AQA A Level Chemistry复习笔记7.3.2 Esters

Esters

Esters are a carboxylic acid derivative which contains the ester group, -COO-

An ester is named after the parent carboxylic acid from which it is derived

Remove the -oic acid suffix from the parent carboxylic acid and replace with -oate

This part of the name comes from the alcohol, e.g. propanol becomes propylThe alkyl chain attached to the oxygen atom of the -COO- group is then added as the first word in the name

Ester names are confusing because the name is written backwards from the way the structure is drawn

Esters Examples Table

Uses of Esters - fragrances and flavourings

Like aldehydes and ketones, esters are important chemicals in the flavourings and fragrances industry

Esters have a fruitier and sweeter smell than aldehydes and ketones and are responsible for many natural flower scents and flavours

Synthetic esters can also be used as artificial fruit flavours in confectionary products e.g. ethyl methanoate is used as a raspberry ester fragrance

Aromas and tastes are often due to complex mixtures of different esters

Uses of Esters - plasticisers

Poly(chloroethene) better known as PVC, is a strong rigid polymer suitable for making drainpipes and guttering

When a suitable plasticising ester is added, it can be made into cling film which is soft and pliable

An ester plasticiser works by penetrating between the polymer chains and increasing the distance between them

This then weakens the polar effects of the carbon-chlorine bond and the rigidity of the 3D structure if reduced allowing the polymer chains to slide over one anotherEsters can also be used as plasticisers, which are additives mixed into polymers to increase the flexibility of the polymer

Intermolecular forces in PVC

Addition of a plasticiser reduced rigidity in PVC

Uses of Esters - solvents

Ethyl ethanoate is a common solvent which has the beneficial properties of low toxicity and low volatility (its boiling point is 77˚C) as well as being relatively cheap

This makes it an ideal solvent for use in glues, fragrances and nail varnishesEsters are also commonly used as solvents for organic compounds

Naturally occurring Esters

Triglycerides found in animal fat and olive oil are naturally occurring esters

They are tri-esters of glycerol (propane-1,2,3-triol) and fatty acids (long chain carboxylic acids) such as stearic acid (CH3(CH2)16COOH)

The reaction of 1 mole of glycerol with 3 moles of a fatty acid in the presence of an acid catalyst leads to the formation of the triglyceride whereby 3 moles of water are eliminated

The synthesis of a triglyceride from glycerol and fatty acid chains