Chemistry Reference
In-Depth Information
Tl
2
O C EtOH ! TlOEt C TlOH
2
.
14
TlOH C EtOH
TlOEt C H
2
O
2
.
15
2.2
Electrochemical Technique (Method B)
The possibility of synthesizing metal alkoxides by the anodic dissolution of metals
into alcohols containing conducting electrolytes was demonstrated for the first time
by Szilard
76
in 1906 for the methoxides of copper and lead. Since then this technique
has proved to be most promising. For example, the electrochemical method for the
preparation of ethoxides of Ti, Zr, Ta, Si, and Ge
77
was patented by the Monsanto
Corporation in 1972, and was later applied by Lehmkuhl
et al
.
78
for the synthesis of
Fe(
II
), Co, and Ni alkoxides M(OR)
2
(R D Me, Et, Bu
n
,andBu
t
).
Turova
et al
.
79
have substantially widened the scope of this technique by the synthesis
of a wide variety of homoleptic metal alkoxides and oxo-metal alkoxides: (i)
soluble
M(OR)
n
,MD Sc, Y, La, lanthanide,
80
Ti, Zr, Hf, Nb,
79
Ta
81
when R D Me, Et, Pr
i
,
Bu
n
; MO(OR)
4
,MD Mo, W when R D Me, Et, Pr
i
;
82-86
2-methoxyethoxides of Y,
lanthanide, Zr, Hf, Nb, Ta, Fe(
III
), Co, Ni, Sn(
II
),
87
and (ii)
insoluble
metal alkoxides
such as Bi(OMe)
3
;
88
Cr(OR)
3
,RD Me, Et, MeOC
2
H
4
;
89
V(OR)
3
;
86
Ni(OR)
2
,RD Me,
Pr
n
,Pr
i
;
90
Cu(OR)
2
,RD Bu
n
,C
2
H
4
OMe;
91
Re
4
O
2
(OMe)
16
.
92
Besides the above, Banait
et al
. have also employed the electrochemical reactions
of some (including polyhydroxy) alcohols for the synthesis of alkoxides of copper
93
and mercury.
94
In 1998, the anodic oxidation of molybdenum and tungsten
95
in alcohols in the pres-
ence of LiCl (as electroconductive additive) was found to yield a variety of interesting
oxo-metal alkoxide complexes, some of which have been authenticated by single-
crystal X-ray crystallograpy.
The electrode ionization reactions of alcohols and anode polarized metals in the
presence of an electroconductive additive, followed by the interaction of the generated
intermediate species and the formation of the final products can by illustrated
96
by the
following reactions (Eqs 2.16 and 2.17):
M ! M
n
C
C
n
e
anode
2
.
16
n
ROH C
n
e
!
n
RO
C
n
H
ž
n
H
ž
!
n
2
H
2
cathode
2
.
17
M
n
C
C
n
RO
! M(OR)
n
where M D anode metal and ROH D an appropriate alcohol.
This process has great promise for the direct conversion of the less electropositive
metals to their alkoxides owing to its simplicity and high productivity as well as its
continuous and non-polluting character (with hydrogen as the major by-product).
The electrochemical technique appears to have been successfully employed in Russia
for the commercial production
96
of alkoxides of Y, Ti, Zr, Nb, Ta, Mo, W, Cu, Ge,
Sn, and other metals.
