Conversion of alcohols to alkyl bromides using PBr3
Description: Treatment of a primary or secondary alcohol with PBr3 results in alkyl bromides.
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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.
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{ 5 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!
will this reaction occur if it’s a tertiary alcohol?
I don’t believe so due to the fact that the reaction proceeds through SN2. In order to convert a tertiary alcohol into an alkyl halide, it is better to use SOCl2 or SOBr2. Correct me if I am wrong.