1 of 15© boardworks ltd 2010. 2 of 15© boardworks ltd 2010 what are esters? esters are carboxylic...
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1 of 15 © Boardworks Ltd 2010
2 of 15 © Boardworks Ltd 2010
What are esters?
Esters are carboxylic acid derivatives with the hydrogen of the hydroxyl group replaced by an alkyl group (hydrocarbon chain)or an aryl group (an aromatic ring).
ethyl ethanoate(contains an alkyl
group)
methyl benzoate(contains an aryl
group)
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Esterification
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Naming esters
The names of esters are based on the carboxylic acid and alcohol from which they are produced.
methylethanoate
ethylmethanoate propylethanoate
The first component of this ester name, the methyl, is derivedfrom the alcohol methanol.
ethanol + methanoic acid propanol + ethanoic acid
The second component of the name, the ethanoate, is derived from the carboxylic acid ethanoic acid.
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Naming esters
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Hydrolysis of esters
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Uses of esters
For example, ethyl butanoate smells of pineapple; pentyl ethanoate smells of pears, and octyl ethanoate smells of oranges.
Shorter chain esters have fruity smells and tastes, which makes them useful as solvents in perfumes and flavourings.
Esters are used as artificial fragrances and flavours as synthesizing the ester isoften cheaper than extraction from the natural source.
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Uses of esters
Esters are also useful as glues, such as those used for constructing plastic model aircraft kits, and as plasticizers to increase the flexibility of plastics.
Esters have low boiling points and evaporate readily. This makes them useful as industrial solvents, for example in paints.
Ethyl ethanoate is one such common solvent, being used in the decaffeination of tea, as well as a laboratory solvent for chromatography.
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Esters in fats and oils
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Naming fatty acids
Fatty acids have systematic names as well as common names. For example, the systematic name for oleic acid is octadec-9-enoic acid. Some common fatty acids are explained below.
polyunsaturated, found in vegetable oils
CH3(CH2)4(CH═CHCH2)2(CH2)6COOH
(octadec-9,12-dienoic acid)
linoleicacid
monounsaturated, found in most fats and olive oil
CH3(CH2)7CH═CH(CH2)7COOH
(octadec-9-enoic acid)
oleicacid
saturated, used for making soaps
CH3(CH2)14COOH
(hexadecanoic acid)
palmiticacid
saturated, found in most animal fats
CH3(CH2)16COOH
(octadecanoic acid)
stearicacid
DescriptionFormula and systematic nameCommonname
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Saturated and unsaturated
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Esters: true or false?
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TRANS-ESTERIFICATION
• ONE ESTER CONVERTED INTO ANOTHER ESTER
RCO-OR’ + R’’OH RCO-OR’’ + R’OH
different alkoxy group
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Trans fats and health
Most naturally occurring isomers of unsaturated fatty acids are the cis form, such as cis-octadec-9-enoic acid, found in olive oil, avocados and nuts.
In the partial hydrogenation of vegetable oils, the trans form of the fatty acid, such as trans-octadec-9-enoic acid, may be formed.
A diet high in trans fats, along with saturated fats, can lead to an increased risk of coronary heart disease (CHD).
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Cholesterol is a lipid that regulates fluidity in cell membranes. It is transported in lipoproteins.
Low-density lipoprotein (LDL) transports cholesterol from the liver to body tissues, depositing it on the walls of blood vessels. It increases the risk of CHD.
High-density lipoprotein (HDL) transports cholesterol away from the tissues to the liver, where cholesterol is metabolized. High HDL levels are linked to a lower risk of CHD.
A diet high in saturated/trans fats is the biggest cause of high LDL cholesterol levels.
Cholesterol and lipoproteins
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Making soap and biodiesel
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SOAPS
• Mixture of animal fat and coconut palm oil;• If mainly animal fat
Less solubleLonger lasting
• If mainly palm oilMore solubleLather quicklyWash away quickly
**antioxidants added to stop soap and air combining to make irritant chamicals**