Conversion of alcohols to alkyl bromides using PBr3
Description: Treatment of a primary or secondary alcohol with PBr3 results in alkyl bromides.
Notes: If the alcohol is on a chiral center, inversion of configuration will occur since this reaction proceeds through an SN2 reaction at carbon.
Examples:
Notes: Note that inversion of configuration has occurred in the second example. Also note that no reaction occurs for alkenyl alcohols (example 4).
Mechanism: Attack of the alcohol oxygen on phosphorus displaces bromide ion (Step 1, arrows A and B) which then attacks the carbon in SN2 fashion (Step 2, arrows C and D). This leads to the alkyl bromide.
{ 3 comments… read them below or add one }
this is most useful specially for the student of class xi &xii
Your reaction with PBr3 and the 2ndary alcohol is incorrect, I believe. Shouldn’t that be a Br instead of an OH in the product?
Yes, thanks for pointing out the error! fixed!