Glacial acetic acid (GAA, CAS 64-19-7) is the anhydrous, concentrated form of acetic acid and one of the most important organic acids in industry. This article explains its chemical formula and structure, the meaning of the term glacial, its physical properties, industrial applications and the key safety points for handling and dilution.
What Is Glacial Acetic Acid?
Acetic acid is a simple carboxylic acid with the chemical formula CH3COOH. The name glacial refers to the pure anhydrous form: because its melting point is 16.6 °C, it solidifies into ice-like crystals in cool environments, and the term has been used since the nineteenth century to describe this frozen, glassy appearance. In contrast, the dilute aqueous solutions sold as vinegar contain only 4 to 8 percent acetic acid. Glacial acetic acid is a colorless, transparent liquid with a sharp, pungent odor, and it is corrosive in concentrated form.
Chemical Formula and Structure
The molecular formula of acetic acid is C2H4O2, and the condensed structural formula is CH3COOH. The molecule consists of a methyl group (CH3) bonded to a carboxyl group (COOH). In the pure liquid, acetic acid molecules form hydrogen-bonded dimers, which is why the liquid behaves as a protic solvent with a relatively high boiling point for its molecular size. As a weak acid, it partially dissociates in water to release hydrogen ions, with a pKa of about 4.76 at 25 °C.
Key Physical and Chemical Properties
| Property | Typical Value |
|---|---|
| CAS number | 64-19-7 |
| Molecular formula | C2H4O2 (CH3COOH) |
| Molecular weight | 60.05 g/mol |
| Fusing point | 16.6 °C |
| Boiling point | 117.9 °C |
| Density (20 °C) | ≈ 1.05 g/cm³ |
| Flash point (closed cup) | 39 °C |
| Refractive index (20 °C) | 1.371 |
| Auto-ignition temperature | ≈ 426 °C |
| Explosive limits in air | 5.4 - 16.0 vol% |
Because the fusing point is close to typical warehouse temperatures in winter, storage areas are often kept above 17 °C or the product is supplied in insulated or heated containers to prevent solidification.
Industrial Applications
Chemical manufacturing: the largest use is the production of vinyl acetate monomer (VAM), followed by acetic anhydride and acetate esters used in solvents, coatings and plastics.
Food industry: food-grade acetic acid is used as an acidulant, preservative and flavoring agent, including vinegar production.
Pharmaceutical and laboratory: used in buffer solutions, as a synthesis intermediate and as a disinfectant in diluted form.
Textile and dyeing: pH adjustment and dye fixation in textile processing.
Agrochemicals: intermediate for pesticides and herbicides.
Rubber and plastics: coagulant in rubber latex processing and raw material for cellulose acetate and other polymers.
Packaging, Dilution and Safety Notes
Glacial acetic acid is commonly packed in plastic or steel drums and IBC containers. A typical loading plan for a 20-foot container is 720 drums of 30 kg, 80 drums of 220 kg, or 20 IBC drums of 1,050 kg. When diluting glacial acetic acid, always add the acid to water slowly with stirring, never the reverse, because the mixing is exothermic and can spatter. The concentrated acid is corrosive to skin and eyes and can cause serious burns; vapors irritate the respiratory tract. Use acid-resistant gloves, goggles and protective clothing, work with ventilation, and store the product away from oxidizers and incompatible bases. In case of contact, flush the affected area with plenty of water and seek medical attention.
Frequently Asked Questions
What is the difference between acetic acid and glacial acetic acid?
Glacial acetic acid is the nearly water-free anhydrous form with a purity of typically 99.5% or higher, while the term acetic acid is often used for both the pure substance and its aqueous solutions. Glacial acetic acid solidifies at 16.6 °C.
Why is it called glacial acetic acid?
The name comes from the ice-like crystals that form when the pure acid freezes at temperatures below 16.6 °C.
Is glacial acetic acid the same as vinegar?
No. Vinegar is a dilute solution of acetic acid in water, typically 4 to 8 percent. Glacial acetic acid is the concentrated anhydrous chemical and is corrosive and dangerous to handle undiluted.
What is glacial acetic acid used for?
It is used mainly to produce vinyl acetate monomer, acetic anhydride and acetate esters, and it serves as an acidulant, solvent and synthesis intermediate in food, pharmaceutical, textile and agrochemical industries.
How should glacial acetic acid be diluted safely?
Add the acid to water slowly while stirring, never water to acid, because dilution generates heat. Use protective equipment and work in a ventilated area.
What are the explosive limits of acetic acid vapor?
Acetic acid vapor forms flammable mixtures with air between about 5.4 and 16.0 percent by volume, with an auto-ignition temperature near 426 °C, so the liquid must be kept away from open flames and hot surfaces.
