Question

Write short notes on the following: (i) Kolbe Electrolysis:

Hint:

Aldol condensation and Kolbe electrolysis are both useful for forming carbon-carbon bonds in organic synthesis.

Answer 1

Kolbe electrolysis is a method of preparing alkyl radicals from carboxylic acids by applying an electric current. When a carboxylate salt (usually sodium or potassium salt of a carboxylic acid) is electrolyzed, it undergoes decarboxylation, forming an alkane: \[ \text{RCOONa} \xrightarrow{\text{electrolysis}} \text{R-H} + \text{CO}_2 \] For example, sodium acetate under Kolbe electrolysis gives ethane.
(ii) Aldol Condensation: % Solution
Solution:
Aldol condensation is a reaction where an aldehyde or a ketone with a hydrogen atom on the α-carbon reacts with another molecule of the same compound or a different one to form a β-hydroxy aldehyde or ketone. Upon heating, this product undergoes dehydration to form an α,β-unsaturated carbonyl compound. For example, acetaldehyde under basic conditions gives β-hydroxy aldehyde: \[ \text{CH}_3\text{CHO} + \text{CH}_3\text{CHO} \xrightarrow{\text{NaOH}} \text{CH}_3\text{CH(OH)CHO} \xrightarrow{\Delta} \text{CH}_3\text{CH=CHCHO} \]
(iii) Rosenmund Reduction: % Solution
Solution:
Rosenmund reduction is a catalytic hydrogenation process that selectively reduces acyl chlorides to aldehydes. In this reaction, acyl chloride is treated with hydrogen gas in the presence of palladium on barium sulfate (Pd/BaSO\(_4\)) and quinoline as a poison: \[ \text{RCOCl} + \text{H}_2 \xrightarrow{\text{Pd/BaSO}_4} \text{RCHO} \] For example, benzoyl chloride is reduced to benzaldehyde under these conditions.