Oxidizing properties of the tert-butyl hydroperoxide-tetra-tert- butoxychromium system

Article abstract of DOI:10.1134/S1070363213110066

tert-Butyl hydroperoxide reacts with the tetra-tert-butoxychromium by oxidizing the latter to chromyl CrV=O (C₆H₆, 20 C). At t-BuOOH-Cr(OBu-t)₄ ratio of 2: 1 or higher, oxygen is released. The occuring processes include the formation of chromium-containing peroxides and peroxytrioxydes. The t-BuOOH-Cr(OBu-t)₄ system oxidizes aromatic hydrocarbons of various structures (anthracene, 9,10-dimethylanthracene, 1,1-diphenylethylene, alkylarenes), as well as primary and secondary alcohols. Depending on the structure of the substrate, the oxidants are: in situ generated oxygen including that in the singlet state, peroxy radicals, or chromium-containing peroxides.

Full text of DOI:10.1134/S1070363213110066

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 11, pp. 2005–2017. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © L.P. Stepovik, A.Yu. Potkina, A.I. Poddelskii, 2013, published in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 11, pp. 1805–1818.
Oxidizing Properties
of the tert-Butyl Hydroperoxide–tetra-tert-Butoxychromium
System
L. P. Stepovika, A. Yu. Potkinaa, and A. I. Poddelskiib
a Lobachevsky Nizhni Novgorod State University, ul. Gagarina 23, Nizhni Novgorod, 603950 Russia
e-mail: lstepovik@mail.ru
b Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, Nizhni Novgorod, Russia
Received November 19, 2012
Abstract—tert-Butyl hydroperoxide reacts with the tetra-tert-butoxychromium by oxidizing the latter to
chromyl CrV=O (C6H6, 20°C). At t-BuOOH–Cr(OBu-t)4 ratio of 2 : 1 or higher, oxygen is released. The occur-
ing processes include the formation of chromium-containing peroxides and peroxytrioxydes. The t-BuOOH–
Cr(OBu-t)4 system oxidizes aromatic hydrocarbons of various structures (anthracene, 9,10-dimethylanthracene,
1,1-diphenylethylene, alkylarenes), as well as primary and secondary alcohols. Depending on the structure of
the substrate, the oxidants are: in situ generated oxygen including that in the singlet state, peroxy radicals, or
chromium-containing peroxides.
DOI: 10.1134/S1070363213110066
Complex or inorganic derivatives of Cr(III) and
Cr(VI) are applied in hydroperoxide oxidation of
organic compounds [1, 2]. To the very best of our
knowledge, no data has been available on the use of
chromium alkoxides in oxidizing systems, and
information on Cr(IV) complexes as oxidation catalyst
has been limited. Chromium oxide meso-tetraphenyl-
porphyrinate is known to oxidize benzyl alcohol to
benzaldehyde, but it does not catalyze alkanes
hydroxylation. C5H5NHCrO2X complexes (X = Cl or
F) in combination with tert-butyl hydroperoxide convert
secondary alcohols as well as propargyl and benzyl
methylene groups into ketones with high yield [1].
oxidizing ability of the system (hereafter referred to as
I+II) towards alkylarenes and their selected oxygen-
containing derivatives. Our preliminary trials revealed
that benzene was not oxidized by I+II.
The reaction of II with I in benzene (room
temperature) was performed at varied molar ratio of
II : I, 1 : 1 to 1 : 10. Starting from 1 : 2 ratio, oxygen
evolution was observed (Table 1). The hydroperoxide
always reacted quantitatively, being reduced to
alcohol. tert-Butyl peroxide was identified among the
products as well. The reaction was studied by NMR
(1H and 13C), ESR, IR, and electronic spectroscopy.
The bright sky blue color of II was due to the
absorption bands of ligands, a doublet with λmax = 635
and 760 nm [8].
Recently, the combined oxidation systems of tert-
butyl hydroperoxide (I) and transition metal (titanium
[3], zirconium [4], vanadium [5]) tert-butoxide or
metal (cobalt, chromium, vanadium [6, 7]) acetyl-
acetonate have been studied. Such systems oxidize
organic substrates under mild conditions (20°C). De-
pending on the substrate structure, metal peroxides,
peroxytrioxides, or in situ generated oxygen may act as
oxidizer.
After addition of I to sky blue solution of II (1 : 1),
the solution first turned wine-red, instantly changed
into blue-green. The electronic absorption spectrum of
the reaction mixture under inert was identical to that of
the parent compound (in the ligand bands range).
However, an additional band appeared at around
400 nm. The spectrum did not change during 24 h. If
the reaction was performed in air, the bands of ligand
disappeared within 5 min, a new band appeared at
371 nm, and the solution became yellow. The
The aim of this work was to study the interaction of
tetra-tert-butoxychromium II with tert-butyl hydro-
peroxide I in an inert solvent, and to estimate the
2005

2006
STEPOVIK et al.
Table 1. Products of tetra-tert-butoxychromium II reaction
with tert-butyl hydroperoxide I (C6H6, 20°C), in moles per
1 mol of II
The reaction of II with I was studied by ESR in the
absence of spin traps and in the presence of 2-methyl-
2-nitrozopropane or C-phenyl-N-tert-butylnitrone. In
the absence of the spin traps, regardless of the solvent
(C6H6, EtPh, 20°C), the ESR spectrum of the reaction
mixture (1 : 1) contained a broad singlet with g =
1.961 and ΔH = 9.0 mT. Since II was diamagnetic, the
recorded signal should likely be assigned to a com-
pound containing Cr(V). In the presence of C-phenyl-
N-tert-butylnitrone, immediately after mixing, a triplet
was registered with hyperfine coupling constants
(HFC) characteristic of the alkoxy radical spin-adduct
[aN = 1.35 mT, aH = 0.17 mT, g = 2.0052]. However,
the HFC constants differed from those of tert-butoxide
radical [12]. Along with anisotropy of the isotropic
spectrum (Fig. 1), that allowed assigning the signal to
the spin-adduct of C-phenyl-N-tert-butylnitrone with a
chromium-containing alkoxy radical, possibly, with
(t-BuO)3CrO·. The spectrum contained a signal with
g = 1.970 as well, characteristic of CrV=O [9, 10], but
it was weak.
II:I molar ratio
Volatile
fraction
а
1:1
1:2
1:4
1:10
t-BuOH
O2
1.86
–
3.48
5.84
11.50
0.57 (0.27b) 1.32 (0.33b) 3.30 (0.33b)
(t-BuO)2
0.05
0.07
0.16
0.43
a Averaged. b Per 1 mol of the hydroperoxide.
electronic absorption spectra of the reactions mixtures
at II : I ratios of 1 : 4 and 1 : 10 were similar, thus
indicating the complete decomposition of the ligand
environment of metal. The spectra of volatile fractions
were identical to those of the reaction mixtures; in
other words, the colored substance condensed with the
solvent. Treatment of the volatile fractions with tri-
phenylphosphine led to disappearance of yellow colora-
tion, the band at 371 nm vanished, and triphenyl-
phosphine oxide was formed. Taking into account that
chromium compounds containing chromyl group
CrV=O oxidized Ph3P to Ph3PO [9–11], the absorption
band at 371 nm could be assigned to the Cr=O bond.
When the I : II ratio was increased to 4–10 : 1, in the
IR spectra of nonvolatile chromium-containing residue
the absorption band at 945 cm–1 prevailed. That band,
absent in the IR spectrum of the parent compound, was
assigned to the CrV=O bond of chromyl [10].
The ESR spectrum of the reaction mixture (1 : 10,
C6H6, 20°C) in the absence of spin trap contained a
singlet assigned to peroxyl radical (g = 2.015 and
ΔH = 1.7 mT). Its intensity decreased with time to
disappear within 15 min. In the isotropic ESR spec-
trum of the same reaction mixture in the presence of 2-
methyl-2-nitrosopropane, a signal of peroxyl radical
with the same g-factor was observed as well, and a
new signal with g = 1.979 was found, assigned to a
CrV ion containing CrV=O bond (1) [9, 10]. The signal
of peroxyl radical decreased with time, while the
signal of chromyl increased (Fig. 2), indicating the
relationship of those species. Likely, the chromium-
containing peroxyl radicals CrIVOO· are observed.
After 25 min, the signal of the peroxyl disappeared; the
signal of CrV=O got stronger, appearing as a singlet of
52Cr (I = 0) (1) with four weak satellites due to another
isotope, 53Cr (I = 3/2), ai(53Cr) = 1.7 mT [9]. Vanishing
of the peroxyl radical signal was accompanied with
appearance of weak signals of 2-methyl-2-nitroso-
propane adducts. In the isotropic spectrum, the follow-
ing signals were identified: a triplet (1 : 1 : 1, g = 2.0056,
and aN = 2.72 mT) assigned to the adduct of the spin
trap with tert-butoxy radical, t-BuN(O·)OBu-t (2) [12];
a triplet with g = 2.006 and aN = 0.78 mT assigned to
the spin-adduct of acyl radical, RC(O)N(O·)OBu-t (3);
and a triplet with broadened lines, g = 2.006, and aN ~
1.35 mT assigned to the adduct of 2-methyl-2-
nitrosopropane with the carbon-centered radical
Н, mT
Fig. 1. ESR spectrum of tetra-tert-butoxychromium–tert-
butyl hydroperoxide (1:1) in the presence of C-phenyl-N-
tert-butylnitrone (C6H6, 20°C).
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OXIDIZING PROPERTIES OF THE tert-BUTYL HYDROPEROXIDE
g 2.015
2007
g 1.979
Н, mT
Fig. 3. ESR spectrum of (t-BuO)4Cr–t-BuOOH (1:10) in
the presence of 2-methyl-2-nitrozopropane (C6H6, 20°C),
25 min after mixing (enlarged). (*) Satellites of 53Cr
isotope. The numbers correspond to the assignments in the
text.
a triplet (1 : 1 : 1), a triplet of doublets (1 : 1), and a
singlet. The triplet signal with g = 2.0066 and aN =
0.79 mT, following [12, 13], was assigned to the
benzoyl-tert-butylnitroxyl PhCON(O·)Bu-t (5), formed
via oxidation of the spin trap with either singlet
oxygen or peroxyl radical. The triplet-doublet signal
with g = 2.0061, aN = 1.33 mT, and aH = 0.138 mT
was assigned to the adduct of C-phenyl-N-tert-butyl-
nitrone with peroxyl radical, most likely with t-
butylperoxyl [12]. The singlet with g = 1.979 was
assigned to chromyl CrV=O [9, 10].
Thus, in the reacting mixture of the alkoxide II and
hydroperoxide I, we were able to identify the
chromium-containing peroxide and alkoxide radicals,
as well as tert-butylperoxide and tert-butoxide radicals;
furthermore, formation of oxygen was confirmed.
Н, mT
Fig. 2. ESR spectrum of tetra-tert-butoxychromium–tert-
butyl hydroperoxide (1:10) in the presence of 2-methyl-2-
nitrozopropane (C6H6, 20°C): (1) immediately after mixing,
(2) 5 min after mixing, (3) 10 min after mixing, and (4) 25 min
after mixing. Signal 1 assigned to CrV=O.
The proposed scheme of Cr(OBu-t)4 interaction
with t-BuOOH is shown in Eqs. (1)–(5). Initially, the
complex was formed; subsequently, nucleophilic substitu-
tion of tert-butoxy group with peroxide occurred:
R'N(O·)Bu-t (4) (Fig. 3). The structure of R and R' was
not identified. We believe that the registered radicals
were decomposition products of the chromium-
containing peroxide.
(t-BuO)4Cr + t-BuOOH → [(t-BuO)4Cr·t-BuOOH]
–t-BuOH
(t-BuO)3CrOOBu-t.
(1)
In the 1H and 13C NMR spectra of the 1 : 1 mixture
of I and II (C6D6, 20°C, green solution), within 2 min
a signal of tert-butanol appeared along with a broad
peak of the (t-BuO)4Cr protons (3.03 ppm). The
After the introduction of C-phenyl-N-tert-butyl-
nitrone to the reaction mixture [II : I = 1 : 10, C6H6,
20°C] with subsequent degassing of the solution, the
ESR spectrum was registered containing three signals:
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STEPOVIK et al.
chromium-containing peroxide decomposed to
chromyl A [Eq. (2)]. The latter, having an unpaired
electron in the π* molecular orbital, could account for
the radical character of the Cr=O bond.
the amount of hydroperoxide increased, in the NMR
spectra of the reaction mixtures the signals of tert-
butyl peroxide, methyl tert-butyl ether, and acetone
were identified, confirming the presence of tert-
butoxide radicals.
(t-BuO)3CrIVOOBu-t
→ t-BuO· + (t-BuO)3CrV=O (A).
(2)
Further interaction of chromyl A with hydro-
peroxide I probably occurred via several pathways. By
analogy with the reactions of aluminum, titanium,
zirconium, and vanadium alkoxides with tert-butyl
hydroperoxide [3–5, 12], those might be the formation
and decomposition of chromium trioxide [Eqs. (3)–(6)].
When four moles of I was added to the above-
described reaction mixture, the intensity of alcohol
1
signals in the H and 13C NMR spectra increased,
whereas the signal of chromium alkoxides got weaker.
After 30 min, the latter signal virtually disappeared. As
(t-BuO)3CrO + t-BuOOH
t-BuOH + (t-BuO)2Cr(O)OOBu-t (B)
(t-BuO)2Cr(O)OOOBu-t (C)
(3)
(4)
B + t-BuOOH
(t-BuO)3CrO + O2
(t-BuO)2Cr(O)O
+
OOBu-t
+ OBu-t
C
(5)
(t-BuO)2Cr(O)OO
Substitution of the alkoxide group in chromyl A
with tert-butylperoxyl group led to peroxide B, its
subsequent reaction with I resulting in chromium-
containing peroxytrioxide C. The latter decomposed
with oxygen release, generating alkoxy and peroxyl
radicals simultaneously. Recently, the experimental
and theoretical evidence was obtained for the moly-
bdenum(VI) trioxide formation in the reaction of
molybdenum(VI) peroxide with alkylhydroperoxide.
Homolysis of the trioxide also resulted in formation
of alkoxy and peroxyl radicals, which were registered
by ESR [14]. Decomposition of the trioxide C
dimer should produce oxygen in the singlet state
[3, 7].
Given the possibility of hydroperoxide addition at
the Cr=O bond [1, 15], the reaction [Eq. (6)] leading to
radical D could not be excluded.
OH
(t-BuO)3CrV=O + t-BuOOH
(t-BuO)3Cr
(t-BuO)3CrIVOO (D)
(6)
_t-BuOH
OOBu-t
(t-BuO)3CrIVOO
(t-BuO)3CrIV
+
OOBu-t
Recombination of the peroxyl radicals according to
Eq. (7) led to regeneration oxochromyl.
OOOO Bu-t
Furthermore, the elimination of hydrogen atoms
induced by radical D followed by transformation of the
hydroperoxide was possible [Eq. (8)].
(t-BuO)3CrVO + O2
+
OBu-t
(7)
SH
(t-BuO)3CrIVOO + SH
(t-BuO)3CrIVOOH
(t-BuO)3CrV=O + OH
H2O
_S
[Cr] OBu-t
[Cr] OH
t-BuOH +
+ H2O
(8)
SH = t-BuOH, t-BuOOH,
C
H.
tert-Butoxy radicals [Eqs. (2), (5), (7)] were
from both hydroperoxyl group and C–H bonds. The
converted into alcohol via detachment of hydrogen
latter reaction explained the excessive yield of tert-
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OXIDIZING PROPERTIES OF THE tert-BUTYL HYDROPEROXIDE
2009
Table 2. Products of 9,10-dimethylanthracene reaction with
t-BuOOH–Cr(OBu-t)4 system (C6H6, 20°C, 1 day), in moles
per 1 mole of the substrate
butanol, even at equimolar ratio of I to II. In excess of
the hydroperoxide, the recombination of two t-BuOO·
radicals should also lead to the release of oxygen.
а
As noted above, the interaction with I could occur
at different bonds of Cr–OBu-t. This was accompanied
with formation of brown chromium-containing
precipitates. In the IR spectra of the precipitates, the
intensity of the C–O and C–H bands decreased, and a
broad band appeared at 3150 cm–1 assigned to
stretching of Cr–OH [10], along with the band at
945 cm–1 (CrV=O). The chromium content in the
precipitates was of 25–30%.
9,10-DMA:t-BuOOH:Cr(OBu-t)4
Products of reaction
1:3:1
10:30:1
0.12
0.05
0.28
0.29
5.08
0.36
0.18
0.28
0.16
0.15
2.00
0.15
III
IV
V
MeOBu-t
t-BuOH
9,10-9,10-Dimethylanthracene
(source)
In order to identify the nature of oxidants in the
I+II system, we studied its interaction with 9,10-
dimethylanthracene and with anthracene. The reactions
were performed in benzene (20°C), at a molar ratio of
9,10-dimethylanthracene to the hydroperoxide of 1 : 3.
The ratio of II:I was ranged from 1 : 3 to 1 : 30. The
main products identified were 9,10-dimethyl-9,10-
epidioxyanthracene III, 9,10-dimethyl-9,10-dihydro-
a Molar ratio.
9,10-di-tert-butylperoxyanthracene IV, 10-methyl-10-
tert-butylperoxy-9-anthrone V, and methyl tert-butyl
ether [Eq. (9) and Table 2].
CH3
CH3
CH3
t-BuOO
H3C
OOBu-t
[(t-BuO)4Cr_t-BuOOH]
O
(9)
+
+
O
OOBu-t
H3C
CH3
CH3
O
V
III
IV
The peroxide III formation indicated the presence
of either singlet oxygen or chromium trioxide
[Cr–OO–OBu-t] in the system [7]. tert-Butylperoxyl
groups at meso positions of IV indicated that peroxyl
radicals were involved in the interaction. The process
could be described by the scheme proposed for the
reactions of 9,10-dimethylanthracene with tert-butyl
hydroperoxide in the presence of cobalt, chromium, or
vanadium acetylacetonates leading to peroxide IV [7].
Table 2 shows that the yield of IV increased when
chromium alkoxide was used in catalytic amount,
confirming the generation of peroxyl radicals from
hydroperoxide I.
[16, 17]. However, diperoxyde IV was thermally stable
[7] and was not converted into anthrone V. Likely,
the peroxide V was formed via the molecular
or homolytic decomposition of the tetraoxide, the
product of two alkylperoxyl radicals dimerization
[Eq. (10)].
Reaction (10) could be facilitated by the nonlinear
structure of the six-membered transition state.
The interaction of anthracene with the studied
system led to anthraquinone, thus, oxidation of C–H
bonds at the meso positions 9 and 10 occurred. The
reaction conditions were similar to those given in
Table 2. With the molar ratio of 1 : 3 : 1, anthraquinone
yield was of 0.28 mol, reaching 0.38 mol when II was
used in catalytic amount with respect to I. Conversion
of anthracene was 30 and 40%, respectively. Either
singlet oxygen, chromium trioxide (formed through the
stage of epidioxy-9,10-anthracene), or tert-butylperoxy
radicals could act as oxidant [7]. Given that
The third peroxy derivative product of that reaction
was peroxyanthrone V, its amount formed was
identical to that of methyl tert-butyl ether. It could be
assumed that the carbonyl group was formed via
decomposition of methyl tert-butylperoxyl group
similar to the case of hydroperoxyl derivatives
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STEPOVIK et al.
H3C OOBu-t
CH3
CH3
H3C OOBu-t
O2
+ t-BuOO
H3C
H3C OO
H3C OOBu-t
H3C OOBu-t
t-BuOO
(10)
+ O2 + MeOBu-t
H3C
O
O
O
O
V
O
t-Bu
O
O
H
OOBu-t
t-BuOO
(11)
_2t-BuOH
t-BuOO
H
1
anthraquinone yield exceeded that of singlet oxygen
(Table 1), the oxidation with t-BuOO· was most
probable [Eq. (11)].
metal complexes O2 [19], metal-containing trioxides,
or peroxyl radicals [7]. The reaction occurred via the
stage of formation and decomposition of 1,2-
dioxethanes. We studied the interaction of the I+II
system with 1,1-diphenylethylene (Table 3). The major
isolated products were benzophenone and the products
of formaldehyde transformations. Formaldehyde was
identified in the form of 2,4-dinitrophenylhydrazone,
but in course of the reaction it was oxidized to formic
acid and underwent the condensation transformations.
In the literature, anthracene conversion to quinone
with quantitative yield by the action of tert-butyl
hydroperoxide in the presence of bis(tributylstannyl-
oxy)chromate (in 1,2-dichloroethane, 80°C) was
described [18]. However, the reaction schemes were
not presented, and the nature of the oxidant was unclear.
The arylalkenes containing only phenyl radicals
and hydrogen atoms at the sp2-hybrid carbon atoms
were inert towards dissolved free singlet oxygen, but
were oxidized with destruction of the double bond by
Similarly to the reaction of phenylethenes with t-
BuOOH in the presence of transition metal acetyl-
acetonates [7], the oxidative degradation of 1,1-
diphenylethylene likely occurred via formation of 1,2-
dioxethane. The latter was produced in the reaction of
phenylalkyl either with chromium compounds contain-
ing CrOOOBu-t or with the radical t-BuOO·. Possibly,
both the oxidants were involved. Participation of tert-
butylperoxyl radicals was indicated by presence of 1,1-
diphenyloxyrane in the products.
Table 3. Products of 1,1-diphenylethylene reaction with t-
BuOOH–Cr(OBu-t)4 system (C6H6, 20°C), in moles per
1 mol of the alkene
a
Ph2C=CH2:t-BuOOH:Cr(OBu-t)4
Products of reaction
1:4:1
10:40:1
0.50b
0.29
0.21
2.29
–
0.76
0.12
0.16
2.54
1.23
Thus, in I+II system, oxygen (including its singlet
form), chromium peroxytrioxide compounds, and tert-
butylperoxyl radicals could act as oxidizers.
Ph2CO
НСООНc
Ph2C=СН2 (source)
t-BuOHd
To clarify the oxidative capacity of the I+II system
and to elucidate the transformation intermediates
nature, we studied the interaction of I+II with alkyl-
arenes and their selected oxygenated derivatives. In
particular, the substrates were alkylarenes containing
t-BuOOH
a
c
b
Molar ratio. 1,1-Diphenyloxyrane also detected. After
treatment with BF3·OEt2, 2,2-diphenylethanal was identified.
Formaldehyde detected. d In the volatile fraction.
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OXIDIZING PROPERTIES OF THE tert-BUTYL HYDROPEROXIDE
methyl, methylene and methine C–H bonds: ethyl-
2011
benzene, sec-butylbenzene, and 1,1-diphenylalkanes
Ph2CHR (R = Me, Et).
Reactions with monophenylalkanes were performed
in solution at 20°C (Table 4). As seen from Table 4, in
the case of ethylbenzene the oxidation products
maintaining the carbon backbone prevailed: aceto-
phenone, 1-phenylethan-1-ol, 1-phenyl-1-hydroper-
oxyethane and unsymmetrical peroxide, the 1-phenyl-
1-tert-butylperoxyethane. In the case of s-BuPh, the
alcohol, hydroperoxide, and unsymmetrical peroxide
were identified as well. In ethylbenzene, regardless of
the II : I ratio (1 : 4 to 1 : 10) immediately after mixing
the reactants and addition 2-methyl-2-nitrosopropane,
ESR spectrum of the reaction mixture contained weak
triplet of doublets with aN = 1.48 mT, aH = 0.36 mT,
and g = 2.0051, assigned to the adduct of α-
phenylethyl radical PhCH(Me)N(O·)Bu-t [12], and a
strong singlet of chromyl (1) [g = 1.979 with satellite
53
splitting with Cr, a(53Cr) = 1.7 mT]. After 5–7 min,
the radical adduct signal intensity decreased, and a
new signal of tert-butoxy radical adduct appeared (2)
(g = 2.0055, aN = 2.72 mT). The intensity of the singlet
did not change.
Н, mT
Fig. 4. ESR of tetra-tert-butoxychromium – tert-butyl
hydroperoxide (1:8) (PhEt, 20°C) in the presence of C-
phenyl-N-tert-butylnitrone: (1) immediately after mixing,
(2) 10 min after mixing, and (3) 15 min after mixing. The
numbers correspond to the assignments in the text.
In the presence of C-phenyl-N-tert-butylnitrone, the
ESR spectrum of I+II in ethylbenzene was a
superposition of triplet, triplet of doublets, and singlet
(Fig. 4). The triplet signal (1 : 1 : 1) was assigned to
benzoyl-tert-butylnitroxyl radical according the
isotropic parameters (g = 2.0066 and aN 0.79 mT) (5).
The signal of nitroxyl with g = 2.0061, aN = 1.310 mT,
and aH = 0.101 mT was assigned to the adduct of C-
phenyl-N-tert-1-butylnitrone with phenylethylperoxy
radical PhCH(Me)OOCH(Ph)N(O·)Bu-t (6) [12]. The
singlet was assigned to chromyl CrV=O (1). After
10 min, the intensity of chromyl signal increased and
additional singlets with close but different the g-factors
appeared. After 15 min, the signals of the peroxyl
radical spin adduct (6) disappeared, the intensity of
triplet (5) and the singlet with g = 1.979 increased, and
a new signal, a triplet of doublets (aN = 1.40 mT, aH =
0.18 mT,a nd g = 2.0056) appeared assigned to the
adduct of the spin trap with alkoxy radical PhCH(OR)·
N(O·)Bu-t (R = PhCHMe or t-Bu) (7) [15, 20].
including formation and oxidation of a secondary
alcohol was proposed to describe the transformation of
the methylene C–H bonds to C=O group in benzyl,
allyl, and propargyl fragments by tert-butylhyd-
roperoxide [1, 15]. Similar processes could be assumed
in the case of alkylarene reactions with I+II. However,
Table 4. Products of alkylarenes (PhR) oxidation with the t-
BuOOH–Cr(OBu-t)4 system (15:1, 20°C) in moles per 1 mol
of the hydroperoxide
Products of
R=CН2СН3
R=CH(CH3)C2H5
reactionа
b
PhCHO
0.01
–
Ketone
PhCOMe 0.52
PhCH(OH)Me 0.26
PhCOMe 0.21
Alcohol
Peroxide
PhC(Me)(Et)OH 0.14
PhCH(Me)OOBu-t 0.04 PhC(Me)(Et)OOBu-t 0.18
The hydroperoxide-type conversion of methylene
group into ketone one in the presence of CrO3 was
reported [1, 15, 20]. It was assumed that the oxidants
involved were the chromium peroxy compounds,
adducts of hydroperoxide and Cr=O bond. The scheme
Hydroperoxide PhCH(Me)OOH 0.04 PhC(Me)(Et)OOH 0.25
a
b
Averaged. Acetaldehyde detected. 0.06 moles of acetic acid
found as well.
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STEPOVIK et al.
Table 5. Products of 1,1-diphenylalkanes reaction with
t-BuOOH in the presence of (t-BuO)4Cr and of 1-hydro-
peroxy-1,1-diphenylalkanes reaction with (t-BuO)4Cr (C6H6,
20°C), in moles per 1 mol of hydrocarbon or hydroperoxide
their formation. Likely, the process was initiated by the
oxygen-centered radicals [Eqs. (2) and (5)]. The
carbon-centered radical reacted with oxygen. The
subsequent transformation of peroxyl radicals (hydro-
gen detachment, formation and decomposition of
tetraoxides, disproportionation according to the Russell
scheme [21] in the case of PhCH (Me)OO· radicals)
were responsible for the formation of compounds
listed in Table 4. In the case of sec-butylbenzene,
significant amounts of the products of carbon back-
bone destruction were identified: PhCOMe,
CH3COOH (acetaldehyde), and phenylethylketone
(traces).
Ph2CНR + t-BuOOH +
Ph2C(R)OOH +
a
b
Products of
reaction
Cr(OBu-t)4
Cr(OBu-t)4
R = Mec
R = Etc
R = Me
R = Et
Ph2C(OH)R
Ph2C(OOH)R
Ph2CO
0.13
0.02
0.10
0.08
0.07
0.20
0.07
0.03e
0.20
0.11
0.01
0.61
0.41
0.29
0.20
0.40
0.09
0.05
0.16e
0.01
PhCOR
0.29
PhOH
0.04
Tracesd
Destruction of the carbon backbone occurred in the
case of I+II interaction with 1,1-diphenylalkanes
Ph2CHR (R = Me, Et) as well (Table 5). Tertiary
hydroperoxides and alcohols, alkylphenylketones,
benzo-phenone, and aldehydes or the corresponding
acids (lesser amounts) were identified. Those com-
pounds could result from transformations of tertiary
alkylperoxyl radicals or metal peroxides [Eqs. (12)–
(14)].
d
R'COOH
–
a
b
c
The molar ratio of 10:30:1. The molar ratio of 10:1. Conver-
sion of Ph2CHMe 53%, Ph2CHEt 55%. d R' = H. e R' = Me.
the ESR data along with the confirmed presence of
oxygen, hydroperoxides, and unsymmetrical tert-butyl
peroxides in the system indicated the homolytic way of
O2
SH
_S
Ph2CHR + ХO
2 Ph2C(R)OO
Ph2CR
Ph2C(R)OO
Ph2C(R)OOH
(12)
(13)
_ХОН
SH
_S
2 Ph2C(R)OH
2 Ph2C(R)O
_O2
X = t-Bu, t-BuO, [Cr], [Cr]O; R = Me, Et.
[Cr]_OC(R)(Ph)OPh
[Cr]_OOC(R)Ph2
[Cr]OPh + PhCOR
(14)
Rearrangement with subsequent decomposition of
alkylperoxyl radicals or chromium peroxide led to
alkylphenylketones [Eq. (14)].
we investigated the interaction of hydroperoxides
Ph2C(R)OOH with alkoxide II in benzene. The
reactants ratio was of 10 : 1, it should have led to
high concentration of peroxyl radicals. The results
presented in Table 5 confirmed participation of
radicals Ph2C(OO·)R in the formation of the specified
products. The interaction of hydroperoxides with
chromium alkoxide is represented by Eqs. (15) and
(16).
The presence of benzophenone could be attributed
to decomposition of alkoxy radicals and recombination
of alkylperoxyl radicals [22].
In order to confirm the role of hydroperoxides and
peroxyl radicals in the oxidation of diphenylalkanes,
(t-BuO)3CrOOR1
R1OOH + Cr(OBu-t)4
R1O + (t-BuO)3Cr=O
(15)
_t-BuOH
R1OOH + R1O
R1OO + R1OH
(16)
R1 = Ph2CR2; R2 = Me, Et.
The ESR spectrum of reaction mixture [Eq. (16)]
(R = Et, C6H6, 20°C) in the presence of C-phenyl-N-
tert-butylnitrone contained triplet of doublets (5)
assigned to nitroxyl oxidation product of the trap
according to HFC, and triplet of doublets (8) with aN =
1.36 mT, aH = 0.18 mT, and g = 2.0056, characteristic
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OXIDIZING PROPERTIES OF THE tert-BUTYL HYDROPEROXIDE
of the spin trap adduct with alkoxy radicals PhCH(OR)
2013
g
g
g
N(O·)Bu-t [with RO• being likely Ph2C(O·)Et]. In
addition to signals (5) and (8), the spectrum contained
a number of singlets with g of 1.970–1.979, assigned
to oxochromyl group CrV=O, their intensity varying
with time. After 13 min, a singlet with g = 1.972
prevailed (Fig. 5). It was reported that the g-factor of
chromyl signal depended on the ligand environment of
the metal [9–11]. Therefore, the reaction mixture
contained several compounds (RO)3CrV=O with
different alkoxy groups. From Figs. 2–4, the signal
with g = 1.979 was assigned to tert-butoxide
derivative. Thus, the ESR data was in line with Eqs.
(15) and (16).
g
As seen from Table 5, the quantitative composition
of the products mixture was determined by the
structure of the R in the starting hydroperoxide. In the
case of 1-hydroperoxy-1,1-diphenylethane, the major
product was acetophenone [Eq. (14)], whereas in the
case of Ph2C(OOH)Et benzophenone prevailed. The
increase of benzophenone yield was 40-fold, and could
not be explained by higher stability of ethyl radical
[Eq. (17)].
Н, mT
Fig. 5. ESR spectrum of tetra-tert-butoxychromium–
1-hydroperoxy-1,1-diphenylpropane (1:8) in the presence
of C-phenyl-N-tert-butylnitrone (C6H6, 20°C): (1) 1 min
after mixing, (2) 13 min after mixing. Signal 5: adduct with
benzoyl radical, signal 8: adduct with Ph2C(O•)Et radical.
could also account for the presence of acetophenone in
the products of s-BuPh oxidation (Table 4).
Ph2C(O·)R → Ph2CO + R·
(17)
R = Me, Et.
Thus, the interaction of alkylarenes with I+II
system included the steps of formation of substrates
peroxyl radicals, their transformation to the final
oxidation products being possible both with and
without destruction of the carbon backbone. The latter
process involved the formation of intermediate 1,2-
dioxethanes.
Likely, the main pathway of benzophenone
formation was recombination of alkylperoxyl radicals
to form hydroperoxide and dioxethane. The latter
decomposed into benzophenone and acetaldehyde,
partially oxidized to acid [Eq. (18)].
Me
Ph2C(Et)OO + H
C
CPh2
O
The ability of C–H bonds to be homolytically
oxidized depends on the α-substituent structure,
decreasing in the presence of electron-acceptor groups.
We performed the interaction of methyl phenylacetate
with I+II at the reagents ratios of 1 : 4 : 1 and 10 : 30 : 1
(catalytic mode, benzene, 20°C). The only isolated
product was methyl benzoylformate with yield of 0.22
and 0.41 mol, respectively. Possibly, the α-hydroxy
acid ester intermediate was formed, capable of sub-
sequent transformation into keto ester. The alkoxide II
was reported to oxidize primary alcohols [8], but at
Cr(OBu-t)4 to RCH2OH ratio of 2 : 7 the aldehyde
yield was less than 1 mol (14%).
H
O
Me
Ph2C(Et)OOH +
H
C
O
CPh2
O
(18)
MeCHO + Ph2CO
The probability of reaction (18) in the case of Ph2C
(Me)OO· should be much lower, due to stronger C–H
bond of methyl group as compared with the methylene
one, and to lower stability of methyl radical. The main
transformation pathway of Ph2C(Me)OO· was forma-
tion of alkoxy radicals and rearrangement to aceto-
phenone and phenol. The equation of type [Eq. (18)]
We performed oxidation of ethyl 2-hydroxy-2-
phenylethanoate with I+II system. The reaction
conditions were the same as described above in
PhCH2COOMe reaction. Ethyl benzoylformate was
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STEPOVIK et al.
Table 6. Products of alcohols (ROH) oxidation with the t-BuOOH–Cr(OBu-t)4 system (C6H6, 20°C), in moles per 1 mole of
alcohol
PhCH(OH)Me
PhCH2OH
10:30:1a
n-BuOH
10:30:1a
Products of reaction
1:4:1a
10:30:1a
1:4:1a
1:4:1a
Carbonyl compound
R'COOH
0.98
–
0.75
–
0.84
0.15c
4.52
–
0.38
0.60c
1.81
–
0.07b
0.56d
5.77
–
Tracesb
0.38d
2.37
t-BuOH
5.12
–
1.30
0.17
ROH (source)
0.38
a The molar ratio of ROH:t-BuOOH:Cr (OBu-t)4. b The products of butanal condensation. c R '= Ph. d R '= Pr.
isolated (0.99 and 0.66 mol, respectively). The highest
conversion of PhCH2COOMe was achieved with
catalytic amount of II and equimolar amount of PhCH·
(OH)COOEt. Given that fact, and taking into account
the data published on secondary alcohols oxidation
with CrO3–t-BuOOH [1, 23, 24], we proposed the intra-
molecular mechanism involving six-membered inter-
mediate complex [Eq. (19)].
(t-BuO)4Cr + t-BuOOH + PhCH(OH)COOEt
O
O
C(Ph)COOEt
H
2 t-BuOH + (t-BuO)2Cr
(t-BuO)2Cr
O + PhCOCOOEt
(19)
O
Bu-t
E
In the catalytic mode, the catalyst could regenerate via
addition of hydroperoxide at the Cr=O bond [Eq. (20)].
EXPERIMENTAL
The reaction products were analyzed by GLC, TLC,
IR, ESR, 1H and 13C NMR, and electron spectroscopy.
Electronic absorption spectra were recorded at room
temperature with Shimadzu UV-1800 unit. IR spectra
were recorded with Shimadzu IR Prestige-21 device
(KBr tablets or thin layer). ESR spectra were recorded
with Bruker EMX spectrometer, at operating
frequency of 9.75 GHz, with diphenylpicrylhydrazyl as
g-factor reference. To improve the resolution of ESR
spectrum and to remove oxygen, the solutions were
degassed. Chromium alkoxide concentration was of
[Cr]=O + t-BuOOH → [Cr](OH)OOBu-t
+ PhCH(OH)COOEt → H2O + E.
(20)
Water hydrolyzed the Cr–OBu-t bond leading to
composition of the alkoxide and precipitation of the
hydrolysis products, thus yield of the benzoylformate
was decreased.
Similar results were obtained in oxidation of 1-
phenylethan-1-ol with I+II. Oxidation of primary
alcohols under identical conditions led to aldehydes
[Eq. (19)] and carboxylic acids (Table 6). The final
product yield depended on the structure of alcohol and
the ratio of initial reagents. Conversion of aldehydes
into acid could be initiated by in situ generated
oxygen, or by chromium peroxy compounds, similarly
to the cases of aluminum and titanium derivatives [25,
26] [Eq. (21)].
1
13
0.005 mol/L. H and C NMR spectra were recorded
with Agilent DD2 NMR 400 spectrometer at operating
frequencies of 400 and 101 MHz, respectively.
Chemical shifts were reported as δ relative to Me4Si.
Chromatographic analysis of the reaction products
in the liquid phase was carried out with Shimadzu GC-
2010A device equipped with a flame ionization
detector and capillary column Equity-5, 30000×
0.32 mm; with nitrogen as carrier gas. The content of
the mixture components was determined at the fol-
lowing temperatures: benzaldehyde, acetophenone,
phenylethylketone, 1-phenylethan-1-ol, 2-phenylbutan-
[Cr]OOBu-t + RCHO → [Cr]OCH(R)OOBu-t
→ [Cr]OCOR + t-BuOH.
(21)
Consequently, chromium-containing peroxy com-
pounds participated in the oxidation of primary and
secondary alcohols, as well as of aldehydes.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 11 2013

OXIDIZING PROPERTIES OF THE tert-BUTYL HYDROPEROXIDE
2015
2-ol, and methyl benzoate at 130ºC; tert-butyl
peroxide, tert-butanol, tert-butyl acetate, methyl tert-
butyl ether, and n-butanol at 50ºC; PhCH2COOMe,
PhC(O)· COOMe, PhCH(OH)COOEt, PhC(O)COOEt,
Ph2CHMe, Ph2CHEt, Ph2C(OH)Me, Ph2C(OH)Et,
Ph2CO, PhCH(Me)OOBu-t, PhC(Me)(Et)OOBu-t,
Ph2C=CH2, and PhOH at 170–180ºC. The analysis was
always performed using external reference compounds.
To isolate the products by column chromatography,
silica gel 60 (0.06–0.2 mm) was used as adsorbent.
following commercial reagents: sec-butylbenzene
(99%), ethyl-D,L-mandelate (97%), 1,1-diphenyl-
ethylene (98%) (all – Acros Organics), and 9,10-
dimethylanthracene (98%, TCI Europe nv).
Interaction of chromium tetra-tert-butoxide with
tert-butyl hydroperoxide (1 : 10) in benzene, 20°C.
0.41 g of t-BuOOH was added to 0.158 g of Cr(OBu-t)4
in 12 mL of benzene. The reaction was exothermic.
The color of the reaction mixture immediately changed
from sky blue to dark orange. After 20 h, the solution
was pale orange, and dark brown precipitate was found
at the flask bottom. The precipitate was filtered off,
dried (0.0183 g), and analyzed. Its IR spectrum
contained absorption bands at ν, cm–1: 3400 (Cr–OH),
944 (Cr=O), 820, 520 (Cr–O–Cr), 1627 (H2O crystal-
lization). The solvent and volatile components of the
filtrate were condensed in a trap cooled with liquid
nitrogen. The residue was a dark brown solid, the band
at 945 cm–1 (CrV=O) dominated in its IR spectrum. In
the condensate (yellow), t-BuOH (0.36 g), tert-butyl
peroxide (0.018 g), MeOBu-t (0.005 g), and Cr (0.010 g)
were found. An aliquot of the condensate was treated
with triphenylphosphine till discoloration of the
solution, after that 0.051 g of Ph3PO was determined.
Quantitative analysis of hydroperoxides was per-
formed by iodometric titration. Carboxylic acids were
identified and analyzed in the form of methyl esters
after treatment with diazomethane. Carbonyl com-
pounds were identified in the form of 2,4-dinitro-
phenylhydrazones according to melting point and TLC
Rf values using the reference substances. Sorbent used
was Silpearl, a wide porous silica gel on aluminum foil
(Silufol UV-254); the eluent was carbon tetrachloride–
diethyl ether 9 : 1. The chromium content was deter-
mined by the Palmer method [27].
Tetra-tert-butoxychromium was synthesized ac-
cording to [28]. Found, %: Cr 15.14, C16N36O4Cr.
Calculated, %: Cr 15.09. Spectral characteristics of the
alkoxide coincided with the literature data [8].
In the parallel experiments, an aliquot of the
condensate was heated (70°C, 5 h) with acetic acid, a
four-fold amount with respect to the chromium
alkoxide. In the solution, 0.40 g of t-BuOH and traces
of tert-butyl acetate were found. The difference
between the amount of alcohol in the volatile fraction
before and after treatment with acid (0.04 g) indicated
the presence of the volatile chromium compounds in
the condensate. [Cr] : [t-BuO] : [Cr=O] = 1 : 2.84 : 0.92,
close to (t-BuO)3CrO.
1,1-Diphenylalkanes Ph2CHR were obtained by
alkylation of benzene with corresponding alcohols.
R = Me, bp 114–115ºC (4 mm Hg), nD21 1.5740; R =
Et, bp 130–132ºC (4 mm Hg), nD20 1.5630 [29].
Tertiary alcohols Ph2C(OH)R (R = Me, Et) were
synthesized using organomagnesium compounds [30],
their constants corresponded to the published data. 1-
Hydroperoxy-1,1-diphenylethane and 1-hydroperoxy-
1,1-diphenylpropane were obtained by treating the
corresponding alcohols with 88% H2O2 in ether in the
presence of conc. H2SO4 at 0–5ºC. Ph2C(OOH)Me was
purified by precipitation with petroleum ether from the
concentrated ether solution, mp 85°C; Ph2C(OOH)Et
was twice recrystallized from hexane, mp 80ºC [31].
1-tert-Butylperoxy-1-phenylethane was synthesized
from α-phenylethylbromide and potassium salt of tert-
butyl hydroperoxide, bp 56ºC (1 mm Hg), nD20 1.4810
[32]. 2-tert-Butylperoxy-2-phenylbutane was obtained
via reaction of 2-phenylbutan-2-ol with tert-butyl
hydro-peroxide in glacial acetic acid, the catalyst was
conc. H2SO4, bp 60–62ºC (1 mm Hg), nD20 1.4780 [33].
Phenylacetic acid methyl ester was obtained by
esterification in the presence of POCl3 [34], bp 215°C,
nD23 1.5055 [35]. The concentration of tert-butyl hydro-
peroxide was more than 99.6–99.8%. We used the
The amount of oxygen was determined in a
separate experiment using the method [6].
Interaction of 9,10-dimethylanthracene with tert-
butyl hydroperoxide in the presence of Cr (OBu-t)4
(10 : 30 : 1). 0.27 g of t-BuOOH was added to 0.034 g
of chromium alkoxide and 0.20 g of 9,10-dimethyl-
anthracene in 25 mL of benzene. The solution became
dark brown immediately, with fine dark brown
precipitate formed. After 20 h, the precipitate that
contained chromium was filtered off. The solvent and
volatile products in the filtrate (t-BuOH, 0.15 g;
MeOBu-t, 0.014 g; t-BuOOH, 0.034 g) were con-
densed in a trap cooled with liquid nitrogen. The
residue was analyzed by column chromatography, the
eluent was benzene. The course of the analysis was
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 11 2013

2016
STEPOVIK et al.
monitored by TLC (benzene, then treatment with
solution of phosphomolybdic acid and heating). Four
fractions were identified: (1) unreacted 9,10-dimethyl-
anthracene (0.032 g), mp 182–183°C; (2) trans-
diperoxyde IV, 0.11 g, after washing with cold (0–5°C)
ethanol, mp 113oC, mp, IR, and NMR (1H, 13C, CDCl3)
data were identical to the published [7]; (3) isolated
yellow crystalline solid (0.047 g); IR spectrum (KBr),
ν, cm–1: 3068, 3034, 2976, 2927, 2861, 1667 (>C=O),
1604 (C=C), 1459, 1362, 1319, 1290, 1196, 1157,
1076, 932, 883, 760, 688; 1H NMR spectrum (CDCl3),
δ, ppm: 1.16 [9H, C(CH3)3], 1.63 [3H, CH3], 7.45–8.29
[8H, Ph, 7.47–7.49 m, 7.64–7.68 m, 7.84–7.86 d,
8.27–8.29 d]; 13C NMR spectrum (CDCl3), δС, ppm:
26.81 [C(CH3)3], 33.41 (CH3), 78.31 [C(CH3)3], 79.63
(CH3C–O), 131.05, 146.71 (condensed rings), 126.53,
127.14, 127.77, 133.22 (Ph), 183.67 (>C=O), mp 97–
98°С. According to IR and NMR spectroscopy, the
product (3) was 10-methyl-10-tert-butylperoxy-9-
anthrone V. The presence of the carbonyl group was
confirmed by reaction with 2,4-dinitrophenylhyd-
razine. Treatment with NaI in acetic acid (60°C, in a
sealed tube) resulted in release of iodine. Found, %: O
(active) 5.17. C19N20O3. Calculated, %: O (active)
5.40. After a month storage (20°C), the compound V
converted into anthraquinone. Fraction (4): 0.043 g of
epidioxyanthracene III. After washing with ethanol
(0–5°C) colorless crystals were isolated, mp 219°C. 1H
NMR spectrum (CDCl3), δ, ppm: 2.14 (6H), 7.2–7.4 m
(8H). 13C NMR spectrum (CDCl3), δC, ppm: 13.70,
79.50, 120.65, 127.37, 140.71.
To quantify 1-hydroperoxy-1-phenylethane, an
aliquot of the reaction solution was treated with excess
of triphenylphosphine. Amount of the hydroperoxide
was determined by the difference of 1-phenylethan-1-
ol amount.
Oxidation of ethyl 2-hydroxy-2-phenylethanoate
with the t-BuOOH-(t-BuO)4Cr system (1 : 4 : 1,
benzene, 20ºC). A mixture of 0.26 g of (t-BuO)4Cr,
0.27 g of t-BuOOH, and 0.14 g of the ester in 10 mL of
benzene was kept at room temperature during 20 h.
The reaction solution became dark brown. It was
decanted from the insoluble precipitate of chromium
compounds. The liquid phase was treated as described
above. In the volatile fraction, 0.37 g of t-BuOH and
0.012 g of (t-BuO)2 were found. In the aqueous acid
extract 0.004 g of H2O2 was found. In the ether extract,
0.004 g of unreacted ether and 0.23 g of ethyl
benzoylformate were identified. After treating the
reaction mixture with 2,4-dinitrophenylhydrazine, 2,4-
dinitrophenylhydrazones of two of ethyl benzoyl-
formate isomers were isolated by column chromato-
graphy (eluent CCl4 : Et2O = 9 : 1) : Z-isomer, mp 158°C
and E-isomer, mp 144oC. Structure of the hydrazones
was confirmed by IR and UV spectroscopy. IR spec-
trum (CCl4), ν, cm–1: Z-form, 3210 [ν(N–H)], 1697
[ν(C=O)]; E-form, 3280 [ν(N–H)], 1722 [ν(C=O)]. UV
(EtOH), λmax, nm: Z-form, 384.5 nm; E-form, 357.5 nm.
The experiments and analysis of the reaction
products not listed in the experimental part were
performed similarly.
Interaction of tert-butyl hydroperoxide with
chromium tetra-tert-butoxide in ethylbenzene (15 : 1,
20ºC). 0.20 g of t-BuOOH was added to 0.05 g of
alkoxide II in 10 mL of ethylbenzene. The reaction
solution immediately turned bright red, and after
20 min it became orange. Next day, the solution was
yellowish, with dark brown precipitate at the bottom.
IR spectrum of the precipitate was identical the case of
the reaction in benzene (10 : 1). The liquid phase was
decanted. Volatile products and solvent were
condensed in a trap cooled with liquid nitrogen. The
residue (brown mass) was hydrolyzed with 10%
H2SO4, extracted with ether, and dried over Na2SO4. In
the condensate and the hydrolyzate, 0.012 g of 1-
hydroperoxy-1-phenylethane, 0.16 g of acetophenone,
0.08 g of 1-phenylethan-1-ol, 0.015 g of 1-tert-butyl-
peroxy-1-phenylethane, and 0.002 g of benzaldehyde
were identified. 0.30 g of tert-butyl alcohol was also
found in the condensate.
ACKNOWLEDGMENTS
The authors thank Yu.B. Malysheva for registration
of NMR spectra and assistance in their interpretation.
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