Esters and Polyesters

reactions of esters

functional group

polyesters

transesterification

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ESTERS AND POLYESTERS
Esters are formed when a carboxylic acid reacts with an alcohol
(bi-product of water)
o RCOOH + R'OH RCOOR' + H2O
Functional group RCOOR'
Esters are named using the alkyl group from the alcohol and the
salt name of the carboxylic acid e.g. if methanol and butanoic acid react they form
methyl butanoate
Isomeric esters occur when you swap the R and the R' groups e.g. ethyl ethanoate
and methyl propanoate are isomers of each other
REACTIONS OF ESTERS
Hydrolysis of an ester
o Ester + water acid + alcohol
o Reversible reaction
o Catalysed using dilute hydrochloric or sulphuric acid
o Heat under reflux
Alkaline hydrolysis of esters e.g. saponification
o Oilfat (ester) + alkali soap (salt) + alcohol
o Heat under reflux
Trans-esterification
o Transfer of one carboxylic ester into another
o E.g. methyl ester + ethanol ethyl ester + methanol
o Reversible reaction
o Acid catalyst used

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TRANS-ESTERIFICATION
No rotation around C=C double bonds because of
the presence of the pi bond
Geometric isomerism (E-Z isomerism) is a type of
stereoisomerism
Margarine is made by partial hydrogenation of
liquid unsaturated oils and fats
o Makes the liquid oils and fats more solid
o Increase the proportion of trans-fats
Trans-fats (E) increase the risk of coronary heart disease
Trans-esterification hardens unsaturated fats and oils with producing fewer
trans-fats
Biodiesel made by reacting natural fats/oils with alcohols to form esters and
alcohol
o E.…read more

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