Classification Of Alcohols.
Method Of Preparation Of Alcohols.
6. By the action of Grignard reagent on epoxides. Grignard reagents react with ethylene oxide (epoxide) to give an additional product which on hydrolysis yields primary alcohol.
7. By the reduction of aldehydes, ketones, acids, and esters. Alcohols can be easily prepared by the reduction of aldehydes and ketones either by hydrogenation in the presence of a metal catalyst such as Ni, Pt or Pd or by the use of chemical reducing agents such as LiAl H4 or NaBH4.
Catalytic hydrogenation has a drawback that it also reduces other functional groups such as
if present in the molecule.
LiAl H4 gives a very good yield of alcohols from aldehydes, ketones, acids, esters, acid chlorides and acid anhydrides in ethereal solution. One advantage of this reagent is that it does not reduce the olefinic bond and hence can reduce unsaturated aldehydes, ketones, etc. , to unsaturated alcohols.
Sodium borohydride (NaBH4) is insoluble in ether but is stable in aqueous solution (LiAlH4, is destroyed by water). It is therefore generally used for the reduction of water-soluble aldehydes, and ketones. NaBH4, is much less reactive and therefore more selective and reduces only aldehydes and ketones.
Industrial Preparation of Alcohols.