Barbier-Wieland degradation

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The stepwise degradation of a carboxylic acid to the next lower homologue. First the ester is converted into a tertiary alcohol using a Grignard reagent (PhMgX) and acid (HX):RCH2COOCH3 → RCH2C(OH)Ph2. The secondary alcohol is then dehydrated using ethanoic anhydride (CH3COOCOCH3) to give an alkene:RCH2C(OH)Ph2 → RCH=CPh2. The alkene is oxidized with chromic acid:RCH=CPh2 → RCOOH+Ph2CO. The result is conversion of an acid RCH2COOH to the lower acid RCOOH.


RCH2C(OH)Ph2 → RCH=CPh2.


Subjects: Chemistry.

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