• 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 (Cr₂O₇^2-) 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

Hydrolysis of esters

• Esters are formed from the condensation reaction between an alcohol and carboxylic acid
• Hydrolysis?of?esters?by?dilute acid?or?dilute alkali and heat followed by acidification?will reform the alcohol and carboxylic acid
  • Hydrolysis by dilute acid, is a?reversible reaction?and an equilibrium is established
  • Hydrolysis by dilute alkali is an?irreversible?reaction?as all the ester is broken down to form a sodium carboxylate salt and an alcohol; acidification is required to change the carboxylate ion into a carboxylic acid

Hydrolysis of esters by either dilute acid (1) or dilute alkali and heat followed acidification (2) will form a carboxylic acid

• Carboxylic acids?are?weak acids?as they do not completely?dissociate?in water
• This means that the position of the equilibrium lies to the left and that the concentration of H+?is much smaller than the concentration of the carboxylic acid
• The solution has a pH value of less than 7

Carboxylic acids are weak acids that do not fully dissociate in water, the position of the equilibrium lies to the left

• Carboxylic acids?are reactive compounds which can undergo many types of reactions including:
  • Redox reactions with reactive metals
  • Neutralisation reactions with alkali
  • Acid-base reactions with carbonates
  • Esterification with alcohols
  • Reduction by LiAlH₄

Carboxylic acids undergo a wide variety of reactions