2 Boardworks A2 Chemistry Acyl Compounds What are esters?Boardworks A2 ChemistryAcyl CompoundsEsters 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).Teacher notesStudents could be made aware that an aryl group is a group created by the removal of a hydrogen atom from an aromatic compound. E.g. the phenyl group (C6H5) derived from benzene (C6H6).See the ‘Aromatic Compounds’ presentation for more information about benzene.ethyl ethanoate (contains an alkyl group)methyl benzoate (contains an aryl group)
4 Boardworks A2 Chemistry Acyl Compounds Naming estersBoardworks A2 ChemistryAcyl CompoundsThe names of esters are based on the carboxylic acid and alcohol from which they are produced.The first component of this ester name, the methyl, is derived from the alcohol methanol.The second component of the name, the ethanoate, is derived from the carboxylic acid ethanoic acid.methylethanoateethylmethanoatepropylethanoateethanol + methanoic acidpropanol + ethanoic acid
7 Boardworks A2 Chemistry Acyl Compounds Uses of estersBoardworks A2 ChemistryAcyl CompoundsShorter chain esters have fruity smells and tastes, which makes them useful as solvents in perfumes and flavourings.For example, ethyl butanoate smells of pineapple; pentyl ethanoate smells of pears, and octyl ethanoate smells of oranges.Esters are used as artificial fragrances and flavours as synthesizing the ester is often cheaper than extraction from the natural source.Teacher notesDifferent sources list different esters as having similar characteristic smells. For example, ethyl ethanoate, ethyl pentanoate, methyl butanoate and pentyl pentanoate (among others) are all said to smell of apples. This could be due to smells in nature being composed of a complex mix of esters and other compounds.Photo credit (wine glass): Sergei Didyk / Shutterstock.comPhoto credit (sweets): Eric Gevaert / Shutterstock.com
8 Boardworks A2 Chemistry Acyl Compounds Uses of estersBoardworks A2 ChemistryAcyl CompoundsEsters 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.Photo credit: Luis Louro / Shutterstock.comEthyl ethanoate is one such common solvent, being used in the decaffeination of tea, as well as a laboratory solvent for chromatography.
9 Boardworks A2 Chemistry Acyl Compounds Esters in fats and oilsBoardworks A2 ChemistryAcyl Compounds
10 Boardworks A2 Chemistry Acyl Compounds Naming fatty acidsBoardworks A2 ChemistryAcyl CompoundsFatty 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.DescriptionFormula and systematic nameCommonnamestearic acidCH3(CH2)16COOH(octadecanoic acid)saturated, found in most animal fatspalmitic acidCH3(CH2)14COOH(hexadecanoic acid)saturated, used for making soapsoleic acidCH3(CH2)7CH═CH(CH2)7COOH(octadec-9-enoic acid)monounsaturated, found in most fats and olive oillinoleic acidCH3(CH2)4(CH═CHCH2)2(CH2)6COOH(octadec-9,12-dienoic acid)polyunsaturated, found in vegetable oils
11 Saturated and unsaturated Boardworks A2 ChemistryAcyl Compounds
13 TRANS-ESTERIFICATION ONE ESTER CONVERTED INTO ANOTHER ESTERRCO-OR’ + R’’OH RCO-OR’’ + R’OHdifferent alkoxy group
14 Boardworks A2 Chemistry Acyl Compounds Trans fats and healthBoardworks A2 ChemistryAcyl CompoundsMost 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.Teacher notesStudents should be aware that trans fats are not saturated, as the process used in their creation (partial hydrogenation) suggests.A diet high in trans fats, along with saturated fats, can lead to an increased risk of coronary heart disease (CHD).
15 Cholesterol and lipoproteins Boardworks A2 ChemistryAcyl CompoundsCholesterol 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.A diet high in saturated/trans fats is the biggest cause of high LDL cholesterol levels.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.
16 Making soap and biodiesel Boardworks A2 ChemistryAcyl Compounds
17 SOAPS Mixture of animal fat and coconut palm oil; If mainly animal fat Less solubleLonger lastingIf mainly palm oilMore solubleLather quicklyWash away quickly**antioxidants added to stop soap and air combining to make irritant chamicals**