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Conversion of Alcohols into Alkyl Halides Reactions with HX, SOCl2, PBr3 Conversion of Alcohol into a Leaving Group • Form Tosylate (p-TsCl, pyridine) • Use strong acid (H3O+) • Convert to Alkyl Halide (HX, SOCl2, PBr3) Alcohols to Alkyl Halides OH HX (HCl or HBr) X rapid S N1 + HOH o 3 alcohol OH o 2 alcohol HX moderate S N1 X + HOH SN1: Carbocations can Rearrange HO Br Br HBr + cis & trans HO Br Br H-Br + cis & trans H Br HO - H2O H Br Lucas Test CH3 ZnCl 2 12M HCl CH3COH CH3 CH3CCl forms is seconds CH3 + HOZnCl 2 CH3 CH3 CH3C CH3 OZnCl2 CH3 H CH3C CH3 Cl Qualitative test for Alcohol Characterization primary OH >10 minutes (if at all) OH ZnCl 2, HCl secondary OH tertiary Cl <5 minutes Cl 1-2 seconds Cl 1o and 2o Alcohols: best to use SOCl2, PBr3, or P/I2 All are SN2 Reactions SOCl2 pyridine OH PBr 3 P, I2 (in situ prep. of PI3) Cl Br I Thionyl chloride mechanism O Cl S Cl SOCl2 OH O O H S Cl + SO2 + HCl pyridine O Cl O Cl H N S + Cl -H O Cl O S Cl