Conversion of Alcohols into Alkyl Halides Reactions with HX,SOCl2,PBr3
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,SOC12,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 (HCI or HBr) +HOH rapid SN1 3 alcohol HX -X OH HOH moderate SN1 2°alcohol
Alcohols to Alkyl Halides OH 3 alcohol o HX (HCl or HBr) X + HO H rapid SN1 OH HX moderate S N1 X + HO H 2 alcohol o
Sy1:Carbocations can Rearrange B HBr cis trans
SN1: Carbocations can Rearrange HO HBr Br + Br cis & trans
HO Br D cis trans HO ⊕
HO H-Br Br + Br cis & trans HO H H - H2O Br Br
Lucas Test CH; CH3 ZnCl2 CH3COH CH:CCI forms is seconds 12M HCI CH3 CH3 HOZnC12 CH3 CH3 ⊕O CHC⊕ CI CH3 H CH3
Lucas Test C H3 COH CH3 CH3 ZnCl2 12M HCl CH3 CH3 C H3 CCl CH3 CH3 C H3 C OZnCl 2 H CH3 CH3 C H3 C C l forms is seconds + HOZnCl 2
Qualitative test for Alcohol Characterization OH CI primary >10 minutes (if at all) OH ZnC12,HCI secondary <5 minutes OH tertiary 1-2 seconds
Qualitative test for Alcohol Characterization OH primary OH secondary OH tertiary ZnCl2 , HCl Cl Cl Cl 1-2 seconds 10 minutes (if at all)
1 and 2 Alcohols:best to use SOC12,PBr3,or P/2 All are Sy2 Reactions S0C12 pyridine OH PBr3 P,I2 (in situ prep. ofPI3)
1 o and 2o Alcohols: best to use SOCl2 , PBr3 , or P/I2 OH SOC l2 pyridine PBr3 Br Cl P, I 2 I (in situ prep. of PI 3) All are SN2 Reactions
Thionyl chloride mechanism SOCh SO2 HCI pyridine
Thionyl chloride mechanism OH S O Cl Cl O H S O Cl Cl O H S Cl O O S Cl O - H+ Cl SOCl2 pyridine N C l + SO2 + HCl