Ch_322b_17.06

Ch_322b_17.06 - Chapter 17.6 lecture note

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Reactions Related to the Aldol Condensation The Perkin Condensation In 1868, the young English chemist W.H. Perkins (1838-1907) discovered the important condensation reaction between ortho-hydroxybenzaldehyde (salicylaldehyde) and acetic anhydride. The product called coumarin is found in nature in lavender oil and sweet clover with the odor of new-mown hay. The discovery launched a new industry of synthetic flavoring agents and perfumes tied to the rapidly developing field of organic chemistry. The Perkin condensation is illustrated by the example below. CH O = + CH 3 COCCH 3 O O benzaldehyde acetic anhydride CH 3 CO 2 K 140 o C CH =CHCOOH 3-phenylpropenoic acid (cinnamic acid)
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A Mechanism for the Perkin Condensation The initial step is similar to the aldol reaction in that an enolate anion of acetic anhydride is formed in low amounts in an acid-base reaction. CH 3 COCCH 3 O = O + CH 3 CO 2 - acetic anhydride pKa ~ 22 acts as base CH 2 -COCCH 3 O O - enolate anion + CH 3 CO 2 H acid-base reaction
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Ch_322b_17.06 - Chapter 17.6 lecture note

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