Reactions of titanium alcoholates Ti(OR)4 (R = n-Bu, t-Bu) with tertiary organic and organometallic hydroperoxides

Article abstract of DOI:10.1134/S1070363206020137

tert-Butyl and cumyl hydroperoxides in the reactions with Ti(OR) ₄ are reduced to alcohols with the evolution of oxygen via formation of titanium-containing peroxides and trioxides. The pathways of the reactions of Ti(OR)₄ with triphenylelement hydroperoxides R₃EOOH (E = C, Si, Ge) depend on element E and on the structure of R; the reactions involve the rearrangement of the peroxides, and with (n-BuO)₄Ti the alkoxy group is oxidized either with preservation or with breakdown of the hydrocarbon skeleton. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S1070363206020137

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 2, pp. 235 244.
Pleiades Publishing, Inc., 2006.
Original Russian Text L.P.Stepovik, M.V.Gulenova, 2006, published in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 2, pp. 249 258.
Reactions of Titanium Alcoholates Ti(OR)4 (R = n-Bu, t-Bu)
with Tertiary Organic and Organometallic Hydroperoxides
L. P. Stepovik and M. V. Gulenova
Lobachevsky Nizhni Novgorod State University, pr. Gagarina 23, Nizhni Novgorod, 603950 Russia
e-mail: gulmv@rambler.ru
Received March 11, 2005
Abstract tert-Butyl and cumyl hydroperoxides in the reactions with Ti(OR)4 are reduced to alcohols with
the evolution of oxygen via formation of titanium-containing peroxides and trioxides. The pathways of the
reactions of Ti(OR)4 with triphenylelement hydroperoxides R3EOOH (E = C, Si, Ge) depend on element E
and on the structure of R; the reactions involve the rearrangement of the peroxides, and with (n-BuO)4Ti the
alkoxy group is oxidized either with preservation or with breakdown of the hydrocarbon skeleton.
DOI: 10.1134/S1070363206020137
Titanium alcoholates are used as catalysts of hydro-
peroxide oxidation of oxygen-containing organic sub-
strates. The compounds Ti(OR)4 (R = Et, i-Pr, t-Bu)
are used in stereoselective epoxidation of allyl alco-
hols (Sharpless epoxidation) [1 3]. The epoxidizing
system is an equimolar mixture of Ti(OR)4, tertiary
hydroperoxide, and dialkyl tartrates (alkyl = ethyl,
isopropyl). The dimer [Ti(tartrate)2(OR)]2 is an active
catalyst. tert-Butyl hydroperoxide I in the presence of
titanium tetraisopropylate (3 : 1) under mild condi-
tions (CH2Cl2, 23 to 20 C) oxidizes substituted
phenols, and also naphthols, phenanthrols, and anthra-
cenols, to the corresponding o-quinones [4]. Primary
and secondary benzyl alcohols are selectively con-
verted to the corresponding aldehydes or ketones in
high yields under the action of I and catalytic amounts
(0.1 mol) of Ti(OPr-i)4 [5]. Aliphatic hydroxy groups,
double bonds (except allyl bonds relative to the OH
group), and phenolic hydroxyls (except those located
in the o-position of the benzene ring) remain intact.
All these reactions involve fast ligand exchange of the
titanium alkoxy groups with allyl and benzyl alcohols,
phenols, and hydroperoxides. The oxygen-containing
substrates are oxidized by the intramolecular mechan-
ism, without generation of free radicals.
titanium alcoholates with hydroperoxides are few.
It was reported that the reaction of Ti(OPr-i)4 with
hydroperoxide I yielded titanium peroxy compounds,
which were not isolated pure [7], and that the isoprop-
oxy group can be oxidized with I to acetone [5]. The
possibility of the oxidation of the alkoxy group in
(n-BuO)4Ti with I was demonstrated in [8].
The major pathway in the reaction of tetra-tert-
butoxytitanium with hydroperoxide I in a 1 : 2 ratio is
the release of oxygen (yield 0.85 0.90 mol) [9 11]
via formation of titanium-containing peroxide and tri-
oxide. The trioxide decomposes along two pathways:
release of oxygen and regeneration of titanium alco-
holate [9] and homolysis of the peroxide bonds [10].
In this study we examined the reactions of titanium
alcoholates with hydroperoxides with the aim to eluci-
date how the reaction pathways are influenced by the
structures of alkoxy groups in titanium alcoholates
and of hydroperoxides, and also by the kind of the
atom bonded to the hydroperoxy group.
Among titanium alcoholates we chose titanium
tetrabutylate II and tetra-tert-butylate III. In the former
compound, alkoxy groups contain -H atoms and thus
are capable of oxidation. We chose tertiary hydroper-
oxides containing methyl and phenyl groups: tert-
butyl hydroperoxide I, cumyl hydroperoxide IV, 1,1-
diphenylethyl hydroperoxide V, triphenylmethyl hy-
droperoxide VI, and heteroanalogs of VI: triphenyl-
silyl hydroperoxide VII and triphenylgermyl hydro-
peroxide VIII. All the reactions were performed in
benzene at room temperature. The alcoholate : hydro-
peroxide ratio was 1 : 2 for methyl(phenyl) hydroper-
oxides and 1 : 1 for triphenylelement hydroperoxides
VI VIII.
Titanium alcoholates in combination with various
oxidants (singlet oxygen, ROOH) were suggested as
reagents for one-step synthesis of epoxidized alcohols
from alkenes [6]. The reactions involve formation of
hydroperoxides and their subsequent transformation
in the presence of titanium alcoholates into epoxy
alcohols via unsaturated alcohols. A scheme of inter-
molecular epoxidation was suggested.
Despite the fact that all the above processes involve
titanium-containing peroxides, data on reactions of
235

236
STEPOVIK, GULENOVA
Table 1. Products of reactions of titanium tetra-tert-butylate (t-BuO)4Ti with hydroperoxides RCOOH (yield, mole
per mole of titanium alcoholate; benzene, 20 C)a
R
Reaction products
Me2(Ph)Cb
Ph2(Me)Cb
Ph3Cc
1.69
Ph3Sic
Ph3Gec
Volatile products
O2
t-BuOH
PhCOMe
0.65
2.86
0.04
0.05
2.54
0.15
0.13
1.58
0.31
0.90
Products of hydrolysis of nonvolatile residued
t-BuOH
PhCOMe
ROH
0.70
0.05
0.88
0.14
1.82
2.29
0.70
0.96
1.80e
0.91f
0.42
0.10g
Alkene
0.03
0.29
[PhC(Me)=CH2]
(Ph2C=CH2)
0.10
PhOH
0.13
0.15
0.04
(traces)
Ph2EO
R COOH
0.03
0.32
0.25h
0.04i
j
j
0.06i
0.07i
a
b
c
d
Averaged results.
(t-BuO) Ti: ROOH = 1: 2.
(t-BuO) Ti : ROOH = 1 : 1.
Metal 1 mol in all the experiments; with
f
4
4
e
Ph GeOOH, the volatile fraction contained 0.47 mol of Ti(OBu-t) . The volatile fraction contained 0.25 mol of alcohol. 0.27
0.25 mol of Ph C(Me)OOH remains unchanged. We also isolated Ph Ge O: 0.39 mol before hydrolysis and 0.04 mol in the
hydrolysis products.
3
4
g
2
6
2
h
i
j
In the form of diphenylsiloxane. Acetic : formic acids 1 : 5. Not determined.
The results of the reactions of titanium alcoholates
with hydroperoxides are given in Tables 1 and 2. In
all the cases, irrespective of the structure of the alkoxy
group bonded to Ti, the reactions with methyl(phenyl)
hydroperoxides involve the release of oxygen and
reduction of the hydroperoxides to the corresponding
alcohols. Scheme (1) illustrating the reaction pathway
is similar to that suggested previously for the reac-
tions of aluminum tert-butylate and alcoholate III
with hydroperoxide I [10 12].
(RO)4Ti + R OOH
(RO)3TiOOR
ROH
A
R O3 O2
R O O H
(1)
R OOH
O2 + (RO)3TiOR ,
R OH +
(RO)3Ti O1
(RO)3Ti O O R
B
R = t-Bu, n-Bu; R = t-Bu, PhCMe2, Ph2CMe.
Scheme (1) involves formation of intermediate tita-
nium-containing peroxides A, as indicated by a high
yield of alcohols ROH in the volatile fraction and of
trioxides B. These compounds mostly decompose to
unsymmetrical titanium alkoxides and molecular
oxygen (partially singlet). In the reactions of hydro-
peroxide I with alcoholates II and III, we detected
formation of 0.35 0.40 mol of singlet oxygen (by its
reaction with anthracene). The yield of oxygen de-
pends on the structure of substituents in titanium
alcoholates and hydroperoxides. In the reaction of IV
with alcoholate III it is almost 1.5 times higher than
in the reaction with II. In the reactions of III with
methyl(phenyl) hydroperoxides, with an increase in
the number of phenyl groups, the yield of oxygen
decreases, but in the reaction with VIII it reaches
0.30 0.32 mol (60 64%) (Table 1). No oxygen
formation was detected in the reactions of II with
triphenylelement hydroperoxides VI VIII.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 2 2006

REACTIONS OF TITANIUM ALCOHOLATES Ti(OR)4 (R = n-Bu, t-Bu)
237
Table 2. Products of reactions of titanium tetrabutylate (n-BuO)4Ti with hydroperoxides RCOOH (yield, mole per mole
of titanium alcoholate; benzene, 20 C)a
R
Reaction products
t-Bub
Me2(Ph)Cb
Ph3Cc
Ph3Sic
Ph3Gec
Volatile productsd
O2
0.34
0.40
0.46
PrCHO
CH3CH=CH2
BuOH
0.20e
0.26
0.01
1.25
0.30
0.58
1.44
0.35f
0.51
1.86
1.67
1.36
2.14
ROH
0.54g
Products of hydrolysis of nonvolatile residue
PrCHO
BuOH
PhOH
Ph2EO
ROH
(Ph3EO)4Ti
PrCOOH
HCOOH
0.17
1.40
0.16
0.71
0.20
1.69
0.30
0.41
0.42h
Traces
1.49
0.10
0.12
0.89
0.29
0.20
1.22
0.20i
0.18k
0.05
0.16j
0.16k
0.10
0.14
0.015
0.10
0.015
Traces
0.02
a
b
c
d
Averaged results. (n-BuO) Ti : ROOH = 1 : 2. (n-BuO) Ti : ROOH = 1 : 1. Formaldehyde was identified qualitatively in all
4
4
e
f
g
the cases. 0.04 mol of butyl butyrate was also detected. Reaction time 10 h at 20 C and 3 h at 60 C. 0.11 mol of acetophenone
was also detected in the volatile fraction and hydrolysis products. 0.05 mol of triphenylmethyl peroxide was also detected.
A mixture of triphenylhydroxysilane and diphenylsiloxane. Ph Ge O. Compounds (Ph EO) Ti (E = Si, Ge) were isolated
h
i
j
k
6
2
3
4
before hydrolysis.
The decomposition of trioxides B occurs concur-
phenylelement hydroperoxides, is also determined by
transformations of titanium peroxy compounds A. The
formation of titanium peroxy derivatives (RO)3Ti
OOR from hydroperoxides Ph3EOOH is favored by
the proton-donor power of these hydroperoxides,
decreasing in the order Ph33SiOOH > Ph3GeOOH >
Ph3COOH, in accordance with extent of d p con-
jugation [13]. Therefore, the reactions of titanium
alcoholates with these hydroperoxides were performed
at a reactant ratio of 1 : 1.
rently with their homolysis across the O2 O3 bond
[10 12]. An ESR monitoring of the reactions of tita-
nium alcoholates with hydroperoxides I, IV, and V in
benzene at 20 C in the absence of spin traps revealed
a singlet (gi 2.0125 2.013) which was assigned to
the peroxy radical (RO)3TiOO. [10 12], since the
t-BuOO. radical is not detected under these conditions.
An ESR monitoring of the reaction of (n-BuO)4Ti
with Ph3COOH also revealed a signal characteristic
of the peroxytitanium radical (gi 2.013), which sug-
gests formation of trioxide B (R = Bu, R = CPh3).
Homolysis of trioxide B across the O1 O2 bond fol-
lowed by recombination of the Ph3COO. radicals ac-
counts for the formation of triphenylmethyl peroxide
[yield 0.05 mol; scheme (2)].
The titanium-containing peroxides (BuO)3TiOOR
decompose along several pathways. The common
reaction for butoxytitanium and all the hydroperoxides
is the oxidation of the alkoxy group (with the preser-
vation of its carbon backbone) to butanal (Table 2).
The aldehyde is formed by intramolecular decomposi-
tion [reaction (3)] of peroxide A in the six-membered
reaction complex [5 8]:
(BuO)3TiOOOCPh3
2Ph3COO
(BuO)3TiO + OOCPh3,
Ph3COOCPh3 + O2.
(2)
O
^
As follows from Tables 1 and 2, the reactions of
titanium alcoholates with hydroperoxides are not lim-
ited to formation and transformations of trioxides B.
The qualitative and quantitative composition of prod-
ucts formed in the reactions of (n-BuO)4Ti and
(t-BuO)4Ti with hydroperoxides, especially with tri-
(BuO)2Ti
O<
CHPr
>H
+ [(BuO) TiO] ,
PrCHO + R OH
2
x
(3)
O
R
R = t-Bu, PhCMe2, Ph3E (E = C, Si, Ge).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 2 2006

238
STEPOVIK, GULENOVA
Butanal partially condenses into an ester, is oxi-
Rearrangement (5) makes the largest contribution
in the case of the reaction of II with VI, which is
caused by the formation of benzophenone. This trans-
formation occurs to a lesser extent in the reactions
with VII and was not detected in the reaction with
Ph3GeOOH.
dized to the acid, and reacts with titanium alcoholate
in the enol form [14]; owing to the latter reaction, up
to 0.17 mol of the aldehyde was detected in the hy-
drolysis products.
Along with butanal, in the volatile fraction from all
the reactions with II we identified formaldehyde, and
in the case of hydroperoxides VII and VIII we de-
tected significant amounts of propene. Formaldehyde
and propene are formed by destructive oxidation of the
alkoxy group. We believe that this reaction occurs as
decomposition [reaction (4)] of peroxides (BuO)3Ti
OOR in the eight-membered intermediate reaction
complex.
It should be noted that the rates of the reactions of
(BuO)4Ti with Ph3EOOH strongly depend on ele-
ment E. In particular, the reaction with Ph3SiOOH is
complete in 10 15 min, that with Ph3COOH, in
30 min, and in the reactions with Ph3GeOOH even
after 3 h about 50% of the hydroperoxide remains
unchanged. However, even under these conditions the
amount of BuOH in the volatile fraction is equal to,
or exceeds 1 mol. This fact suggests that the peroxide
(BuO)3TiOOGePh3 (A) is formed fairly rapidly but
decomposes slowly.
O^CH2 CH2
^
(BuO)2Ti
CHCH3
O
O---H
R
Thus, the reaction of (BuO)4Ti with tertiary hydro-
peroxides depends on the structure of their substitu-
ents and on the kind of the element bonded to the
hydroperoxy group. Methyl(phenyl) hydroperoxides
react with the release of oxygen. All the hydroperox-
ides ROOH oxidize the alkoxy group to butanal, and
in the case of the Ph3Si and Ph3Ge derivatives this
group undergoes destructive oxidation with the forma-
tion of formaldehyde and propene.
R OH + CH2O + CH3CH=CH2 + [(BuO)2TiO]x, (4)
R = Ph3C, Ph3Si, Ph3Ge.
The destructive oxidation is the most characteristic
of organometallic hydroperoxides (E = Si, Ge), which
may be due to steric factors. In going from C to Si
and Ge, the covalent radius of the element appreciably
increases (0.077, 0.117, and 0.122 nm, respectively
[15]), as does also the volume of the Ph3E group,
which makes the formation of the eight-membered
ring more preferable.
The reaction of (t-BuO)4Ti with hydroperoxides
V and VI occurs within 10 20 h, and 30 min is suf-
ficient for the completion of the reactions with tri-
phenylelement hydroperoxides. With titanium tetra-
tert-butylate, reactions (3) and (4) are impossible.
However, transformations of the tert-butoxy group do
occur, as indicated by the presence of carboxylic acids
(HCOOH, CH3COOH) in the products of hydrolysis
of the nonvolatile residues (Table 1). Also, in the
volatile fraction of products from the reaction of III
with VIII, we qualitatively detected isobutylene oxide,
which may be formed by the decomposition [reac-
tion (6)] of the titanium peroxy compound involving
the -H atom of the alkoxy group.
Propene was determined quantitatively in the
form of isopropyl chloride after the treatment with
HCl. Formaldehyde was identified in the form of its
dimedone derivative and 2,4-dinitrophenylhydrazone,
and also in the form of formic acid, which, in turn,
was identified as methyl ester in the hydrolysis prod-
ucts. We failed to determine H2CO quantitatively,
because of its strong tendency to enter condensations.
The IR spectra of hydrolysis products of the nonvola-
tile residues after the removal of volatiles contain
GePh3
H
O O
1
a number of bands at 1020 1080 cm assignable to
(t-BuO)2Ti
the stretching vibrations of the C O C groups.
CH2
O C
The third pathway [reaction (5)] involving the loss
of the peroxide oxygen consists in the rearrangement
of titanium-containing peroxides and decomposition
of the forming titanium alkoxy compounds C, similar-
ly to aluminum peroxy compounds [16].
Me Me
(6)
Me2C CH2 + Ph3GeOH + [(t-BuO)2TiO]x.
O
In contrast to the reactions of (BuO)4Ti, transfor-
mations involving the tert-butoxy group do not pre-
vail. Along with the release of oxygen [scheme (1)], a
significant contribution is made by rearrangement (5)
of titanium peroxy compounds A. This process is the
(BuO)3TiOOEPh3
(BuO)3TiOEPh2(OPh)
C
Ph2EO + (BuO)3TiOPh.
(5)
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REACTIONS OF TITANIUM ALCOHOLATES Ti(OR)4 (R = n-Bu, t-Bu)
239
most characteristic of hydroperoxides V VII. The
yield of acetophenone and benzophenone reaches
0.30 0.32 mol. The IR spectrum proves the presence
tives (t-BuO)3TiOE(R)(Ph)OPh to Ph(R)EO and
phenoxytitanium (E = C, R = Me, Ph; E = Si, R =
Ph). The phenoxy group in phenoxytitanium under-
goes further oxidation with the formation of a com-
plex mixture of products.
1
of benzophenone [ (C=O) 1680 cm ] in the nonvola-
tile fraction of the reaction products before hydrolysis.
1
Also, the spectrum contains a band at 1265 cm
In the reaction of III with VIII, the contribution of
the rearrangement of (t-BuO)3TiOOGePh3 is low; the
amount of phenol is 0.04 0.05 mol. Ph3GeOOH is
reduced to the hydroxygermane transforming under
the reaction conditions into hexaphenylgermanoxane.
In contrast to the reactions with VI and VII, the vola-
tile fraction contained up to 0.50 mol of the starting
titanium alcoholate and 0.8 0.9 mol of t-BuOH,
which is almost two times lower than in the similar
reactions with VI and VII (Table 1). Table 1 shows
that one of the major products of the reaction of
(t-BuO)4Ti with Ph3GeOOH is oxygen. In specially
performed reactions of III with VIII in a 1 : 2 ratio,
the oxygen yield was 0.60 0.64 mol. An anthracene
test showed that oxygen was released in the singlet
form; 0.05 mol of anthraquinone was obtained.
assigned to the C O stretching vibrations in the
phenoxy group [comparison with the spectrum of an
authentic sample of (t-BuO)3TiOPh]. The similar band
is also present in the spectrum of the nonvolatile
residue from the reaction of III with Ph3SiOOH.
Diphenylsiloxane was isolated after hydrolysis of
compound C.
The stoichiometry of rearrangement (5) suggests
formation of equimolar amounts of Ph2EO and phen-
oxytitanium. However, actually the yield of phenol
was always considerably lower, and in some cases it
was not detected at all. We assumed further oxidation
of the phenoxy group. To check this assumption, we
performed oxidation of phenol with the system alco-
holate III t-BuOOH in a 1 : 1 : 2 ratio in benzene and
the reaction of specially synthesized (t-BuO)3TiOPh
with hydroperoxide I (1 : 1). The reaction mixtures
become dark brown, as in the reactions of III with
V VII. From the volatile fraction, we isolated 4.2
4.5 and 1.7 mol of t-BuOH, respectively, and from the
hydrolysis products of the nonvolatile residue, 0.40
0.45 mol of unchanged phenol in both cases. Hence,
more than 0.50 mol of phenoxy groups react with the
oxidants.
The formation of oxygen in the reaction of III with
VIII can be accounted for by scheme (1). The hydro-
peroxide is reduced to hydroxytriphenylgermane,
which subsequently reacts with the starting alcoholate
to form tri-tert-butoxytriphenylgermyloxytitanium [re-
actions (7) (9)]:
Ph3GeOOH + Ti(OBu-t)4
t-BuOH + Ph3GeOOTi(OBu-t)3,
(7)
To identify transformation products of the phenoxy
groups, the systems (t-BuO)4Ti PhOH t-BuOOH and
(t-BuO)4Ti Ph3SiOOH were studied by ESR and IR
spectroscopy. The ESR spectra of reaction mixtures
from reactions of phenol with the system III I, re-
corded in the presence of a spin trap (2-methyl-2-ni-
trosopropane), contained no signals from adducts of
alkoxy or phenoxy radicals. Hence, the peroxide bond
does not undergo homolysis. We detected a weak
unidentified signal of a complex structure, which
was apparently a superposition of signals from spin
adducts of several carbon-centered radicals. The IR
spectra of the hydrolysis products after steam distilla-
tion of phenol (dark brown viscous mass) contained
A
A + Ph3GeOOH
Ph3GeOTi(OBu-t)3 + Ph3GeOH + O2,
Ph3GeOH + Ti(OBu-t)4
(8)
(9)
Ph3GeOTi(OBu-t)3 + t-BuOH.
If reactions (7) (9) are the major pathway of the
reaction of Ph3GeOOH with III, t-BuOH should be
released in an amount of 1 mol. As will be shown
below, the subsequent transformations of titanium
triphenylgermyloxy derivative yield hexaphenylger-
manoxane and alcoholate III.
1
bands at 1055 1280 cm characteristic of stretching
vibrations of the Ph OH and C=C O C groups and
a broad band of OH stretching vibrations (3400 cm ).
We have not isolated pure any products of phenol
oxidation.
Thus, if there are no energetically favorable path-
ways for intramolecular decomposition of peroxides
A, their further reaction with hydroperoxides results
in the reduction of the hydroperoxides and release of
oxygen.
1
Thus, the reaction of (t-BuO)4Ti with hydroperox-
ides V VII involves formation of the corresponding
titanium-containing peroxides, which undergo a rear-
rangement, and decomposition of the alkoxy deriva-
Tables 1 and 2 show that the hydroperoxide reduc-
tion products R OH were detected both in the free
state and (to a greater extent) in the metal-bound
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 2 2006

240
STEPOVIK, GULENOVA
form. Special experiments showed that triphenylmeth-
anol, 2-phenylpropan-2-ol, and 1,1-diphenylethanol
enter exchange reactions with II and III. Under the
conditions of the hydrolysis and in the course of the
reactions, these alcohols are partially dehydrated to
alkenes. The reactions of the alkenes with the system
alcoholate III hydroperoxide IV or V account for the
presence of acetophenone and benzophenone, respec-
tively, in the reaction products [17].
at least a half of Ti was in the form of (BuO)2TiO.
In 12 h, we obtained an additional 0.49-mol crop of
D. The yield of 1-butanol in the volatile fraction
reached 2.5 mol.
Triphenylhydroxygermane
also reacts with
(BuO)4Ti or [(BuO)2TiO]x to form tetrakis(triphenyl-
germyloxy)titanium. However, this reaction is ex-
tremely slow and mainly occurs after the removal of
the major fraction of the solvent; 0.06 to 0.16 mol of
(Ph3GeO)4Ti (E) is formed.
The triphenylelement hydroxides formed by de-
composition of the titanium peroxy compounds react
further with metal alcoholates. The reaction pathway
depends on the structure of the alkoxy group. From
the reactions of (n-BuO)4Ti with Ph3EOOH (VII,
VIII), we isolated tetrakis(triphenylsiloxy)- and tetra-
kis(triphenylgermyloxy)titanium, respectively. It is
known [14, 18 20] that alcoholate II enters an ex-
change reaction with Ph3EOH to form (Ph3EO)4Ti:
The IR spectra of the isolated and independently
synthesized (Ph3SiO)4Ti samples are identical and
consistent with the published data [18, 21]. The spec-
tra of the (Ph3GeO)4Ti samples isolated from the
reaction of II with VIII and prepared by an independ-
ent synthesis are also identical and similar to the IR
spectrum of the Si derivative. The spectra contain
1
bands of the Ge Ph bonds (1100, 1440 cm ), and
1
also a very strong band at 835 cm and a medium-
(BuO)4Ti + 4Ph3EOH > (Ph3EO)4Ti + 4BuOH, (10)
1
intensity band at 870 cm . By analogy with the
D, E
spectrum of D [18], these bands can be assigned to
as(Ge O Ti) and as(Ti O Ge), respectively. We
found no published data on the IR spectra of E.
E = Si (D), Ge (E).
Variation of the reactant ratio does not lead to
formation of unsymmetrical triphenylsiloxyalkoxy
derivatives of titanium [20].
The reaction of (t-BuO)4Ti with VII yields mixed
alkoxy(siloxy) titanium derivatives; their hydrolysis
yields Ph3SiOH. In the reaction with VIII, up to
0.40 mol of (Ph3Ge)2O (isolated before hydrolysis) is
formed (Table 1). We assumed that Ph6Ge2O could
form by disproportionation of the mixed titanium
alcoholate by reactions (8) and (9) and by decom-
position of the disproportionation product [reactions
(12), (13)].
Compounds D and E are colorless finely crystalline
extremely thermostable substances moderately soluble
(especially D) in benzene. In the reaction under con-
sideration, (Ph3SiO)4Ti starts to form 25 30 min after
the start of the reaction, and its yield is 0.20 mol,
i.e., almost 0.80 mol of Ph3SiOH is bound to Ti.
However, Ph3SiOH is formed by decomposition of
the titanium-containing peroxy compound [reactions
(3), (4)], and in the process alcoholate II is removed
from the reaction sphere. Therefore, reaction (7) is
improbable.
2Ph3GeOTi(OBu-t)3
(Ph3GeO)2Ti(OBu-t)2 + Ti(OBu-t)4,
(Ph3GeO)2Ti(OBu-t)2
(12)
(13)
(Ph3Ge)2O + [(t-BuO)2TiO]x.
We assumed that compound D could form in the
last steps by the reaction of [(BuO)2TiO]x with
Ph3SiOH [Eq. (11)], as it is known that the Ti O Ti
bonds in titanoxanes are cleaved in the presence of
Ph3SiOH with the formation of tetrakis(triphenylsil-
oxy)titanium [20]:
Also, hexaphenyldigermanoxane and alcoholate III
can form by intermolecular condensation of the tita-
nium germyloxy compound followed by decomposi-
tion of titanoxane F by reactions (14) and (15):
2(t-BuO)3TiOGePh3
Ph6Ge2O + (t-BuO)3TiOTi(OBu-t)3,
(14)
(15)
[(BuO)2TiO]x + 4Ph3SiOH
F
(Ph3SiO)4Ti + 2BuOH + H2O.
(11)
F
(t-BuO)4Ti + [(t-BuO)2TiO]x.
Water can hydrolyze the BuO Ti bonds.
Formation of binuclear oxides by reaction (14) is
one of the pathways of decomposition of metal alkox-
ides [22]. Disproportionation of titanium compounds
to Ti(OR)4 was demonstrated by the example of hexa-
kis(trimethylsiloxy)titanoxane [23].
To check this hypothesis, the residue obtained by
the reaction of alcoholate II with hydroperoxide VII
after the separation of (Ph3SiO)4Ti was treated with
triphenylhydroxysilane. In so doing, we assumed that
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REACTIONS OF TITANIUM ALCOHOLATES Ti(OR)4 (R = n-Bu, t-Bu)
241
To confirm the occurrence of reactions (12) (15),
we performed the reaction of III with triphenylhy-
droxygermane in benzene (20 C) at a reactant ratio of
1 : 1 and obtained 0.46 mol of hexaphenyldigerman-
oxane and 1.09 mol of t-BuOH. Distillation of the
benzene solution after the separation of the germanox-
ane gave 0.42 mol of Ti(OBu-t)4. The reaction of III
with Ph3GeOH in a 1 : 16 ratio gave 4.0 mol of
t-BuOH and 2.24 mol of Ph6Ge2O; 10.87 mol of
Ph3GeOH remained unchanged. These results confirm
the lack of the catalytic effect of the titanium alco-
holate on the formation of hexaphenyldigermanoxane.
Hence, (triphenylgermyloxy)tri-tert-butoxytitanium is
unstable. Similar transformations (12) (15) occur in
the reaction of triphenylgermyl hydroperoxide with
alcoholate III.
authentic samples). The sorbent (Silpearl) was coarse-
porous silica gel on aluminum foil (Silufol UV-254);
eluent benzene or benzene diethyl ether, 9 : 1. The
amount of the released oxygen was determined from
the weight of benzoic acid formed by the reaction of
O2 with benzaldehyde [26]. The amount of hydroper-
oxides was determined by iodometric titration.
Titanium tetra-tert-butylate and tetrabutylate were
prepared by treatment of TiCl4 with the corresponding
butyl alcohol in the presence of NH3 [27]; Ti(OBu-t)4,
bp 82 83 C (2 mm Hg), nD20 1.4420 [14]; Ti(OBu-n)4,
bp 138 140 C (1 mm Hg), n2D0 1.4918 [14].
Ph3SiOOH was prepared from Ph3SiCl and 96%
hydrogen peroxide; mp 110 111 C [28]. Ph3GeOOH
was prepared similarly from Ph3GeBr; mp 136 C
[29]. 1-Hydroperoxy-1,1-diphenylethane and triphen-
ylmethyl hydroperoxide were prepared from the corre-
sponding alcohols by the reaction with 90% hydrogen
peroxide in the presence of concentrated sulfuric acid.
Ph2C(OOH)Me: colorless crystals (from petroleum
ether), mp 82 C [30]; Ph3COOH: pale yellow lustrous
crystals (from hexane), mp 83 84 C [30]. The activity
of all the peroxides synthesized was no less than
99.0%. The concentration of tert-butyl and cumyl
hydroperoxides used in the study was no less than
99.6 99.8%.
EXPERIMENTAL
The IR spectra were recorded on Specord IR-75
and Specord M-80 spectrophotometers (thin liquid
film between KBr windows). The ESR spectra were
taken on a Bruker ER-200D-SRC spectrometer
equipped with an ER-4105DR double cavity (operat-
ing frequency 9.5 GHz) and an ER-4111VT temper-
ature control unit. In determination of the g factors,
diphenylpicrylhydrazyl was used as reference. Chro-
matographic analysis of reaction products in the liquid
phase was performed with a Tsvet-2-65 chromato-
graph equipped with a flame ionization detector; the
carrier gas was Ar. High-boiling products (benzyl
alcohol, benzaldehyde, phenol, acetophenone, -meth-
ylstyrene, benzophenone, 2-phenylpropan-2-ol, 1,1-di-
phenylethanol, 1,1-diphenylethylene, etc.) were ana-
lyzed on a 1200 3-mm column (stationary phase
15% Reoplex-400 on Chromaton N-AW-DMCS, 100
230 C). Acetone, butanol, butanal, tert-butanol, and
tert-butyl hydroperoxide were analyzed on an LKhM-
80 chromatograph equipped with a 1200 3-mm col-
umn; carrier gas He, stationary phase 15% dinonyl
phthalate on Chromaton N-AW-DMCS, 40 80 C.
Titanium tetra-tert-butylate was analyzed on a 2400
3-mm column, stationary phase 15% Apieson L on
Chromaton N-AW-DMCS, 180 C. The chromato-
grams were treated by the method of external refer-
ence, with authentic samples used in each case. All
manipulations with the metal-containing compounds
were performed under dry deoxygenated argon.
Reactions of hydroperoxides with titanium alco-
holates (general procedure). Titanium alcoholate was
added to the hydroperoxide in benzene. The mixture
was kept at room temperature until the reaction for
peroxide became negative. The solvent and volatiles
were condensed in a trap cooled with liquid nitrogen.
The nonvolatile residue was hydrolyzed with 10%
sulfuric acid in ether; the reaction products were thor-
oughly extracted with ether. The volatile fractions and
ether hydrolyzates were analyzed by GLC. In aqueous
acidic hydrolyzates, t-BuOH [24] and metal were
determined (the metal, by precipitation as hydroxide
followed by calcination to TiO2).
Reaction of cumyl hydroperoxide IV with tita-
nium tetrabutylate, 2 : 1. A mixture of 0.58 g of
Ti(OBu)4 and 0.52 g of PhCMe2OOH in 9 ml of
benzene was kept at room temperature for 24 h; 16 ml
of O2 was released (normal conditions). The reaction
solution was bright yellow. In the condensate of
volatile reaction products, we found 0.056 g of
PrCHO, 0.27 g of BuOH, 0.12 g of PhCMe2OH, and
0.008 g of PhC(O)Me; formaldehyde was identified
qualitatively as 2,4-dinitrophenylhydrazone. The
residue was a light yellow resinous mass. In the ether
extract after the hydrolysis, we found 0.09 g of BuOH,
0.02 g of PrCHO, 0.28 g of PhCMe2OH, 0.014 g of
PhC(O)Me, and 0.01 g of PhC(Me)=CH2. The residue
The content of tert-butoxy groups was determined
by the Denig`es method [24], and the content of ali-
phatic acids in nonvolatile residues, according to [25].
Carbonyl compounds were identified in the form of
2,4-dinitrophenylhydrazones by the melting points
and by TLC (comparison of Rf values with those of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 2 2006

242
STEPOVIK, GULENOVA
from a parallel run was analyzed for formic and bu-
tyric acids [25]. The xylene solution after the titration
with alkali was separated, and the alkaline solution
was concentrated. The residue was acidified with
H2SO4, and the products were extracted with diethyl
ether. After the treatment with diazomethane, methyl
butyrate and methyl formate were identified. Found,
g: HCOOH 0.001 and PrCOOH 0.02.
In a parallel run, the residue after the separation of
triphenylmethyl peroxide and volatiles was steam-
distilled. From the bottoms, we isolated 0.33 g of
Ph3COH, mp 160 C.
Reaction of triphenylsilyl hydroperoxide VII
with titanium tetrabutylate, 1 : 1. To 0.38 g of
(BuO)4Ti in 7 ml of benzene, we added 0.32 g of
Ph3SiOOH. After mixing the components, the reaction
mixture became orange-red, and in 15 min a colorless
crystalline precipitate formed; the test for peroxy
compounds was negative. The mixture was allowed
to stand for 20 h for more complete precipitation. The
precipitate was filtered off and washed with small
portions of hexane. (Ph3SiO)4Ti was obtained; yield
0.23 g. Found, %: C 75.92; H 5.63; Si 9.58; Ti 4.42
[18]. C72H60O4Si4Ti. Calculated, %: C 75.26; H 5.23;
Si 9.76; Ti 4.17.
Reaction of titanium tetra-tert-butylate III with
1-hydroperoxy-1,1-diphenylethane V, 1 : 2. To a
solution of 0.73 g of Ph2(Me)COOH in 10 ml of
benzene, we added 0.58 g of (t-BuO)4Ti. Oxygen was
released. Within 1 min after mixing the components,
the mixture became lemon-yellow, and within 15 min,
red-brown. In the condensed solvent, we found 0.32 g
of tert-butyl alcohol and 0.02 g of acetophenone. The
residue was a dark brown mobile mass, which was hy-
drolyzed as described above. In the ether extract, we
determined chromatographically 0.11 g of t-BuOH,
0.31 g of Ph2C(OH)CH3, 0.028 g of PhC(O)CH3,
0.089 g of Ph2C=CH2, 0.009 g of Ph2C=O, and
0.016 g of PhOH. In the hydrolyzate, we found by
iodometric titration 0.09 g of unchanged Ph2(Me)
COOH. 1-Hydroperoxy-1,1-diphenylethane was iden-
tified by products of its acid decomposition [phenol
and PhC(O)Me] in the presence of p-toluenesulfonic
acid [31].
After the separation of (Ph3SiO)4Ti, in the con-
densed solvent we found chromatographically 0.12 g
of butyl alcohol and 0.02 g of butanal; propene was
identified qualitatively. On treatment of a part of the
condensate with 2,4-dinitrophenylhydrazine, we ob-
tained a precipitate of hydrazones (derived from buta-
nal and formaldehyde; TLC). The mixture of 2,4-di-
nitrophenylhydrazones was separated by column chro-
matography (silica gel, eluent benzene ether, 18 : 1).
2,4-Dinitrophenylhydrazones of butanal (mp 120 C)
and formaldehyde (mp 163 C) were isolated. The
melting points were consistent with the published
data. The presence of formaldehyde was also proved
by preparation of its dimedone derivative (mp 189 C).
Reaction of Ph3COOH (VI) with (BuO)4Ti, 1 : 1.
No oxygen evolution was observed on mixing 0.83 g
of triphenylmethyl hydroperoxide and 1.02 g of
Ti(OBu)4 in 10 ml of benzene. The test for peroxide
compounds became negative within 30 min. The
orange-red reaction solution was allowed to stand for
24 h; the crystalline precipitate was filtered off. It was
identified by elemental analysis as triphenylmethyl
peroxide. Found, %: C 87.96; H 5.86. C38H30O2.
Calculated, %: C 88.03; H 5.79. Yield 0.09 g; melting
point of the product and of its mixture with an authen-
tic sample 183 C.
The residue (colorless solid) was hydrolyzed with
10% H2SO4; the reaction products were extracted with
ether. In the ether extract, we found 0.12 g of 1-buta-
nol, 0.008 g of PhOH, and 0.048 g of butyric acid
[25]. The solvent was removed; in the dry residue we
found 0.08 g of Ph3SiOH and [Ph2SiO]n [32].
The color of the aqueous layer did not disappear
after extraction with ether but disappeared after treat-
ment with potassium permanganate, which suggests
the presence of readily oxidizable substances, proba-
bly phenol oxidation products.
In the volatile fraction of the filtrate, we found
0.28 g of BuOH and 0.06 g pf PrCHO. Along with
butanal, we also identified formaldehyde by TLC in
the form of 2,4-dinitrophenylhydrazone.
Quantitative determination of propene. The vola-
tiles from a separate experiment were condensed in
a trap that was preliminarily filled with HCl-saturated
benzene. After completion of the distillation, the
contents were thawed, allowed to stand for 1 h, and
washed with a dilute sodium carbonate solution to
remove excess HCl. The isopropyl chloride formed in
the process (0.05 g) was determined chromatographi-
cally.
The residue (yellow oily mass) was treated as
described above. In the ether extract, we found 0.38 g
of butanol, 0.04 g of butanal, 0.07 g of phenol, and
0.22 g of benzophenone (melting point of 2,4-dinitro-
phenylhydrazone and of the mixture with an authentic
sample 240 C).
In a separate experiment, we found 0.02 g of butyr-
ic acid and 0.002 g of formic acid (determined as
methyl esters [25]).
Reaction of triphenylgermyl hydroperoxide VIII
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REACTIONS OF TITANIUM ALCOHOLATES Ti(OR)4 (R = n-Bu, t-Bu)
243
with alcoholate II was performed similarly. From the
reaction of 0.43 g of Ph3GeOOH and 0.44 g of
Ti(OBu)4, we isolated 0.27 g of (Ph3GeO)4Ti. Color-
less crystalline substance; does not melt up to 360 C;
moderately soluble in benzene. Found, %: C 65.50;
H 4.64; Ge 21.89; Ti 3.83 [18]. C72H60Ge4O4Ti.
Calculated, %: C 65.16; H 4.53; Ge 21.87; Ti 3.61.
its mixture with an authentic sample of Ph6Ge2O had
mp 186 C. The filtrate was distilled under reduced
pressure, and 1.01 g of Ti(OBu-t)4 was recovered;
bp 73 C (1.5 mm Hg), n2D0 1.4420, which is consistent
with the published data [14].
In a parallel run, in the volatile fraction of the re-
action products we determined chromatographically
0.54 g of t-BuOH.
Reaction of Ph3GeOOH (VIII) with (t-BuO)4Ti,
1 : 1. To 0.58 g of (t-BuO)4Ti in 15 ml of benzene,
we added 0.59 g of Ph3GeOOH. Immediately after
mixing the components, the reaction mixture became
lemon-yellow, and oxygen evolved (12.5 ml, normal
conditions). The test for peroxide oxygen became
negative within 15 min. The crystalline precipitate
was filtered off; its mixture with an authentic sample
of Ph6Ge2O showed no melting point depression
(mp 185 C). Yield of Ph6Ge2O (before hydrolysis)
0.42 g. In the condensate of the volatile fraction, we
found 0.11 g of tert-butyl alcohol and 0.27 g of titani-
um tetra-tert-butylate; an epoxide was detected quali-
tatively [33]. By treatment of a part of the condensate
with BF3 Et2O, the epoxide was isomerized into a
carbonyl compound [34], which was identified in the
form of 2,4-dinitrophenylhydrazone. This hydrazone
(derived from isobutyraldehyde; mp 186 C) was iso-
lated by column chromatography (silica gel, eluent
benzene ether, 18 : 1).
ACKNOWLEDGMENTS
The authors are grateful to V.K. Cherkasov for the
assistance in measuring the ESR spectra and for the
interest in the study.
The study was financially supported by the Compe-
titive Center for Basic Natural Science (project no.
A 04-2.11-1086).
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