esters
- Created by: danni :)
- Created on: 04-12-12 10:07
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- THE WONDERFUL WORLD OF ESTERS
- SYNTHESIS OF ESTERS
- carboxylic acid + alcohol --> ester +water
- RCOOH + ROH --> RCOOR +H2O
- slow reaction and subject to equilibrium : easier to use a more reactive acyl chloride or acid anhydride
- e.g., ethanoyl chloride + ethanol --> ethyl ethanoate +HCl
- ethanoic anhydride + ethanol --> ethyl ethanoate + ethanoic acid
- carboxylic acid + alcohol --> ester +water
- naming esters
- names starts with an alkyl word derived from the alcohol (e.g., methanol= methyl)
- second part is the name of the acid used replacing -oic with -oate.
- Properties of esters
- volatile
- don't form hydrogen bonds so have relatively low melting and boiling points
- not very soluble in water or any other polar solvents
- fruity/ flowery smell
- reactions of esters
- hydrolysis: reverse reaction of esterification in which the ester splits to form the original alcohol and acid
- acid hydrolysis: esters can be split by boiling with water and much more effectively by using a dilute acid. the acid is a catalyst and the reaction is reversible unlike base hydrolysis
- base hydrolyis: boil with potassium hydroxide. more efficient because when the acid is released it is neautralised by alkali to from potassium salt. sometimes called saponification
- uses of esters
- biodiesels
- made from vegetable oils. tend to clog fuel injection nozzles. needs to be more volatile so is obtained by transesterification. forms methyl esters
- margarine
- Can be made by partial hydrogenation: controlled amount of hydrogen is added to the oil in the presence of a catalyst (usually nickel)
- advantage: no interference with the order of the fatty acids on the triol
- disadvantage: some trans isomers are formed which are believed to increase blood cholesterol.
- Can be made by partial hydrogenation: controlled amount of hydrogen is added to the oil in the presence of a catalyst (usually nickel)
- advantage: no trans fatty acids produced
- disadvantage: some stearic acid moves to middle carbon of triol which is believed to be harmful to health.
- margarine
- glycerol acids of three fatty acids + three molecules of methanol --> glycerol + methyl esters of three fatty acids
- made from vegetable oils. tend to clog fuel injection nozzles. needs to be more volatile so is obtained by transesterification. forms methyl esters
- margarine
- Can be made by partial hydrogenation: controlled amount of hydrogen is added to the oil in the presence of a catalyst (usually nickel)
- advantage: no interference with the order of the fatty acids on the triol
- disadvantage: some trans isomers are formed which are believed to increase blood cholesterol.
- Can be made by partial hydrogenation: controlled amount of hydrogen is added to the oil in the presence of a catalyst (usually nickel)
- biodiesels
- polyesters
- a condensation polymer is formed when monomers join together with the elimination of a simple molecule such as water or chlorine
- a homopolymer is made from a single type of monomer. it must have a group at one end that can react with the group at the other end e.g., hydroxyacids
- polyesters are not biodegradeable because enzymes haven't evolved that can hydrolyse the ester linkages in artificial fibres
- SYNTHESIS OF ESTERS
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