• 05
  • 02
  • 03
  • 04
  • 05
  • 05
  • 05
  • 05
  • 05
PRODUCT DETAILS
ACIDS > Acetic Acid

Acetic acid is an organic compound with the chemical formula CH3COOH. It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar, and has a distinctive sour taste and pungent smell.

Formula: C2H4O2,  IUPAC ID: Acetic acid, Melting point: 16 °C, Density: 1.05 g/cm³, Molar mass: 60.05 g/mol, Boiling point: 118 °C.

Uses

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.

Vinyl acetate monomer

The major use of acetic acid is for the production of vinyl acetate monomer (VAM). In 2008, this application was estimated to consume one third of the world's production of acetic acid. The reaction is of ethylene and acetic acid with oxygen over a palladium catalyst, conducted in the gas phase.

    2 H3C–COOH + 2 C2H4 + O2 → 2 H3C–CO–O–CH=CH2 + 2 H2O

Vinyl acetate can be polymerized to polyvinyl acetate or to other polymers, which are components in paints and adhesives.

Ester production

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 catalyzed reaction from acetic acid and the corresponding alcohol:

    H3C-COOH + HO-R → H3C-CO-O-R + H2O, (R = a general alkyl group)

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 anhydride

The product of the condensation of two molecules of acetic acid is acetic anhydride. The worldwide production of acetic anhydride is a major application, and uses approximately 25% to 30% of the global production of acetic acid. The main process involves dehydration of acetic acid to give ketene at 700-750 °C. Ketene is thereafter reacted with acetic acid to obtain the anhydride:

    CH3CO2H → CH2=C=O + H2O
    CH3CO2H + CH2=C=O → (CH3CO)2O

Acetic anhydride is an acetylation agent. As such, its major application is for cellulose acetate, a synthetic textile also used for photographic film. Acetic anhydride is also a reagent for the production of heroin and other compounds.
Use as solvent

Glacial acetic acid is an excellent polar protic solvent, as noted above. It is frequently used as a solvent for recrystallization to purify organic compounds. Acetic acid is used as a solvent in the production of terephthalic acid (TPA), the raw material for polyethylene terephthalate (PET). In 2006, about 20% of acetic acid was used for TPA production.

Acetic acid is often used as a solvent for reactions involving carbocations, such as Friedel-Crafts alkylation. For example, one stage in the commercial manufacture of synthetic camphor involves a Wagner-Meerwein rearrangement of camphene to isobornyl acetate; here acetic acid acts both as a solvent and as a nucleophile to trap the rearranged carbocation.

Glacial acetic acid is used in analytical chemistry for the estimation of weakly alkaline substances such as organic amides. Glacial acetic acid is a much weaker base than water, so the amide behaves as a strong base in this medium. It then can be titrated using a solution in glacial acetic acid of a very strong acid, such as perchloric acid.

Medical use

Diluted acetic acid is used in physical therapy using iontophoresis.

Vinegar

Vinegar is typically 4-18% acetic acid by mass. Vinegar is used directly as a condiment, and in the pickling of vegetables and other foods. Table vinegar tends to be more diluted (4% to 8% acetic acid), while commercial food pickling employs solutions that are more concentrated. 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.