Transcript Conversion of Alcohols into Alkyl Halides

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
Cl + SO2 + HCl
pyridine
O
O
O
H
S
Cl
O
Cl
H
N
S
+
Cl
-H
O
Cl
O
S
Cl