negative oxygen of the alkoxide ion formed ⇒ solvation stabilizes the alkoxide
ion and increases the acidity of the alcohol.
R OH+ O − H
Alcohol Alkoxide ion
(stablized by solution)
OH
H
R OH
H
+ +
ii) If the R– group of the alcohol is bulky, solvation of the alkoxide ion is
hindered ⇒ the alkoxide ion is not so effectively stabilized ⇒ the alcohol is a
weaker acid.
- Relative acidity of acids:
Relative Acidity
H 2 O > ROH > RC≡CH > H 2 > NH 3 > RH
Relative Basicity
R– > NH 2 – > H– > RC≡C– > RO– > HO–
- Sodium and potassium alkoxides are often used as bases in organic synthesis.
11.10 CONVERSION OF ALCOHOLS INTO MESYLATES AND
TOSYLATESS
- Alcohols react with sulfonyl chlorides to form sulfonates.
- These reactions involve cleavage of the O–H bond of the alcohol and not the
C–O bond ⇒ no change of configuration would have occurred if the alcohol had
been chiral.
+ OCH 2 CH 3
Ethyl
ethyl
H (−baseHCl) OCH 2 CH 3
Methanesulfonyl
chloride
Ethanol methanesulfonate
( mesylate)
S
O
CH 3 Cl
O
S
O
CH 3
O
