Acetic acid and its uses

Acetic acid systematically named acetic acid is an acidic, colorless liquid and organic compound with the chemical formula CH3COOH (also written CH3CO2H, C2H4O2, or HC2H3O2).Vinegar contains at least 4% acetic acid, which makes acetic acid the main ingredient in vinegar besides water and other trace elements.Acetic acid is the second simplest carboxylic acid (after formic acid).It is an important chemical reagent and industrial chemical, mainly used in the production of cellulose acetate for photographic film, polyvinyl acetate for wood glue, and synthetic fibers and fabrics.In households, dilute acetic acid is often used as a descaling agent.In the food industry, acetic acid is regulated under the Food Additive Code E260 as an acidity regulator and flavoring.In biochemistry, the acetyl group derived from acetic acid is the basis of all life forms. When combined with Coenzyme A,it is central to carbohydrate and fat metabolism.The annual global demand for acetic acid is about 6.5 million tons (t/a), of which about 1.5 t/a is met through recycling; the remainder is made from methanol.Vinegar is primarily dilute acetic acid, usually produced by fermentation and subsequent oxidation of ethanol.

Uses 

Acetic acid is a chemical reagent used to produce chemical compounds.The largest single use of acetic acid is the production of vinyl acetate monomer, closely followed by the production of acetic anhydride and esters.The amount of acetic acid used in vinegar is relatively small.

Vinyl acetate monomer:

The main use of acetic acid is in the production of vinyl acetate monomer (VAM).In 2008, it was estimated that this application consumed one-third of the world's acetic acid production.The reaction consists of ethylene and acetic acid with oxygen over a palladium catalyst and is carried out in the gas phase.

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

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

Ester production:

The main esters of acetic acid are commonly used as solvents for inks, paints and coatings.Esters include ethyl acetate, n-butyl acetate, isobutyl acetate and propyl acetate.They are usually produced by the catalytic reaction of acetic acid and the corresponding alcohol:

CH3COO−H + HO−R → CH3COO−R + H2O, R = universal alkyl

For example, acetic acid and ethanol produce ethyl acetate and water.

CH3COO−H + HO−CH2CH3 → CH3COO−CH2CH3 + H2O

However, most acetates are produced from acetaldehyde using the Tishchenko reaction.In addition, ether acetate is used as a solvent for nitrocellulose, acrylic paints, varnish removers, and wood stains.First, ethylene glycol monoethers are produced from ethylene oxide or propylene oxide with alcohol and 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, used as a resist solvent). This application consumes about 15% to 20% of the world's acetic acid.Ether acetates, such as 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.Acetic anhydride is the major application for global production, accounting for approximately 25% to 30% of global acetic acid production.The main process involves the dehydration of acetic acid to ketene at 700–750 °C.The ketene is then reacted with acetic acid to give the anhydride:

CH3CO2H → CH2=C=O + H2O

CH3CO2H + CH2=C=O → (CH3CO)2O

Acetic anhydride is an acetylating agent.Therefore, its main application is cellulose acetate, a synthetic textile that is also used in photographic film.Acetic anhydride is also a reagent in the production of heroin and other compounds.

Use as a solvent:

As a polar protic solvent, acetic acid is often used in 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, approximately 20% of acetic acid production was used in TPA production.Acetic acid is often used as a solvent for reactions involving carbocations, such as Friedel-Crafts alkylations.For example, one stage in the commercial production of synthetic camphor involves the Wagner-Meerwein rearrangement of camphene to isobornyl acetate; here acetic acid acts as both a solvent and a nucleophile to trap the rearranged carbocation.Glacial acetic acid is used in analytical chemistry to evaluate weakly basic substances such as organic amides.Glacial acetic acid is a much weaker base than water, so amides behave as strong bases in this medium. It can then be titrated with a strong acid such as perchloric acid in glacial acetic acid.

Medical uses:

Injecting acetic acid into tumors has been used to treat cancer since the 1800s.In many parts of the developing world, acetic acid is used as part of cervical cancer screening.The acid is applied to the cervix and the test is positive if a white area appears after about a minute.When used as a 1% solution, acetic acid is an effective preservative with broad-spectrum activity against Streptococci, Staphylococci, Pseudomonas, Enterococci, and others.It can be used to treat skin infections caused by Pseudomonas strains resistant to typical antibiotics.Although diluted acetic acid is used in iontophoresis, there is no high-quality evidence to support this approach in the treatment of rotator cuff disease.As a drug for the treatment of otitis externa, it is included in the list of essential drugs of the World Health Organization.

Foods:

Acetic acid contains 349 kcal (1,460 kJ) per 100 g [55] Vinegar is usually not less than 4% by mass.Legal limits on acetic acid content vary by jurisdiction. Vinegar is used directly as a condiment for pickling vegetables and other foods.Vinegar tends to be more dilute (4% to 8% acetic acid), and commercial food pickling uses more concentrated solutions.Acetic acid is not as widely used as vinegar in commercial use worldwide, but it is by far the oldest and best known application.