Ethanoic acid is the acid present in vinegar. It can be prepared by the complete oxidation of acidified heptaoxochromate(VI) solution. Ethanol also undergoes oxidation to ethanal and then to ethanoic acid. Complete oxidation to thid organic acid is achieved by dropping the ethanol into a large excess of the oxidizing agent used in the reaction and distilled by reflux. Note that in the preparation of this acid, hydrochloric acid cannot be used because of its high volatility. The apparatus used must all be glass because the hot form of this acid attacks rubber and cork.
This Organic acid can also be prepared by the following methods:
(i) Boiling methyl cyanide, CH-H-HCN with an acid
(ii) Distilling anhydrous sodium ethanoate, CH-H-HCOONa, with concentrated tetraoxosulphate(VI) acid.
Some of the physical properties of this organic acid
(i) Ethanoic acid turns blue litmus red
(ii) Dilute solution of this acid has a sour taste.
(iii) It has a boiling point of 118*C
(iv) It is a colorless liquid with a characteristic pungent and choking smell.
(v) This acid is very soluble in water
(vi) Pure anhydrous form of this acid is often called glacial ethanoic acid because it readily freezes into ice-like crystals at temperatures below 17*C.
The Chemical Properties of Ethanoic acid are:-
(i) Ethanoic acid is stable and not easily decomposed by heat
(ii) It is unaffected by ordinary reducing agents, dehydrating agents and oxidizing agents.
(iii) This organic acid liberates carbon(IV) oxide from trioxocarbonate(IV) and hydrogentrioxocarbonates(IV)
(iv) This organic acid also neutralizes alkalis or bases to form salts that are known as ethanoates, and water only.
(v) It attacks strongly electropositive metals such as calcium and magnesium
(vi) This acid reacts with ethanol to form esters
(vii) Anhydrous or glacial form of this acid reacts with phosphorus(V) chloride to form ethanoyl chloride( an acyl chloride), which is a colorless liquid that fumes in air. Note that the formation of acyl chloride is one of the most common reactions of carboxylic acids.
(viii) The hot form of this acid forms monochloroalkanoic acid with chlorine in the presence of iodine, sunlight or phosphorus as a catalyst. Prolonging this reaction would lead to the formation of dichlotoethanoic acid and trichloroethanoic acid in succession.
(viii) This organic acid can be reduced to an alkanol by a reducing agent, lithium tetrahydridoaluminate.
Uses of Ethanoic acid
(i) Ethanoic acid is used in manufacturing ethenyl ethanoate(vinyl acetate), used in vinyl resins
(ii) This acid is used in making ethanoic anhydride, which is used in making aspirin
(iii) It is used in the manufacture of dyes
(iv) Cellulose ethanoate(cellulose acetate), made from ethanoic acid, is used making packaging materials, vanishes and the filter tips of cigarettes. It is also used in making synthetic fibres such as artificial silk or rayon.
(v) It is used in making compounds such as propanone(acetone).
(vi) It is also used in coagulating rubber and in preserving and flavoring food.