Esters

Esters are organic compounds with the functional group . They are derivatives of carboxylic acids, formed via a condensation reaction with alcohols.

General formula:

The naming of esters can be split into two: the part that comes from the alcohol and the part that comes from the carboxylic acid.

• The alcohol group gives the –yl ending

• The carboxylic acid gives the –anoate ending

Considering the nomenclature, one way of forming esters is the reversible reaction of carboxylic acid with an alcohol, using a strong acid catalyst and heating under reflux.

The reverse of this reaction (ester → carboxylic acid/carboxylate ion + alcohol) can happen by two different types of hydrolysis:

1. Acid hydrolysis

• Reversible reaction

• Reagent: dilute HCl

• Condition: heat under reflux
  

Example:

Propyl butanoate + water → butanoic acid + propanol

2. Base Hydrolysis

• Irreversible reaction

• Reagent: NaOH

• Condition: heat under reflux

• Addition of HCl to the carboxylate will form the carboxylic acid

• Under alkaline conditions, animal fats and vegetable oils can undergo hydrolysis

• When these fats and oils are heated with NaOH or KOH, they form soap

Glycerol (propane-1,2,3-triol)

• Glycerol has 3 alcohol groups which means it can form hydrogen bonds quite easily

• They are used in glues and in food

The carboxylate salts can act as soaps

Soap has a hydrophilic and hydrophobic end which makes it useful to wash grease away. The hydrophilic end mixes with water and the hydrophobic end mixes with grease. As a result, water and grease can be mixed and washed away.