Unusual behaviour of Lithium aluminium hydride




Conversion of amides into amines by reduction (RCONH2 =RCH2NH2)
Amides are organic compounds with chemical formula RCONH2 in which R refers to the hydrocarbon chainand can either be aromatic or aliphatic. Therefore amides are derivative of carboxylic acids where hydroxyl (-OH) is replaced by amino group (-NH2)  or they are organic compounds in which amino groups are attached to carbonyl groups of carboxylic acids or they are conjugate base of anion(the anion H2N-) or organic amine(an anion R2N-). They are reduced by LiAlH4 / lithium aluminum hydride (reduction by hydride transfer {-H}), usually LiAlH4 is a powerful reducing agent and reduces ketones, esters, aldehydes, carboxylic acids, nitriles and amide quite rapidly and on hydrolysis gives alcohol as the product. In this case it is different; LiAlH4 reduces amide to amine instead of alcohol. Reduction is the gain of electron and decreasing of oxidation number or it is a chemical reaction in which hydrogen is added to the molecule or oxygen is removed  from the molecule.  Reaction in this reduction proceeds as indicated below;
RCONH2(amide) =  RCH2NH2 (amine)+Water (H2O)                     
      (In presence of   ether, Lithium aluminum hydride (LiAlH4) and Water (H2O))                                       
The effect of amide reduction is to convert amide’s carbonyl (-C=O) group to (-CH2) group. This kind of reaction is specific for amides but not other carboxylic derivatives. For this type of reaction it can be noted that it imitates the characteristics of reactions of Clammansen Reduction and Wolf-kishner Reduction which convert carbonyl group (-C=O) to methylene (-CH2).



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