C7 Further Chemistry

Lesson 4

Learning objective: To understand the processes involved during the synthesis of an ester.

• Must: Know the properties and uses of esters including natural fats and oils. – grade D

• Should: Be able to make an ester and name the ester formed – grade C.

• Could: Explain each techniques used during the synthesis of an ester.

• Keywords: Reflux, distillation, purification, drying and glycerol.

Esters

• Esters have strong sweet smells which are often floral or fruity. Esters can be used in food flavourings and perfumes.

• Esters are used as solvents, for example, in some glues.

• Esters occur naturally but they can also be man-made (synthetic).

Making esters

• Discover:• Follow the

instructions for AC7.5

• Make sure you wear goggles at all times.

• Answer all of the questions.

Techniques used to make a liquid ester

• Heating under reflux.• Many organic reactions are

quite slow and need heating to achieve a reasonable reaction rate. However, most organic chemicals are quite volatile, and if heated they will evaporate and be lost. The solution to this problem is to heat the reaction mixture under reflux.

Techniques used to make a liquid ester

• Distillation.• Distillation is a widely used

method for separating mixtures. To separate a mixture of liquids, the liquid can be heated to force components, which have different boiling points, into the gas phase. The gas is then condensed back into liquid form and collected.

Techniques used to make a liquid ester

• Tap funnel – purification.• Reagents are added which

react with the unused reactants e.g. sodium carbonate solution to remove acids and then with calcium chloride solution to remove unchanged ethanol. The bottom aqueous layer is run off and discarded.

Techniques used to make a liquid ester

• Drying• During esterification

water is formed as a by-product.

• To remove the water and ‘dry’ the liquid ester add a few granules of anhydrous calcium chloride.

Esterification reactions

• An ester is formed by heating a carboxylic acid and an alcohol in the presence of an acid catalyst – normally concentrated sulphuric acid.

CH3COOH + C2H5OH CH3COOC2H5 + H2Oacid catalyst

Naming of Esters

• Esters are named from the acid and alcohol stem.

CH3 CO

O C2H5

Alcohol Stem

Acid Stem

Naming of Esters

• The alcohol stem comes at the start of the ester name

• The acid stem provides the second part of the name

• The name of the ester usually ends with –anoate.

• The previous ester is ethyl ethanoate.

Some Esters and usesEthyl 2-methylbutanoate CH3CH2CH(CH3)COOCH2CH3 Apple flavour 3-Methylbutyl ethanoate CH3COOCH2CH2CH(CH3)2 Pear flavour 1-Methylpropyl ethanoate CH3COOCH(CH3)CH2CH3 Banana flavour Ethyl methanoate HCOOCH2CH3 Raspberry flavour Butyl butanoate CH3CH2CH2COOCH2CH2CH2CH3 Pineapple flavour Phenylmethyl ethanoate CH3COOCH2C6H5 Oil of Jasmine 2-Ethanoyloxybenzoic acid (acetylsalicylic acid)

OCOCH3

COOH

Aspirin

Methyl 2-hydroxybenzoate (methyl salicylate)

OH

COOCH3

Muscle rub

Ethyl ethanoate CH3COOCH2CH3 Glue solvent Methyl 2-cyanopropenoate CH2=C(CN)COOCH3 Superglue Ethenyl ethanoate CH3COOCH=CH2 PVA glue

Why do plants and animals contain oils and fats.

• Living organisms make fats and oils as an energy store.

Natural fats and oils.

• Natural fats and oils are important raw materials for the chemical industry.

• Natural fats and oils come from animals and vegetables.

• They are very closely related chemically.• They are all esters of a molecule called

glycerol

Glycerol.

• It belongs to the alcohol family.

• How many hydroxyl groups are there?

• 3 OH groups.• It’s proper name is

propane-1,2,3-triol.

Animal and vegetable fats and oils.

• Examples of animal fats and oils include; butter, dripping, lard, suet and fish oils

• Examples of vegetable oils include; sunflower, rapeseed, olive, palm and soyabean.

• Animal fats and oils are often saturated.• Vegetable oils are often unsaturated.

Saturated and unsaturated?

• In a saturated fat or oil all the carbon-carbon bonds are single bonds.

• An unsaturated fat or oil has at least one carbon-carbon double bond.