Structure and characteristics of chitosan cobalt-containing hybrid systems, the catalysts of olefine oxidation

Article abstract of DOI:10.1134/S0036024411070211

Cobalt-containing hybrid organo-inorganic materials based on the chitosan-SiO₂, chitosan-Al₂O₃, and chitosan-cellulose systems were obtained. The surface structure and processes that occur during the formation of metal-containing materials, the catalytic properties of which were studied in the oxidation reactions of alkene, were investigated by EPR spectroscopy using a stable pH-sensitive nitroxyl radical, 4-dimethylamino-2-ethyl-5,5-dimethyl-2-(pyridin-4-yl)-2,5-dihydro-1H-imidazole- 1-oxyl, as the adsorbed probe molecules.

Full text of DOI:10.1134/S0036024411070211

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2011, Vol. 85, No. 7, pp. 1155–1161. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.V. Mekhaev, A.V. Pestov, L.S. Molochnikov, E.G. Kovaleva, M.G. Pervova, Yu.G. Yaltuk, I.A. Grigor’ev, I.A. Kirilyuk, 2011, published in Zhurnal
Fizicheskoi Khimii, 2011, Vol. 85, No. 7, pp. 1261–1267.
STRUCTURE OF MATTER
AND QUANTUM CHEMISTRY
Structure and Characteristics
of Chitosan CobaltꢀContaining Hybrid Systems,
the Catalysts of Olefine Oxidation
A. V. Mekhaeva, A. V. Pestova, L. S. Molochnikovb, E. G. Kovalevab, M. G. Pervovaa,
Yu. G. Yaltuka, I. A. Grigor’evc, and I. A. Kirilyukc
a Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620219 Russia
b Ural State Forest Engineering University, Yekaterinburg, 620032 Russia
c Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
eꢀmail: yatluk@ios.uran.ru
Received June 7, 2010
Abstract—Cobaltꢀcontaining hybrid organo–inorganic materials based on the chitosan–SiO2, chitosan–
Al2O3, and chitosan–cellulose systems were obtained. The surface structure and processes that occur during
the formation of metalꢀcontaining materials, the catalytic properties of which were studied in the oxidation
reactions of alkene, were investigated by EPR spectroscopy using a stable pHꢀsensitive nitroxyl radical,
4ꢀdimethylaminoꢀ2ꢀethylꢀ5,5ꢀdimethylꢀ2ꢀ(pyridinꢀ4ꢀyl)ꢀ2,5ꢀdihydroꢀ1Hꢀimidazoleꢀ1ꢀoxyl, as the adsorbed
probe molecules.
Keywords: chitosan cobaltꢀcontaining hybrid systems, catalysis, olefine oxidation, probe molecules.
DOI: 10.1134/S0036024411070211
INTRODUCTION
EXPERIMENTAL SECTION
Materials and Instruments
The use of hybrid organo–inorganic materials as
supports is a new area in the development of new
We used microcrystalline cellulose (MCC) with an
metalꢀcontaining catalytic materials. It allows us to ash content of 0.16% and a humidity of 1.1% proꢀ
duced by JSC Polyex; Basic aluminum oxide; BSꢀ50
silicon oxide; and chitosan produced by JSC Sonat
(Moscow), for which the degree of deacetylation
obtain supports with specific surfaces that are capable
of retaining the metallic component of a catalytic sysꢀ
tem more strongly. Chitosan, polyꢀDꢀ ꢀglucosamine,
β
1
(DD) as determined by H NMR spectroscopy was
is a commercially available amino polymer that is a
perfect complexing agent, due to the strong donor
properties of both the amino and hydroxyl groups [1].
Chitosan is thus widely used in obtaining various cataꢀ
lytic materials, including those containing Au0 that are
used in the hydroamination of alkenes [2]; Pd0, used
for the reduction of ketones [3]; the Pd0–Ni0 bimetalꢀ
lic system, used for carbonylation [4]; Os(VIII), used
for hydroxylation [5]; Co2+, used for hydration [6];
and Cu2+, used for the oxidation of catecholamines
[7]. Metalꢀcontaining hybrid organo–inorganic
materials can also be used as antibacterial composites
[8], as sorbents of proteins [9], and as pervaporation
membranes [10]. This work is devoted to investigating
0.84, the molecular weight as determined by viscosimꢀ
etry was 250 kDa [11], and the ash content was 0.19%.
The hybrid chitosan–support (SiO2, Al2O3, cellulose)
systems were obtained by depositing chitosan on the
support surface. To measure pH near the surface of the
samples, we used an aqueous solution of stable
pHꢀsensitive nitroxyl radical (NR), 4ꢀdimethylꢀ
aminoꢀ2ꢀethylꢀ5,5ꢀdimethylꢀ2ꢀ(pyridinꢀ4ꢀyl)ꢀ2,5ꢀ
dihydroꢀ1Hꢀimidazoleꢀ1ꢀoxyl [12], with a concentraꢀ
tion of 10–4 mol/l. The EPR spectra of the nitroxyl
radical solutions were registered using an ADANI
PSꢀ110X EPR spectrometer (Belarus) in the 3 cm
wavelength range at room temperature and under
optimum conditions of microwave power and ampliꢀ
tude of the magnetic field modulation.
Citrateꢀphosphate (pH 3.5–7.8) and citrateꢀsalt
(pH 1.6–4.8) buffer solutions were used to vary the pH
within the NR sensitive range of 2.5–7.5; the ionic
the surface of hybrid catalytic support (SiO2, Al2O3
,
cellulose)–chitosan–Co2+ systems by means of EPR
spectroscopy, and to assesing their catalytic properties
in the reaction of alkene oxidation.
strength of the solutions,
I, was maintained at
0.1 (KCl). Determination of pH in the pores and near
1155

1156
MEKHAEV et al.
Table 1. Composition of cobaltꢀcontaining hybrid systems (the numerator corresponds to the obtained value; the denomꢀ
inator, to the calculated value. In %)
System
С
Н
N
Cl
Co
Formula
0.5C6H11NO4
C6H11NO4 0.7CoCl2
С6Н11NО4 Co0.88Cl0.96
43.12
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
6.15
ꢀꢀꢀꢀꢀꢀꢀ
0.59
ꢀꢀꢀꢀꢀꢀꢀ
1.30
ꢀꢀꢀꢀꢀꢀꢀ
1.38
ꢀꢀꢀꢀꢀꢀꢀ
MCC–chitosan–Co2+(I)
10С6Н10О5
16Al2O3
24SiO2
⋅
⋅
Co0.4(OH)0.17Cl0.63
43.12
6.04
0.40
1.28
1.33
3.64
ꢀꢀꢀꢀꢀꢀꢀ
0.79
ꢀꢀꢀꢀꢀꢀꢀ
0.47
ꢀꢀꢀꢀꢀꢀꢀ
2.69
ꢀꢀꢀꢀꢀꢀꢀ
2.18
ꢀꢀꢀꢀꢀꢀꢀ
Al2O3–chitosan–Co2+(II)
SiO2–chitosan–Co2+ (III)
⋅
⋅
3.82
0.58
0.74
2.63
2.19
4.02
ꢀꢀꢀꢀꢀꢀꢀ
0.89
ꢀꢀꢀꢀꢀꢀꢀ
0.58
ꢀꢀꢀꢀꢀꢀꢀ
2.03
ꢀꢀꢀꢀꢀꢀꢀ
3.07
ꢀꢀꢀꢀꢀꢀꢀ
⋅
⋅
4.26
0.65
0.82
2.02
3.07
the sample surface was performed by means of spin pH values; the amount added was determined by meaꢀ
pHꢀprobes, following the method of multiple batches: suring the pH of an aqueous solution containing the
0.05 g of sample was kept in 5 ml of buffer aqueous same contents of the components.
solution containing nitroxyl radicals for two days
(established experimentally). The solution was then
decanted, and pH was determined using a Mettler
Toledo (Switzerland) ionometer and a glass electrode;
the surface moisture was removed from the sediment
by blotting it with filter paper or by centrifugation.
Measurements of the EPR spectra of the samples conꢀ
taining nitroxyl radicals were performed in unsealed
quartz ampoules.
Chromatographic measurements were performed
using a GSꢀ17A (Shimadzu, Japan) gas–liquid chroꢀ
matograph with a flame ionization detector. The peaks
were identified by relying on standard specimens. Our
chromatography–mass spectrometric study was perꢀ
formed on a Fisons MDꢀ800 chromatography–mass
spectrometer (ionization by electron impact, 70 eV;
capillary column, 30 m
phase).
×
0.25 mm; HPꢀ5 stationary
CHN analysis was performed using an automatic
analyzer developed by PerkinElmer, Inc. The surface
area of the samples was determined by nitrogen
adsorption in accordance with the BET method using
a TriStar 3000 V.6.03A instrument. The instrument
error was 0.1 m2/g. The elemental compositions of the
hybrid system surfaces were determined using an anaꢀ
lytical setup based on a VEGA II LMH scanning elecꢀ
tron microscope and an INCA ENERGY energy disꢀ
persive microanalysis system.
RESULTS AND DISCUSSION
The presence on the support surface of a polymer
that is capable of acquiring metal ions of high coordiꢀ
nation numbers is needed to fix these ions more firmly
on metalꢀcontaining composites. This role was played
by chitosan on the surfaces of the inorganic (SiO2,
Al2O3) and organic (MCC) supports. Cobalt(II) ions
were sorbed from an aqueous ethanol solution (Fig. 1).
The composition of the catalysts was characterized by
elemental analysis. According to the data, the sorption
capacity of the hybrid systems relative to cobalt(II)
ions is different and declines in the following order:
SiO2 > Al2O3 > MCC. We must note that in this case,
there is a difference between the mechanisms of bindꢀ
ing ions for different supports, since their surfaces have
the same coating influencing the process.
Synthesis of CobaltꢀContaining Chitosan–Support Systems
A mixture containing 0.24 g of CoCl2 · 6H2O, 2 g of
chitosan–support hybrid system and 20 ml of ethanol
was stirred under reflux for 24 h. The obtained sediꢀ
ment was filtered off, rinsed with ethanol (15 ml ×
3
times) and dried at room temperature until the weight
became constant. The data are shown in Table 1.
As follows from the data on the elemental analysis,
chitosan plays the role of a complexing agent; in this
case, all of the amino groups are involved in the coorꢀ
dination by cobalt ions (ratio, Co : NH2 = 1 : 1–1.5).
In the case of the Al2O3–chitosan system, some of the
Investigating the Catalytic Properties
of CobaltꢀContaining Hybrid Systems
We added 2 ml of water, 0.32 ml of octenꢀ1 amino groups do not participate in the complexation,
(2 mmol), and 0.2 g of catalyst to 10 ml of ethanol. but the Co : Cl ratio corresponds to the composition of
The reaction mixture was kept under constant stirring the initial salt that provides the coordination mechaꢀ
at 75°С for 24 h. The catalyst was filtered out, the filꢀ nism for binding cobalt ions (Fig. 2). In the case of the
trate was extracted by methylene chloride, and the SiO2–chitosan system, the Co : Cl ratio is ~1. The
extract was analyzed by gas–liquid chromatography need to obey the law of electroneutrality for the
(GLC). This experiment was repeated for the same obtained composites requires assuming that the supꢀ
quantities of reagents, but acetonitrile or triglyme were port, in addition to being a weak acid, also plays a
used instead of ethanol. A 1 M solution of HCl was coordinating role with respect to cobalt ions, which
used for the reaction in the aqueous ethanol at various accords with the covalent mechanism of binding
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STRUCTURE AND CHARACTERISTICS
1157
HOH2C
Co2+
HOH2C
O
HO
O
HO
O
NH2
O
H2N
O
HO
HO
NH2
HOH2C
s
NH2
HOH2C
O
O
OH
s
s
CoCl2
O
OH
s
s
s
Co2+
H2N
s
s
s
s
CH2OH
CH2OH
H2N
s
s
s
s
s
s
O
CH2OH
O
O
CH2OH
O
O
O
s: SiO2, Al2O3, МCC
H2N
OH
H2N
OH
Fig. 1. Scheme for obtaining cobaltꢀcontaining hybrid systems (where s is the support).
HOH2C
O
HOH2C
O
O
O
HO
HO
NH2
O
NH2
O
O
O
H2O
H2O
HO H2N
HO H2N
HOH2C
Cl
HOH2C
H2O
Co2+
Co2+
Cl
Cl
OH
Al
OH
Si
O
O
O
O
Fig. 2. Scheme for the mechanism of binding cobalt by hybrid systems.
cobalt ions (Fig. 2). In the case of the MCC–chitosan order to confirm our hypothesis, we present the pubꢀ
lished data on studying the sorption of Co2+ ions from
aqueous solutions and on the nature of the interaction
between the metal center and amino groups of chitoꢀ
san. According to [15], maximum adsorption starts to
decrease with increasing pH due to the formation of
system, metal ions are sorbed in the form of a basic
salt, and hydroxyl groups on the surface provide
weaker coordination binding than Al2O3
.
The elemental composition of the surface shows
that chitosan does not cover it completely and some
part of the functional groups remains on the support
surface in free form. The more complex structure of
the composite surface was characterized by investigatꢀ
ing its acid–base properties via EPR spectroscopy of
the nitroxyl radicals (NR) used as pH probes. The NR
titration curves on the surface of the cobaltꢀcontaining
system are shown in Figs. 3–5. The shift in these
curves relative to the calibration curve left or right
allows us to determine whether the surface has a posiꢀ
tive or negative charge, respectively [13, 14].
The technique for introducing cobalt(II) ions into
the hybrid materials from the ethanol solutions could
lead to the formation of sediments of basic cobalt
chloride or chloride–alcoxide micelles on the surface
of these materials. In the case of the MCC–chitosan
(Fig. 3) and Al2O3–chitosan (Fig. 4) systems, the
titration curves of the cobaltꢀcontaining materials at
pH > 5 are shifted slightly to the left relative to the
titration curves of the initial samples. Consequently,
the occurrence of basic cobalt chloride on the surface
of these materials does not lead to a change in the surꢀ
face charge, but changes its value slightly. This is due
to the effective neutralization of a positive charge of
cobalt ions by negative chloride and hydroxide ions. In
aN, %
80
40
0
1
2
3
2
4
6
8
pH
Fig. 3. Dependence of the change in the
a parameter on
N
the pH of the solution:
curve; , to the titration of the MCC–chitosan system;
, to the titration of the MCC–chitosan–Co system.
1 corresponds to the calibration
2
2+
3
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1158
MEKHAEV et al.
N, %
a
N, %
a
80
80
40
0
40
0
1
2
3
1
2
3
2
4
6
8
2
4
6
8
pH
pH
Fig. 4. Dependence of the change in the
a
parameter on
Fig. 5. Dependence of the change in the a parameter on
N
N
the pH of the solution:
1
corresponds to the calibration
the pH of the solution: 1 corresponds to the calibration
curve; corresponds to the titration of the Al O –chitosan
2
curve;
2
corresponds to the titration of the SiO –chitosan
2
3
2
2+
2+
system;
system.
3
, to the titration of the Al O –chitosan–Co
system;
system.
3, to the titration of the SiO –chitosan–Co
2
2
3
cobalt hydroxocomplexes. The maximum sorption of tion are in the form of aqua complexes [17]. The latter
cobalt ions by chitosan found at pH 6–8 in [16] is in
good agreement with the data from [15] and is deterꢀ
mined by the formation of Со(ОН)2 phase or poorly
soluble basic salts. No chemical interaction with
amino groups of chitosan occurs in this case [17].
are sorbed by the chitosan primary amino groups,
thereby charging the surface positively; in this case,
the titration curves of systems I–III (Figs. 3–5) are
shifted left relative to the corresponding curves for the
initial samples and to the calibration curve. A further
reduction in pH leads to the neutralization of ОН–
groups, and no further changes in pH near the particle
surface are observed upon a change in external pH.
This indicates the presence of a horizontal section
(step) on the titration curve. The value of the horizonꢀ
tal section is lower for system III than for systems I and
II, since some of the ОН– groups are replaced by resiꢀ
dues of silicic acid. At high pH values, Co2+ ions iniꢀ
tially cause a substantial decrease in the negative surꢀ
face charge for the case of system III; their transforꢀ
mation into the form coordinated by the chitosan NH2
groups thus influences the surface charge to a lesser
degree upon declining pH. Our results indicate the
participation of chitosan amino groups in the comꢀ
The SiO2–chitosan system behaves differently.
Even at the highest pH values, the titration curve of the
sample modified with cobalt (Fig. 5) was appreciably
shifted to the left relative to the NR calibration curve
of the initial sample, although it remains to the right of
the calibration curve. Accordingly, the formation of
the chloride hydroxyl cobalt micelles immediately
leads to a considerable reduction in the negative surꢀ
face charge of the SiO2–chitosan system. The differꢀ
ent behavior of the titration curve for system III is
most likely associated with the initially lower content
of Cl– ions in the cobalt micelles (Co : Cl = 1 : 1), i.e.,
to its higher content of ОН– ions. Acid sites on the
SiO2 surface (silanol groups) also likely interact with
the basic cobalt chloride particles precipitating on the
surface, thereby replacing the Cl– ions. In both cases, plexation with Co2+ ions. During the interaction of the
the titration curve must shift left due to the neutralizaꢀ
tion of the negative surface charge. In investigating the
samples in the aqueous medium at high pH values, the
transformation of systems I–III thus occurs; hydraꢀ
tion of the surface, followed by hydrolysis leading to
the formation of colloidal particles based on chloroꢀ
hydroxo complexes of cobalt(II), is observed.
hybrid materials with the cobaltꢀcontaining solution,
at least a part of glucosamine rings are consequently
turned outward and are capable of becoming ligands.
Our data thus completely describe the structure of
the surface of cobaltꢀcontaining hybrid systems,
including features of the structure related to the supꢀ
port used and the pH of the medium. This allows us to
investigate the influence of different factors upon
using synthesized hybrid systems as heterogenic cataꢀ
lysts in the transformation reaction of terminal alkenes
These micelles of cobalt(II)chloroꢀhydroxocomꢀ
plexes begin to dissolve at pH
≤
5 for all investigated
systems I–III. The dependence of sorption of cobalt
ions on pH [15] shows that the maximum adsorption
starts to decline at pH < 5, and Co2+ ions in the soluꢀ by the example of octenꢀ1.
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STRUCTURE AND CHARACTERISTICS
1159
Catalytic Properties of Hybrid Systems
data on a mixture of different functional derivatives
during the oxidation of olefin; these products were
identified by gas–liquid chromatographic and massꢀ
The reactions occurred in aqueous ethanol without
the creation of an inert atmosphere in the presence of
cobaltꢀcontaining hybrid systems, thereby providing spectrometric analysis.
OH
4
OH
4
4
O
O /H O
2
2
cat
EtOH
O
5
or
MeCN
6
5
OH
O
CH3
6
O
O
5
The ratio between the reaction products in depenꢀ least favorable for the oxidation of olefins only in the
dence on the catalyst used is shown in Table 2. The
system based on MCC has the most activity in the oxiꢀ
dation of octenꢀ1, while the Al2O3ꢀbased system is less
active by a factor of 100. The ratio between the reacꢀ
tion products is almost the same for all cobaltꢀconꢀ
taining systems, indicating that the mechanism of the
process is defined only by cobalt. Additional study of
the catalytic activity of hybrid systems containing no
metal showed there was no conversion of octenꢀ1. As
was shown earlier, the chemical surroundings of a
metal ion depend on the hybrid system, which is why
the catalysts have different activities. It should thus be
case of Al2O3–chitosan, where the metal ion is sorbed
in the form of CoCl2
.
As we can see from Table 2, the main products are
alcohols. Products of further oxidation are also
observed, indicating the presence of successive reacꢀ
tions catalyzed by cobalt. The structure of the
obtained compounds most likely indicates a radical
mechanism for the oxidation reaction of octenꢀ1. Oxiꢀ
dation of the double bond leads to the production of
heptanal and hexyloxirane, while the allylic oxidation
of octenꢀ1 causes the formation of 1ꢀoctenꢀ3ꢀol and
noted that the chemical surroundings of the metal are 2ꢀoctenꢀ1ꢀol:
OH
•
4
H O
2
–H•
H
4
[O]
4
•
H O
2
4
OH
–H•
4
Octenꢀ2ꢀal, in turn, can be a product of the further oxidation of 2ꢀoctenꢀ1ꢀol, and octanolꢀ1 appears due to the
disproportionation of 2ꢀoctenꢀ1ꢀol.
2
+
OH
OH
4
4
4
O
In addition,
nꢀoctyl acetate is found in the reaction medium, indicating the participation of the solvent in the
successive reactions:
O
O
[O]
OH
6
OH
–H O
2
O
OH
6
NH
O
H O
2
OH
6
N
–NH
3
O
O
6
6
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1160
MEKHAEV et al.
Table 2. Results from the transformation of octeneꢀ1 into
ethanol for systems I–III
cient of hydrogen atoms was negligible [18] and was
therefore not taken into account. It was found that at
an aqua pH value of 6.3–6.5, the pH value of the aqueꢀ
ous ethanol solution would be expected to be 7.1–7.3.
To study the influence of cobalt transformation on the
catalytic activity upon a change in pH value, we selected
pH values that correspond to the 3.4 < pH > 5.6 step on
the titration curve (Fig. 3) to the range before and after
the step. According to the data in Table 2, a decline in
the pH value reduces the conversion of octenꢀ1; this
occurs due to a reduction in the catalytic activity of
system III to the value that corresponds to system II.
This confirms our previous conclusions on dissolving
micelles of chloroꢀhydroxo cobalt(II) complexes and
the formation of Co2+ ions in the form of CoCl2, as this
salt is responsible for the least activity in the oxidation
reaction of octenꢀ1. Additional analysis of the systems
after the reaction showed that the content of cobalt
falls by 13% at pH 6.1 and by 88% at pH 3.7. A
decrease in the activity, however, leads to a certain
increase in the selectivity of the process of alcohol proꢀ
duction.
Parameter
sp, m2/g
I
II
3.2 96.4
6.1 6.1
96 27
30
III
s
28.6
3.7
18
pH
η
6.1
52
2.9
8
ηsp
0.3
1.8
0.6
0.3
Products, wt %
heptanal
3.4
4.5
4.7
0.0
0.0
1ꢀoctenꢀ3ꢀol
hexyloxirane
2ꢀoctenal
32.5 31.7 30.0 44.0 44.0
2.9 1.4 4.8 0.0 0.0
14.9 20.8 17.5 31.0 31.0
46.3 34.8 38.1 25.0 25.0
2ꢀoctenꢀ1ꢀol +
octanolꢀ1
octylacetate
0.0
6.8
4.9
0.0
0.0
Note:
η
is the conversion of octeneꢀ1, %;
η
is the specific converꢀ
sp
2
sion of octeneꢀ1, %/m ; and pH of the reaction corresponds
to the pH of the aqueous solution.
No changes in the structure of the reaction prodꢀ
ucts are observed with declining polarity of the
medium by replacing ethanol for acetonitrile during
the oxidation of octenꢀ1 (Table 3). The sequence of
the system activities remains the same, I > III > II, and
the main products of oxidation are still alcohols. A furꢀ
ther drop in the polarity of the solvent via the use of
triglyme leads to the absence of any conversion in
octenꢀ1.
Table 3. Results from the transformation of octeneꢀ1 into
acetonitrile for systems I–III
Parameter
sp, m2/g
I
II
III
s
3.2
96.4
67
28.6
90
η
69
ηsp
21.5
0.7
3.1
Products, wt %
heptanalꢀ1
5.1
29.2
9.1
5.5
24.8
7.4
3.8
26.2
6.9
CONCLUSIONS
1ꢀoctenꢀ3ꢀol
hexyloxirane
The investigated cobaltꢀcontaining hybrid systems
demonstrated the possibility of catalyzing the oxidaꢀ
tion of terminal alkenes by the example of octenꢀ1; the
main product of this process is a mixture of alcohols.
The MCCꢀbased system is the one most active and
most likely to provide the best coordination surroundꢀ
ings of the metal center. The practical value of the catꢀ
alytic properties established in this work is the possibilꢀ
ity of transforming the products of oil cracking (termiꢀ
nal olefins) into primary alcohols using these catalytic
systems with the subsequent reduction of a mixture of
incomplete oxidation products. Our estimate of the
conversion of alkenes into saturated alcohols by the
example of octenꢀ1 indicates a total yield of ~60%.
2ꢀoctenal
27.7
24.1
4.8
31.4
25.4
5.6
26.8
31.4
4.9
2ꢀoctenꢀ1ꢀol + octanolꢀ1
octyl acetate
Note: η is the conversion of octeneꢀ1, %; η is the specific converꢀ
sp
2
sion of octeneꢀ1, %/m ; and pH of the reaction corresponds
to the pH of the aqueous solution.
Note that, in the case of system I, no formation of
ester is observed. This could be due to the basic form
of the cobalt and the absence of a Lewis etherification
catalyst; Al2O3 and SiO2 correspond to this type of catꢀ
alyst.
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We estimated the influence of pH on the structure
and ratio of the products obtained via oxidation of
octenꢀ1 using the example of system III, which exhibꢀ
its medium catalytic activity. It should be noted that
direct measurement of the activity of hydrogen ions in
organic solvent–water mixtures is impossible using an
ionometer. The estimated pH values for these soluꢀ
tions were recalculated with allowance for the dilution
factor. The effect of the media on the activity coeffiꢀ
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