Ch_322b_19.02

Ch_322b_19.02 - Chapter 19.2 lecture note

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The Claisen Condensation: Formation of ! -Ketoesters from Esters with Enolizable Hydrogens Esters with enolizable H undergo a reaction similar to the aldol condensation in the presence of alkoxide bases. Alkoxide bases are used so that competing nucleophilic addition to the acyl carbon does not destroy or change the ester function. -C-C-OR H :O: = pK a 25 ~ ~ + B: - -C-C-OR :O: : - -C=C-OR :O: - enolate anion of ester -C C OR O !" !" hybrid -C-C-OR O H + RO - Na + -C-C-OR OR O - H Na + competing nucleophilic addition -C-C-OR O H + RO - Na + no change
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Condensation Step The enolate anion of an ester reacts as a nucleophile by way of the carbanion center in adding to the acyl carbon of a second ester: -C-C-OR H :O: = -C-C-OR O : - + enolate anion -C C-OR :O: - H C-C-OR O reversible nucleophilic addition tetrahedral intermediate -C C-OR :O: - H C-C-OR O cleavage -C-C C-C-OR O O H ! -keto ester + RO -
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Example: The Condensation of Ethyl Acetate. Ludwig Claisen (1851-1930)
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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_19.02 - Chapter 19.2 lecture note

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