System vanadium alkoxy compound-tert-butyl hydroperoxide-oxidant of hydrocarbon C-H bonds

Article abstract of DOI:10.1134/S1070363207070183

Vanadium alkoxy compounds [(t-BuO)₄V, (t-BuO)₃VO] react with tert-butyl hydroperoxide (C₆H₆, 20°C) to liberate oxygen, partly in the singlet form, and to form alkoxyl and peroxyl radicals via the intermediacy of vanadium peroxides and trioxide. These systems are capable of oxidizing hydrocarbon C-H bonds. The process is radical in nature and involves formation of carbon-centered radicals and their reaction with oxygen generated in the systems. Vanadium-containing peroxides, too, take part in the oxidation reaction.

Full text of DOI:10.1134/S1070363207070183

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 7, pp. 1254 1262.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
No. 7, pp. 1173 1181.
L.P. Stepovik, M.V. Gulenova, A.N. Tishkina, V.K. Cherkasov, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77,
System Vanadium Alkoxy Compound tert-Butyl
Hydroperoxide Oxidant of Hydrocarbon C H Bonds
a
a
b
b
L. P. Stepovik , M. V. Gulenova , A. N. Tishkina , and V. K. Cherkasov
a
Lobachevskii Nizhni Novgorod State University,
pr. Gagarina 23, Nizhni Novgorod, 603950 Russia
e-mail: gulmv@rambler.ru
b
Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, Nizhni Novgorod, Russia
Received February 5, 2007
Abstract Vanadium alkoxy compounds [(t-BuO) V, (t-BuO) VO] react with tert-butyl hydroperoxide
4
3
(
C H , 20 C) to liberate oxygen, partly in the singlet form, and to form alkoxyl and peroxyl radicals via the
6 6
intermediacy of vanadium peroxides and trioxide. These systems are capable of oxidizing hydrocarbon C H
bonds. The process is radical in nature and involves formation of carbon-centered radicals and their reaction
with oxygen generated in the systems. Vanadium-containing peroxides, too, take part in the oxidation reaction.
DOI: 10.1134/S1070363207070183
Vanadium compounds catalyze peroxide oxidation
of hydrocarbons. The decomposition of H O is acetic
alkoxides (RO) V with t-BuOOH involve formation
of alkoxyvanates in which the oxidation degree of
vanadium is +5 [10].
4
2
2
acid in the presence of V(V) complexes is accom-
panied by liberation of singlet oxygen [1]. The oxida-
tion of anthracene gives rise to anthraquinone in a
nearly quantitative yield. Acyclic and alkylaromatic
alkenes udergo oxidative cleavage into carbonyl
compounds under the action of the H O V(V)
The aim of the present work was to study reactions
of vanadium alcoholates [(t-BuO) V (I), (t-BuO) VO
4
3
(
II)] with tert-butyl hydroperoxide (III) in an inert
solvent (C H ) and also the oxidative ability of these
6
6
2
2
systems toward hydrocarbon C H bonds.
CH COOH system [2].
3
The reactions of vanadium alcoholates II and I
with t-BuOOH in benzene were performed in benzene
Systems on the basis of vanadium alkoxides and
tert-butyl hydroperoxide oxidize organic substrates in
at room temperature and (t-BuO) VO t-BuOOH and
3
aprotic solvents. In the presence of (t-BuO) VO,
3
(
t-BuO) V t-BuOOH ratios of 1:2 and 1:3, respec-
4
(
t-BuO) V, and V(O)(acac) , tert-butyl hydroperoxide
4 2
tively. In the latter case, 1 mol of t-BuOOH is
consumed to oxidize V(IV) to vanadyl V(V) by
scheme (1).
converts alkanes to isomeric ketones [3 5]. The yield
of the oxidation products depends on temperature, as
well as initial concentrations and ratio of hydroper-
oxide and vanadate [4, 5]. The function of oxidants
was initially believed to belong to vanadium-contain-
ing peroxides, but, in view of the fact that the decom-
position of t-BuOOH in the presence of V(O)(acac)2
is a homolytic process [6], a mechanism was proposed
involving a V(O)(acac)2 2t-BuOOH intermediate
complex and V(V) peroxides.
(t-BuO)4V + t-BuOOH
(t-BuO)3VOOBu-t
t-BuOH
I
III
(
t-BuO) V=O + t-BuO .
(1)
3
II
Vanadyl II was isolated individual (up to 0.50 mol),
and t-BuO radicals were detected by ESR as spin
adducts with 2-methyl-2-nitrosopropane (IV). The
yield of t-BuOH attains 1.4 mol, which is greater than
expected by reaction (1). Probably, tert-butoxyl
radicals abstract hydrogen from alcoholate alkoxy
groups and also partially disproportionate to form
alcohol and isobutylene oxide. The latter was iden-
tified as 2-methylpropanal after treatment with BF3
The reactions of aluminum [7, 8] and titanium tert-
butoxides [9] with t-BuOOH in benzene and chloro-
benzene at a 1:2 reactant ratio liberate 0.80 0.90 mol
of oxygen which oxidizes hydrocarbons to carbonyl
compounds, alcohols, and hydroperoxides, which the
participation of free radicals [7 9]. It should be noted
that Al and Ti in these reactions do not change their
oxidation degree, whereas the reactions of vanadium
Et O.
2
1254

SYSTEM VANADIUM ALKOXY COMPOUND tert-BUTYL HYDROPEROXIDE OXIDANT
1255
The reactions of vanadium compounds I and II
with t-BuOOH in benzene involve liberation of
oxygen (Table 1). The first stage is substitution of the
alkoxy group by the hydroperoxide tert-butylperoxy
group to give vanadyl peroxide A [3, 4] [scheme (2)].
Table 1. Products of the reaction of vanadium tert-butoxy
derivatives with t-BuOOH, (C H , 20 C, mol/mol
6
6
vanadium alcoholate)a
(t-BuO) V
(t-BuO) V=O
4
3
Reaction
products
(
t-BuO) VO + t-BuOOH
1: 3
1: 10
1: 2
3
t-BuOH + (t-BuO) V(O)OOBu-t.
(2)
Volatile reaction productsb
2
A
O2
t-BuOH
0.85
3.36
0.11
0.01
2.33
8.80
0.48
0.13
0.95
2.36
0.07
By analogy with the reactions of aluminum [7] and
titanium alcoholates [8], further reaction of peroxide
A with the second mole of hydroperoxide III provides
an unstable vanadium-containing trioxide
scheme (3)].
(
(
t-BuO)2
CH ) C=O
c
0.01
3
2
d
Hydrolysis products of nonvolatile residued
B
t-BuOH
2.56
0.16
2.24
0.12
2.17
0.09
[
H O
2
2
(
t-BuO) V(O)OOBu-t + t-BuOOH
2
a
b
Averaged results. Traces of PhOBu-t were also detected by
c
t-BuOH + (t-BuO) V(O)OOOBu-t.
(3)
TLC. 4-Methylpen-3-en-2-one was qualitatively identified
by TLC. One mol of vanadium was used in all experiments.
2
d
B
The latter predominantly decomposes, liberating
singlet oxygen and concurrently generating alkoxyl
and peroxyl radicals [scheme (4)].
vanadium-containing peroxyl radical (t-BuO) V(O)
OO [7, 9], since t-BuOO is not detected by ESR in
the absence of spin traps.
2
In the presence of a spin trap, C-phenyl-N-tert-
butylnitrone (V), the ESR spectra of the systems al-
coholate I, II t-BuOOH in benzene (Fig. 2) are a
superposition of a triplet signal and a triplet of doub-
lets with asymmetric lines. The triplet signal (1:1:1)
1
(
t-BuO) V=O + O ,
3
2
B
(t-BuO) V(O)OO + OBu-t,
(4)
3
(
t-BuO) V(O)O + OOBu-t.
2
is assignable, by its isotropic parameters [g 2.0069
and a ( N) 0.790 mT], to benzoyl-tert-butylnitroxyl
i
i
1
1
5
To fix and quantify O , we reacted compounds I
2
and II with t-BuOOH in the presence of typical
acceptors of singlet oxygen: anthracene and 9,10-di-
methylanthracene. The reactions of the systems I t-
BuOOH and II t-BuOOH with anthracene gave 0.80
(
a)
gi 2.0150
0
.50 mol of anthraquinone. The reaction in the system
I t-BuOOH 9,10-dimethylanthracene (1:3:1) gave
up to 0.45 0.50 mol of 9,10-dimethylepidioxyanthra-
1
cene which was isolated and characterized by H
NMR spectroscopy [CDCl , , ppm: 1.48 s (3H), 7.2
and 7.4 (both m, AA BB , 2H)] [11].
3
H
0
.5 mT
Evidence for the homolytic nature of the decom-
position of trioxide B was obtained by ESR spec-
troscopy. No addition of t-BuOOH to a benzene solu-
(
b)
gi 2.0150
tion of V(OBu-t) (20 C) in the absence of spin traps,
4
the signal characteristic of V(IV) disappears, and a
very broad singlet appears. A more clear picture was
obtained at reduced temperature in toluene. Five
minutes after the reagents had been mixed at 70 C,
the ESR signal looked like a singlet assigned, based
H
0
.5 mT
Fig. 1. ESR spectrum in the absence of spin traps.
(a) (t-BuO) V t-BuOOH (1:3), 5 min after reagent
of g 2.015, to a peroxyl radical [12, 13] (Fig. 1a).
i
4
A singlet with the same g factor was also detected in
the system (t-BuO) VO t-BuOOH (C H , 20 C)
mixing {toluene, 70 C, c [V(OBu-t) ] 0.15 M}.
4
(b) (t-BuO) VO t-BuOOH (1:2) 5 min after reagent
3
6
6
3
(
Fig. 1b). Most probably, this signal belongs to a
mixing [benzene, 20 C, c (t-BuO) VO 0.20 M].
3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 7 2007

1256
STEPOVIK et al.
oxygen [2]. tert-Butoxyl radical was registered as spin
adduct 3 with 2-methyl-2-nitrosopropane (IV) [t-
1
1
2
1
15
2
BuN(O )OBu-t (3), g 2.0055, a ( N) 2.715 mT] [7].
2
i i
2
2 2
Thus, the systems V(OBu-t) t-BuOOH and
4
(
t-BuO) VO t-BuOOH generate oxygen during de-
3
composition of the vanadium-containing trioxide and
are similar in this respect to systems on the basis of
aluminum and titanium tert-butoxides.
H
0
.5 T
Razuvaev and co-workers [4, 5] suggested mole-
cular reactions of hydrocarbons with vanadium com-
pounds containing a VOOR group for performing
conversions of alkanes under the action vanadium
alcoholate hydroperoxide systems. However, the
schemes of C H oxidation were not detalized. It was
Fig. 2. ESR spectrum of the system (t-BuO) VO t-BuOOH
3
(
1:2) in benzene in the presence of C-phenyl-N-tert-
butylnitrone (V), 20 C, measured 10 min after reagent
mixing and degassing. Figures over the lines relate to
the numbers of radical species.
shown that the oxidation in M(OBu-t) t-BuOOH
n
radical 1 by oxidation of the spin trap with either
singlet oxygen or peroxyl radicals [7, 14]. Nitroxyl 2
systems (M = Al, n = 3; M = Ti, n = 4) is homolytic
in nature, which was evidenced by the identification
of carbon-centered and their corresponding peroxyl
radicals.
1
5
[
g 2.0059, a ( N) 1.325 mT, a (H) 0.120 mT] cab be
i i i
an adduct of spin trap V with t-BuOO or (t-BuO)2
V(O)OO , or their superposition [7, 15].
We studied the reactions of (t-BuO) V t-BuOOH
4
X
and (t-BuO) VO t-BuOOH with hydrocarbons
3
Ph C N Bu-t Ph C N Bu-t
containing primary, secondary, and tertiary C H
bonds (hexane, toluene, ethylbenzene, triphenyl-
methane). The standard was ethylbenzene. The work-
ing concentrations of vanadium alcoholates were 0.1
O O
H O
1
2
0
.3 M. The principal oxidation products were 1-phe-
X = (t-BuO) V(O)OO, t-BuOO.
nylethyl hydroperoxide (VI), acetophenone, and
2
1
-phenylethan-1-ol (Table 2).
The intensity of the peroxyl signal (Fig. 1b) does
not decrease over the course of 1.5 2 h, implying that
the species is generated with time. After degassing of
the reaction solutions, the signal did not get narrower.
This is accounted for by an effect of the liberated
The oxidation of ethylbenzene was studied by ESR
spectroscopy. 2-Methyl-2-nitrosopropane was added
to a solution of alcoholate II hydroperoxide III in
PhEt (20 C), and an ESR spectrum was measured
immediately after mixing. The spectrum contained a
triplet of doublets with the following HFC constants:
Table 2. Products of the reaction of ethylbenzene with the
15
a ( N) 1.496 mT, a (H ) 0.378 mT, a [H(CH )]
i
i
i
3
systems vanadium alkoxy compound tert-butyl hydro-
peroxide, 20 C (moles per mole metal alcoholate) a
0.048 mT, and g 2.0062. The spectrum was assigned
i
to an adduct of the -phenylethyl radical with spin
trap IV: PhCH(Me)N(O )Bu-t (4) [16]. A signal with
the same parameters is also observed in the spectrum
of the system (t-BuO) V t-BuOOH. Additionally, an
adduct of the tert-butoxyl radical was found [g
(
t-BuO) V
(t-BuO) V=O
3
4
Reaction
products
4
1
1
2
1
2
i
1
5
t-BuOHb
2.0055, a ( N) 2.720 mT] (Fig. 3). It should be noted
i
3.49
3.15
5.02
0.80
1.85
0.53
1.40
2.31 3.71
0.20 0.65
0.27 1.09
0.11 0.33
0.02 1.01
b
that consecutive measurements of spectra within
10 min showed an increasing signal of the tert-
butoxyl radical, whose intensity reached that of the
-phenylethyl radical and remained unchanged for at
least 40 min (Fig. 4). These findings provide evidence
for a radical mechanism of the reaction of the system
with substrates and for release of carbon-centered
radicals from the solvent cage.
Me CO
2
b
PhC(O)Me
PhCH(OH)Me
PhCH(OOH)Me
0.50
0.07
0.30
0.74
traces
0.16
c
c
a
Averaged results. (1) Under argon; (1 ) in the presence of
powdered molecular sieves (4 , calcined at 300 C in a
b
vacuum for 8 h); (2) under oxygen. In the volatile fraction.
c
Acetaldehyde was quantitatively identified. Among products
Let us consider the possible ways of formation of
the compounds listed in Table 2. Oxygencentered
of hydrolysis of the nonvolatile residue.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 7 2007

SYSTEM VANADIUM ALKOXY COMPOUND tert-BUTYL HYDROPEROXIDE OXIDANT
1257
radicals [scheme (4)] can abstract hydrogen from the
methylene group and initiate oxidation of the hydro-
carbon. The radicals that form react with oxygen
generated by the systems to give the peroxyl radicals
PhCH(Me)OO which undergo further transformations
(a)
4
4
4
4
4
4
3
3
3
[scheme (5)].
PhCH Me + RO
PhCHMe
2
ROH
O2
(
5)
PhCH(OO )Me,
H
R = t-Bu, t-BuO, (t-BuO) V, (t-BuO) VO.
0.5 T
3
2
(
b)
As follows from Table 2, the product yields in the
reaction in the system (t-BuO) VO t-BuOOH (1:2) is
3
less than half that in the reaction in the system
(
t-BuO) V t-BuOOH (1:3). The strongest difference
4
is in the yield of hydroperoxide VI. In our opinion,
this can be explained by the fact that in the latter case
the quantity of alkoxyl radicals, specifically tert-
butoxyl, capable of abstracting hydrogen from ethyl-
benzene is much greater than in the system (t-BuO)3
VO t-BuOOH [scheme (1)].
H
0
.5 T
Fig. 3. (a) ESR spectrum of the system (t-BuO) V
4
t-BuOOH (1:3) in ethylbenzene, measured immediately
after reagent mixing [in the presence of 2-methyl-2-
nitrosopropane (IV), 20 C]; (3) signals of the adduct
with the tert-butoxyl radical, (4) signal of the adduct
with the -phenylethyl radical. (b) Methyl hydrogen
splitiing.
Evidence for scheme (5) was obtained from the
results of the oxidation of ethylbenzene with oxygen,
initiated by di-tert-butyl peroxalate (50 C, 2 h). We
isolated (per 1 mol of peroxalate): 1.15 mol of hydro-
peroxide VI, 0.8 mol of acetophenone, 0.94 mol of
4
3
4
1
-phenylethan-1-ol, 2 mol of CO , and 1.50 mol of
3
4
4
3
2
4
4
t-BuOH. The close quantities of ketone and alcohol
suggest formation of the alkylperoxyl radicals
PhCH(Me)OO and their disproportionation to alcohol
and ketone by the Russell scheme (6) [17].
2
PhCH(Me)OO
PhC(O)Me
H
0
.5 T
+
PhCH(OH)Me + O2.
(6)
Fig. 4. ESR spectrum of the system (t-BuO) V
t-BuOOH (1:3) in ethylbenzene, 30 min after reagent
mixing [in the presence of 2-methyl-2-nitrosopropane
4
The yield of products of the oxidation of ethyl-
benzene with the systems (t-BuO) V t-BuOOH and
4
(
t-BuO) V t-BuOOH under oxygen after 3 4 h at
3
(
IV), 20 C].
room temperature (Table 2, exp. no. 2) reaches
4 mol [per 1 mol of (t-BuO) V] in the first case and
3
4
the termination of the oxidation of ethylbenzene with
the systems in hand.
is no more than 2.5 mol in the second, and then
remains almost invariable with time. We found 0.50
The above experiments provide evidence to show
that the oxidation is initiated by radicals generated by
decomposition of peroxytrioxide B. It should be noted
that the gain in the quantity of ketones on the oxida-
tion of alkanes with vanadium alcoholate hydroper-
oxide systems in the presence of oxygen was reported
earlier by Spirina et al. [4]. However, the referees
gave no explanation for this phenomenon.
0
.70 mol of PhCH(OH)CH , 1.40 1.90 mol of
3
PhC(O)CH , and 1 2 mol of hydroperoxide VI. The
3
latter was identified by its reaction with triphenyl-
phosphine: The reaction gave triphenylphosphine
oxide, and the gain in the quantity of t-BuOH cor-
responded to the quantity of the hydroperoxide. In the
reactions in an oxygen atmosphere, the content of
t-BuOH in the volatile fraction was as high as 5.0
5
.5 mol, which implies decomposition of vanadium
Along with disproportionation and hydrogen ab-
straction reactions, alkylperoxyl radicals can
alcoholates. The latter fact is probably responsible for
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 7 2007

1258
STEPOVIK et al.
undergo homolytic SR2 substitution to form peroxide
C. This compound can also be formed by an exchange
reaction between hydroperoxide VI and the tert-
butoxy group on metal [scheme (7)].
systems that in the latter case the quantity of aceto-
phenone is always greater compared to alcohol, and
in certain cases alcohol was not detected at all. This
can be explained by the fact that ketone is formed by
several routes [schemes (6) and (8)], and also by
partial oxidation of alcohol. The systems alcoholate I,
II hydroperoxide III oxidize 1-phenylethan-1-ol
(C H , 20 C). Successive treatment of V(OBu-t) with
PhCH(OO )Me + t-Bu(O)V<
t-BuO
>
V(O)OOCH(Me)Ph (7)
6
6
4
C
alcohol and hydroperoxide III (1:1:1) gives 0.50
0.60 mol of acetophenone and 2.46 2.60 mol of
t-BuOH. The conversion of 1-phenylethan-1-ol is
PhCH(OOH)Me + t-Bu(O)V<
t-BuOH
VI
5
0 65%. No radicals were detected by ESR. We
Peroxide C is involved in the formation of the final
products of the oxidation of ethylbenzene. The quan-
tities of hydroperoxide after hydrolysis of the reaction
mixtures or nonvolatile residues (Table 2) correspond
to its quantities in the postreaction mixtures. However,
if the reaction solution is kept for 10 12 h at room
temperature, peroxide C decomposes. A dark green
precipitate forms, whose IR spectrum contains the
suppose that the prevailing reaction route is formation
and decomposition of V(IV) peroxide rather than
oxidation of alcoholate I to vanadyl [Scheme (9)].
(
t-BuO) V + PhCH(OH)Me + t-BuOOH
4
2
t-BuOH + {(t-BuO) V[OCH(Ph)Me]OOBu-t}
2
t-BuOH + PhCOMe + (t-BuO) VO.
(9)
1
2
following bands, , cm : 1631 (carboxylate ion),
1
004 (V=O), and 762 (V O) [18], as well as a very
Along with the above routes of the reactions of the
alcoholate I, II hydroperoxide III oxidative systems
with alkylarene C H bonds, the possibility exists of
formation of carbon-centered and hydroperoxyl ra-
dicals under the action of oxygen on C H bonds.
These radicals can react with each other to form hyd-
roperoxide or, via oxidation of the -phenylethyl
radical, acetophenone and water which can hydrolyze
V OBu-t bonds [scheme (10)].
1
strong broad at 3418 cm , assigned to stretching
vibrations of the hydroxyl group (V OH). The spec-
trum shows no bands characteristic of t-BuO groups.
Peroxide C decomposes along two routes [scheme
(8)].
C
a
b
PhCH Me + O2
[PhCHMe + OOH]
2
>
V(O)OH + PhC(O)Me >V(O)OCH(Me)OPh (8)
a
PhCH(OOH)Me,
PhCOMe +H O.
(
10)
b
2
>
V(O)OPh + CH CHO
3
However, as known, the oxidation of hydrocarbons
with oxygen to hydroperoxide by scheme (10a) pre-
dominantly occurs in the gas phase [20]. The reaction
The first route a leads to ketone and the second b
involves rearrangement with subsequent decomposi-
tion of alkoxy compound to acetaldehyde and
phenoxyvanadium. Acetaldehyde was identified as
,4-dinitrophenylhydrazone and phenol, as 2,4,6-tri-
bromophenol. Acetaldehyde is partially oxidized to
acetic acid. The formation of phenol and acetaldehyde,
of t-BuOOH with (t-BuO) V in the presence of water
4
acceptor (molecular sieves) gives the same quanti-
tative yield of oxidation products (Table 2, exp.
no. 1 ). Consequently, reaction (10) in the systems in
hand is unlikely.
2
along with acetophenone and PhCH(OH)CH , was
earlier observed [19] in the nickel acetylacetonate-
catalyzed oxidation of ethylbenzene with oxygen at
3
Other hydrocarbons containing primary, secondary,
or tertiary C H bonds can follow the same transforma-
tion routes as ethylbenzene. Methyl oxidation was
observed in toluene only. Benzaldehyde, 0.26 mol,
was found in the volatile fraction and 0.53 mol of
benzoic acid and traces of benzyl alcohol in products
of hydrolysis of the nonvolatile residue. Upon the
1
20 C. The largest quantities of PhOH and CH CHO
3
were found in the decomposition of hydroperoxide VI
at the same temperature but in an inert atmosphere.
A radical mechanism of this process was suggested
[19].
oxidation of hexane by the system (t-BuO) V t-
4
It is seen from of the results of the oxidation of
ethylbenzene in the presence of di-tert-butyl per-
oxalate and vanadium alkoxy compound t-BuOOH
BuOOH (1:3), in the volatile fraction we found
t-BuOH (3.11 mol per 1 mol of vanadium alcoholate),
hexan-2-one (0.10), and hexan-3-one (0.10), and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 7 2007

SYSTEM VANADIUM ALKOXY COMPOUND tert-BUTYL HYDROPEROXIDE OXIDANT
1259
hydrolysis of the nonvolatile residue gave t-BuOH
1.72), hexan-2-one (0.02), hexan-3-one (0.11),
hexan-2-ol (0.04), and hexan-3-ol (0.06). In addition,
a small quantity of a mixture of carboxylic acids was
found, implying destructive oxidation of hexanones,
as well as ketone condensation products.
3-mm column packed with 15% Reoplex-400, 90
180 C. The chromatograms were treated by the ex-
ternal reference technique.
(
All operations with vanadium-containing alkoxy
compounds were performed under dry oxygen-free
argon.
Upon the reaction of the system with triphenyl-
methane (1:3:1) we found 3.39 mol of t-BuOH,
The number of tert-butoxy groups was determined
by the Deniges method [22] and aliphatic acids in
nonvolatile residues were determined by the procedure
in [23]. Carboxylic acids were identified as methyl
esters after treatment with diazomethane [24]. Car-
bonyl compounds were determined as 2,4-dinitro-
phenylhydrazones by TCL on Silufol UV-254 plates
0
0
.20 mol of Ph COOH and its conversion products:
3
.13 mol of Ph CO and 0.03 mol of PhOH. The latter
2
undergoes oxidation under the reaction conditions.
The starting triphenylmethane, 0.55 mol, was also
isolated.
(
eluent benzene or benzene diethyl ether, 9:1). Cer-
Consequently, the yield of oxidation products and
the conversion of substrates depend on the structure
of the latter. The highest values are characteristic of
ethylbenzene and the lowest with triphenylmethane.
This is explained both by the reactivity of C H bonds
in alkylarenes and their corresponding peroxyl
radicals and by steric factors [21].
tain hydrazones were isolated individual and charac-
terized by melting points. The quantity of released
oxygen was determined by the weight of benzoic acid
formed by the reaction of O with benzaldehyde [25].
Analysis for vanadium was performed by oxidimetry
2
[26].
Vanadium tetra-tert-butoxide (I) was synthesized
EXPERIMENTAL
by an exchange reaction of vanadium trichloride and
lithium tert-butoxide (1:2) in hexane, followed by
refluxing for 2 h. After removal of the solvent and
The IR spectra were measured on a Specord IR-75
instrument (liquid film between KBr windows). The
ESR spectra were taken on a Bruker ER-200D-SRC
instrument equipped with an ER 4105DR double
resonator (working frequency 9.5 GHz) and an ER
distillation, V(OBu-t) was isolated as a dark blue
4
liquid highly sensitive to oxygen and moisture, bp
89 90 C (1 mm Hg) [27].
Tri-tert-butoxyvanadyl (II) was prepared by the
4
111VT temperature control unit. The g factors were
reaction of lithium tert-butoxide with VOCl , mp 97
3
determined using diphenyl picryl hydrazyl (DPPH) as
reference. Analysis was performed in an ESR cell.
Reaction solutions were degassed for better resolution
and removal of oxygen released on reactions of I, II,
and III. Spin traps IV and V were added at the initial
reaction stages.
9
[
8 C (2 mm Hg); colorless crystals, mp 47 48 C
28]. The concentration of tert-butyl hydroperoxide
used in the work was no less than 99.6 99.8%.
Reaction of vanadium tetra-tert-butoxide with
tert-butyl hydroperoxide (1:1) in benzene, 20 C. To
0
.32 g of (t-BuO) V in 5 ml of benzene, 0.08 g of
4
Chromatographic analysis of reaction products in
the liquid phase was performed on a Tsvet-2-65
instrument with FID, carrier gas argon, adsorbent
Chromaton N-AW-DMCS. Volatile components
t-BuOOH was added. Immediately after the reagents
had been mixed, the reaction solution got bright red
and then yellow. Benzene and volatile products were
removed into a trap cooled with liquid nitrogen. In the
volatile fraction we found 0.09 g of tert-butanol. The
condensate gave positive reactions on the oxirane ring
(
acetone, tert-butanol, tert-butyl hydroperoxide) were
analyzed on a 2400 3-mm column packed with 10%
PEGA on a TZKM brick, temperature 55 80 C. High-
boiling products (benzaldehyde, acetophenone, benzo-
phenone, phenol, 1-phenylethan-1-ol, styrene, etc.)
were analyzed on a 3000 3-mm column packed with
(with iodonic acid [29] and with pyridine under
heating [30]).
Tri-tert-butoxyvanadyl was isolated using a device
constructed of two ampules sealed together (H-shaped
device). One of the ampules was preliminarily sealed.
The residue after removal of the solvent and volatile
reaction products (colorless crystals in a yellow terry
material) was dissolved in 3 ml of benzene, and the
solution was placed to the second ampule of the
device. The device was degassed. Benzene was re-
moved at 20 C at reduced pressure, and the knee of
5
%
SE-30 on Inerton-AW, 100 190 C. tert-
Butyl peroxide in benzene was analyzed on a 3000
-mm column packed with 5% SP-2401 on Chroma-
3
ton N-AW-DMCS, 50 C. Anthracene, 9,10-dimethyl-
anthracene, and anthraquinone were analyzed on a
3
000 3-mm column packed with 5% OV-15 on Iner-
ton Super, 180 210 C. Hexan-2- and -3-ones and
hexan-2- and -3-ols were determined on a 1200
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 7 2007

1260
STEPOVIK et al.
the ampule with its content was sealed. When the
residue was heated, tri-tert-butoxyvanadyl sublimed
in the first ampule, yield 0.12 g, mp 47 C [28].
and 0.01 g of 1-phenylethan-1-ol. Part of the distilled
solvent was treated with 2,4-dinitrophenylhydrazine.
The precipitate of 2,4-dinitrophenylhydrazones (ace-
tophenone, acetone, and acetaldehyde) was analyzed
by TLC, eluent petroleum ether ethanol, 18:1. The
residue, a dark orange mobile liquid, was dissolved in
diethyl ether and treated with 10% H SO . The ether
In a parallel experiment, the residue after removal
of volatile components was dissoled in diethyl ether,
treated with 10% sulfuric acid, extracted with small
portions of diethyl ether, and dried over Na SO .
2
4
2
4
extract contained 0.36 g of t-BuOH, 0.02 g of
PhCH(OH)Me, 0.05 g of PhC(O)Me, and 0.007 g of
According to chromatography, the ether extract con-
tained 0.16 g of t-BuOH. The aqueous acid hydro-
lysate contained 0.05 g of t-BuOH.
PhCH=CH . Phenol and tert-butyl hydroperoxide
2
were not found in the reaction products. By iodo-
metric titration, 0.09 g of PhCH(Me)OOH was found.
To identify the latter, the residue of hydrolysis
products was dissolved in benzene and heated in the
presence of a catalytic amount of p-toluenesulfonic
acid at 60 C for 3 h [24]. Phenol, 0.04 g, was found
by chromatography. The formation of this product
suggests presence of PhCH(Me)OOH. The aqueous
layer was analyzed for t-BuO groups (0.06 g) by the
Deniges method.
Reaction of vanadium tetra-tert-butylate with
tert-butyl hydroperoxide (1:3) in benzene, 20 C.
To 0.62 g of V(OBu-t) in 10 ml of benzene, 0.49 g
4
of t-BuOOH was added (room temperature), hydrogen
evolution was observed. The reaction solution got
intensively yellow. A day after, benzene and volatile
reaction products were removed at 20 C at reduced
pressure. On treatment of part of the condensate with
2
4
,4-dinitrophenylhydrazine hydrazones of acetone and
-methylpent-3-en-2-one precipitated (TLC). In the
Reaction of ethylbenzene with the system
volatile fraction, 0.45 g of t-BuOH, 0.001 g of acetone,
.029 g of (t-BuO) , and traces of PhOBu-t were
V(OBu-t) t-BuOOH under oxygen. A solution of
4
0
2
1
.38 g of V(OBu-t) in 40 ml of ethylbenzene satur-
4
found, and isobutylene oxide was qualitatively
detected [30, 31]. The latter was identified as 2-me-
thylpropanal 2,4-dinitrophenylhydrazone after treat-
ated with oxygen. The solution remained blue-colored.
When 1.08 g of t-BuOOH was added, the solution
first got orange and then yellow. Dry oxygen was
slowly bubbled through the solution for 4 h and then
it was divided into halves. The first half was hydro-
lyzed with 10% H SO and extracted with benzene.
ment with the benzene solution with BF etherate
3
[
31]. 2-Methylpropanal hydrazone was isolated by
column chromatography (adsorbent Silicagel-60,
.060 0.20 mm, eluent benzene diethyl ether, 18:1),
mp 182 C.
2
4
0
The extract contained 0.82 g of acetophenone and
.25 g of 1-phenylethan-1-ol. The solution was then
0
heated at 45 C in the presence of a catalytic amount
of p-toluenesulfonic acid. Acetaldehyde was simul-
taneously distilled into a trap with 2,4-dintrophenyl-
hydrazine (2,4-dintrophenylhydrazone, mp 167 C).
The residue contained 0.56 g of phenol.
The residue, a dark yellow tarry material was hydro-
lyzed with 10% H SO and extracted with ether. In
the ether extract, 0.30 g of t-BuOH was found. In the
aqueous acid layer, 0.04 g of tert-butanol [22] and
2
4
0.01 g of hydrogen peroxide were found; the latter
was identified by the procedure in [32].
Triphenylphosphine, 0.50 g, was added to the
second half. Heat release was observed. After hydro-
lysis, chromatographic monitoring showed an increas-
ing content of tert-butanol (up to 0.63 g) at invariable
content of acetophenone. Ethylbenzene was removed,
the residue was dissolved in methanol, and the solu-
For quantitative determination of the released
oxygen, the parallel reaction was performed in an
evacuated H-shaped ampule. Benzaldehyde, 0.35 g,
was placed in one knee of the ampule (the starting
reagent ratio is the same as above). Benzoic acid,
tion was poured into water to isolate 0.53 g of Ph PO,
3
0
.35 g [1.60 mol per 1 mol of V(OBu-t) ] was found,
4
mp 154 C. Mixed sample gave no melting point
depression.
which corresponds to 0.046 g of O (0.80 mol per
2
1
mol of the starting vanadium alcoholate).
The reactions with of p-toluenesulfonic acid and
Oxidation of ethylbenzene with the system
Ph P showed that the oxidation of ethylbenzene gave,
3
V(OBu-t) t-BuOOH (1:1:3). A mixture of 0.63 g
4
along with tert-butanol and acetophenone, no less than
.72 g of 1-phenylethyl hydroperoxide.
of V(OBu-t) in 10 ml of benzene with 0.50 g of t-
4
0
BuOOH in 5 ml of ethylbenzene was prepared. No
oxygen liberation was observed. After 20 h (20 C)
the solvent and volatile compounds were condensed
in a trap cooled with liquid nitrogen. The condensate
contained 0.34 g of t-BuOH, 0.05 g of acetophenone,
In a separate experiment, the reaction solution was
let to stand until peroxy compounds disappeared
completely (12 h, 20 C); therewith, a dark green
precipitate formed. The solvent and volatile com-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 7 2007

SYSTEM VANADIUM ALKOXY COMPOUND tert-BUTYL HYDROPEROXIDE OXIDANT
1261
ponents were removed at reduced pressure at room
temperature. The volatile fraction contained t-BuOH
and acetophenone. After hydrolysis of the residue,
phenol and 1-phenylethan-1-ol were found.
Cherkasov, V.K., Izv. Akad. Nauk SSSR, Ser. Khim.,
2002, no. 4, p. 590.
8
. Martynova, I.M., Stepovik, L.P., and Dodonov, V.A.,
Zh. Obshch. Khim., 2001, vol. 71, no. 5, p. 785.
Oxidation of 1-phenylethan-1-ol with the system
9. Stepovik, L.P., Gulenova, M.V., and Martynova, I.M.,
(
1
1
t-BuO) V t-BuOOH (1:1:1), C H . 1-Phenylethan-
Zh. Obshch. Khim., 2005, vol. 75, no. 4, p. 545.
4
6
6
-ol, 0.22 g, was added to 0.63 g of (t-BuO) V in
0 ml of benzene. The solution changed from bright
10. Alyasov, V.N., Korneva, S.P., Vyshinskaya, L.I.,
Maslennikov, V.P., Aleksandrov, Yu.A., and Razu-
vaev, G.A., Zh. Obshch. Khim., 1984, vol. 54, no. 8,
p. 1837.
4
blue to dark blue. Hydroperoxide III, 0.16 g, was
added. Heat release was observed, and the solution
got yellowish orange.
1
1. Gekhman, A.E., Stolarov, I.P., Moiseeva, N.I., Ru-
baijlo, V.L., Vargaftik, M.N., and Moiseev, I.I., Inorg.
Chim. Acta, 1998, vols. 275 276, p. 453.
The condensed solvent contained 0.34 g of t-BuOH
and 0.11 g of acetophenone. The condensate was
treated with a solution of 2,4-dinitrophenylhydrazine
to isolate acetophenone 2,4-dinitrophenylhydrazone,
mp 246 247 C. Mixed sample gave no melting point
depression. The residue, a thick brownish-green
material, was dissolved in ether, hydrolyzed with 10%
H SO , and extracted with ether. The extract con-
12. Milas, N.A. and Plesnicar, B., J. Am. Chem. Soc.,
1983, vol. 105, no. 5, p. 1498.
1
1
3. Bersohn, M. and Thomas, J.R., J. Am. Chem. Soc.,
964, vol. 86, no. 5, p. 959.
1
4. Zubarev, V.E., Metod spinovykh lovushek. Primenenie
v khimii, biologii, meditsine (Method of Spin Traps.
Application in Chemistry, Biology, and Medicine),
Moscow: Mosk. Gos. Univ., 1984.
2
4
tained 0.15 g of tert-butanol, 0.03 g of acetophenone,
and 0.08 g of the starting alcohol. The aqueous acid
hydrolysate contained 0.10 g of tert-butanol.
1
1
1
1
5. Merritt, M.V. and Johnson, R.A., J. Am. Chem. Soc.,
1977, vol. 99, no. 11, p. 3713.
6. Janzen, E.G. and Blackburn, V., J. Am. Chem. Soc.,
The reactions of the other hydrocarbons with the
systems vanadium alcoholate I, II tert-butyl hydro-
peroxide and analysis of the reaction products were
performed in a similar way.
1
969, vol. 91, no. 16, p. 4481.
7. Howard, J.A. and Ingold, K.U., J. Am. Chem. Soc.,
968, vol. 90, no. 4, p. 1056.
1
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