Chapter 10: Carboxylic acids and their derivatives

Carboxylic acids are formed by the oxidation of primary alcohols or aldehydes. Carboxylic acids are weak acids. Carboxylic acid contains carboxyl group -COOH.

Naming Carboxylic Acids

Physical Properties

Solubility

  1. Acids are very soluble in organic solvents
  2. Benzoic acid is insoluble in cold but soluble in hot water
  3. Soluble in water is due to hydrogen bonding.

 

Boiling point

  1. Boiling point increases as the size increases. Carboxylic acids have high boiling points for their relative mass.

It arises from intermolecular hydrogen bonding due to O-H bonds.

Preparation

  1. Oxidation of Aldehydes

RCHO + [O] → RCOOH

  1. Hydrolysis of easters

Acid-catalyzed hydrolysis of esters forms a carboxylic acid and an alcohol.

  1. Hydrolysis of acyl chlorides

RCOCl + H2O → RCOOH + HCl

  1. Hydrolysis of nitriles

RCN + 2H2O → RCOOH + NH3

  1. Hydrolysis of amides

RCONH2 + H2O → RCOOH + NH3

 

Chemical properties

  • Carboxylic acids are weak acids which means they donot dissolve compeletly in water.

      CH3COOH + H2O → CH3COO + H3O+

  • Esterification

It involves the reaction of carboxylic acid with an alcohol.

CH3COOH + CH3OH ←→

CH3COOCH3 + H2O

Esters

  • Esters have the general formula RCOOR’.
  • Esters can be made when alcohols and carboxylic acids are reacted in the presence of a sulphuric acid catalyst

  • The alcohol gives the first part of the name, and the acid gives the second part of the name
  • Esters are used as solvents, plasticizers, perfumes, and food flavorings
  • ​Acid-catalyzed hydrolysis of esters forms a carboxylic acid and an alcohol

  • Base catalyzed hydrolysis of ester forms a carboxylate salt and an alcohol

 

Vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol). Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap.

Acid Chlorides

The acid chloride is also known as acyl chloride. They are the derivative of carboxylic acids, where -OH group is replaced by a -Cl group.

  • Acyl chlorides react with alcohols to form esters in a nucleophilic addition-elimination reaction.

  • Acyl chlorides will react with a variety of nucleophiles

  • Ethanoic anhydride is used to make aspirin.

  • The advantages of using ethanoic anhydride rather than ethanoyl chloride is that: it’s cheaper, less corrosive, and safer, produces a less toxic by-product and does not react with water readily.

Amino Acids

  • α -amino acids contain both the amine functional group and the carboxylic acid functional group (carboxyl group) attached to the same carbon atom.
  • Amino acids are amphoteric, meaning they have both acidic and basic properties and can exist as zwitterions, having no charge overall.
  • ​The isoelectric point is the pH at which the overall charge of a molecule is zero.