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esters 4.1.3 c, d, e – synthesis, naming, hydrolysis, uses ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation Notes e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate Notes Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester Naming esters Named from the original alcohol and carboxylic acid CH3OH + CH3COOH from ethanoic acid CH3COOCH3 + H2O CH3COOCH3 METHYL ETHANOATE from methanol ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE Preparation From carboxylic acids, acyl chlorides and acid anhydrides Reactivity Unreactive compared with acids and acyl chlorides ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE Preparation From carboxylic acids, acyl chlorides and acid anhydrides Reactivity Unreactive compared with acids and acyl chlorides Isomerism Esters are structural isomers of carboxylic acids STRUCTURAL ISOMERISM – FUNCTIONAL GROUP Classification Functional Group Name CARBOXYLIC ACID ESTER R-COOH R-COOR PROPANOIC ACID METHYL ETHANOATE Physical properties O-H bond gives rise to hydrogen bonding; get higher boiling point and solubility in water No hydrogen bonding insoluble in water Chemical properties acidic react with alcohols fairly unreactive hydrolysed to acids PREPARATION OF ESTERS - 1 Reagent(s) alcohol + carboxylic acid Conditions reflux with a strong acid catalyst (e.g. conc. H2SO4 ) Equation Notes e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester For more details see under ‘Reactions of carboxylic acids’ PREPARATION OF ESTERS - 3 Reagent(s) alcohol + acid anhydride Conditions reflux under dry conditons Equation Notes e.g. CH3OH(l) + (CH3CO)2O(l) ——> CH3COOCH3(l) + CH3COOH(l) methanol ethanoic methyl ethanoic anhydride ethanoate acid Acid anhydrides are not as reactive as acyl chlorides so the the reaction is slower. The reaction is safer - it is less exothermic. Acid anhydrides are less toxic. HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH METHANOIC ACID ETHYL METHANOATE + C2H5OH ETHANOL HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH METHANOIC ACID ETHYL METHANOATE METHYL ETHANOATE + C2H5OH ETHANOL HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + METHANOIC ACID C2H5OH ETHANOL ETHYL METHANOATE CH3COOH ETHANOIC ACID METHYL ETHANOATE + CH3OH METHANOL HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2 O alkaline CH3COOCH3 + NaOH CH3COOH + CH3OH ——> CH3COO¯ Na+ + CH3OH HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2 O alkaline CH3COOCH3 + NaOH CH3COOH + CH3OH ——> CH3COO¯ Na+ + CH3OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2 O alkaline CH3COOCH3 + NaOH CH3COOH + CH3OH ——> 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 ESTERS Despite being fairly chemically unreactive, esters are useful as ... • flavourings apple pear banana pineapple rum • solvents nail varnish remover - ethyl ethanoate • plasticisers 2-methylbutanoate 3-methylbutylethanoate 1-methylbutylethanoate butylbutanoate 2-methylpropylpropanoate
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