Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and hydrochloric acid. This reaction is named after Erik Christian Clemmensen .
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Dear Nadia
Basically any reagent which contains functional groups labile in acidic conditions (such as acetals), due to the use of concentrated HCl
certain types of aldehydes and ketones do not give normal reduction products. Under Clemmensen conditions, 1435 a-hydroxy ketones give either ketones (hydrogenolysis of the OH,19-54) or alkenes, and 1,3-diones usually undergo rearrangement (e.g., MeCOCH2-COMe ! MeCOCHMe2).1436 Neither method is suitable for a,b-unsaturated ketones.
March's Advanced Organic Chemistry, 7th ed. (p 1836)
الكيتونات التي فيها مجاميع فعالة أخرى تتأثر بالوسط الحامضي لا يمكن اختزالها بواسطة اختزال كليمنسن
One thing is that the Clemmensen reduction is done under acidic conditions whereas the Wolff-Kishner reaction is done under basic condition, and that I think decides somewhat which to choose depending of the nature and other groups present in the reactant.
Clemmensen reduction is preferably used for reducing aryl-alkyl ketones. Since it is performed under strong acidic conditions, so Ketones containing acid sensitive groups like acetal can not be reduced by this method.