Methods of Preparation of Monocarboxylic Acids:
1. From oxidation of primary alcohols
Primary alcohols are oxidized with potassium permanganate or potassium dichromate to aldehydes which on further oxidation give carboxylic acids.
2. By oxidation of aldehydes and ketones.
This method is already part method 1.
Aldehydes are easily oxidised to carboxylic acids even with mild oxidising agents like Tollen's reagent.
3. From hydrolysis of nitriles and cyanides
the nitriles are hydrolysed in dilute acqueous acidic or alkaline medium.
4. From Grignard reagents
The reaction is carried out by bubbling CO2 through th etheral solution of suitable Grignard reagent.
5. By hydrolysis of esters
Hydrolysis of esters with mineral acids or alkalines gives carboxylic acids
6. Carboxylaiton of alkenes
Heating alkenes with CO and steam under pressure with phospoiric acid at 673 K. This reaction is called Koch reaction.
7. From trihalogen derivatives of hydrocarbons
Hydroysis of 1,1,1,-trihalogen derivatives of alkanes with acqueous KOH.
8. Preparation of aromatic acids from alkyl benzenes
the alkyl side cahin of benzene ring can be easily oxidized to carboxylic group iwth alkalines KMnO4, chromic anhydride or conc. HNO3.