Esters Revision

• Matching names/structures of esters.

Give examples of:

• saturated and unsaturated hydrocarbons.

• cis–trans (E/Z) isomerism.

• esterification reaction.

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

The products of hydrolysis depend on the conditions used...

Acidic CH3COOCH3 + H2O CH3COOH + CH3OH

Alkaline CH3COOCH3 + NaOH → CH3COO¯ Na+ + CH3OH

If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt

The carboxylic acid can be made by treating the salt with HCl

CH3COO¯ Na+ + HCl → CH3COOH + NaCl

USES OF ESTERSUSES OF ESTERS

Despite being fairly chemically unreactive, esters are useful as ...

• flavourings apple 2-methylbutanoatepear 3-methylbutylethanoatebanana 1-methylbutylethanoatepineapple butylbutanoaterum 2-methylpropylpropanoate

• solvents nail varnish remover - ethyl ethanoate

• plasticisers

© Pearson Education Ltd 2009This document may have been altered from the original

• Describe a triglyceride as a triester of glycerol (propane-1,2,3-triol) and fatty acids.

• Compare the structures of saturated fats, unsaturated fats and fatty acids.

What you should be able to do

NATURALLY OCCURING ESTERS - NATURALLY OCCURING ESTERS - TRIGLYCERIDESTRIGLYCERIDES

• triglycerides are the most common component of edible fats and oils

• they are esters of the alcohol glycerol (propane-1,2,3-triol)

Saponification

• alkaline hydrolysis of triglycerol esters produces soaps• a simple soap is the salt of a fatty acid• as most oils contain a mixture of triglycerols, soaps are not pure• the quality of a soap depends on the oils from which it is made

CH2OH

CHOH

CH2OH

Draw the displayed formula of hexadecanoic acid (palmitic acid)

Draw the skeletal formula of hexadecanoic acid

http://upload.wikimedia.org/wikipedia/commons/f/f0/Caproic_acid_acsv.svg

• Write down the reaction between hexadecanoic acid and propan-1-ol

hexadecanoic acid and propan-1-ol →

propylhexadecanoate + water

C15H31COOH + C3H7OH →

C15H31COOC3H7 + H2O

© Pearson Education Ltd 2009This document may have been altered from the original

Formation of a triglyceride

Skeletal formula of octadec-9-enoic (oleic acid)

Structure of octadeca-9,12-dienoic acid

• Compare the structures of cis and trans isomers of unsaturated fatty acids.

• Compare the link between trans fatty acids, the possible increase in ‘bad’ cholesterol and the resultant increased risk of coronary heart disease and strokes.

• Describe and explain the increased use of esters of fatty acids as biodiesel fuels.

You should be able to:

Cis and trans configurations around a double bond

Skeletal formula of octadec-9-enoic (oleic acid)

Draw the two skeletal formulae of the cis and trans forms of this structure

Structures of cis and trans-octadec-9-enoic acid.

Transesterification for the production of biodiesel

http://www.biodiesel-fuel.co.uk/what-is-biodiesel/

Homework suggestions

• How many C=C bonds are there in a molecule of C17H35COOH?

• How many straight-chain structural isomers are there for this formula?

• Draw and name one pair of cis–trans isomers for this formula.

• Check your fridge. Do your margarines or other fat-containing foods give helpful data about the types of fat they contain?