Low-temperature oxidation of phenylalkenes with tert-butyl hydroperoxide in the presence of aluminum and titanium tert-butylates

Article abstract of DOI:10.1023/A:1013911322179

Tert-Butyl hydroperoxide in the presence of aluminum and titanium tert-butylates oxidizes phenylalkenes to carbonyl compounds, as well as unsaturated alcohols and their epoxidation products; the process involves free radicals. Organometallic peroxides tak

Full text of DOI:10.1023/A:1013911322179

Russian Journal of General Chemistry, Vol. 71, No. 10, 2001, pp. 1593 1597. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 10, 2001,
pp. 1681 1685.
Original Russian Text Copyright
2001 by Martynova, Stepovik, Dodonov.
Low-Temperature Oxidation of Phenylalkenes with tert-Butyl
Hydroperoxide in the Presence of Aluminum
and Titanium tert-Butylates
I. M. Martynova, L. P. Stepovik, and V. A. Dodonov
Lobachevskii Nizhny Novgorod State University, Nizhny Novgorod, Russia
Received July 31, 2000
Abstract tert-Butyl hydroperoxide in the presence of aluminum and titanium tert-butylates oxidizes
phenylalkenes to carbonyl compounds, as well as unsaturated alcohols and their epoxidation products; the
process involves free radicals. Organometallic peroxides take an active part in the formation of secondary
oxidation products.
The systems tert-butyl hydroperoxide (I) alumi-
num tert-butylate (II) and hydroperoxide I titanium
tetra-tert-butylate (III) in benzene at 20 C evolve
oxygen; the yield of the latter attains 80 85% [1 3].
The oxygen is generated by reactions of the com-
ponents of the systems (I + II or I + III) via inter-
mediate formation of a metal mono-tert-butyl per-
oxide and, presumably, a metal-containing trioxide
[3] is explained by formation of metal-containing
peroxides. The latter are formed by direct reaction of
the resulting hydroperoxides with metal alcoholate or
by nucleophilic addition of aluminum-containing
peroxides by the carbonyl group in primary oxidation
products.
It is also known that under the action of alkyl
hydroperoxides in the presence of vanadium, moly-
bdenum, titanium, or cobalt complexes olefins convert
into epoxides [4 6]. Thus, tert-butyl hydroperoxide
with titanium tetraisopropylate and (+)- or ( )-diethyl
tartrate converts allyl alcohols into epoxides in high
yields [4, 6, 7].
[1, 2] [scheme (1)]:
(
t-BuO) M + t-BuOOH
(t-BuO)n 1MOOBu-t
n
t-BuOH
O
(
t-BuO)n 1
M
O Bu-t
t-BuOOH
(1)
t-Bu O
H
The aim of the present work was to study the
oxidative ability of the systems I + II or I + III, as
well as to find out which carbon hydrogen bonds in
phenyl-substituted alkenes are attacked by the oxygen
generated by these systems. Phenyl-substituted
alkenes comprise, apart from C H bonds of the
aromatic ring, reactive vinyl and methylene C H
bonds [8 10].
O
(t-BuO)n 1MOOOBu-t
(t-BuO) M + O2
n
t-BuOOH
A
M = Al, n = 3; M = Ti, n = 4.
The oxygen generated by the systems selectively
For the starting substrates we chose 3-phenyl-1-
oxidizes methine and, especially, methylene carbon
hydrogen bonds of alkanes and alkylarenes [1, 2]. The
radical oxidation with the above systems of methylene
and methine bonds involves, depending on the struc-
ture of the hydrocarbon, initial formation of oxo, as
well as hydroxy [1 3] and hydroperoxy groups [1, 3].
It was shown that in tetra- and trisubstituted alkenes
containing at least one -methyl group, the evolving
oxygen attacks this methyl group exclusively, while
the double bond is preserved [3]. The process is most
frequently completed by carbon carbon bond cleavage
in the starting substrate. The destruction both of
saturated and [1, 2] and of unsaturated hydrocarbons
propene (IV) and 4-phenyl-1-butene (V).
The reactions of alkenes IV and V with systems
I + II and I + III were accomplished in benzene at
20 C at an alkene IV, V : alcoholate II, III : hydro-
peroxide I molar ratio of 1:1:2. The conversion was
40 to 60% (see table). The major reaction products
were carboxylic acids [benzoic and acetic (with alkene
IV)], carbonyl compounds (alkenyl phenyl ketones
and benzaldehyde), as well as unsaturated alcohols
and their epoxidation products. The composition of
the reaction products (see table) provide unambiguous
evidence showing that the oxidative systems studied
1
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1594
MARTYNOVA et al.
Compositions of products of the reactions of alkenes
containing trioxide and identified by the spin-trap
PhCH R (IV, V) with systems t-BuOOH (I) (t-BuO) M
technique [10], can initiate oxidation of alkenes IV
2
n
[M = Al, n = 3 (II); M = Ti, n = 4 (III); molar ratio 1: 2: 1, and V by abstracting hydrogen from their methylene
2
0 C, benzene, 24 h, mole per mole alkene IV, V)] group. The resulting radicals react with dissolved
oxygen,
[scheme (3)].
yielding
finally
PhCHR
hydroperoxides
B
b
Reaction
products
IV (R = CH=CH2)b V (R = CH CH=CH )
2
2
a
t-BuO
O2
M = Al M = Ti M = Al
Volatile reaction productsc
M = Ti
PhCH R
PhC(OO )HR
2
t-BuOH
PhCH2R
PhCHR
PhCH(OOH)R.
(3)
t-BuOH
t-BuOOH
PhCHO
2.65
0.20
0.09
0.06
2.31
Traces
0.25
2.64
0.17
0.18
0.15
2.69
Traces
0.15
B
As the products of the oxidation of alkene IV with
systems I + II and I + III we identified benzaldehyde
and benzoic and acetic acids. The high yields of the
aldehyde and acids which may be formed by oxidation
of the corresponding aldehydes suggests that these
compounds may be formed by direct reaction of the
carbon-centered and hydroperoxyl radicals via inter-
mediate formation of 1,2-dioxetane C whose decom-
position gives rise to benzaldehyde and acetaldehyde.
PhC(O)R
0.05
0.04
Products of hydrolysis of nonvolatile residued, e
t-BuOH
1.69
0.14
3.61
Traces
0.06
1.61
0.15
0.05
0.15
3.23
Traces
0.08
t-BuOOH
PhCH(OOH)Rf 0.05
ROHg
0.07
0.11
0.18
Epoxidation
products
HOCH CH2h
O
HOCH CH CH2
2
O
0
0.20
0.13
.15
0.10
0.10
0.14
0.10
0.10
0.01
0.02
H H
Ph C C CH
PhCH CH=CH + OOH
2
3
PhC(O)OH
MeC(O)OH
O O
C
a
b
Averaged results. Conversion, %: 0.51 (IV, M = Al), 0.60
(4)
(
IV, M = Ti), 0.50 (V, M = Al), and 0.37 (V, M = Ti).
c
d
Oxygen evolution is qualitatively detected. Aluminum and
e
PhCHO + MeCHO
titanium, by 1 mol in all experiments.
f
Acetaldehyde is
identified by TLC. Hydroperoxides are identified by the
Scheme (4) is realized with alkene IV only.
However, benzaldehyde and benzoic acid were also
detected with alkene V. Moreover, the observation of
allyl alcohol and hydroxymethyloxirane with alkene
V, as well as of vinyl alcohol and hydroxyethanal
products of catalytic decomposition in the presence of
g
benzenesulfonic acid: PhOH and RCHO.
h
Determined as
MeC(O)OR.
Determined as hydroxyethanal.
subject the hydrocarbon skeleton of phenylalkenes IV
and V to a deep destruction.
(
with alkene IV) suggest that the hydrocarbon skele-
ton of the alkene decomposes in an alternative way.
Presumably, this process, as well as epoxidation of
the double bond involves organometallic peroxides D
formed by reactions of alcoholates II and III with
hydroperoxides B [scheme (5)].
We suppose that the oxygen generated by reaction
1) reacts with the benzyl methylene group of hydro-
carbons IV and V to give hydroperoxyl and carbon-
centered radicals [1, 8]. The carbon-centered radical
is oxidized with the hydroperoxyl radicals to a
carbonyl compound, or they dimerize to give hydro-
peroxide B [scheme (2)].
(
PhCH(OOH)R + (t-BuO) M
n
PhC(R)HOOM(OBu-t)n 1 + t-BuOH
D
PhCH R + A
PhCHR + OOH
(5)
2
(
t-BuO) M
n
a
b
(2)
PhC(O)R + HOM(OBu-t)n 1 PhCHO + ROM(OBu-t)n 1
M = Al, n = 3; M = Ti, n = 4.
PhC(O)R + H O PhCH(OOH)R
2
B
M = Al, n = 3; M = Ti, n = 4; R = CH=CH ; R =
2
Aluminum- and titanium-containing peroxides D
undergo intramolecular decomposition by two path-
ways. Hydrogen migration from the benzyl group to
CH CH=CH .
2
2
However, it is not inconceivable that the tert-
butoxyl radical formed by decomposition of the metal- the oxygen atom attached to metal yields alkenyl
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 10 2001

LOW-TEMPERATURE OXIDATION OF PHENYLALKENES
1595
phenyl ketones [scheme (5), pathway a]. The second
pathway involves destruction of the hydrocarbon
skeleton, as evidenced by the presence of unsaturated
alcohols and benzaldehyde among the reaction pro-
ducts [scheme (5), pathway b].
for the allyloxy group in the case of system I + II we
can write scheme (7):
Aluminum and titanium tert-butoxy(hydroxy)
derivatives react with the t-BuOM bond, which is
confirmed by the absence of OH absorption from the
IR spectra of nonvolatile residues. Organometallic
peroxides D are difficult to identify because of the
facility of their subsequent transformations [scheme
(
7)
An intramolecular scheme of epoxidation of allyl
alcohols by systems I + II and I + III have been
proposed in [7, 14, 15]. However, Adam et al. [16]
proposed an intermolecular scheme of epoxidation in
the presence of titanium alcoholates. We found no
direct reaction of the double bonds of substrates IV
and V with oxygen.
(
5), pathways a and b]. However, that alkene oxida-
tion can involve formation of such peroxides and their
decomposition with destruction of the hydrocarbon
skeleton was proved in our previous work [3]. The
products of reaction of 2,3-dimetyl-2-butene with
system I + II are identical to those obtained by in-
dependent synthesis from the corresponding hydro-
peroxide, 3-hydroperoxy-2,3-dimethyl-1-butene, and
alcoholate II [3].
Thus, the oxygen generated by the systems alu-
minum tert-butylate or titanium tetra-tert-butylate
tert-butyl hydroperoxide selectively react with C H
bonds of the benzyl methylene group to give carbon-
centered and hydroperoxyl radicals. The latter oxidize
benzyl-like radicals, yielding carbonyl compounds
with preservation or cleavage of C C bonds, as well
as hydroperoxides. Oxidation of benzene or vinyl
carbon hydrogen bonds, as well as direct reaction of
the evolved oxygen with the alkene double bond were
not found.
Earlier, with alkylaromatic ketones as example, we
showed that system I + II smoothly and selectively
oxidizes a methylene group to carbonyl [11], giving
rise to -dicarbonyl compounds. The latter under the
reaction conditions undergo carbon carbon bond c
leavage to form carboxylic and percarboxylic acids
[
12]. Similar transformations might be expected for
allyl phenyl ketone PhC(O)CH CH=CH arising in
2
2
the reaction with alkene V. However, as seen from
the table, no this process takes place. Therefore, it is
reasonable to suggest that the destruction scheme we
proposed [scheme (5)] deserves attention.
EXPERIMENTAL
The IR spectra were recorded on a Specord IR-75
instrument.
Unsymmetrical metal alkoxy derivatives undergo
further transformations. Thus, vinyloxy derivatives
react with t-BuOH [9], expelling acetaldehyde
Chromatographic analysis was performed on a
Tsvet 2-65 chromatograph, flame-ionization detector,
carrier gas argon. Volatile components (tert-butanol,
methyl acetate, vinyl acetate, and allyl acetate) were
analyzed on a 2400 3-mm column, packing 10%
PEGA on TZKM brick, 55 70 C. 3-Phenyl-1-propene,
[scheme (6)].
CH =CHOM(OBu-t)
+ t-BuOH
n 1
2
M(OBu-t)n + AcH.
(6)
4
-phenyl-1-butene, benzaldehyde, phenol, and 1-
Aldehydes are oxidized to aluminum acyloxy com-
pounds under the reaction conditions [13]. The IR
spectra of nonvolatile residues show broad bands at
1
1
570 1600 cm , characteristic of COO stretching
vibrations, while among the hydrolysis products we
found carboxylic acids.
The hydroxyethanal and hydroxymethyloxirane
found among the products of hydrolysis of nonvolatile
residues, too, result from transformations of aluminum
and titanium alkoxy derivatives.
These transformations involve oxidation of the
double bond of the alkenyloxy group. For instance,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 10 2001

1596
MARTYNOVA et al.
aluminum and titanium, by precipitation as metal
hydroxide and calcination to Al O and TiO , res-
pectively. Carboxylic acids were identified as methyl
esters after treatment with diazomethane [19]. Car-
bonyl compounds were identified as 2,4-dinitro-
phenylhydrazones by the melting point and by TLC
The residue (viscous orange substance) was dis-
solved in distilled diethyl ether and treated with 10%
sulfuric acid. The ethereal layer was dried with
sodium sulfate. The ether extract contained 0.69 g of
t-BuOH, 0.11 g of t-BuOOH, 0.06 g of PhCH(OON)
CH CH=CH , 0.06 g of hydroxymethyloxirane, and
2
3
2
2
2
(
Silufol UV-254, eluent benzene). Analysis of volatile
0.10 g of benzoic acid. The aqueous-acidic hydro-
lyzate contained 0.21 g of aluminum and 0.23 g of
t-BuOH. For determination of alkoxy groups, the
residue from a parallel run, after removal of benzene
and volatile reaction products, was dissolved in
benzene and treated with acetic anhydride [28]. We
found 0.11 g of allyl acetate (corresponds to 0.07 g
of allyl alcohol).
fractions for hydroperoxide I was performed by
chromatography. Hydroperoxides formed by oxidation
of phenyl-substituted alkenes were determined by
iodometric titration and identified by the acid decom-
position products: PhOH and RCHO [20].
Aluminum tri-tert-butylate (II) was obtained by
reaction of tert-butanol with aluminum [21] and
purified by sublimation [160 170 C (1 mm)]. Found
Al, %: 11.12. C H AlO . Calculated Al, %: 10.96.
Reactions of alkenes IV and V with systems I +
II and I + III and analysis of reaction products
were performed in a similar way. The IR spectra of
1
2
27
3
tert-butoxytitanium (III) was purified by vacuum
1
9
the nonvolatile residues contain absorption bands at
distillation, bp 80 C (2 mm), nD 1.4436 [22].
-Phenyl-1-propene (IV) and 4-phenyl-1-butene
V) were obtained by treatment of ethereal solutions
20 and 2975 cm 1 (=CH ), at 1645 cm (C C), and
1690 and 1710 cm [ (C=O)], which is evidence for
the formation of benzaldehyde and alkenyl phenyl
ketones before hydrolysis.
1
9
2
1
3
(
of phenylmagnesium bromide and benzylmagnesium
chloride with allyl bromide [23, 24]. The refractive
indices and boiling points of the products coincide
with those reported in [25].
The presence of epoxy compounds among the re-
action products was proved by quantitative reactions
(color reaction with pyridine on heating [29] and
1-Phenyl-2-propen-1-one was obtained by decom-
silver iodate precipitation [30]).
position of the corresponding Mannich salt [26], bp
1
9
Hydroperoxides B were identified by paper chro-
matography [1], as well as by the formation of phenol
and RCHO [20]. The reaction mixture was allowed to
stand for 24 h at room temperature and treated as
described above. The residue after hydrolysis was
dissolved in benzene and divided into two. The first
5
7 59 C (2 mm), n 1.4180, mp 264 266 C (2,4-di-
D
nitrophenylhydrazone). Hydroxymethyloxirane was
synthesized by treatment of allyl alcohol with tert-
butyl hydroperoxide in the presence of vanadium
acetylacetonate [6]; colorless liquid, bp 48 C (8 mm),
1
8
1
n
1.4314. IR spectrum, , cm : 860, 920, 1250,
D
part was treated with benzenesulfonic acid (c 2
3
050 (epoxide ring), 3460 (OH). Found OH, %: 21.41.
3
10
M) and heated at 50 60 C for 3 h. By analyzing
C H O . Calculated OH, %: 22.97. Hydroxyethanal
6
12
2
both fractions, we followed the increasing amount of
hydroperoxide decomposition products (PhOH and
RCHO).
was prepared by treatment of aqueous ethylene glycol
and ferrous sulfate heptahydrate [27], mp 94 C (from
ethanol). The melting point of glyoxal phenylosazone
is 176 C [25]. The concentration of the tert-butyl
hydroperoxide used was no less than 99.5 99.8%.
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 10 2001