Ch_322b_18.13

Ch_322b_18.13 - Chapter 18.13 lecture note

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Base-Promoted Hydrolysis of Esters: Saponification Base-promoted hydrolysis of esters is called saponification (L. sapo , soap) because traditional soap-making involves the alkaline hydrolysis of fats (esters of glycerol). RCOR' + NaOH H 2 O alkaline hydrolysis O = RCO 2 - Na + + R'OH sodium carboxylate alcohol ester
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Two Possible Mechanisms for the Alkaline Hydrolysis of Esters The operating mechanism for the alkaline hydrolysis of esters was elucidated by carefully designed experiments using stereochemical and isotopic probes . (1) acyl carbon-oxygen cleavage : RC OR' O = RCOR' + NaOH O R-C-OR' O - OH Na + tetrahedral intermediate RCOH O + R'ONa RCOH O + R'ONa RCO 2 - Na + + R'OH fast (2) alkyl carbon-oxygen cleavage: RCO R' O RCOR' + NaOH O S N 2 RCO R' O OH !" !" transition state RCO 2 - Na + + R'OH
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Some Observations Kinetic Studies The rate of alkaline hydrolysis follows the second-order rate expression : rate = k [RCO 2 R'][HO - ] Since this result is consistent with either mechanism, it cannot
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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_18.13 - Chapter 18.13 lecture note

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