Acetic acid and glacial acetic acid are the same chemical substance at very different concentrations, and confusing the two is one of the most common sourcing mistakes in the chemical trade. Both carry CAS 64-19-7, but their water content, corrosivity, freezing behaviour and end uses are quite different.
What Is Acetic Acid?
Acetic acid, also called ethanoic acid, is a simple carboxylic acid with the molecular formula CH3COOH, equivalent to C2H4O2, and the CAS number 64-19-7. It is a colourless liquid with a sharp, sour odour and taste, and it occurs naturally in plants, animals and fermentation processes.
Dissolved in water at low concentration, it forms the vinegar used in cooking and food preservation. Industrial production routes include methanol carbonylation, oxidation of hydrocarbons and fermentation.
What Is Glacial Acetic Acid?
Glacial acetic acid is the anhydrous, concentrated form of the same substance, containing at least 99 percent acetic acid with only traces of water. It is named for its habit of freezing into ice-like crystals when it is cooled below about 16.7 °C, which is only slightly under normal room temperature in cool climates.
It is produced by removing water from concentrated acetic acid solutions, usually by distillation with a drying agent. Because of its high purity and low water content, glacial acetic acid is strongly corrosive and must be handled with appropriate equipment.
Key Differences Between Acetic Acid and Glacial Acetic Acid
| Property | Dilute acetic acid | Glacial acetic acid |
|---|---|---|
| CAS number | 64-19-7 | 64-19-7 |
| Acetic acid content | Typically a few percent, as in vinegar | 99 percent or more, anhydrous |
| Water content | High | Trace only |
| Appearance | Clear aqueous solution | Clear liquid that freezes near 16.7 °C |
| Density | Close to that of water | About 1.05 g/cm³ |
| Corrosivity | Mild | Strongly corrosive to skin, eyes and many metals |
| Flash point | Not applicable in dilute form | About 39 °C |
| Typical use | Food, cleaning, pH adjustment | Industrial synthesis and reaction media |
In short, water content is the central difference between the two. Concentration then drives every other property: the glacial grade is far more corrosive, denser and combustible at elevated temperature, while dilute acetic acid is mild enough for food contact.
Applications of Dilute Acetic Acid
Food and beverage: vinegar is used for pickling, preservation, dressings and as a flavouring acidulant.
Household and industrial cleaning: the mild acidity dissolves scale and mineral deposits in descaling products and cleaning agents.
pH adjustment: applied in personal care, pharmaceutical and water-treatment formulations to bring a system to the required acidity.
Preservation: inhibits microbial growth in a range of food and feed products.
Industrial Applications of Glacial Acetic Acid
Vinyl acetate monomer: the principal outlet, feeding into polyvinyl acetate and polyvinyl alcohol production.
Acetic anhydride: used for cellulose acetate and for acetylation reactions in fine chemicals.
Esters: ethyl acetate and butyl acetate are made from glacial acetic acid and are used as solvents for paints, inks and adhesives.
Purified terephthalic acid: glacial acetic acid serves as the reaction solvent in the manufacture of terephthalic acid for polyester.
Reaction medium and laboratory reagent: provides consistent reactivity and concentration control in synthesis and textile processing.
Choosing the Right Grade, Safety and Storage
Buyers should specify the concentration, purity and grade required by the process. Food-contact applications need grades that comply with food safety requirements, while chemical synthesis generally calls for industrial or reagent grade glacial acetic acid supplied with a certificate of analysis.
Glacial acetic acid is corrosive to skin, eyes and respiratory tissue and can cause serious burns; it is also combustible at elevated temperature with a flash point near 39 °C and is commonly classified with hazard statements including H226 (flammable liquid and vapour) and H314 (causes severe skin burns and eye damage). Handling calls for splash goggles, acid-resistant gloves and effective ventilation, with eyewash and safety shower facilities nearby.
Store the glacial grade away from ignition sources and from incompatible materials such as strong oxidizers. Because it freezes below about 16.7 °C, tanks and lines may need trace heating or protected indoor storage in cold weather, and dilution of the glacial material should always be carried out by adding acid to water under controlled conditions.
Frequently Asked Questions
Q: What is the difference between acetic acid and glacial acetic acid?
Glacial acetic acid is the nearly water-free, concentrated form of acetic acid, while ordinary acetic acid solutions such as vinegar contain a large proportion of water.
Q: Is glacial acetic acid the same as acetic acid?
They share the same chemical identity and CAS number 64-19-7, but the glacial grade is the pure, anhydrous form with much higher concentration and corrosivity.
Q: Why is glacial acetic acid called glacial?
Because it freezes into ice-like crystals when cooled below about 16.7 °C, which is close to the temperature of a cool room.
Q: Can glacial acetic acid be used in food?
Glacial acetic acid is not added directly to food. Food applications use dilute acetic acid or food-grade vinegar solutions of the appropriate concentration.
Q: What is the CAS number of acetic acid?
Both acetic acid and glacial acetic acid share the CAS number 64-19-7.
Q: Which is more dangerous, acetic acid or glacial acetic acid?
Glacial acetic acid is more dangerous because of its high concentration and strong corrosivity, whereas dilute acetic acid is comparatively mild.
Q: How is the glacial grade stored in winter?
Keep it in a closed container or heated tank above its freezing point, away from ignition sources and strong oxidizers, and dilute it by adding acid to water.