Orgo II Tutorial: Synthesis of Alkyl Halides with PBr/SOCl2
\({\bf{PBr3:}}\) Net reaction: 3ROH + PBr3 --> 3RBr + H3PO3 (replaces the OH w/ a Br) > *** does NOT use a carbocation re-arrangement so it is NOT susceptible to re-arrangements Intermediate steps: ROH + PBr3 --> P(OR)3 + 3HBr formation of trialkylphosphiate and HBr (replacing the bromine atoms with OR groups from the alcohol) P(OR)3 + 3HBr --> 3RBr + H3PO3
\({\bf{SOCl2:}}\) works on primary/secondary alcohols and converts to alkyl chlorides (tertiary/quaternary too hindered). preserves configuration unless pyridine is present (Sni mechanism) |dw:1537639786958:dw|
next step: attack with pyridine to remove the H on the ROH group |dw:1537640122836:dw|
the end product of the above steps is called an alkylchlorosulfite, which can react with another prydine molecule, kicking off the second chloride to produce an alkyl chloride, as originally desired |dw:1537640606344:dw|
Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is Organic Chemistry 12th edition by Solomons, et. al.
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