Explain the chemical properties of ethanol.

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Solution

The chemical properties of ethanol are as follows:-

1. Dehydration

(a) Intramolecular dehydration: Ethanol, when heated with excess conc. $H_{2} S O_{4}$ at 443K undergoes intramolecular dehydration (i.e. removal of water from a molecule of ethanol) to give ethene.

$C H_{3} C H_{2} O H E t h a n o l C o n c . H_{2} S O_{4} - ------- \to 443 K C H_{2} = C H_{2} + H_{2} O E t h e n e$

(b) Intermolecular dehydration: When excess of ethanol is heated with conc. $H_{2} S O_{4}$ at 413K, it undergoes intermolecular dehydration. (i.e. removal of water from two molecules of ethanol) to give diethyl ether.

$C_{2} H_{5} - O H + H O - C_{2} H_{5} C o n c . H_{2} S O_{4} - ------- \to 413 K C_{2} H_{5} - O - C_{2} H_{5} + H_{2} O D i e t h y l e t h e r$

2. Reaction with sodium: Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas.

$2 C_{2} H_{5} O H + 2 N a \to 2 C_{2} H_{5} O N a + H_{2} ↑$

3. Oxidation: Ethanol is oxidized to ethanoic acid with alkaline KMnO_4 or acidified $K_{2} C r_{2} O_{7}$ During this reaction, the orange colour of $K_{2} C r_{2} O_{7}$ changes to green. Therefore, this reaction can be used for the identification of alcohols.

$C H_{3} C H_{2} O H 2 [O] - ------- \to K_{2} C r_{2} O_{7} / H^{+} C H_{3} C O O H + H_{2} O E t h a n o i c a c i d$

4. Esterification: Ethanol reacts with ethanoic acid in the presence of conc. $H_{2} S O_{4}$ to form ethyl ethanoate and water. The compound formed by the reaction of an alcohol with carboxylic acid is known as an ester (a fruity smelling compound) and the reaction is called esterification.

$C_{2} H_{5} O H E t h a n o l + C H_{3} C O O H E t h a n o i c a c i d c o n c . H_{2} S O_{4} - ------ \to C H_{3} C O O C_{2} H_{5} + H_{2} O E t h y l e t h a n o a t e$

5. Dehydrogenation: When the vapour of ethanol is passed over heated copper catalyst at 573 K, it is dehydrogenated to acetaldehyde.

$C H_{3} C H_{2} O H E t h a n o l C u - -- \to 573 K C H_{3} C H O + H_{2} A c e t a l d e h y d e$

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