Acetic acid (CAS 64-19-7) is an organic compound that exists as a colorless liquid with a pungent, characteristic odor. At concentrations of 99 percent or above it is known as glacial acetic acid (GAA), because it freezes into an ice-like solid at about 16.6 degrees Celsius. Glacial acetic acid is a fundamental chemical raw material used across synthesis, analysis, biochemistry and food processing. This article reviews its main applications.
Chemical and Physical Properties of Glacial Acetic Acid
Acetic acid has the formula CH3COOH and is the second simplest carboxylic acid. It is a weak acid that undergoes neutralization reactions with bases to form acetate salts, and it reacts with alcohols in esterification reactions to form esters, many of which have pleasant, fruity aromas. Glacial acetic acid is miscible with water, ethanol, ether and many organic solvents. It has a boiling point near 118 degrees Celsius and is hygroscopic, absorbing moisture from the air. Because it is corrosive and flammable, these properties require specific precautions during storage and handling.
Applications in Organic Synthesis
Glacial acetic acid plays a vital role in organic synthesis as a starting material, reaction medium and catalyst. It is used to produce acetic anhydride, acetate esters, vinyl acetate monomer and acetyl derivatives that feed the manufacture of plastics, fibers, pharmaceuticals, dyes and agrochemicals. Its dual role as both reactant and solvent makes it valuable in acetylation reactions and in the preparation of fine chemicals. In the production of purified terephthalic acid, acetic acid is used as the process solvent on an industrial scale.
Applications in Analytical Chemistry
In analytical chemistry, acetic acid is commonly used as a solvent, extractant and pH-adjusting reagent. It aids in the separation and purification of target components from complex samples, and it is a standard component of buffer systems used in chromatography and electrophoresis. Glacial acetic acid is frequently applied in titration analysis, sample preparation and as a mobile-phase modifier in high-performance liquid chromatography.
Applications in Biochemistry and Biotechnology
Acetic acid finds extensive applications in biochemical experiments. It is used to precipitate and separate proteins and nucleic acids, to adjust the pH of culture media and buffers, and to prepare reagents for molecular biology workflows. In downstream bioprocessing, acetic acid is also a product of fermentation and a feedstock for the production of biochemicals such as cellulose acetate and polyhydroxyalkanoates.
Applications in the Food Industry
Acetic acid is widely used in the food industry to regulate acidity and enhance flavor. It serves as a seasoning that improves the taste of pickled foods, sauces, dressings and vinegar preparations, and it is recognized internationally as a food additive with the designation E260. Food-grade acetic acid must meet strict purity requirements, and it is used only at levels permitted by food regulations to ensure safety.
Storage, Handling and Safety Considerations
Glacial acetic acid is corrosive and can cause severe burns to skin, eyes and mucous membranes, and its vapors irritate the respiratory tract. It is flammable with a flash point around 39 degrees Celsius, and it should be kept away from strong oxidizers, bases and ignition sources. Storage requires corrosion-resistant containers, ideally in a cool, ventilated area, with secondary containment to prevent spills. Personal protective equipment including chemical-resistant gloves, goggles and protective clothing should always be worn when handling the material.
Frequently Asked Questions
What is glacial acetic acid?
Glacial acetic acid is acetic acid at a concentration of approximately 99 percent or higher. It is called glacial because it freezes into ice-like crystals at about 16.6 degrees Celsius.
Is 99% acetic acid the same as vinegar?
No. Vinegar typically contains 4 to 8 percent acetic acid diluted in water. 99% acetic acid is a concentrated, corrosive chemical and must never be consumed directly.
What is acetic acid used for in food?
Acetic acid is used as an acidity regulator and flavor enhancer, designated E260, in pickled foods, sauces, dressings and vinegar products.
Why is acetic acid important in organic synthesis?
Acetic acid is a versatile building block for acetic anhydride, acetate esters, vinyl acetate and acetyl derivatives, which are used in plastics, fibers, pharmaceuticals and fine chemicals.
Can acetic acid be used to precipitate proteins?
Yes, acetic acid is commonly used in biochemistry to precipitate and separate proteins and nucleic acids and to prepare buffer solutions.
What is the CAS number of acetic acid?
The CAS registry number of acetic acid is 64-19-7, and its molecular formula is CH3COOH.
