Conversion into RX

1
Conversion into R-X
SN1 reaction HI gt HBr gt HCl gt HF 30 gt 20 gt 10 lt
Me Acid catalyzed
SN2-type
E-products unavoidable Rearrangements
2
A trick to enhance SN2 and to avoid elimination
and rearrangements
3
Use of PBr3
- Only for 10 and 20 without rearrangement
4
Use of thionyl chloride
No skeletal rearrangements !!
5
Synthesis of Ethers
Intermolecular dehydration of alcohols
H2SO4
R-OH HO-R R-O-R
H2O alkene
Step 1 Step 2 Step 3
6
Williamson synthesis R-ONa R L
R O R
NaL - L must be a good leaving group
(tosylate, Br, I) - Versatile for the synthesis
of asymmetric ethers - Usual limitation of SN2
reactions
7
Using reversible formation of ethers to protect
OH functions
Example HOCH2CH2CH2Br
NaCCH NaOCH2CH2CH2Br
HCCH But HOCH2CH2CH2Br
(CH3)3COCH2CH2CH2Br
(CH3)3COCH2CH2CH2Br NaCCH
(CH3)3COCH2CH2CH2CCH
(CH3)3COCH2CH2CH2CCH
HOCH2CH2CH2CCH
8
As an alternative
9
Ether Cleavage
Very strong acid are needed
10
Epoxides
Lets do the following experiment
Epoxide (oxyrane)
11
Reactions of epoxides
Ring opening with acid with base