web.chem.ucsb.edu_~zhang_zlm-chapter 10-alcohol
Post on 29-Dec-2015
7 Views
Preview:
TRANSCRIPT
-
LMZ/CHEM109A/ Winter 2010 Chapter 10: Reactions of alcohols, amines, ethers, epoxides and sulfur-containing compounds I. Nucleophilic substitution reactions for the conversion of alcohols to other functional groups A. Introduction:
B. Conversion of alcohol to alkyl halide (Reaction at C-O bond) (sec. 11.1): in-situ converting OH into good leaving groups 1. Conversion of alcohol to alkyl bromide by reaction with HBr (or NaBr, H2SO4) R* OH + HBr + H2O
racemic mixture
SN1R* Br
3R* OH + HBr + H2O
inversionSN2R* Br
1
Mechanism?
2. Conversion of alcohol to alkyl chloride by reaction with Lucas reagent (HCl, ZnCl2)
R* OH + HCl + H2Oracemic mixture
SN1R* Cl
3R* OH + HCl + H2O
inversionSN2R* Cl
1
ZnCl2ZnCl2
Mechanism?
3. Reaction of alcohols (especially 1 or 2) with thionyl chloride (Sec. 11.9) R
R'H
OH
RR'
HX
R' = H or alkyl or aryl stereochemistry??
SOCl2 (+ SO2 + HCl)
Mechanism?
4. Reaction of alcohols (especially 1 or 2) with phosphorus halide (Sec. 11.8)
RR' H
OH
RR'
HX
R' = H or alkyl or aryl inversion for 1 and 2 C
PCl3, PBr3, or PCl5 (+ HOPX2X= Br or Cl)
(Note: For the synthesis of alkyl chloride, thionyl chloride generally gives better yields than PCl3 or PCl5.)
Mechanism (for reaction with PBr3)?
H3CC
CH2CH3
H OHPBr3
e.g. 1
C. Conversion of alcohols to tosylate (Reaction at O-H bond) (Sec. 10.3)
RR'
HOH
RR'
OH
+ NEt3HCl(or pyridinumchloride)R' = H or alkyl or aryl retension
CH3SO
OCl
tosyl chlorideSO
OCH3
tosylate(p-TosCl)
NEt3 or pyridine
HC
Et
Me OH CH3SO
OCl
pyridine
e.g. 2
D. Conversion of alcohol to other functional groups via halides or tosylates: Stereochemical consequences (sec/ 10.3)
PCl3or PBr3
RR' H
O-H
RR'
OTosH + HCl
retension
CH3SO
OCl Nu e.g. N3
SN2
RR'
NuHinversion
retension + inversion : overall inversion
RR' H
OH
RR'
HX + H2O
inversion
Nu e.g. N3SN2
RR' H
Nuinversion
double inversion : overall retention
(p-TosCl)
top related