Glacial acetic acid formula and names
The formula of acetic acid is CH3COOH, which can also be written C2H4O2. Its systematic name is ethanoic acid and its molar mass is 60.05 g/mol. “Glacial” is not a different compound: it is the name used for acetic acid that contains almost no water.
| Item | Value |
|---|---|
| Formula | CH3COOH (C2H4O2) |
| Molar mass | 60.05 g/mol |
| CAS number | 64-19-7 |
| Systematic name | Ethanoic acid |
| Other names | Methanecarboxylic acid, vinegar acid |
| HS code (6-digit) | 2915.21 |
| UN number | UN 2789 (glacial, or solutions with more than 80% acid) |
The molar mass follows from the atomic masses: 2 × 12.011 (carbon) + 4 × 1.008 (hydrogen) + 2 × 15.999 (oxygen) = 60.052, which rounds to 60.05 g/mol. The US tariff lists acetic acid under subheading 2915.21.00; check the full tariff line for your own country with your customs broker.
Why it is called “glacial”
Water-free acetic acid freezes at about 16.6 °C (61.9 °F), not far below normal room temperature. In a cool warehouse or in winter it sets into a solid mass of ice-like crystals, which is where the name “glacial” comes from. Water lowers the freezing point, which is why dilute solutions and vinegar do not solidify at these temperatures.
Solidified acid melts back to a liquid when it is warmed. Its vapour is flammable above the flash point of 40 °C (104 °F), so keep open flames and other ignition sources away and follow the thawing advice on the supplier’s safety data sheet (SDS).
Grades and concentration
There is no single, universal purity at which acetic acid becomes “glacial”, and reference works differ slightly:
- The Kirk-Othmer Encyclopedia of Chemical Technology considers glacial acetic acid to be 99.50% by weight or higher, and mentions another grade with a minimum of 99.70%.
- Hawley’s Condensed Chemical Dictionary describes glacial acetic acid as the pure compound, 99.8% minimum, and lists the USP glacial grade at 99.4% by weight.
- Hawley’s also lists technical grades of 80% and 99.5%, and commercial strengths of 6, 28, 30, 36, 56, 70, 80 and 99.5%.
Vinegar, by comparison, is an aqueous solution of about 4–12% acetic acid, according to Ullmann’s Encyclopedia of Industrial Chemistry. Because the word “glacial” covers a range, compare suppliers on the guaranteed assay printed on the Certificate of Analysis (CoA), not on the name alone.
Key properties
Glacial acetic acid is a clear, colourless liquid with a strong smell of vinegar. It is miscible with water in all proportions, and dissolving it gives off some heat. It also mixes freely with ethanol, ether and acetone. Its vapour is about twice as heavy as air, so it sinks and collects in low areas.
| Property | Value |
|---|---|
| Appearance | Clear, colourless liquid with a strong vinegar odour |
| Melting (freezing) point | 16.6 °C (61.9 °F) |
| Boiling point | 117.8 °C (244 °F) at 760 mmHg |
| Flash point | 40 °C (104 °F) |
| Autoignition temperature | 516 °C (961 °F) |
| Flammable limits in air | 5.4% to 16% |
| Specific gravity | 1.051 at 20 °C (68 °F) |
| Vapour density (air = 1) | 2.07 |
| Vapour pressure | 11.4 mmHg at 20 °C (68 °F) |
| Solubility in water | Miscible in all proportions |
Values are from NOAA’s CAMEO Chemicals database, except solubility, which is from the CRC Handbook of Chemistry and Physics as recorded in the Hazardous Substances Data Bank (HSDB). CAMEO gives temperatures in degrees Fahrenheit; the Celsius figures are rounded conversions.
How acetic acid is made
The US Food and Drug Administration’s regulation for acetic acid, 21 CFR 184.1005, notes that it occurs naturally in plant and animal tissues and is produced either by fermentation of carbohydrates or by organic synthesis. It names three principal synthetic routes:
- Methanol carbonylation: carbon monoxide reacts with methanol made from natural gas.
- Acetaldehyde oxidation: acetaldehyde made from ethylene is oxidised to acetic acid.
- Butane oxidation: butane is oxidised in the liquid phase.
Methanol carbonylation was already the leading route in 1991, when the Kirk-Othmer encyclopedia attributed about half of world production to it and about a third to acetaldehyde oxidation. Fermentation remains the traditional route for vinegar.
What glacial acetic acid is used for
Most acetic acid is used to make other chemicals. The Kirk-Othmer encyclopedia (online edition, 2014) puts vinyl acetate production at 32% of use, followed by terephthalic acid production and acetate esters in equal shares, and then acetic anhydride.
- Vinyl acetate monomer (VAM): the largest single use, as a building block for polymers.
- Purified terephthalic acid (PTA): acetic acid is the solvent in which para-xylene is oxidised to terephthalic acid, a raw material for polyester.
- Acetate esters such as ethyl acetate and butyl acetate, which are widely used solvents.
- Acetic anhydride, which is used to make cellulose acetate and other acetyl compounds.
- Other chemicals: chloroacetic acid, pharmaceuticals, dyes and insecticides.
- Textiles and dyeing: as a dyeing auxiliary and in textile printing.
- Other industrial uses: latex coagulant, oil-well acidising, photographic fixing baths, etching in semiconductor manufacture, and laboratory analysis.
The last three groups of uses are listed in the HSDB record for acetic acid.
Food uses and US limits
In food, the FDA affirms acetic acid as generally recognised as safe (GRAS) for use as a curing and pickling agent, flavour enhancer, flavouring agent, pH control agent, and solvent and vehicle; it may also be used in boiler water additives. The ingredient must meet the Food Chemicals Codex specification. The same regulation gives the maximum levels, as served, that result from good manufacturing practice:
| Food category | Maximum level as served |
|---|---|
| Condiments and relishes | 9.0% |
| Gravies and sauces | 3.0% |
| Cheeses and dairy product analogs | 0.8% |
| Meat products | 0.6% |
| Chewing gum | 0.5% |
| Fats and oils | 0.5% |
| Baked goods | 0.25% |
| All other food categories | 0.15% or less |
These are US limits; check the food regulations of your own market before use.
Hazards, storage and transport
Glacial acetic acid is both corrosive and flammable. NOAA’s CAMEO database summarises the main hazards:
- It is corrosive to metals and to body tissue; contact with the skin or eyes causes burns.
- Breathing the vapour causes coughing, chest pain and irritation of the nose and throat, and may cause nausea and vomiting. The US National Institute for Occupational Safety and Health (NIOSH) sets its IDLH (immediately dangerous to life or health) concentration at 50 ppm.
- The vapour is flammable above the flash point of 40 °C (104 °F) and forms ignitable mixtures with air between 5.4% and 16%.
- It can explode with nitric acid if not kept cold, has reacted violently with potassium hydroxide, and a mixture with ammonium nitrate ignites when warmed.
For storage, the US National Fire Protection Association’s Fire Protection Guide (as recorded in HSDB) advises a dry, well-ventilated place, separated from oxidising materials and alkaline substances, and the International Chemical Safety Card adds a fireproof store separated from food and feedstuffs. Keep containers tightly closed, plan for the acid freezing in cool stores, and allow time for it to thaw before use. Kirk-Othmer notes that acid stronger than 99% may be stored and shipped in aluminium, which slowly forms a protective layer of basic aluminium acetate.
For transport, CAMEO lists these entries:
| Product | UN number | US DOT hazard labels |
|---|---|---|
| Acetic acid, glacial | UN 2789 | Corrosive, flammable liquid |
| Acetic acid solution, more than 80% acid | UN 2789 | Corrosive, flammable liquid |
| Acetic acid solution, more than 10% but not more than 80% acid | UN 2790 | Corrosive |
Confirm the classification, packing group and labels for your shipment on the current SDS and with your freight forwarder.
Questions to ask a supplier
- What is the guaranteed minimum assay (for example 99.5% or 99.8%), and what are the limits for water and other impurities?
- Which specification does the grade meet: technical, USP, Food Chemicals Codex (food grade) or analytical reagent (AR)?
- Can you share a recent Certificate of Analysis and the current SDS for this grade?
- What packing do you offer, and how will the shipment be classified and labelled?
- How should the cargo be handled in cold weather, given that the acid freezes at about 16.6 °C?
Enquire with Scapex Exports
Scapex Exports is an exporter and supplier of industrial and fine chemicals from India. Related products in our catalogue include acetic acid glacial, food-grade glacial acetic acid, glacial acetic acid AR and acetic anhydride. Each product page links to its COA and MSDS, and our guide to acetyl chloride versus thionyl chloride covers two related reagents.
Tell us the grade, the specification you need, the quantity, packing and destination port, and we will reply with a quotation.
Frequently asked questions
What is glacial acetic acid?
It is acetic acid, CH3COOH, with almost no water, usually 99.5% or more by weight. It is called glacial because it freezes into ice-like crystals at about 16.6 °C.
What is the difference between acetic acid and glacial acetic acid?
They are the same compound. Acetic acid is often sold as a solution in water, while glacial acetic acid is the nearly water-free form. Vinegar contains only about 4–12% acetic acid.
What is the freezing point of glacial acetic acid?
About 16.6 °C (61.9 °F), so it can solidify in a cool store or in winter. It boils at about 117.8 °C (244 °F).
Is glacial acetic acid flammable?
Yes. Its flash point is 40 °C (104 °F), and it is also corrosive. It is shipped as UN 2789 with corrosive and flammable liquid labels.
What is glacial acetic acid used for?
Mainly to make vinyl acetate monomer, acetate esters and acetic anhydride, and as the solvent for terephthalic acid production. It is also used in food as a pickling and pH control agent, and in textiles, dyeing and laboratories.
Sources: NOAA CAMEO Chemicals datasheets for acetic acid, glacial, acetic acid solution, more than 80% acid and acetic acid solution, more than 10% but not more than 80% acid; US eCFR, 21 CFR 184.1005 Acetic acid; Hazardous Substances Data Bank (HSDB) record for acetic acid via PubChem, citing the Kirk-Othmer Encyclopedia of Chemical Technology, Hawley’s Condensed Chemical Dictionary, Ullmann’s Encyclopedia of Industrial Chemistry and the CRC Handbook of Chemistry and Physics; US Harmonized Tariff Schedule, subheading 2915.21.00.