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  Preparation of Carboxylic Acids, Chemistry tutorial

Introduction:

The Carboxylic acids can be made up using the diverse methods.

Oxidation of Primary Alcohols and Aldehydes or ketones:

The Oxidation of primary alcohols and aldehydes or ketones provides carboxylic acids.

1598_Oxidation of Primary Alcohols and aldehydes.jpg

Fig: Oxidation of Primary Alcohols and aldehydes

The alcohol is heated under reflux with surplus oxidizing potassium dichromate (VI) or manganese (VII). The acid is separated from the reaction mixture.

For illustration:

CH3 CH OH + (K2Cr2O7/H+) reflux → CH3 CHO + (K2Cr2O7/H+) reflux → CH3COOH

Benzoic acid can be made up from the oxidation of alky benzenes by using the acidified potassium tetraoxomanganate (vii) as the oxidizing agent.

709_Preparation of Benzoic acid.jpg

Fig: Preparation of Benzoic acid

This reaction will merely be possible if 'R' is methyl or other alkyl group however not 3o alkyl groups.

From Grignard's Reagent and CO2:

This process is especially employed for the preparation of fatty acids.

1113_Grignard’s Reagent.jpg

Fig: Grignard's Reagent

Hydrolysis of Nitriles:

The hydrolysis of nitriles, R - C = N, in the acidic or alkaline medium provide carboxylic acids.

46_Hydrolysis of Nitriles.jpg

Fig: Hydrolysis of Nitriles

The reaction comprises the formation of an amide as the intermediate which is further hydrolyzed to a carboxylate. The carboxylate reacts by a dilute mineral acid to form the carboxylic acid.

Hydrolysis of Esters (Saponification):

The hydrolysis of esters might be accomplished through boiling under reflux with concentrated aqueous sodium hydroxide.

11_Hydrolysis of Esters.jpg

Fig: Hydrolysis of Esters

Cannizzaro Reaction:

This reaction is only undergone through aromatic aldehydes and those aliphatic ones having no α-hydrogen atoms.

For illustration:

2C6H5CHO + NaOH → C2H5COONa+ + C6H5CH2OH

                     40-60%

If an appropriate aldehyde is treated by a concentrated aqueous solution of alkali at room temperature, it experiences simultaneous oxidation and reduction to yield the suitable salt of the carboxylic acid and an alcohol.

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