PREPARATION OF ALKYL HALIDES
PREPARATION OF ALKYL HALIDES
Mono haloalkanes or Alkyl halides can be prepared by a number of methods.Some important synthetic methods are as follows:
AS A MAIN REAGENT
A number of reagents such as halogen acids, PCl5, PCl3, SOCl2 etc. react with aliphatic alcohols to produce corresponding alkyl halides.
Alcohols react with halogen acids (HCl ,HBr or HI) to produce alkyl halides.
CH3-OH + HCl® CH3-Cl + H2O (in the presence of ZnCl2/H2SO4)
C2H5OH + HI® C2H5I + H2O
C2H5OH + HBr® C2H5Br + H2O
CH3-CH2-CH2-OH + HCl ® CH3-CH2-CH2-Cl + H2O
When alcohols are treated with phosphorus penta chloride, corresponding alkyl chlorides are obtained.
Above reaction is carried out in the presence of Pyridine. Pyridine absorbs HCl as it is formed.
TRI BROMIDE (PBr3)
TRI IODIDE (PI3)
OF ALKANES
Alkanes react with chlorine and bromine in presence of sunlight and undergo photo chemical series of substitution reactions to yield alkyl halides.
REMEMBER: THIS IS NOT AN APPROPRIATE METHOD FOR THE LABORATORY PREPARATION OF ALKYL HALIDES
BECAUSE THE RESULTANT MIXTURE CONTAINS POLYHALOGEN DERIVATIVES WHICH ARE DIFFICULT TO SEPARATE.
we know that alkenes are unsaturated hydrocarbons.Therefore when alkenes are treated with halogen acid, addition reaction takes place and alkyl halides are formed. Additionof HX takes place according to MARKONIKOV’S PRINCIPLE.
The order of reactivity of halogen acid is as follows: