Properties and reactions of Esters

Formation of Esters

• Esters are formed by the reaction of a carboxylic acid on an alcohol.

• The reaction requires heating and an acid catalyst

Reactions of esters

Hydrolysis is the splitting with water. (Hydro = water, lysis = Splitting/breaking)

Adding an ester to water produces the alcohol and acid. The reaction is in equilibrium. (Equilibrium = the reaction goes in both directions depending on the concentrations of reactants and products)

Fats, Oils and Soaps

• Propan-1,2,3-triol has the common name of Glycerol. It is an alcohol with 3 –OH groups

• When glycerol reacts with carboxylic acids it can form three ester links. The resulting molecule is called a triglyceride

+ 3H20

• Fats and oils are both triglycerides. Fats are solid at room temperature, oils are liquid at room temperature.

• Fats contain few double bonds. They are saturated.

• Oils contain many double bonds. They are polyunsaturated

• Most fats contain a mixture of long chain carboxylic acids. These are called fatty acids.

• The ester links in fats and oils can be hydrolysed by sodium hydroxide solution to form glycerol and sodium salt of the acid, which is soap. This reaction is called saponification

Saponification

• Saponification works by having a polar and a non-polar end.

• The non-polar tail dissolves the non-polar grease.

• The polar head dissolves in water