Acetic acid

The chemical compound acetic acid (from Latin acetum, meaning "vinegar"), or more properly ethanoic acid, is the acid that gives vinegar its sour taste. It is a carboxylic acid with chemical formula CH₃COOH and structure

        H       O   
         \     //        
      H - C - C 
         /     \
        H       OH

CH₃-COOH

Pure acetic acid is a colourless flammable liquid that melts at 16.6 °C and boils at 117.9 °C. It has a density of 1.049 g/mL, slightly higher than that of water. Since pure acetic acid is solid slightly below room temperature, it is often called glacial acetic acid.

In solution, acetic acid can lose the proton of the hydroxyl group, turning into the acetate ion CH₃COO^-. The pKa of acetic acid is about 4.8 at 25 °C, meaning that about half of the acetic acid molecules are in the acetate form at a pH of 4.8.

In the body, acetic acid is produced for example after the consumption of alcoholic beverages: the ethanol is first converted into acetaldehyde, which is then converted into acetic acid by the enzyme acetaldehyde dehydrogenase and converted further to acetyl-CoA by acetate-CoA ligase.

Vinegar typically contains about 4%-8% acetic acid and some other acids as well. The name "acetic acid" derives from the Latin acetum for vinegar. The acetic acid in vinegar is produced from alcoholic beverages (typically wine) by acetic acid bacteria, which generate energy by oxidizing ethanol to acetic acid in the presence of oxygen.

Acetic acid is used as a food additive, as a photographic chemical, in the manufacture of plastics such as polyethylene terephthalate (PET, packaging) or cellulose acetate, in the production of vinyl acetate (paints and adhesives) and solvent esters.

For industrial uses, it is manufactured by liquid-phase oxidation of n-butane or recovered during the production of cellulose acetate and polyvinyl alcohol.

Concentrated acetic acid is corrosive and has to be handled with care, since it can cause skin burns, permanent eye damage, and irritation to the mouth, nose, throat, and lungs. It does not pose any cancer risk or environmental hazard.

The CAS number of acetic acid is 64-19-7; the UN number of concentrated acetic acid solution is UN 2789 and lower concentrations have UN 2790.