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Acetic acid is one of the commonest organic acids and has been known for quite a long time in the form of vinegar. It is also present free in a number of fruit juices. In the combined state it occurs in many oils and essential oils.
Formula: CH3COOH, IUPAC Name: Ethanoic acid
Acetic acid is a colourless, corrosive liquid with a pungent smell at ordinary temperatures. But below 290K, it solidifies to an icy mass called glacial acetic acid. It boils at 391K and its specific gravity is 1.08 at 273K. It is miscible with water, alcohol and ether in all ratios. It is a good solvent for phosphorus, sulphur, iodine and inorganic compounds.
Since acetic acid contains an alkyl group and an acid moiety (each of the two parts into which a thing is divided), it exhibits the properties of both these groups.
In acetic acid, halogen atoms successively replace the three hydrogen atoms of the alkyl group.
Acetic acid ionizes in polar media to give hydrogen ion that is responsible for its acidic behaviour.
Accordingly, acetic acid can react with alkalis and alkali metal carbonates and also with metals.
Acetic acid turns blue litmus to red, neutralizes alkalis to form salt and water. It also decomposes carbonates and bicarbonates to liberate carbon dioxide indicated by effervescence.
Bicarbonate test is used as an identification test for the presence of carboxylic group in a compound.
Acetic acid reacts with strongly electropositive metals like sodium and zinc to give the respective acetate and liberate hydrogen.
Acetic acid reacts with alcohols in the presence of dehydrating agents like anhydrous zinc chloride or concentrated sulphuric acid to form esters.
Dry distillation of the anhydrous alkali salts of acetic acid with soda-lime yields methane.
Though acetic acid is resistant to reduction, prolonged heating under pressure with concentrated hydriodic acid and red phosphorus gives ethane. This is also possible by heating the acid with hydrogen at high temperature and under pressure in the presence of a nickel catalyst.
In the presence of lithium aluminium hydride, acetic acid can be reduced to ethanol. Hydrogenation in the presence of ruthenium or copper-chromium oxide catalyst gives the same result.
On prolonged heating with a strong oxidizing agent, acetic acid is oxidized to carbon dioxide and water.
- Ethanoic aid is used in the manufacture of dyes, perfumes and rayons
- Manufacture of rubber from latex and casein from milk. It is used for coagulation.
- In the form of salts in medicine and paints.
- In the form of acetates of aluminium and chromium is used as mordants.
- In dilute form is used as vinegar and in the concentrated form as a solvent.
- In form of organic esters as perfumes.
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