydride gas is converted to crude anhydride through condensation and hot melting, followed by purification through heat treatment, vacuum distillation, condensation, and separation. The currently dominant o-xylene oxidation method involves passing o-xylene vapor with air over V₂O₅-TiO₂-based catalyst in a fixed-bed reactor; this method is preferred due to higher yields and lower byproduct formation. Advances in catalyst technology, particularly V₂O₅-TiO₂-K₂SO₄ and VPO catalysts, have improved production efficiency and reduced costs. Technologies such as double-bed reactor systems and phthalic anhydride recovery using maleic anhydride as a liquid eutectic mixture have enhanced process economics.

Reaction Equation (o-Xylene Oxidation):

C₈H₁₀ + 3 O₂ → C₈H₄O₃ + 3 H₂O

Reaction Equation (Naphthalene Oxidation):

C₁₀H₈ + 4.5 O₂ → C₈H₄O₃ + 2 CO₂ + 2 H₂O

Typical Grades:

5. AVAILABLE FORMS AND SPECIFICATIONS

Phthalic anhydride is commercially available primarily in flake and liquid (molten) forms. The flake form provides convenience for storage, transportation, and dosing and is the most widely used commercial form. The liquid form is transported at 150-180°C in specially insulated and heated tankers, providing direct feed capability to large-scale industrial facilities.

Typical Specifications:

6. APPLICATIONS AND USES

6.1. Plasticizers – Largest Application (~90%)

The largest application of phthalic anhydride, accounting for approximately 90% of total consumption, is in the production of plasticizers (phthalate esters). Phthalate esters such as diethylhexyl phthalate (DOP), diisononyl phthalate (DINP), and dibutyl phthalate (DBP) are used to make PVC flexible, durable, and processable. These plasticizers are used in a wide range of products including wire and cable, flooring, automotive parts, medical devices, toys, and packaging materials. Phthalic anhydride serves as the primary raw material in the synthesis of these plasticizers through esterification reactions with alcohols.

6.2. Resins and Coatings

Phthalic anhydride is a critical raw material in the production of alkyd resins. Alkyd resins are formed by reaction with fatty acids and multifunctional alcohols and are used as binders in the paint, varnish, and coating industry. Phthalic anhydride is also used in the production of unsaturated polyester resins, which are widely used in fiberglass-reinforced composites, marine applications, automotive parts, and construction materials. Additionally, it serves as an intermediate in the synthesis of polyester polyols, contributing to the production of polyurethane foams and coatings.

6.3. Dyes and Pigments

Phthalic anhydride is an important intermediate in the dye and pigment industry. It is used in the synthesis of anthraquinone-based dyes, which are preferred in the textile, paper, and plastics industries due to their high durability. It serves as the primary raw material in the production of phthalocyanine pigments (particularly copper phthalocyanine blue and green), which are widely used in printing inks, plastics, automotive coatings, and paints due to their brilliant colors, high lightfastness, and chemical resistance.

6.4. Pharmaceutical and Agricultural Chemicals

Phthalic anhydride is an important intermediate in the pharmaceutical industry for the synthesis of various drugs. It is used in the production of phenolphthalein, barbiturates, and certain anti-inflammatory drugs. It also plays a role in the synthesis of agricultural chemicals (pesticides, herbicides, fungicides) and food additives. High-purity phthalic anhydride is required for pharmaceutical applications.

6.5. Other Applications

Phthalic anhydride is used in the synthesis of numerous valuable derivative compounds including phthalimide, anthraquinone, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, diallyl phthalate, and 2-ethylanthraquinone. These derivatives are used in flame retardants, specialty polymers, hydrogen peroxide production, and many other industrial applications.

7. PHYSICAL AND CHEMICAL SPECIFICATIONS

7.1. Solubility Profile

Phthalic anhydride exhibits a broad solubility profile in organic solvents. It is soluble at 6 g/L in water at 20°C, with slow hydrolysis occurring during dissolution. It dissolves well in ethanol, benzene, and pyridine. It is soluble in hot ether but only slightly soluble in cold ether. This solubility profile is important for solvent selection in organic synthesis reactions.

7.2. Thermal Properties

The thermal properties of phthalic anhydride are critical for determining processing and storage conditions. The melting point is 131.6°C and serves as an indicator of product purity. The boiling point ranges from 284-295°C. The flash point is 151.7°C (open cup) and 152°C (closed cup). The ignition temperature is 584°C, which is important for fire safety. Explosive limits range from 1.7-10.5% by volume.

8. STORAGE AND HANDLING

Phthalic anhydride should be stored below 30°C in cool, dry, well-ventilated areas protected from light, in tightly closed original containers. It is sensitive to moisture; contact with moisture causes slow hydrolysis to phthalic acid, degrading product quality. The flake product is packaged in plastic-lined woven bags or multi-layer moisture-proof kraft paper bags. The liquid form is transported in specially insulated and heated tankers maintained at 150-180°C. The shelf life is 3 months under proper storage conditions. Temperatures above 40°C may cause melting or agglomeration. Storage areas should be separated from strong oxidizing agents, strong bases, and acids. Fire safety measures should be implemented, and static electricity accumulation should be prevented.

Handling Notes:

• May form agglomerates in high humidity (moisture sensitive)

• Can create organic dust explosion risk

• Use local exhaust ventilation for large quantities

• Avoid prolonged skin contact (may cause irritation)

• Use dust mask in case of significant dust generation

9. SAFETY AND HEALTH INFORMATION (GHS CLASSIFICATION)

Phthalic anhydride presents significant health and safety risks. It causes serious irritation to skin, eyes, and respiratory tract. It can cause respiratory sensitization (asthma-like allergic reactions) and skin sensitization. It is harmful if swallowed. Exposure to dust or vapor in particular can cause severe respiratory irritation and allergic reactions. Skin contact can cause irritation, redness, blistering, and prolonged or repeated contact may lead to difficult-to-heal ulcers. Eye contact poses a risk of serious, irreversible damage. It is subject to FDA/EPA/OSHA regulations with established workplace exposure limits.

10. HAZARD STATEMENTS (H-CODES)

The hazard statements define the potential hazards of phthalic anhydride. H302 indicates harmful if swallowed. H315 indicates causes skin irritation. H317 indicates may cause an allergic skin reaction. H318 indicates causes serious eye damage. H334 indicates may cause allergy or asthma symptoms or breathing difficulties if inhaled. H335 indicates may cause respiratory irritation.

11. PRECAUTIONARY STATEMENTS (P-CODES)

The precautionary statements specify the measures to be taken for safe handling of phthalic anhydride. P202 advises not to handle until all safety precautions have been read and understood. P261 recommends avoiding breathing dust and vapor. P280 specifies wearing protective equipment. P302+P352 requires washing with plenty of soap and water upon skin contact. P304+P340 requires moving to fresh air upon inhalation. P305+P351+P338 requires rinsing eyes with water upon contact. P310 requires immediately calling a poison center or doctor. P333+P313 requires getting medical attention if skin irritation occurs. P342+P311 requires calling a poison center or doctor if respiratory symptoms occur.

12. TOXICOLOGICAL INFORMATION

Phthalic anhydride has a significant toxicological profile with acute and chronic health effects. The oral LD50 is 1530 mg/kg in rabbits and 8.0 g/kg in rats. The dermal LD50 in rabbits is greater than 3160 mg/kg. It causes severe irritation to skin, eyes, and respiratory tract. It can cause skin sensitization (allergic contact dermatitis) and respiratory sensitization (asthma-like reactions). It is not classified as carcinogenic (not listed by IARC). Exposure limits: NIOSH REL: TWA 6 mg/m³ (1 ppm), IDLH 60 mg/m³; OSHA PEL: TWA 12 mg/m³ (2 ppm); ACGIH TLV: TWA 1 ppm.

Health Effects:

The health effects of phthalic anhydride can be severe and persistent. Inhalation causes severe respiratory tract irritation, coughing, shortness of breath, and choking sensation. Skin contact results in redness, burning, blistering, and difficult-to-heal ulcers. Eye contact causes serious, irreversible damage. Ingestion causes burning and irritation of the mouth, throat, and gastrointestinal tract. Chronic exposure can lead to asthma-like allergic reactions and allergic contact dermatitis. Workplace exposure limits must be strictly observed, and appropriate personal protective equipment must be used.

13. FIRST AID MEASURES

First aid measures for phthalic anhydride vary depending on the type of exposure. In case of inhalation, move the person to fresh air, give oxygen if breathing is difficult, perform artificial respiration if breathing has stopped, and seek medical attention if symptoms persist. For skin contact, remove contaminated clothing, wash the affected area with plenty of soap and water for at least 15 minutes, and seek medical attention if irritation persists. For eye contact, rinse immediately with plenty of water for at least 15 minutes, remove contact lenses, keep eyelids open, and seek immediate medical attention. In case of ingestion, rinse the mouth, drink plenty of water, do NOT induce vomiting, and seek immediate medical attention.

14. FIREFIGHTING MEASURES

Phthalic anhydride is combustible and can form explosive dust-air mixtures in air. In case of fire, use water spray, CO₂, dry chemical powder, or alcohol-resistant foam for extinguishing. Thermal decomposition may produce irritant and toxic gases (carbon monoxide, carbon dioxide, phthalic acid vapors). Self-contained breathing apparatus (SCBA) and full protective clothing should be used during firefighting. Explosion-proof equipment should be used due to dust explosion risk. Although not classified as explosive, phthalic anhydride dust can form combustible dust clouds. Proper grounding and dust collection systems should be used. Static electricity accumulation should be avoided.

15. ENVIRONMENTAL INFORMATION

Phthalic anhydride is a substance that requires careful environmental management. It is toxic to aquatic organisms. In the environment, it hydrolyzes to phthalic acid. Bioaccumulation potential is low. Waste disposal should be carried out according to local regulations; incineration is recommended. Discharge to water bodies and sewer systems should be avoided. Environmental exposure should be minimized.

16. TRANSPORT INFORMATION

Phthalic anhydride is classified as a dangerous good with UN number 2214. Hazard class is 8 (Corrosive) and Packing Group III. During transport, it should be protected from moisture, impact, and excessive heat. Packaging must be intact and leak-proof. It is classified as a marine pollutant. ADR/RID label: Corrosive (Class 8). The liquid form is transported in specially insulated and heated tankers maintained at 150-180°C.

17. REGULATORY INFORMATION

Phthalic anhydride is registered and regulated in all major industrial markets including the EU, USA, Canada, Australia, Japan, Korea, and China. It is REACH registered in the EU. In Turkey, KKDİK compliance is mandatory and registration is required. It is listed on the TSCA in the USA. It is listed on the DSL in Canada, AICS in Australia, ENCS in Japan, KECL in Korea, and IECSC in China.

Regulatory Status:

18. OTHER NAMES AND SYNONYMS

Phthalic anhydride is known by various names across different industries and regions. Phthalic Acid Anhydride, 1,3-Isobenzofurandione, and o-Phthalic Anhydride are the most common synonyms. It is also known as "Anhydride Phtalique" in French and "Anhydrid Kyseliny Ftalove" in Czech.

Database Identifiers:

19. RAW MATERIALS AND DERIVATIVE PRODUCTS

19.1. Raw Materials (Upstream)

Two primary raw materials are used in phthalic anhydride production. The currently dominant method uses o-xylene, a petroleum refining byproduct. The traditional method uses naphthalene, obtained from coal tar or petroleum fractions. Air (oxygen) is required for the oxidation reaction. Vanadium pentoxide (V₂O₅) and various support materials are used as catalysts.

19.2. Derivative Products (Downstream)

Phthalic anhydride has a very wide range of derivative products. The most important derivatives are plasticizers (DOP, DINP, DBP). Alkyd resins and unsaturated polyester resins are also important derivatives. Phthalimide, anthraquinone, and various phthalate derivatives are other significant derivatives. These derivatives are used in a wide variety of industries including plastics, paints, coatings, pharmaceuticals, agricultural chemicals, flame retardants, and specialty polymers.

20. SUMMARY AND CRITICAL WARNINGS

SUMMARY:

Phthalic anhydride (C₈H₄O₃, CAS 85-44-9) is an aromatic dicarboxylic acid anhydride that appears as a white, needle-like crystalline solid. It has a melting point of 131.6°C, boiling point of 284-295°C, and density of 1.53 g/cm³. It has a solubility of 6 g/L in water at 20°C (with slow hydrolysis) and is soluble in ethanol, benzene, and pyridine. It is produced industrially by catalytic oxidation of naphthalene or o-xylene. The largest application is in the production of plasticizers (phthalate esters) accounting for approximately 90% of consumption. It is also used in the production of alkyd resins, unsaturated polyester resins, dyes, pigments, pharmaceuticals, and agricultural chemicals. From a health perspective, it causes severe irritation to skin, eyes, and respiratory tract and can cause respiratory and skin sensitization. It is classified as UN 2214 (Class 8 - Corrosive). It is sensitive to moisture and should be stored below 30°C.

Key Properties:

Major Application Areas:

Key Safety Points:

• SEVERE IRRITANT: Causes severe irritation to skin, eyes, and respiratory tract

• SENSITIZER: Can cause respiratory and skin sensitization (asthma, allergic dermatitis)

• CORROSIVE: Classified as UN 2214, Class 8

• COMBUSTIBLE: Combustible; dust-air mixtures can be explosive

• MOISTURE SENSITIVE: Sensitive to moisture; slowly hydrolyzes to phthalic acid

• USE PPE: Protective gloves, goggles, respiratory protection (for dust/vapor) are mandatory

CRITICAL WARNINGS:

Industrial Importance: Phthalic anhydride is one of the most important intermediates in the global chemical industry. Annual production volume reaches millions of tons, and it is a fundamental raw material for the plasticizer, resin, dye, and pharmaceutical industries. Due to its indispensable role in the PVC industry, it is one of the most critical indirect raw materials for the construction, automotive, packaging, and medical device sectors.

Health Risks: Phthalic anhydride causes severe irritation to skin, eyes, and respiratory tract. It can cause respiratory sensitization (asthma-like allergic reactions) and skin sensitization (allergic contact dermatitis). Exposure limits (OSHA PEL: 12 mg/m³, NIOSH REL: 6 mg/m³, ACGIH TLV: 1 ppm) must be strictly observed. Engineering controls (local exhaust ventilation, water spray systems) and personal protective equipment (respirator, protective goggles, nitrile/neoprene gloves) are mandatory to prevent workplace exposure.

Storage and Transport: Phthalic anhydride is sensitive to moisture; contact with moisture causes slow hydrolysis and quality degradation. It should be stored below 30°C in cool, dry, well-ventilated areas. Shelf life is 3 months. Temperatures above 40°C may cause melting or agglomeration. Classified as UN 2214 (Class 8 - Corrosive); special precautions are required during transport. The liquid form is transported in specially insulated and heated tankers maintained at 150-180°C.

Reactivity: Phthalic anhydride is incompatible with strong oxidizing agents, strong bases, and strong acids. It undergoes esterification with alcohols and forms phthalimide derivatives with amines. It slowly hydrolyzes with water; contact with large quantities of water may cause exothermic reaction and pressure increase.

Dust Explosion: Phthalic anhydride dust can reach explosive concentrations in air (explosive limits: 1.7-10.5% by volume). Explosion-proof equipment, proper grounding, and dust collection systems should be used to prevent dust explosion risks. Static electricity accumulation should be avoided.

Environment: Phthalic anhydride is toxic to aquatic organisms. In the environment, it hydrolyzes to phthalic acid. Discharge to water bodies and sewer systems should be avoided. Waste disposal should be carried out according to local regulations; incineration is recommended.

Important Disclaimer: This Technical Data Sheet (TDS) is for informational purposes only. For complete safety, handling, storage, and regulatory compliance information, always refer to the official Safety Data Sheet (SDS/MSDS) provided by the manufacturer/supplier. All local, national, and international regulations must be followed when working with phthalic anhydride.