Acetic anhydride is a simple and highly reactive acid anhydride, appearing as a colorless liquid with a strong, vinegar-like odor.
It plays a key role in industrial acetylation reactions and serves as a vital intermediate in the manufacture of cellulose acetate (used in cigarette filters), pharmaceuticals (notably aspirin and paracetamol), resins, solvents, and industrial explosives.
Because of its broad utility, acetic anhydride remains one of the most widely traded and regulated chemical intermediates globally.

Chemical Structure

Structural Formula: (CH₃CO)₂O
Molecular Description: Two acetyl groups linked through a central oxygen atom, forming a simple carboxylic acid anhydride.

Physical and Chemical Properties

Property	Specification
Appearance	Clear, colorless liquid with a strong, pungent odor
Density (20 °C)	~1.082 g/cm³
Melting Point	−73 °C
Boiling Point	139–140 °C
Vapor Pressure (36 °C)	~10 mmHg
Refractive Index (nD, 20 °C)	~1.390
Solubility in Water	Reacts rapidly (hydrolyzes exothermically); ~2.6% soluble at 20 °C
Flash Point (Closed Cup)	54 °C (129 °F)
Explosion Limits (air)	2.0–10.2 vol%
Oral Toxicity (LD₅₀, rat)	~1.78 g/kg

Advantages

Primary acetylation agent in the synthesis of aspirin and paracetamol
Essential in producing cellulose acetate for filters, plastic films, and fibers
Widely used in resin, pharmaceutical, fragrance, and dye production
Intermediate for modified starches (E1414, E1420, E1422) in food and pharma industries
Functions as an efficient dehydrating and acetylating agent in chemical processes

Limitations and Hazards

Highly reactive with water and alcohols; hydrolyzes exothermically
Corrosive to skin, eyes, and mucous membranes — causes severe burns on contact or inhalation
Flammable and reactive with metals; requires specialized storage and transport
Strictly regulated precursor (U.S. DEA List II chemical) due to potential illicit use in heroin synthesis

Applications

Pharmaceuticals: Acetylation of salicylic acid to produce aspirin
Plastics & Fibers: Manufacture of cellulose acetate for films, textiles, and cigarette filters
Resins & Coatings: Intermediate for resins, dyes, and fragrance chemicals
Food Industry: Used in modified starch production (E1414–E1422)
Industrial Chemicals: Effective dehydrating agent in various syntheses

Safety and Regulatory Information

GHS Label: ⚠️ DANGER
Hazard Statements:
- H226 – Flammable liquid and vapor
- H302 – Harmful if swallowed
- H314 – Causes severe skin burns and eye damage
- H330 – Fatal if inhaled
Recommended PPE:
- Chemical-resistant protective clothing
- Safety goggles or full face shield
- Nitrile or Viton® gloves
- Approved respirator (limit ≤ 5 ppm per ACGIH TLV/OSHA PEL)

Storage and Handling

Store in a cool, dry, well-ventilated area, away from moisture, open flames, and strong acids
Use airtight, corrosion-resistant containers clearly labeled and tightly sealed
Avoid contact with water or incompatible materials
In case of leak or spill: absorb with dry inert material; keep away from ignition sources
Firefighting media: CO₂, dry chemical, or alcohol-resistant foam

Summary

Acetic Anhydride is an indispensable reagent in acetylation chemistry with broad industrial use in pharmaceuticals, cellulose derivatives, and coatings.
Its high reactivity and strict regulatory classification demand careful handling and storage, but its efficiency and versatility make it a cornerstone compound in organic synthesis.