Describe the following:
(i) Cross aldol condensation
(ii) Decarboxylation

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Solution

(i) Cross aldol condensation:
It is aldol condensation between two different carbonyl compounds. If both carbonyl compounds have alpha hydrogen atoms, then four different products can be obtained. Thus, ethanal and propanal will give following products.
$C H_{3} - C H O + C H_{3} - C H_{2} - C H O (i) d i l N a O H - ------ \to (i i) Δ C H_{3} - C H = C H - C H O + C H_{3} - C H_{2} - C H = C (C H_{3}) - C H O + C H_{3} - C H = C (C H_{3}) - C H O + C H_{3} - C H_{2} - C H = C H - C H O$
(ii) Decarboxylation:
When anhydrous sodium salt of carboxylic acid is fused with soda lime (sodium hydroxide and calcium oxide in the ratio 3:1) it gives hydrocarbon containing one carbon atom less than the carboxylic acid. The net result is loss of a molecule of carbon dioxide from carboxylic acid.
$C H_{3} C O O N a + N a O H C a O - - \to Δ C H_{4} + N a_{2} C O_{3}$

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(a) Describe the following:

(i) Acetylation (ii) Cannizzaro reaction

(iii) Cross aldol condensation (iv) Decarboxylation

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