Uses of Esters

Animals and vegetable fats and oils are esters of propane- 1,2,3- triol (glycerol)
* Differ by melting points of mixture of esters they contain
* Melting points < room temperature then it’s a liquid- an oil * Melting points > room temperature then t’s an solid- a fat
Contain three molecules of long chain carboxylic acids, fatty acids
Since they are based on glycerol, they are referred to as triglycerides
Can be hydrolysed in acidic conditions to give a mixture of glycerol and fatty acids
Also hydrolysed by boiling with sodium hydroxide
  * Both products are useful- glycerol and mixture of sodium salts of three acids which formed parts of ester (soaps)
  * Soap can be mixture containing many different salts and its type depends on the fatty acids initially present in the ester
    * These sodium salts are ionic and dissociate to form Na+ and RCOO-
    * RCOO- has two distinct ends: long hydrocarbon chain (non-polar) and COO- group (polar and ionic)
    * Hydrocarbon will mix with grease, will COO- mixes with water
    * Tadpole-shaped molecules allows grease and water to mix so used as cleaning agents

Name	Formula	Details
steric acid	CH3(CH2)16C02H	present in most animal fats
palmitic acid	CH3(CH2)14C02H	used in making soaps
oleic acid	CH3(CH2)7CH=CH(CH2)7C02H	monounsaturated- it has one double bond, present in most fats and in olive oil
linoleic acid	CH3(CH2)4(CH=CHCH2)2(CH2)6CO2H	polyunsaturated, present in many vegetable oils

Three O-H bonds so forms H-bonds and is v. soluble in water
Used in pharmaceutical and cosmetic preparations
* Because it attracts water, it is used to prevent ointment and creams drying out
Used as a solvent in medicines, and is present in toothpaste
Used as a solvent in food industry, e.g. food colourings
Used to plasticise various materials like sheets and gaskets, cellophane, and special quality papers
  * Plasticisers introduced between molecules of polymer which makes up material
  * Allows molecules to slide over each other, material becomes flexible and smooth
  * PVC may contain 50% plasticiser, such as asters of hexanedioc acid. Over time plasticiser leaks away, leaving the plastic brittle and inflexible

Possible solution to over-reliance on crude oil as a source of fuel to power motor vehicles
Renewable fuel as it’s made from oils derived from crops such as rape seed
* Rape seed oil is a triglyceride ester
To make biodiesel the oil is reacted with methanol (with a strong alkali as a catalyst) to form a mixture of methyl esters which can be used as a fuel in diesel vehicles with little/ no modification
Process being introduced commercially , but as chemistry is relatively simple, some people are making their own biodiesel at home with used chip shop oil
* For example, Germany has thousands of filling stations supplying biodiesel, and it is cheaper than ordinary diesel fuel. All fossil diesel fuel in France contains between 2% and 5% biodiesel