Esters

Uses

• Have characteristic sweet smells used as food flavouring and perfumes

• Used as plasticiers but will ‘escape’ over time leaving the plastic stiff and brittle

• Used as solvents for polar organic molecules

Hydrolysis of esters

• Will undergo hydrolysis in acid or alkaline solution

• Hot and alkaline is preferred as acid conditions makes the reaction reversible + slow

Alkaline Hydrolysis - products and use

• Leads to formation of sodium salt of the carboxylic acid and alcohol

• e.g. RCOOR + NaOH → RCOONA + ROH

• If excess H2SO4 or HCl is added to sodium salt then carboxylic acid reforms

• e.g. HCOONA + HCl → HCOOH + NaCl

• Sodium salts of long chain carboxylic acids is used in soaps

Acid Hydrolysis

• Reversal of esterification

• e.g. CH3CH2COOCH3 + H2O → CH3CH2COOH + CH3OH

Triglycerides

• Triesters of fatty acids and glycerol

• Occur naturally as fats and oils

• Fats are soldies at room temperatures and contain saturated acids

• Oils are liquids at room temperature and show some degree of unsaturation in the acid

Formation of triglyceride

Alkaline Hydrolysis of triesters

• Leads to formation of glycerol and sodium salts of the long chain carboxylic acids

• Used to make soap

Acid Hydrolysis of triesters

• Forms glycerol and the carboxylic acids

Biodiesel

• Alternative, renewable fuel made from oil obtained from crops such as rapeseed oil

• Can be converted into biodiesel by transesterification by using methanol

Why only methyl esters of long chain acids used as biodiesel?

• They are non-toxic

• Biodegradable

• Burns cleaner than petrol

• Cheaper than ordinary diesel fuel