Chemistry Reference
In-Depth Information
4.10
Reactions with Thiols
Although the reactions (Eq. 2.248) of thiols are quite facile with alkoxides of germa-
nium,
890
tin,
891
and antimony,
892
the alkoxides of titanium,
893
zirconium,
893
alumi-
nium,
893
and silicon
893
do not undergo such reactions:
M
OR
x
C
x
R
0
SH
M
SR
0
x
C
x
ROH
2
.
248
Qualitatively this difference might be understood on the basis of Pearson's concept of
hard and soft acids and bases.
The convenient preparation of thiolates of titanium
894
and uranium
213
from their
respective dialkylamides, but not from alkoxide analogues, demonstrates the oxophilic
nature of these metals in their higher oxidation states.
4.11 Reactions with Halogens, Hydrogen Halides, Acyl Halides, and
Metal Halides
4.11.1
Reactions with Halogens
The reactions of metal alkoxides with halogens were investigated by Nesmeyanov
et al
.
895
who observed that the reaction between titanium tetra-
n
-butoxide and chlor-
ine or bromine yielded the dihalide dibutoxide coordinated with one mole of alcohol
as TiX
2
OBu
2
.BuOH and
n
-butyl propionate. The reaction may be represented by
Eqs (2.249) - (2.252):
Ti
OCH
2
R
4
C X
2
! TiX
2
OCH
2
R
2
C 2RCH
2
O
2
.
249
2RCH
2
O ! RCH
2
OH C RCHO
2
.
250
TiX
2
OCH
2
R
2
C RCH
2
OH ! TiX
2
OCH
2
R
2
.
RCH
2
OH
2
.
251
2RCHO ! RCH
2
COOR
2
.
252
where R D C
3
H
7
.
It was observed that the treatment of ferric trimethoxide with excess of chlorine at
ambient temperature yielded FeCl
3
.
2MeOH. However, when the above reaction was
carried out at 72
Ž
C, only partial replacement occurred, yielding ferric monochloride
dimethoxide.
210
Jones
et al
.
379
observed that uranium tetraethoxide reacted with bromine to yield
uranium monobromide tetraethoxide which was then used for the preparation of the
pentaethoxide (Section 2.10.1)
2U
OEt
4
C Br
2
! 2U
OEt
4
Br
2
.
253
4.11.2 Reactions with Hydrogen Halides
In view of an interesting gradation observed (Section 2.4) in the reactivity of tetra-
halides of silicon, titanium, zirconium, and thorium with ethyl and isopropyl alcohols,
the reverse reactions of alkoxides of these elements with hydrogen chloride (bromide)
were investigated by Mehrotra
896
,
897
who demonstrated that the reaction products of
