Carboxylic Acids - Preparation
- Carboxylic acids are compounds with a -COOH functional group
- They can be prepared by a series of different reactions
Oxidation of primary alcohols & aldehydes
- Carboxylic acids can be formed from the oxidation of primary alcohols and aldehydes by either acidified K2Cr2O7 or acidified KMnO4 and reflux
- The oxidising agents themselves get reduced causing the solutions to change colour
- In K2Cr2O7 the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions
- In KMnO4 the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions
Oxidation of primary alcohols (1) and aldehydes (2) gives carboxylic acids
Hydrolysis of nitriles
- Carboxylic acids can also be prepared from the hydrolysis of nitriles using either dilute acid or dilute alkali followed by acidification
- Hydrolysis by dilute acid results in the formation of a carboxylic acid and ammonium salt
- Hydrolysis by dilute alkali results in the formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid
- The -CN group at the end of the hydrocarbon chain is converted to a -COOH group
Hydrolysis of nitriles by either dilute acid (1) or dilute alkali and acidification (2) will form a carboxylic acid