1) Alkoxide ions are somewhat stronger bases than hydroxide ions because
alcohols are weaker acids than water.
2) Addition of sodium hydride (NaH) to ethanol produces a solution of sodium
ethoxide (CH 3 CH 2 ONa) in ethanol.
H 3 CH 2 C O H + H− H 3 CH 2 C O− + H 2
Stronger acid
pKa = 1 6
Stronger base
(from NaH)
Weaker base Weaker acid
pKa = 3 5
ethyl alcohol
3) Potassium tert-butoxide ions, (CH 3 ) 3 COK, can be generated similarily.
(H 3 C) 3 C O H + H− (H 3 C) 3 C O− + H 2
Stronger acid
pKa = 1 8
Stronger base
(from NaH)
Weaker base Weaker acid
pKa = 3 5
tert-butyl
alcohol
- Alkyllithium (RLi):
- The C—Li bond has covalent character but is highly polarized to make the
carbon negative.
RL
G−<G+i
2) Alkyllithium react as though they contain alkanide (R:–) ions (or alkyl
carbanions), the conjugate base of alkanes.
C C H ++CH 3 CH 3
Stronger acid
pKa = 2 5
Stronger base
(from CH 3 CH 2 Li)
Weaker base Weaker acid
pKa = 50
HC− CH 2 CH 3 hexane H C −
3) Alkyllithium can be easily prepared by reacting an alkyl halide with lithium
metal in an ether solvent.
3.15 ACIDS-BASE REACTIONS AND THE SYNTHESIS OF
