Reduction by Alkyl Halides

Reduction by Alkyl Halides

Alkanes can be prepared by the reduction of alkyl halides with the help of different methods. 

 1)Reduction by dissolve metals An alkane is prepared or produced When Zn reacts with alkyl group in the presence of aqueous acid such as hydrochloric acid.or acetic acid

 Equation

 RX + Zn +HX________ZnX+ RH 
Similarly 
 RCl+ Zn + HCl______ZnCl2 + RH
 Transferring of electron from metals,to the substrate , followed by the transfer of proton from the acids.
 Zn__________Zn2+  2e  
RCl ________ R• + Cl
 R + e _________R••-
 R••- + HCl_______RH + Cl- 
Zn2+ ,2Cl- ________ZnCl2 

 2)Reduction by Lithium Aluminium hydride

 Reduction by Lithium Aluminium hydride readily reduced primary and secondary alkyl halides to alkane while tertiary alkyl halide gives alkenes. 
 4RX + LiAlH4 + 4RH+AlX3+LiX 

Hydride transfer occur as fallow:

 H3Al__H+RX____RH+AlH3+X-
 H2Al__H+RX____RH+ AlH2X 
 XHAl__H+RX __ RH+ AlHX2
 X2Al _H+RX___,RH+ AlX3 
Tertiary alkyl halides are reduced by sodium boroanhydride which does not reduce primary alkyl halides.

 Hydrogenolysis

 Alkanes can be prepared by the hydrogenolysis of alkyl halides in the presence of palladium charcoal used as a catalyst. 
 R----X + H2»»»»» R---H+ HX