# Mechanism for the formation of an alkyl halide from alcohol and phosphorus trihalide [duplicate]

I was reading about synthesis of alkyl halides from $\ce{PX3}$. I want to know the mechanism for this reaction. According to Solomons and Fryhle, no rearrangement takes place in case of $\ce{PBr3}$ , which leads me to think that the mechanism is SN2. But what about phosphorus bromides and iodides?

A Google search confirmed that the mechanism for reaction with phosphorus tribromide is indeed SN2, but I could not find anything on trichlorides and iodides. I need help for those.

Thanks.

• Why do you think they may be different? – Waylander Apr 24 '18 at 11:59
• HBr undergoes AMK addition to an alkene in the presence of peroxide whereas other hydrogen halides do not. I think that anything is possible in chemistry and I do not want to make a mistake if a tricky question based on this appears in my exam. – Anurag B. Apr 24 '18 at 12:21
• The HBr is quite different from the phosphorus halides as there is no protonation step on the alcohol – Waylander Apr 24 '18 at 14:15
• chemistry.stackexchange.com/questions/69063/… – Mithoron Apr 24 '18 at 15:25
• Thanks for the links @Mithoron ! The reaction with $PCl_3$ looks like S_N^2 or S_N^i to me but I can't quite tell which. Which one is it? – Anurag B. Apr 25 '18 at 9:03