LEARNATHON
III

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### Theory:

Ethanoic acid ($$CH_3COOH$$), commonly known as acetic acid, is one of the most important compounds of the carboxylic acid circle of relatives. Its molecular formula is $$C_2H_4O_2$$. The structural formula for ethanoic acid is,

Ethanoic acid

Preparation of ethanoic acid:

Ethanoic acid is prepared on a large scale through the oxidation of ethanol in the presence of alkaline potassium permanganate or acidified potassium dichromate.

$\begin{array}{l}{\mathit{CH}}_{3}{\mathit{CH}}_{2}\mathit{OH}\underset{2\left[O\right]}{\overset{{\mathit{KMnO}}_{4}/{\mathit{OH}}^{-}}{⟶}}\phantom{\rule{0.147em}{0ex}}{\mathit{CH}}_{3}\mathit{COOH}\phantom{\rule{0.147em}{0ex}}+{H}_{2}O\\ \mathit{Ethanol}\phantom{\rule{8.379em}{0ex}}\mathit{Ethanoic}\phantom{\rule{0.147em}{0ex}}\mathit{acid}\end{array}$

Physical properties of ethanoic acid:
• Colourless liquid with a strong odour.
• Acids are sour in taste, and so is ethanoic acid.
• They are miscible in water irrespective of their proportions.
• They have a higher boiling point than the corresponding groups of aldehyde, alcohol and ketones.
• Pure ethanoic acid on cooling forms ice-like flakes. As it resembles glaciers, it is known as glacial acetic acid.
Chemical properties of ethanoic acid:

a) Reaction with metal:

The reaction of active metals (such as Na, Zn, etc.) with ethanoic acid forms ethanoate with the liberation of hydrogen gas.

$$2CH_3COOH + Zn \rightarrow (CH_3COO)_2Zn + H_2$$
Zinc ethanoate

$$2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2$$
Sodium ethanoate

b) Reaction with carbonates and bicarbonates:

Ethanoic acid reacts with weak bases such as sodium carbonate ($$Na_2CO_3$$) and sodium bicarbonate ($$NaHCO_3$$), forming its salt, water along with the liberation of brisk effervescence ($$CO_2$$).

$$2CH_3COOH + NaCO_3 \rightarrow 2CH_3COONa + CO_2 + H_2O$$
Sodium ethanoate

$$CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + CO_2 + H_2O$$
Sodium ethanoate

c) Reaction with base:

Sodium ethanoate and water is formed when ethanoic acid reacts with sodium hydroxide.

$$CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O$$
Sodium ethanoate

d) Decarboxylation (removal of $$CO_2$$):

The reaction of soda lime (solid mixture of 3 parts of $$NaOH$$ and one part of $$CaO$$) with the sodium salt of ethanoic acid produces methane gas.

$$CH_3COOH \xrightarrow {NaOH /CaO} CH_4+ Na_2CO_3$$
Methane
gas

Uses of ethanoic acid:
• Lower concentrations of acetic acid (vinegar) are used as a food additive, flavouring agent, and preservative.
• They are used in the manufacturing of plastics.
• Used in making dyes, pigments and paints.
• It is used as a laboratory reagent and for printing on fabrics.
• They are also used for coagulating rubber from latex.
• Ethanoic acid is used in the production of pharmaceuticals.