Chemistry Reference
In-Depth Information
Table 2.7
Boiling points and molecular complexities of titanium and zirconium tetra
alkoxides
B.p. (
Ž
C/mm)
Molecular complexity
R
Ti(OR)
4
Zr(OR)
4
Ti(OR)
4
Zr(OR)
4
C
2
H
5
103/0.1
190/0.1
2.4
3.6
CH
3
CH
2
CH
2
CH
2
142/0.1
243/0.1
-
3.4
CH
3
(CH
2
)
7
214/0.1
-
1.4
3.4
(CH
3
)
2
CH
49/0.1
160/0.1
1.4
3.0
(C
2
H
5
)
2
CH
112/0.1
181/0.1
1.0
1.0
(C
3
H
7
)
2
CH
156/0.1
163/0.1
1.0
1.0
(CH
3
)
3
C
93.8/5.0
89/5.0
1.0
1.0
CH
3
(CH
2
)
4
175/0.8
256/0.01
1.4
3.2
(CH
3
)
2
CH(CH
2
)
2
148/0.1
247/0.01
1.2
3.3
(CH
3
C
2
H
5
)CHCH
2
154/0.5
238/0.01
1.1
3.7
(CH
3
)
3
CCH
2
105/0.05
188/0.2
1.3
2.4
(C
2
H
5
)
2
CH
112/0.05
178/0.05
1.0
2.0
(CH
3
C
3
H
7
)CH
135/1.0
175/0.05
1.0
2.0
(CH
3
C
3
H
i
7
)CH
131/0.5
156/0.01
1.0
2.0
(CH
3
)
2
C
2
H
5
C
98/0.1
95/0.1
1.0
1.0
undergo molecular dissociation at the concentrations at which the tetrabutoxide is
almost dissociated.
456
Similarly dimeric dichloride dibutoxide as well as monomeric
trichloride monobutoxide also do not undergo any dissociation over a wide concen-
tration range. The above results appear to indicate that the presence of the more
electronegative chlorine atom increases the positive charge and acceptor properties
of the central titanium atom, and consequently the strength of the alkoxide bridges
increases which prevents the molecules from depolymerizing.
Barraclough
et al
.
457
measured the molecular complexities of titanium alkoxides
in dioxane solvent and observed that the complexities are concentration dependent
except with monomeric
tert
-butoxide which shows concentration-independent molec-
ular weight. For the normal alkoxides, as the concentration is increased, the molecular
weight increases and there was no indication of a limiting value of molecular weight
up to a concentration of 0.5
M
.
Titanium isopropoxide shows an average association of 1.4, whereas its tertiary and
higher secondary alkoxides are essentially monomeric in refluxing benzene.
113
,
273
,
274
,
432
Titanium tetrakis(hexafluoroisopropoxide) also shows an average molecular association
of 1.5 in boiling benzene.
458
On the basis of the boiling points measured for various normal alkoxides at different
pressures, Cullinane
et al
.
459
observed that the results do not conform to the relation,
log
p
D
a
b
/
T
(
p
is the pressure in mm at which boiling point T was observed and
a
and
b
are constants). However, the latent heats and entropies of vaporization and the
Trouton constants indicate that titanium tetraethoxide exhibits anomalous behaviour,
i.e.
it shows a distinctly higher Trouton constant (42.5) than those observed for
n
-
propoxide,
n
-butoxide,
n
-amyloxide, and
n
-hexyloxide (29.1, 35.6, 39.4, and 40.5,
respectively).
Bradley
et al
.
306
,
307
measured the heat of formation of liquid trimeric titanium ethoxide
and the value was found to be
H
f
Ti
OC
2
H
5
4
liq
D349 š 1
.
4kcalmol
1
, from
which the standard heat of formation of monomeric gaseous titanium ethoxide was
