- Thionyl chloride (SOCl 2 ) converts 1° and 2° alcohols to alkyl chlorides (usually
without rearrangement):
+SOCl 2 reflux +
( 1 oor 2o)
R OH R Cl HCl + SO 2
i) A 3° amine is added to promote the reaction by reacting with the HCl.
R 3 N: + HCl R 3 NH+ + Cl–
- The reaction mechanism involves the initial formation of the alkyl chlorosulfite:
RCH 2 O
H
+
O
OH
O−
O
H
+
O
O
O
H
Cl S Cl S
Alkyl chlorosulfite
RCH 2 +
Cl
Cl
RCH 2 S
Cl
Cl−
RCH 2 S
Cl
+ Cl
i) Then a chloride ion (from R 3 N: + HCl R 3 NH+ + Cl–) can bring about
an SN2 displacement of a very good leaving group, ClSO 2 – , which, by
decomposing (to SO 2 and Cl– ion), helps drive the reaction to completion.
RCH 2 O
O
−O
O
S O 2
Cl
Cl^ − + RCH 2 Cl + S
Cl
S + Cl−
11.15 SYNTHESIS OF ETHERS
11.15A ETHERS BY INTERMOLECULAR DEHYDRATION OF ALCOHOLS
- Alcohols can dehydrate to form alkenes.
R–OH + HO–R H
+
−H 2 O^ R–O–R
