Acetic acid is a colourless liquid organic compound with the chemical formula CH3COOH. Commonly known as vinegar, it is used in various household and industrial applications as well as in the food industry. With a pungent sour taste and characteristic aroma, acetic acid is one of the most widely used acids commercially. In this article, we will explore the various properties, production methods and uses of acetic acid.
Chemical Properties
As a carboxylic acid, acetic acid contains a carboxyl group bonded to an alkyl group. Its molecular formula indicates that it contains a methyl group bonded to a carbonyl group which in turn is bonded to a hydroxyl group. This gives acetic acid a relatively lower molecular mass of 60.052 g/mol. Some key chemical properties of acetic acid include:
- Its melting point is 16.7°C and boiling point is 118.1°C.
- It is miscible in water, alcohols and ethers. However, it is immisible in hydrocarbons.
- It is a monoprotic acid that ionizes only once to produce hydronium and acetate ions in an aqueous solution.
- Commercially obtained acetic acid contains 99.5% acetic acid along with traces of water.
Production Methods
Most acetic acid produced is through chemical synthesis rather than extraction or distillation from natural sources. Some common production methods include:
Carbonylation of Methanol
This catalytic process involves the carbonylation of methanol with carbon monoxide at high pressures. In the presence of a catalyst such as iodomethane, methyl iodide is formed which reacts with water to produce acetic acid and hydrogen iodide. This is the predominant industrial process and accounts for over 90% of global production.
Oxidation of Ethanol
Passing air or oxygen through a heated solution of ethanol produces Acetic Acid. The oxidation is catalyzed by chromium or cobalt salts. Although this process is lower yielding than carbonylation, it is more environmentally friendly.
Anaerobic Bacterial Fermentation
Certain bacteria like Acetobacter can ferment ethanol or sugars like glucose anaerobically to produce acetic acid. This natural fermentation process is employed in traditional vinegar production methods. However, it has low product yields.
Uses of Acetic Acid
Some important uses of acetic acid arising from its versatile properties include:
Vinegar production
As commonly known, acetic acid fermented from ethanol is the main component of vinegar used extensively in cooking, food preservation and cleaning. The food grade acetic acid content in vinegar is 4-8%.
Production of Esters and Acetate salts
Reaction of acetic acid with alcohols produces esters like ethyl acetate that find applications as solvents. Various acetates used as food additives, pharmaceuticals or fragrances are prepared from the neutralization of acetic acid.
Textile Industry
Dyeing, printing and finishing of natural and synthetic fibers uses acetic acid. Its ability to dissolve and hydrolyze fibers makes it useful in applications such as descaling, degumming and scouring.
Production of Purified Terephthalic Acid (PTA)
PTA is the precursor to polyester production and around 6 million tons are synthesized annually by the catalytic oxidation of p-xylene with acetic acid as solvent.
Household Chemicals
Its disinfecting and degreasing properties allow use of acetic acid in household cleaners, diluted solutions as herbicides and food preservatives. Trace amounts are also used in paint removers.
With exceptional functional properties and economical large scale production processes, acetic acid today holds immense significance both commercially and domestically. Its key role as an intermediate chemical makes it one of the top organic chemical commodities worldwide. From household applications to large industrial uses, this versatile carboxylic acid will continue to be widely consumed in the future. With growing market demand and versatile applications, the production and usage of acetic acid is expected to further increase in the years to come.
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