ACETIC ACID
~ also known as Ethanoic acid; 64-19-7; Ethylic acid; Acetic acid, glacial; Methanecarboxylic acid etc. is the second simplest carboxylic acid (after methanoic acid) and is a weak monoprotic acid. Global demand for acetic acid is about 6.5 million metric tons per year (Mt/a), of which ~1.5 Mt/a is met by recycling; the rest made from methanol.
Chemical structure: CH3COOH (CH3CO2H, C2H4O2). It has a methyl group attached to a carboxyl group.
Properties: hygroscopic, corrosive liquid with a vinegar-like odor. At physiological pHs, acetic acid is usually fully ionised to acetate.
Production:
Acetic acid is produced industrially both synthetically and by bacterial fermentation
a) Methanol carbonylation (approximately 75% of acetic acid in the chemical industry): Methanol and carbon monoxide react to produce acetic acid, using metal carbonyl as a catalyst for carbonylation, iodomethane as an intermediate, in 3 steps.
b) Acetaldehyde oxidation: This is the second most common industrial method, which requires hot temperatures and metal catalysts e.g. naphthenate salts of Mn, Co, Cr. Light naphtha (flammable liquid hydrocarbon mixture) components eg butane, are oxidized in air/ O2 to peroxides -> decomposed to acetic acid 2 C4H10 + 5 O2 → 4 CH3CO2H + 2 H2O .
Valuable side-products may also form, like butanone ethyl acetate, formic acid, butanone, ethyl acetate, formic acid, and propionic acid.
c) Ethylene oxidation: Acetaldehyde may be prepared from ethylene using the wacker process, then oxidised. A more recent one-step process uses palladium as a metal catalyst supported on a heteropoly acid such as silicotungstic acid. It is competitive with methanol carbonylation for smaller plants. Unlike traditional oxidation catalysts, the selective oxidation process will use UV light to produce acetic acid at ambient temperatures and pressure.
d) Oxidative fermentation: Acetobacter can produce vinegar from apple cidar, wine, fermented grain, malt, rice, mashed potato, in aerobic conditions. C2H5OH + O2 → CH3COOH + H2O
Most vinegar is now made in submerged tank culture, where alcohol is fermented in a continuously stirred tank, with oxygen is supplied via bubbling air through the solution.
e) Anaerobic fermentation: Clostridium or Acetobacterium can convert sugars to acetic acid without creating ethanol as an intermediate. C6H12O6 → 3 CH3COOH . They can also use methanol, CO, or a mixture of CO2 and H2.
Chemical reactions and Uses: The main use of acetic acid is the production of vinyl acetate monomer, followed by acetic anhydride and ester production. The major esters of acetic acid are often used as solvents for inks, paints and coatings. The worldwide production of acetic anhydride is huge and involves 25% to 30% of the worldwide production of acetic acid. As an acetylation agent, it’s primary use is for cellulose acetate textile and photographic film. Glacial acetic acid is a great polar protic solvent for industrial use and also as solvents for resins, paints, and lacquers.
In medicine, acetic acid has been injected into tumors for treatment purposes and also used in cervical colposcopy and turns white if cervical cancer is present. It is a broad spectrum antiseptic and may be even used for topical pseudomonas infections that are resistant to antibiotics. It is also used in certain areas for otitis externa treatment.
In the food industry, vinegar is 4–18% acetic acid by mass and is used as both a condiment and for pickling.
>> see the worldwide chemical supplier marketplace of acetic acid and much more
Recent Comments