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COOH Reactions

(a) Soda Lime Decarboxylation: Sodium or potassium salts of carboxylic acids on heating with sodalime (NaOH and CaO) give alkanes with one carbon less than the parent acids. In this reaction while NaOH takes part in the reaction, CaO simply helps in fusion of NaOH.

The reaction can be employed for descending down the series i.e. decreasing one carbon in a chain.

(b) Kolbe’s electrolytic decarboxylation: the aqueous solutions of sodium or potassium salts of carboxylic acids on electrolysis give alkanes at anode. This reaction is called Kolbe’s electrolysis.


(c) Dry distillation of calcium salts of carboxylic acids: calcium salts of carboxylic acids on heating give aldehydes or ketones.

(i) When calcium formate is distilled, formaldehyde is formed.


(ii) When calcium formate is distilled with calcium acetate, acetaldehyde is formed.


(iii) When calcium acetate is distilled alone, acetone is formed.


(d) Reduction: (i) partial reduction: carboxylic acids are reduced to primary alcohols with lithium aluminium hydride (LiAIH₄), or with hydrogen (H₂) in the presence of copper chromite (CuCr₂O₄) catalyst. Here, -COOH group is reduced to –CH₂OH.

The reduction of acids, however, does not take place with NaBH₄.

(ii) Complete reduction: carboxylic acids are reduced to alkanes on reaction with HI in the presence of phosphorus at about 500 K. Here, -COOH group is reduced to –CH₃.

(c) Hunsdiecker Reaction: Silver salts of carboxylic acids on treatment with Br₂ in the presence of some inert solvent such as CCl₄ give alkyl bromides with one carbon atom less than the parent acids.