Write any three methods for the preparation of Carboxylic acid.

Explanation

Preparation of carboxylic acids :
i) From primary alcohols : Primary alcohols on oxidation with acidified `KMnO_(4)` (or) `K_(2)Cr_(2)O_(7)` (or) Chromium trioxide `(CrO_(3))` gives carboxylic acids.
`R-CH_(2)OH + (O) underset(H^(+)//OH^(-))overset(KMnO_(4))to R-COOH`
`CH_(3)-(CH_(2))_(8)-CH_(2)_OH overset(CrO_(3)//H^(+))to CH_(3)-(CH_(2))_(8)-COOH`
ii) From Alkyl benzenes : Aromatic carboxylic acids are prepared by the oxidation of alkyl benzens with `KMnO_(4)` or `CrO_(3)`, any alkyl group irrespective of chain length is oxidised to `-COOH`.

iii) From Nitriles and Amides : Nitriles on hydrolysis in the presence of `H^(+)` or `OH^(-)` gives amides which on hydrolsis give acids
`R-CN underset(H^(+)" (or) "OH^(-))overset(H_(2)O)to R-underset(O)underset(||)C-NH_(2)overset(H_(2)O)to R-COOH`
`CH_(3)-CN underset(H^(+)"(or)"OH^(-))overset(H_(2)O)to CH_(3)COOH + NH_(3)`
`underset("Benzenamide")(C_(6)H_(5)-underset(O)underset(||)C-NH_(2)) underset(H^(+)"(or)" OH^(-))overset(H_(2)O)to underset("Benzoic acid")(C_(6)H_(5)-COOH -NH_(3))`