0201-Ch17(2) - Fischer Esterification Esters can be...

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Fischer Esterification Esters can be prepared by treating a carboxylic acid with an alcohol in the presence of an acid catalyst, commonly H 2 SO 4 , ArSO 3 H, or gaseous HCl (Note: NOT H 3 O + , an aqueous solution of an acid). Ethyl ethanoate (Ethyl acetate) Ethanol (Ethyl alcohol) Ethanoic acid (Acetic acid) + + H 2 SO 4 H 2 O OH O HO O O 1 Ch-17
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Fischer esterification is an equilibrium reaction . By careful control of experimental conditions, it is possible to prepare esters in high yield. If the alcohol is inexpensive relative to the carboxylic acid, it can be used in excess to drive the equilibrium to the right. Alternatively, water can be removed by azeotropic distillation and a Dean-Stark trap (Figure 16.1). = An application of the Le Chatelier - Braun principle . 2 Ch-17 Fischer Esterification Ethyl ethanoate (Ethyl acetate) Ethanol (Ethyl alcohol) Ethanoic acid (Acetic acid) + + H 2 SO 4 H 2 O OH O HO O O
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A key intermediate in Fischer esterification is the tetrahedral carbonyl addition intermediate (TCAI) formed by addition of ROH to the C=O group. C OCH 3 O H O R H C OH O R C 3 O R HOCH 3 + HOH + H + H + TCAI 3 Ch-17 Fischer Esterification Problem : Draw detailed mechanisms for both acid-catalyzed reactions, the esterification and the hydrolysis reaction.
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4 Ch-17 Fischer Esterification Step 1 : Proton transfer from the catalyst (protonated alcohol) to the carbonyl oxygen atom forms the resonance-stabilized protonated carboxylic acid, a better electrophile.
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This note was uploaded on 04/17/2011 for the course ENY 3005 taught by Professor Staff during the Fall '08 term at University of Florida.

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0201-Ch17(2) - Fischer Esterification Esters can be...

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