Ch_322b_18.12

Ch_322b_18.12 - Chapter 18.12 lecture note

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Esters Synthesis of Esters Direct Esterification of Carboxylic Acids Carboxylic acids and alcohols react in the presence of a small amount of strong acid to give esters. Esterifications are acid-catalyzed equilibrium reactions . Catalytic amounts of concentrated sulfuric acid or hydrochloric acid are used. Usually a large excess of the alcohol (10- or 15-fold) is used to drive the equilibrium to the product side. Product formation is also promoted by removing the water as it is formed. COOH benzoic acid + CH 3 OH methanol H + COOCH 3 + H 2 O methyl benzoate
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Mechanistic Studies by Isotopic Labeling Mechanistic insight on the key bonding changes was obtained by studies using isotopically enriched methanol. C 6 H 5 C-OH O = + CH 3 18 O H H + C 6 H 5 C- 18 O CH 3 O + H 2 O All the isotopic label appears in the methoxy oxygen. This result rules out an S N 2 mechanism: C 6 H 5 C-O: O + CH 3 - 18 O H : H C 6 H 5 C-OCH 3 O + H 2 18 O
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The Mechanism of Acid-Catalyzed Esterification C 6 H 5 -C-OH :O: = : +H + -H + fast and reversible
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_18.12 - Chapter 18.12 lecture note

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