Acetic Acid CH3COOH
Aka CAS No. 64-19-7, Ethanoic acid, Acetyl hydroxide, Ethylic acid, Hydrogen acetate, Methanecarboxylic acid
Acetic acid which is also known as CAS No. 64-19-7, is an organic acid that gives vinegar its sour taste and pungent smell. It is a weak acid - only a partially dissociated acid in an aqueous solution. Pure, water-free acetic acid (glacial acetic acid) is a colorless liquid that absorbs water from the environment and freezes at 16.5°C (62°F) to a colorless crystalline solid. The pure acid and its concentrated solutions are extremely corrosive. Acetic acid is one of the simplest carboxylic acids. Acetic acid is an important chemical reagent and industrial chemical used in the production of
- polyethylene terephthalate mainly used in soft drink bottles;
- cellulose acetate, mainly for photographic film and
- polyvinyl acetate for wood glue, as well as synthetic fibers and fabrics.
In households, diluted acetic acid is often used in descaling agents. In the food industry, acetic acid is used under the food additive code E260 as an acidity regulator and as a condiment.
The global demand of acetic acid is around 6.5 million tons per year of which approximately 1.5 million tons is met by recycling. The rest is manufactured from petrochemical feed stocks or from biological sources. Diluted acetic acid produced by natural fermentation is called vinegar.
Acetic acid is produced industrially both synthetically and by bacterial fermentation. Today, the biological route accounts for only about 10% of world production, but it remains important for the production of vinegar, as many nations' food purity laws stipulate that vinegar used in foods must be of biological origin.
About 75% of acetic acid made for use in the chemical industry is made by methanol carbonylation. Alternative methods account for the rest. Total worldwide production of virgin acetic acid is estimated at 5 million metric tons per year. Approximately half of it is produced in the United States.
Acetic acid is a chemical reagent for the production of chemical compounds. The largest single use of acetic acid is in the production of vinyl acetate monomer, closely followed by acetic anhydride and ester production. The volume of acetic acid used in vinegar is comparatively small. The major use of acetic acid is for the production of vinyl acetate monomer (VAM). This application consumes approximately 40% to 45% of the world's production of acetic acid.
The major esters of acetic acid are commonly used solvents for inks, paints and coatings. The esters include ethyl acetate, n-butyl acetate, isobutyl acetate, and propyl acetate. They are typically produced by catalysed reaction from acetic acid and the corresponding alcohol.
Most acetate esters, however, are produced from acetaldehyde using the Tishchenko reaction. In addition, ether acetates are used as solvents for nitrocellulose, acrylic lacquers, varnish removers, and wood stains. First, glycol monoethers are produced from ethylene oxide or propylene oxide with alcohol, which are then esterified with acetic acid. The three major products are ethylene glycol monoethyl ether acetate (EEA), ethylene glycol monobutyl ether acetate (EBA), and propylene glycol monomethyl ether acetate (PMA, more commonly known as PGMEA in semiconductor manufacturing processes, where it is used as a resist solvent). This application consumes about 15% to 20% of worldwide acetic acid. Ether acetates, for example EEA, have been shown to be harmful to human reproduction.
Acetic acid comprises typically 4 to 18% of vinegar. Vinegar is used directly as a condiment and also in the pickling of vegetables and other foods. Table vinegar tends to be more diluted (4% to 8% acetic acid), while commercial food pickling, in general, employs more concentrated solutions. The amount of acetic acid used as vinegar on a worldwide scale is not large, but is by far the oldest and best-known application.
Diluted solutions of acetic acids are also used as a stop bath during the development of photographic films and in descaling agents to remove lime scale from taps and kettles. In the clinical laboratory, diluted acetic acid lyse red blood cells in order to facilitate microscopic examination.
The acidity is also used for treating the sting of the box jellyfish by disabling the stinging cells of the jellyfish, preventing serious injury or death if applied immediately and for treating outer ear infections in people. In this manner, acetic acid is used as a spray-on preservative for livestock silage, to discourage bacterial and fungal growth. Glacial acetic acid is also used as a wart and verruca remover.
Some organic or inorganic salts are also produced from acetic acid.
