Catalytic oxidation of olefins and alcohols with hydrogen peroxide in a two-phase system giving mono- and dicarboxylic acids

Article abstract of DOI:10.1007/s11172-006-0047-z

The present study considered the influence of various factors on the catalytic activity of systems based on a combination of tetrakis(oxodiperoxotungsto)phosphate(3-) with quaternary ammonium cations, for example, with methyltri-n-octylammonium [Me(n-C₈H₁₇) ₃N]⁺. The catalysts were tested in oxidation of cycloolefins (cyclohexene and cyclooctene), alcohols (octan-1-ol and phenylmethanol), and unsaturated fatty acids (cis-9-octadecenoic and 12-hydroxy-9Z-octadecenoic acids) with a 30% hydrogen peroxide solution. These reactions proceed under mild conditions (atmospheric pressure, 80-90°C) to give carboxylic acids. The catalytic systems were characterized by vibrational (IR and Raman) spectroscopy. The state of the systems formed from various precursors, viz., polyoxometallates and phase-transfer catalysts, was studied. It was demonstrated for the first time that the structure formation of peroxo complexes depends on the nature of the halide anion of the quaternary ammonium salt used. The melting points of individual catalytic complexes were determined. The optimal conditions for oxidation were found.

Full text of DOI:10.1007/s11172-006-0047-z

Russian Chemical Bulletin, International Edition, Vol. 54, No. 8, pp. 1847—1854, August, 2005
1847
Catalytic oxidation of olefins and alcohols
with hydrogen peroxide in a twoꢀphase system
giving monoꢀ and dicarboxylic acids
Z. P. Pai,ꢀ A. G. Tolstikov, P. V. Berdnikova, G. N. Kustova, T. B. Khlebnikova, N. V. Selivanova,
A. B. Shangina, and V. G. Kostrovskii
G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences,
5 prosp. Akad. Lavrent'eva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383) 330 8056. Eꢀmail: zpai@catalysis.nsk.su
The present study considered the influence of various factors on the catalytic activity of
systems based on a combination of tetrakis(oxodiperoxotungsto)phosphate(3–) with quaterꢀ
nary ammonium cations, for example, with methyltriꢀnꢀoctylammonium [Me(nꢀC8H17)3N]+.
The catalysts were tested in oxidation of cycloolefins (cyclohexene and cyclooctene), alcohols
(octanꢀ1ꢀol and phenylmethanol), and unsaturated fatty acids (cisꢀ9ꢀoctadecenoic and
12ꢀhydroxyꢀ9Zꢀoctadecenoic acids) with a 30% hydrogen peroxide solution. These reactions
proceed under mild conditions (atmospheric pressure, 80—90 °C) to give carboxylic acids. The
catalytic systems were characterized by vibrational (IR and Raman) spectroscopy. The state of
the systems formed from various precursors, viz., polyoxometallates and phaseꢀtransfer cataꢀ
lysts, was studied. It was demonstrated for the first time that the structure formation of peroxo
complexes depends on the nature of the halide anion of the quaternary ammonium salt used.
The melting points of individual catalytic complexes were determined. The optimal conditions
for oxidation were found.
Key words: phaseꢀtransfer catalysis, peroxopolyoxotungstates, oxidation, cycloalkenes,
alcohols, unsaturated fatty acids, carboxylic acids.
Scheme 1
Monoꢀ and dicarboxylic acids are of interest as prodꢀ
ucts of largeꢀscale industry (adipic, suberic, benzoic, etc.
acids) or intermediates in the synthesis of biologically
active compounds.
Carboxylic acids can be prepared by oxidation of oleꢀ
fins with ozone or oxometallic reagents, such as potasꢀ
sium permanganate. Ruthenium tetroxide is used, as a
rule, together with NaOCl4 or NaOI4, organic hydroperꢀ
oxides, or peracids. The selectivity of these reactions with
respect to the target carboxylic acid is at most 40—50%
due to formation of a large amount of byꢀproducts and
partial oxidation of hydrocarbons to CO2 and H2O. For
this reason, a twoꢀstep method is used for the industrial
production of carboxylic acids, for example, adipic acid
(Scheme 1). This process includes initial oxidation of
cyclohexane with atmospheric oxygen yielding a mixture
of cyclohexanol and cyclohexanone followed by oxidaꢀ
tion with nitric acid to give adipic acid.1
The second step affords 6,6ꢀnitrohydroxyiminohexaꢀ
noic acid as one of the main intermediates, whose conꢀ
centration in the reaction mixture has a substantial effect
on the yield of adipic acid. In addition to 6,6ꢀnitroꢀ
hydroxyiminohexanoic acid, the reaction gives other inꢀ
termediates, which are transformed into lower dicarboxyꢀ
lic acids (glutaric, succinic, and oxalic).2 The addition of
the steps of separation and purification of the final prodꢀ
uct to the technological process is associated with inꢀ
vestments in plants for the production of adipic acid.
Besides, the use of nitric acid as an oxidizer results in
the formation of toxic nitrogen oxides. The aboveꢀmenꢀ
tioned drawbacks are typical also of other technologiꢀ
cal methods for the synthesis of monoꢀ and dicarboxylic
acids.
The synthesis of carboxylic acids by direct catalytic
oxidation of unsaturated hydrocarbons (Scheme 2) is of
great interest. An aqueous hydrogen peroxide solution is
among the most suitable oxidizers.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1794—1801, August, 2005.
1066ꢀ5285/05/5408ꢀ1847 © 2005 Springer Science+Business Media, Inc.

1848
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Pai et al.
Scheme 2
Table 1. Quaternary ammonium salts Q•X•nH2O (1) used in
the synthesis of the catalytic complexes
Salta
Q+
X–
n
Manufacturer
(concentration;
m.p.b/°C)
Cat is a catalyst
1Aa
1Ab
Bun4N+
Bun4N+
F–
3
Fluka Chemie
(>98%; 58—60)
Acros (95%; 70)
Acros (98%; 83—86)
Acros (Aliquat® 336)
Aldrich or
The advantages of this method are that the process
occurs in one step, is efficient and ecologically safe, and
requires inexpensive reagents.
Cl–
Cl–
Cl–
Br–
0
1
0
1
+
1Bb C5H5N(nꢀC16H33
1Cb MeN(nꢀC8H17 3
1Bc C5H5N(nꢀC16H33
)
+
)
+
Systems based on peroxopolyoxometallates combined
with phaseꢀtransfer catalysts, viz., quaternary ammonium
salts, are recognized as the most efficient catalysts for
oxidative cleavage of unsaturated hydrocarbons in a twoꢀ
phase medium.3—7
To use peroxopolyoxometallateꢀbased multicompoꢀ
nent systems, it is necessary to study in detail both the
formation of active catalytic complexes and the mechaꢀ
nism of oxidation reactions of organic substrates.
The aim of the present study was to synthesize peroxoꢀ
polyoxotungstophosphate complexes combined with quaꢀ
ternary ammonium cations and to use these complexes
for oxidation of various organic substrates.
)
Lancaster (98%; 67—71)
a Hereinafter, The letters A, B, and C in the notations of the
compounds correspond to different Q+, the letters a, b, and c
correspond to the F–, Cl–, and Br– anions, respectively.
b www.acros.be.
Quaternary ammonium halides (QAH) 1 listed in Table 1
and H3PW12O40 (reagent grade) or Na2WO4•2H2O (reagent
grade) with H3PO4 (reagent grade) were used in experiments.
Tungstophosphoric heteropolyacid (HPA) was additionally
purified by recrystallization from water. The purity of HPA was
checked by 31Р NMR spectroscopy. The number of water molꢀ
ecules in crystal hydrates of HPA was determined gravimetriꢀ
cally; the calcination temperature was 500 °C. Sodium tungstate
was transformed into H2WO4 by treating an aqueous Na2WO4
solution with concentrated HCl (stirring for 30 min). The reꢀ
sulting yellow gelꢀlike compound was washed with water until
the reaction for Cl– became negative and then centrifuged. The
precipitate was separated on a glass filter and dried in air at room
temperature. According to the results of IR spectroscopic analyꢀ
sis, the finely dispersed precipitate thus obtained corresponded
to H2WO4.
Synthesis of catalytic complexes. Compounds 2Aa, 2Ab, 2Bb,
and 2Bc (Tables 2 and 3) were synthesized according to a known
procedure.9 A 25% H2O2 solution (34 mL, 250 mmol) was added
to a solution of H3PW12O40•15.4•H2O (4.0101 g, 1.27 mmol) in
water (5 mL). The reaction mixture was stirred at room temꢀ
perature for 0.5 h, and then salt 1 (3.81 mmol) was added
portionwise as dry salt 1Bc (1.5334 g) or solutions of salts 1Aa
Experimental
Cyclohexene (99%), cyclooctene (98%, Acros), benzyl alcoꢀ
hol (highꢀpurity grade), octanꢀ1ꢀol (reagent grade), cisꢀ9ꢀoctaꢀ
decenoic (oleic) acid (highꢀpurity grade), and dichloromethane
(analytical grade) were used. 12ꢀHydroxyꢀ9Zꢀoctadecenoic (riꢀ
cinoleic) acid was isolated from castor oil: triglycerides were
subjected to alkaline hydrolysis (saponification) to prepare a
mixture of unsaturated fatty acids, which were separated by
chromatography on a column with silica gel8 (L100/160 µm,
Merck, hexane—ethyl acetate, 7 : 2, as the eluent, ricinoleic
acid, Rf 0.12). The structure of the resulting compound was
1
confirmed by H and 13C NMR and IR spectroscopy. The conꢀ
centration of hydrogen peroxide (special purity grade) in an
aqueous solution was determined by iodometric titration.
Table 2. Catalytic complexes Q3{PO4[WO(O2)2]4} (2 and 3)
Comꢀ
pounda
Value of Q
in the complex
Precursors
Characteristics of the sample (m.p./°C)
Oxometallate
QAH
[Bun4N]3+ (A)
H3PW12O40•15.4H2O
H3PW12O40•15.4H2O
1Aa
1Ab
1Bb
1Bc
1Cb
1Cb
White crystalline compound (129—130)
White crystalline compound (127—128)
White crystalline compound (130—131)
Bright yellow crystalline compound (65—68)
Yellowish syrupꢀlike substance
+
2Aa
2Ab
2Bb
2Bc
2Cb
3Cb
[Bun4N]3 (A)
+
[C5H5N(nꢀC16H33)]3+ (B) H3PW12O40•15.4H2O
[C5H5N(nꢀC16H33)]3 (B) H3PW12O40•15.4H2O
[Me(nꢀC8H17)3N]3+ (C)b
H2WO4 + H3PO4
+
c
[Me(nꢀC8H17)3N]3 (C)
H2WO4 + H3PO4
Yellowish syrupꢀlike substance
a The letters A, B, and C in the notations of compounds 2 and 3 correspond to different Q+, the letters a, b, and c
correspond to the F–, Cl–, and Br– anions, respectively.
b According to the results of IR spectroscopy, the composition of the catalyst is partially inconsistent with this formula.
c The catalyst was prepared with the use of colloidal H2WO4.

Catalytic oxidation of unsaturated hydrocarbons
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1849
(1.2022 g), 1Ab (1.060 g), and 1Bb (1.3640 g) in water (2 mL).
The solid precipitate was filtered off on a glass filter, washed
with a small amount of water, and dried in air.
dropwise with stirring to the aqueous phase (1 : 1) to pH 3 and
the reaction mixture was kept at 8—10 °C for ~10 h. The crystalꢀ
line precipitate that formed was filtered off, washed with a small
amount of cold water (<5 °C), and dried in air. The identificaꢀ
tion was carried out by IR spectroscopy.
nꢀOctanoic acid was isolated from the reaction mixture by
extraction with CH2Cl2 (1×10 mL and 3×5 mL). The extract
was concentrated on a water bath to obtain an oily liquid, which
was dried in a desiccator over CaCl2 (n24 1.4290).
Compounds 2Cb and 3Cb (see Table 2) were synthesized
according to a procedure published earlier.10 The procedures for
the synthesis of compounds 2Cb and 3Cb differ in that colloidal
H2WO4 was used in the synthesis of 2Cb, whereas solid H2WO4
was used in the synthesis of 3Cb. A mixture of 25% H2O2 (3.8 mL,
28.1 mmol) and H2WO4 (4.55 mmol) was vigorously stirred in a
temperatureꢀcontrolled glass reactor at 60 °C until the solution
turned completely colorless and cooled to room temperature.
Then an H3PO4 solution (1.143 mmol) was added with vigorous
stirring and cooling (T < 20 °C). Salt 1Cb (0.9215 g, 2.28 mmol)
dissolved in CH2Cl2 (18.2 mL) was added with stirring to the
resulting solution for 2 min. The reaction mixture was stirred for
15 min. Then the organic phase was separated, dried over Na2SO4
(~15 h), filtered, and concentrated at 40—50 °C to obtain a
yellowish syrupꢀlike substance.
The IR spectra of the samples as Nujol mulls or in KBr
pellets were recorded on a Bomem MBꢀ102 Fourierꢀtransform
IR (FTIR) spectrometer in the 400—4000 cm–1 region. The
Raman spectra were measured on a Bruker 100/S Fourierꢀtransꢀ
form spectrometer in the 100—1200 cm–1 cm–1 with the use of a
NdꢀYAG laser (λ = 1.06 µm, power was 100 mW) as the radiaꢀ
tion source.
Results and Discussion
Catalytic complexes. In our earlier investigations11 and
studies by other authors,3—5,9,10 the in situ synthesis of
the catalyst has been demonstrated to give mixtures of
structurally different peroxo complexes, for example,
the tungsten peroxo complexes Q3{PO4[WO(O2)2]4},
Q2[W2O3(O2)4(H2O)2], and Q2{HPO4[WO(O2)2]2}. The
complex anion {PO4[WO(O2)2]4}3– shows the highest
catalytic activity. Hence, when developing procedures for
the synthesis, we sought to prepare a catalytic system
involving this anion (see Table 2, Fig. 1) using QAH with
A
Catalytic oxidation of organic substrates. Selective catalytic
oxidation of cycloalkenes, alcohols, and unsaturated fatty acids
was carried out in a shaken (>600 rpm) "catalytic duck" reacꢀ
tor11 or in a temperatureꢀcontrolled conical flask equipped with
a reflux condenser with the use of a magnetic stirrer (600 rpm).
The temperature of 80—90 °C was maintained with an accuracy
of 0.1 °C using a water thermostat. The reaction mixture was
prepared as follows: a weighed sample of the catalyst was placed
in the reactor, the substrate was added, the reaction mixture was
stirred, 30% H2O2 was added, and heating was switched on. The
conversion of unsaturated hydrocarbons and alcohols was deterꢀ
mined by GLC on a Tsvetꢀ500 chromatograph equipped with a
flame ionization detector and a 3 m × 2 mm steel column (0.4%
OVꢀ225 on graphitized thermal carbon black, nitrogen as the
carrier gas, the evaporator temperature was 150 or 180 °C, the
column temperature was 100 or 140 °C, the detector temperaꢀ
ture was 120 °C). The conversion of unsaturated fatty acids was
monitored by TLC on Silufol plates (Chemapol) using a 3 : 2
hexane—ethyl acetate mixture as the eluent. In some experiꢀ
ments, oxidation products were analyzed by GLC on a Tsvetꢀ500
chromatograph equipped with a flame ionization detector and a
1 m × 3 mm stainless steel column (SKTFT 15% on Inerton
AWꢀDMCS as the stationary phase, the column temperature
was varied in the range of 100—325 °C, the rate of temperature
rise was 15 K min–1, the evaporator temperature was 300 °C,
helium as the carrier gas). The component contents were deterꢀ
mined by internal normalization; the accuracy of measurements
was 10 rel. %.
a
1000
800
800
600
ν/cm–1
A
b
c
1000
600
ν/cm–1
A
1000
800
600
ν/cm–1
A
d
Procedures for isolation of carboxylic acids from the reaction
mixture. To quantitatively extract adipic, suberic, and benzoic
acids, the reaction mixture was cooled to room temperature, a
10% NaHCO3 solution (30 mL) was added, the mixture was
transferred to a separating funnel, CH2Cl2 (30 mL) was added,
and the reaction mixture was stirred. The organic layer was
separated from the aqueous layer by washing 2—3 times with a
saturated NaHCO3 solution. Hydrochloric acid was added
1000
800
600
ν/cm–1
Fig. 1. IR spectra of complexes 2Aa (a), 2Ab (b), 2Bb (c), and
2Bc (d) prepared by the reactions of H3PW12O40, H2O2, and
correspondingly QAH 1Aa, 1Ab, 1Bb, and 1Bc.

1850
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Pai et al.
various anions (1Aa with F–, 1Ab, 1Bb, and 1Cb with Cl–,
and 1Bc with Br–). As can be seen from Table 2 and
Fig. 1, the absorption bands in the IR spectra of complex
compounds 2Aa, 2Ab, and 2Bb prepared with the use of
quaternary ammonium fluoride (QAF) or chloride (QAC)
correspond to the {PO4[WO(O2)2]4}3– anion and agree
well with our results11 and the published data.3,4,10
spond to the K2[W2O3(O2)4(H2O)2] (956, 851, 619, 568,
558, 331, and 318 cm–1) and [Bu4N]3{PO4[WO(O2)2]4}
(980, 860, 591, 578, 534, 330, 298, and 259 cm–1) comꢀ
pounds and are consistent with the results of the study.9
In the synthesis of complex 2Bc with the use of quaꢀ
ternary ammonium bromide (QAB) 1Bc, the reaction mixꢀ
ture warmed up and vigorous foaming occurred in the
step of precipitation of the peroxo complex. These pheꢀ
nomena were not observed in reactions with the use of
QAF and QAC. In the IR spectrum of the yellow crystalꢀ
line compound (2Bc) prepared by precipitation of the
peroxo complex with QAB (1Bc), the absorption bands of
The IR spectrum of complex compound 2Aa (see
3–
Fig. 1) shows absorption bands of the PO4 ion (1085,
1052, and 1038 (sh) cm–1), the W=O bond (971 cm–1),
the O—O bond (856 and 845 cm–1), and antisymmetꢀ
ric and symmetric vibrations of W—O—O (590 and
521 cm–1). The spectrum also has other absorption bands
(722, 736, 651, 577, and 550 cm–1) associated with abꢀ
sorption of the cation.
3–
the PO4 ion (1089, 1069, and 1032 (sh) cm–1) only
partially consistent with the published data.9,10 Other abꢀ
sorption bands in the spectrum do not correspond to
the catalyst [C5H5N(CH2)15Me]3{PO4[WO(O2)2]4} (see
Fig. 1, d).
The IR spectrum of complex compound 2Ab shows
3–
absorption bands of the PO4 ion (1082, 1051, and
1036 (sh) cm–1), the W=O bond (970 cm–1), the O—O
bond (855, 844 cm–1), antisymmetric and symmetric viꢀ
brations of W—O—O (591 and 521 cm–1), and absorption
bands at 721, 735, 650, 574, and 549 cm–1 characterizing
the cation.
The observed influence of QAB (1Bc) on decomposiꢀ
tion of the peroxo complex can be attributed to the higher
reducing power of the bromine salts compared to QAF
and QAC (QBr > QCl > QF), which is also true for the
series of halogens F2 > Cl2 > Br2, whose standard redox
potentials (E°)12 are 2.87, 1.359, and 1.065 V, respecꢀ
The IR spectrum of compound 2Bb has absorption
bands of the PO43– ion (1088, 1061, and 1038 (sh) cm–1),
the W=O bond (988 and 961 cm–1), the O—O bond
(856 and 844 cm–1), antisymmetric and symmetric vibraꢀ
tions of W—O—O (591 and 526 cm–1), and absorption
tively. Apparently, the redox reactions W2O5 + 2 Br–
+
2 H+ → Br2 + 2 WO2 + H2O resulting in decomposition
of tungsten peroxo complexes can occur in solution upon
the addition of QAB.
bands at 722, 650, 571, and 548 cm–1
.
This assumption is also supported by the characteristic
features encountered by mixing with KBr and compacting
into wafers for measurements of IR spectra. As can be
seen from Fig. 3, the spectra of catalysts 2Aa and 2Bb,
which were synthesized with the use of QAF (1Aa) and
QAC (1Bb), respectively, recorded in KBr pellets (a, c)
differ from the spectra measured as Nujol mulls (b, d).
The spectra b and d correspond to the structures of the
complexes synthesized, whereas the absorption bands in
the spectra a and c are inconsistent with these structures,
which can be associated with decomposition of the comꢀ
plexes due to interaction of the Br– ions with the peroxide
groups. The longer the time from the preparation of the
sample to the onset of exposure, the larger discrepanꢀ
cies observed in the spectra. An analogous situation is
also characteristic of the tungsten peroxo complexes
[W2O3(O2)4(H2O)2]2–. The IR spectra of the potassium
salt of this complex are shown in Fig. 4.
The Raman spectra (Fig. 2) were recorded for catalyst
2Aa and the complex salt, which was prepared from the
filtrate after isolation of 2Aa according to the procedure
described earlier.11 The spectra a and b (see Fig. 2) correꢀ
a
1200
800
400
ν/cm–1
b
Attempts to change the conditions of the synthesis in
the step of addition of QAH (variations in the temperaꢀ
ture (5—30 °C) and pH, the addition of either dry QAH
or QAH predissolved in water) were unsuccessful. Thereꢀ
fore, regardless of the nature of the quaternary cation,
QAB do not allow one to perform the synthesis of cataꢀ
lytic systems of the desired composition including tungꢀ
sten peroxo complexes.
1200
800
400
ν/cm–1
Fig. 2. Raman spectra of the catalysts based on
peroxopolyoxometallates: К2[W2O3(O2)4(H2O)2] (a) and
[Bun4N]3{PO4[WO(O2)2]4} (b).
Of all the complexes synthesized (see Table 2), tetraꢀ
nꢀbutylammonium tetra(diperoxotungsto)phosphate (2Aa

Catalytic oxidation of unsaturated hydrocarbons
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1851
A
A
a
b
1000
800
600
ν/cm–1
1000
800
600
ν/cm–1
A
A
c
d
1000
800
600
ν/cm–1
1000
800
600
ν/cm–1
Fig. 3. IR spectra of the catalytic complexes Q3{PO4[WO(O2)2]4}: [Bun4N]3{PO4[WO(O2)2]4} 2Aa and 2Ab (a, b) and
[C5H5N(CH2)15CH3]3{PO4[WO(O2)2]4} 2Bb and 2Bc (c, d); a and c, in KBr pellets; b and d, as Nujol mulls.
and 2Ab) is most stable on storage. This complex can be
kept at room temperature for one month. The changes in
the IR spectrum of methylꢀtriꢀnꢀoctylammonium
di(diperoxotungsto)hydrophosphate (3Cb) characterized
by absorption bands at 1264, 1088, 1056, 1033 (sh), 973,
892, 855, 846, 741, 733, 702, 651, 625, 591, 576, 549, and
523 cm–1 are observed after three days. The Nꢀ
hexadecylpyridinium tetra(diperoxotungsto)phosphate
complex (2Bb) is less stable. This complex remains unꢀ
changed for only one day. Therefore, the order of deꢀ
creasing stability for the above complexes is as follows:
K2[W2O3(O2)4(H2O)2] > [Bun4N]3{PO4[WO(O2)2]4} (2Aa,
rocking speed (m) >500 rpm, i.e., the observed plot of the
reaction rate vs. the rocking speed is characterized by the
presence of a plateau. At the same time, a plateau was
achieved already at m = 300 rpm when the reaction was
performed in a conical flask with magnetic stirring of a
twoꢀphase solution. It should also be noted that the volꢀ
ume of the reaction mixture for the reactors under conꢀ
sideration was ~1/3 of the reactor volume. An interesting
result was obtained when we performed parallel experiꢀ
ments on oxidation of benzyl alcohol with the use of the
aboveꢀdescribed reactors at m = 600 rpm, all other factors
being the same. It was found that the degree of conversion
of the alcohol (a peak at 120 °C) in a "catalytic duck" after
1.5 h (Fig. 5, a, b) is higher than that in a conical flask
equipped with a stirrer. Moreover, the conversion of the
alcohol in a "catalytic duck" after 3 h (see Fig. 5, a´ and b´)
was 100%, and byꢀproducts were virtually absent (a´).
The yield of the target product, viz., PhCO2H, was
98—99%, whereas large amounts of byꢀproducts, includꢀ
ing benzyl benzoate (peak at 210 °C), were present in the
organic phase prepared by the reaction in a reactor
equipped with a stirrer (b´) in spite of a rather high degree
of conversion of the alcohol (a peak at 120 °C), the yield
of PhCO2H being 60%. Therefore, the above experimenꢀ
tal data suggest that not only the reaction rate but also the
reaction mechanism depend substantially on the mode of
stirring of a twoꢀphase mixture. This is consistent with the
2Ab)
>
[Me(nꢀC8H17)3N]2{HPO4[WO(O2)2]2} (3Cb)
>
> [C5H5N(CH2)15Me]3{PO4[WO(O2)2]4} (2Bb)
The fact that we synthesized individual complex comꢀ
pounds 2Aa, 2Ab, 2Bb, and 3Cb rather than mixtures of
compounds, for example, 2Aa + 1Aa is supported not
only by the data from IR and Raman spectroscopy but
also by the melting points (see Table 2), which differ
substantially from the melting points of QAH (see Table 1).
It is not inconceivable that the resulting compounds conꢀ
tain halide ions as impurities, because the complexes were
not thoroughly washed off from F– and Cl– ions.
Oxidation of organic substrates. Experiments on oxiꢀ
dation of various organic substrates with 30% H2O2
showed that the use of a "catalytic duck" reactor allows
one to prepare products in the highest yields at a given

1852
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Pai et al.
A
1
2
1
a
a
a´
3
3
1000
800
600
ν/cm–1
2
1
A
3
b
1
b
b´
3
2
1000
800
600
ν/cm–1
A
Fig. 5. Chromatograms of the organic phase of the reaction
mixture prepared by oxidation of benzyl alcohol: a, a "catalytic
duck"; b, a conical flask equipped with a stirrer; the reaction
time was 1.5 (a, b) and 3.0 h (a´, b´); solvents: 1, (EtOH);
2, PhCH2OH; 3, PhCHO.
c
face are not increased. In this connection, the observed
rates of the same reaction, which are obtained by mixing
twoꢀphase solutions in different hydrodynamic modes,
can hardly be expected to have a good convergence. For
the above reasons, the data on oxidation of alcohols and
cycloolefins reported in the studies,3,4,14,15 are difficult to
compare with each other. The conditions of mixing of
nonviscous liquids can be standardized by performing reꢀ
actions in a rocking "catalytic duck" reactor placed on a
highꢀspeed rocking platform.
1000
800
600
ν/cm–1
Fig. 4. IR spectra of the salt К2[W2O3(O2)4(H2O)2]: in KBr
pellets (a), as Nujol mulls immediately after mixing (b) and after
storage at 6.5 °C for 1.5 months (c).
conclusions drawn in the study13 that the use of reactors
equipped with a stirrer can give rise to an effect of the soꢀ
called slipping of the stirrer. In this case, in spite of an
increase in the rotational speed of the stirrer, the rate of
stirring and, consequently, the surface area of the interꢀ
Study of oxidation of various organic substrates
(Table 3) demonstrated that oxidation accompanied by
Table 3. Catalytic oxidation of olefinic compounds and alcohols with hydrogen peroxide
Substrate
Catalyst
T/°C
[H2O2]/[Sub]
Resulting acid
Yield (mol.%)
Cyclohexenea
Cyclooctenea
Octanꢀ1ꢀola
3Cb
2Aa
3Cb
2Ab
2Bb
3Cb
90
85
90
90
90
90
2
8
2
6
2
2
5
4
Hexaneꢀ1,6ꢀdioic
Octaneꢀ1,8ꢀdioic
nꢀOctanoic
nꢀOctanoic
Benzoic
72
60
80
81
67
81
98
86
82
<2
84
84
∼4
Benzyl
alcohola
Benzoic
Benzoic
Oleic acidb
2Bb
2Bb
80
80
Nonaneꢀ1,9ꢀdioic
nꢀNonanoic
cisꢀ9,10ꢀEpoxyoctadecanoic
Nonaneꢀ1,9ꢀdioic
3ꢀHydroxynonanoic
12ꢀHydroxyꢀ9,10ꢀepoxyoctadecanoic
Ricinoleic acidb
4
a The reaction conditions: the reaction time was 3 h; [Sub]/[Cat] = 200.
b The reaction time was 1 h, [Sub]/[Cat] = 50.

Catalytic oxidation of unsaturated hydrocarbons
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1853
double bond cleavage occurs at temperatures higher than
80 °C to give monoꢀ and dicarboxylic acids in high yields.
Oxidation of cycloolefins for 3 h affords adipic acid in
yields of up to 72% (70% after 24 h in the study4), and the
yield of suberic acid is no lower than 60%, the conversion
of cyclohexene and cyclooctene being 85%.
cording to the results of our study (see Table 3), oxidation
of oleic acid affords nonaneꢀ1,9ꢀdioic and nꢀnonaꢀ
noic acids with selectivity of 82—86%, as well as
cisꢀ9,10ꢀepoxyoctadecanoic acid (<2%), the conversion
of oleic acid being 95% (Scheme 3).
Oxidation of linear alcohols with hydrogen peroxꢀ
ide was investigated using oxidation of octanꢀ1ꢀol at
[Sub]/[Cat] = 200 (Sub is the substrate) at 90 °C as an
example. After 3 h, the reaction afforded octanoic acid in
80% yield (in the study,3 the yield was 85% after 6 h).
Oxidation of benzyl alcohol at 83 °C gave PhCO2H in
98—99% yield (85% at 90 °C in the study3) due to a more
thorough choice of the optimal ratio [H2O2]/[Sub] = 3. In
spite of the fact that, according to the stoichiometry of the
reaction
Scheme 3
i. 30% H2O2 (4 equiv.), 2Bb (2 mol.%), 80 °C, 1 h.
PhCH2OH + 2 H2O2 → PhCOOH + 3 H2O,
The aboveꢀmentioned yields are substantially higher
than the yields of the acids reported in the study,6 where
oxidation of oleic acid was performed under analogous
conditions but at 90 °C. The total yield of azelainic and
nonanoic acids was 57 and 64% after 5 and 10 h, respecꢀ
tively.
Under the conditions of oxidation of oleic acid, riciꢀ
noleic acid is converted into nonaneꢀ1,9ꢀdioic and
3ꢀhydroxynonanoic acids with selectivity of 84%
(Scheme 4). In addition, the reaction produces 12ꢀhydrꢀ
oxyꢀ9,10ꢀepoxyoctadecanoic acid (~4%) (see Table 3).
this ratio is 2, an excess of H2O2 is required to achieve
more complete oxidation.
The dependence of the yield of benzoic acid on the
[H2O2]/[Sub] ratio (Fig. 6) is indicative of the presence of
a transition region in the range from 1.8 to 3.0. In this
connection, the portionwise addition of a hydrogen perꢀ
oxide solution to the reaction mixture (three equal porꢀ
tions during the reaction) used in the study14 was, apꢀ
parently, reasonable. Since decomposition of H2O2 is
excluded or, at least, is reduced to a minimum, the
[H2O2]/[Sub] ratio would be expected to be close to the
stoichiometric value.
Scheme 4
Our experiments demonstrated that the oxidative
cleavage of unsaturated fatty acids at 80 °C in the presence
of Nꢀhexadecylpyridinium tetra(diperoxotungsto)phosꢀ
phate (2Bb) gave rise to diꢀ and monocarboxylic acids. In
addition, the reaction mixture contained a small amount
(~5%) of the partial oxidation product, viz., epoxide. Acꢀ
Yield (%)
100
80
60
40
20
To conclude, our experimental data allow the optimiꢀ
zation of the procedure for the synthesis of promising
catalytic complexes based on tungsten peroxo complexes
combined with phaseꢀtransfer catalysts for oxidation in
twoꢀphase solutions. In addition, we refined the reaction
conditions for oxidation of various organic substrates for
the preparation of industrially important monoꢀ and diꢀ
carboxylic acids.
2
4
6
8
[H2O2]/[Sub]
Fig. 6. The yield of benzoic acid as a function of the [H2O2]/[Sub]
molar ratio in oxidation of benzyl alcohol. The reaction condiꢀ
tions: [Me(nꢀC8H17)3N]3{PO4[WO(O2)2]4} (3Cb) as the cataꢀ
lyst, [Sub]/[Cat] = 200, 83 °C, 3 h.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ32425)

1854
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Pai et al.
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Received September 5, 2003;
in revised form April 13, 2004