Chapter 18-2

Chapter 18-2 - CHEM 262 Wei You Chapter 18. Functional...

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11 CHEM 262 Wei You Chapter 18. Functional Derivatives of Carboxylic Acids (2)
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22 Rxn with H2O - Acid Chlorides low-molecular-weight acid chlorides react rapidly with water higher molecular-weight acid chlorides are less soluble in water and react less readily CH 3 CCl O H 2 O CH 3 COH O HCl + + Acetyl chloride
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33 Rxn with H2O - Anhydrides low-molecular-weight acid anhydrides react readily with water to give two molecules of carboxylic acid higher-molecular-weight acid anhydrides also react with water, but less readily CH 3 COCCH 3 O O H 2 O CH 3 COH O HOCCH 3 O + + Acetic anhydride
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44 Mech: Rxn with H2O - Anhydrides O CH 3 -C-O-C-CH 3 H H O-H O O H H CH 3 -C-O-C-CH 3 H H O-H CH 3 -C-O-C-CH 3 O O H H H-O-H H + + + Tetrahedral carbonyl addition intermediate + O O O CH 3 -C-O-C-CH 3 O H O H H + O H H CH 3 C O O O C O CH 3 H H O H H + CH 3 C O O O C CH 3 O H H H H H + H + O
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55 Rxn with H2O - Esters Esters are hydrolyzed only slowly, even in boiling water hydrolysis becomes more rapid if they are heated with either aqueous acid or base Hydrolysis in aqueous acid is the reverse of Fischer esterification the role of the acid catalyst is to protonate the carbonyl oxygen and increase its electrophilic character toward attack by water (a weak nucleophile) to form a tetrahedral carbonyl addition intermediate collapse of this intermediate gives the carboxylic acid and alcohol
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66 Rxn with H2O - Esters Acid-catalyzed ester hydrolysis R OCH 3 C O H 2 O H + OH C R OCH 3 OH H + R OH C O CH 3 OH + +  Tetrahedral carbonyl addition intermediate
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77 Rxn with H2O - Esters Hydrolysis of an esters in aqueous base is often called saponification each mole of ester hydrolyzed requires 1 mole of base for this reason, ester hydrolysis in aqueous base is said to be base promoted hydrolysis of an ester in aqueous base involves formation of a tetrahedral carbonyl addition intermediate followed by its collapse and proton transfer O RCOCH 3 NaOH H 2 O O RCO -  Na + CH 3 OH + +
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This note was uploaded on 06/12/2010 for the course CHEM 261 taught by Professor Austell during the Spring '08 term at UNC.

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Chapter 18-2 - CHEM 262 Wei You Chapter 18. Functional...

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