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.
Ester production
The major esters of acetic acid are commonly used solvents for paints, inks and coatings. The esters includen-butyl acetate, ethyl acetate, isobutyl acetate, and propyl acetate. They are produced by catalysed 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 are produced from acetaldehyde using the Tishchenko reaction. Additionally, ether acetates are used as solvents for nitrocellulose, acrylic lacquers, wood stains and varnish removers. 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). 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.
Vinyl acetate monomer
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 reaction is of ethylene and acetic acid with oxygen over a palladium catalyst.
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 applied in paints and adhesives.
Acetic anhydride
The condensation product 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. Acetic anhydride may be produced directly by methanol carbonylation bypassing the acid, and Cativa production plants can be adapted for anhydride production.
Acetic anhydride is a strong 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 aspirin, 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. Pure acetic acid is used as a solvent in the production of terephthalic acid (TPA), the raw material for polyethylene terephthalate (PET). Although currently accounting for 5–10% of acetic acid use worldwide, this specific application is expected to grow significantly in the next decade, as PET production increases.
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. Acetic acid is the solvent of choice when reducing an aryl nitro-group to an aniline using palladium-on-carbon.
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.
Vinegar
In the form of vinegar, acetic acid solutions (typically 5% to 18% acetic acid, with the percentage usually calculated by mass) are used directly as a condiment, and also in the pickling of vegetables and other foodstuffs. Table vinegar tends to be more diluted (5% to 8% acetic acid), while commercial food pickling generally employs more concentrated solutions. The amount of acetic acid used as vinegar on a worldwide scale is not large, but historically this is by far the oldest and most well-known application.
