Incorporation of carbon dioxide into molecules of acetylene hydrocarbons on heterogeneous Ag-containing catalysts

Article abstract of DOI:10.1007/s11172-015-1228-4

The reaction between 2-(2-phenylethynyl)aniline and carbon dioxide on heterogeneous Ag-containing catalysts can lead either to benzoxazine-2-one or to 4-hydroxyquinoline-2(1Н)-one, depending on the reaction conditions (nature of the base, CO₂ p

Full text of DOI:10.1007/s11172-015-1228-4

Russian Chemical Bulletin, International Edition, Vol. 64, No. 12, pp. 2796—2801, December, 2015
2796
Incorporation of carbon dioxide into molecules of acetylene hydrocarbons
on heterogeneous Agꢀcontaining catalysts
E. D. Finashina,a O. P. Tkachenko,a A. Yu. Startseva,a V. G. Krasovsky,a L. M. Kustov,a,b and I. P. Beletskayab
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: finesta@mail.ru
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1/3 Leninskie Gory, 119992 Moscow, Russian Federation
The reaction between 2ꢀ(2ꢀphenylethynyl)aniline and carbon dioxide on heterogeneous
Agꢀcontaining catalysts can lead either to benzoxazineꢀ2ꢀone or to 4ꢀhydroxyquinolineꢀ2(1Н)ꢀ
one, depending on the reaction conditions (nature of the base, CO2 pressure). The structures of
the products were confirmed by 1Н and 13С NMR spectroscopy. The maximum yield of the
products (60 and 30% for benzoxazineꢀ2ꢀone and 4ꢀhydroxyquinolinꢀ2(1Н)ꢀone, respectively)
is achieved on the catalyst Ag(1%)/γꢀAl2O3(F). According to the results of physicochemical
studies, the high activity of the catalysts in the reactions proceeding via triple bond activation
results from the combination of three factors. First, the catalyst contains metallic silver partiꢀ
cles with the size >2 nm; second, metallic silver particles coexist with silver cations; and third,
strong acid sites are present on the support surface.
Key words: carbon dioxide, heterogeneous Agꢀcontaining catalysts, alkyne compounds,
benzoxazines, hydroxoquinolines.
It is known that carbon dioxide is a cheap renewable
The purpose of this work is to search for a simple and
efficient heterogeneous catalytic system active in the reꢀ
actions of СО2 with alkylanilines, in particular, with 2ꢀ(2ꢀ
phenylethynyl)aniline (1). This reaction of carbon dioxide
results in its incorporation into the substrate molecule to
form polyfunctional heterocyclic compounds.
source of С1. The use of carbon dioxide in chemical synꢀ
theses does not presently exceed 1% of the volume of conꢀ
sumable CO2. Therefore, the development of new catalytic
systems that make it possible to involve an inert molecule
of carbon dioxide into chemical reactions occurring under
mild conditions and providing valuable polyfunctional orꢀ
ganic compounds for fine synthesis and pharmacology is
an urgent task.1,2
Experimental
The use of toxic and expensive reagents can be avoided
using these processes. Silver salts act as πꢀLewis acids
capable of activating the triple bond in the substrate moleꢀ
cule in the presence of organic bases, for example, 1,8ꢀdiꢀ
azabicyclo[5.4.0]undecꢀ7ꢀene (DBU). These salts are efꢀ
ficient catalysts for the reactions of carbon dioxide with
propargyl alcohols and propargylamines occurring with
the formation of the corresponding cyclic carbonates and
oxazolidinones.3—5
Another example of the reactions between alkynes and
СО2 catalyzed by silver salts and base is the direct carbonylꢀ
ation to form propiolic acids, valuable polyfunctional comꢀ
pounds widely used in fine synthesis.6,7
The chemicals used in this study were 2ꢀ(2ꢀphenylethynyl)ꢀ
aniline (1, Oakwood Chemical, 99+%), 3ꢀaminopropyltriethoxyꢀ
silane (APTES, 99%), 2ꢀphenylindole (95%), DBU (90%),
DABCO (diazabicyclo[2.2.2]octane, 98%, Sigma—Aldrich), soꢀ
dium tetrahydroborate (+98%), nꢀhexane (99%, Acros Organꢀ
ics), DMSO, ethyl acetate, cesium hydroxide, ammonium carꢀ
bonate, silver nitrate, copper(I) iodide (reagent grade), carbon
dioxide (special purity grade, Reakhim). They were used withꢀ
out further purification. Silica gel L5/40 (LA CHEMA) and plates
for thinꢀlayer chromatography (Kavalier, Czechoslovakia) were
used as received.
The following supports were used for the preparation of the
heterogeneous catalysts: zeolite HꢀBeta (СР 7119), mesoporous
silicate material МСМꢀ41, γꢀAl2O3(F) (3.5 wt.% fluorine), SiO2
КСС No. 3 (Reakhim), TiO2 (Aerolist 7709 Rutile, Degussa),
and WО3(18%)—ZrO2 (SaintꢀGobain).
The reactions of СО2 with various alkylanilines also
catalyzed by the silver salts in the presence of organic
bases produce substances with a wide range of biological
activity, such as benzoxazinꢀ2ꢀone8,9 or 4ꢀhydroxoquinoꢀ
line derivatives.10
Fluorinated alumina was prepared by treating γꢀAl2O3 (La
Roche) with a solution of ammonium fluoride followed by drying
and heating for 2 h in air at 550 °С.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2796—2801, December, 2015.
1066ꢀ5285/15/6412ꢀ2796 © 2015 Springer Science+Business Media, Inc.

Heterogeneous Agꢀcontaining catalysts
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015 2797
For surface modification with amino groups, mesoporous
silicate МСМꢀ41 was preꢀtreated for 3 h in a dry air flow at 550 °С
(SBET = 896 m2 g–1) and then refluxed for 24 h in toluene with
APTES excess in an argon atmosphere. The support was filtered,
washed with toluene and diethyl ether from APTES residues,
and dried in vacuo. The modified support was designated as
APTES—MCMꢀ41.
The characteristics of the used supports and conditions of
their precalcination are presented in Table 1.
The heterogeneous catalysts were prepared by the incipient
wetness impregnation method.
To reduce the samples with supported silver nitrate, they
were treated in flowing hydrogen. The temperature was increased
from room temperature to 450 °С with a heating rate of 4 °С min.
The samples were then cooled to ~20 °C and purged with Ar for
15 min. The Ag(1%)/APTES—MCMꢀ41 sample was reduced by
the treatment with an aqueous solution of sodium borohydride
(1.2 moles of NaBH4 (mole of Ag)–1). After reduction, the cataꢀ
lysts were washed with water to remove sodium borohydride
excess and dried in air for 24 h.
4ꢀHydroxyꢀ3ꢀphenylquinolinꢀ2(1Н)ꢀone (3). The reaction
was carried out in a temperatureꢀcontrolled reactor with a jacket,
and СО2 was introduced into the reactor through a needle inꢀ
serted into a bottom sampler. The reactor was loaded with comꢀ
pound 1 (0.3 mmol), Ag (0.03 mmol), DBU (0.3 mmol), and
DMSO (2 mL). The mixture was stirred for 24 h at 60 °С. To
isolate the product, the reaction mixture was filtered and exꢀ
tracted with 1 М NaOH (3×4 mL). The aqueous layer was acidiꢀ
fied with a solution of 2 М HCl to the neutral pH and extracted
with EtOAc (5×15 mL). The organic layer was collected, washed
with a solution of 2 М HCl (2×80 mL), dried over Na2SO4, and
filtered. The solvent was removed on a rotary evaporator (T = 35 °С,
P = 60 mbar) to obtain 4ꢀhydroxyquinolinꢀ2(1Н)ꢀone 2 as dry
white crystals. 1H NMR (400 MHz, CDCl3), δ: 4.37 (s, 2 H);
6.78 (dd, 2 H, J1 = 7.5 Hz, J2 = 5.5 Hz); 7.19 (t, 1 H, J = 8.4 Hz);
7.45—7.62 (m, 4 H); 7.76 (d, 1 H, J = 6.5 Hz); 7.86 (t, 2 H,
J = 9.4 Hz); 8.44 (d, 1 H, J = 8.3 Hz). 13С NMR (100 MHz,
DMSOꢀd6), δ: 114 (C(1)); 115.32 (C(2)); 116.13 (C(3)); 121.51
(C(4)); 123.54 (C(5)); 127.26 (C(6)); 128.08 (C(7), C(8)); 130.94
(C(9)); 131.61 (C(10), C(11)); 134.54 (C(12)); 138.47 (C(13));
157.71 (C(14)); 163.10 (C(15)).
Cesium carbonate Cs2CO3 was synthesized by the reaction
of cesium hydroxide with ammonium carbonate.
The structures of the obtained products were confirmed by
1H and 13С spectroscopy.
(Z)ꢀ4ꢀBenzylideneꢀ1,4ꢀhydroxoꢀ2Нꢀ3,1ꢀbenzoxazinꢀ2ꢀone
(2). The catalyst (0.0125 mmole of Ag), DABCO (0.2 equiv.),
compound 1 (0.125 mmol), and anhydrous DMSO (1 mL) were
consequently introduced into a preꢀdried autoclave equipped
with a stirrer. The autoclave was closed and purged with СО2
three times, after which CO2 was fed and an operating pressure
was established. The reaction mixture was stirred for 24 h at
~20 °C and P(СО2) = 10 atm. After the reaction, the autoclave
was cooled in an iceꢀcold bath and the СО2 pressure was slowly
released. Benzoxazinꢀ2ꢀone 2 was isolated from the reacꢀ
tion solution using column liquid chromatography on silica gel
L5/40μ. An nꢀhexane—ethyl acetate (2 : 1) mixture served as an
eluent. TLC was used for express analysis of the reaction mixture
and fractions collected from the column. The fractions containꢀ
ing the product were combined, and the solvent was pumped out
under reduced pressure to obtain benzoxazinꢀ2ꢀone 2 as dry
white crystals. 1H NMR (400 MHz, CDCl3), δ: 6.26 (s, 1 H);
6.88 (d, 1 H, J = 8.1 Hz); 7.11 (t, 1 H, J = 7.6 Hz); 7.28—7.41
(m, 4 H); 7.59 (d, 1 H, J = 7.9 Hz); 7.80 (d, 2 H, J = 7.6 Hz);
8.72 (s, 1 H). 13С NMR (100 MHz, CDCl3), δ: 105.82 (С(1));
114.90 (С(2)); 116.05 (С(3)); 122.98 (С(4)); 124.21 (С(5));
127.29 (С(6)); 128.54 (С(7), С(8)); 129.25 (С(9), С(10));
130.36 (С(11)); 133.67 (С(12)); 134.03 (С(13)); 144.91 (С(14));
148.57 (С(15)).
1H and 13С NMR spectra were measured on a Bruker AM300
spectrometer (solvents CDCl3 and DMSOꢀd6), and the data of
HSQC, HMBC, APT, and NOESY procedures were used for
signal assignment.
Diffuse reflectance infrared Fourier transform spectra
(DRIFTS) were recorded at ~20 °C on a Nicolet 460 Protégé
spectrometer with the diffuse reflectance attachment. Catalyst
samples were placed in ampules with a KBr window, and a CaF2
powder served as a reference sample. For a satisfactory signal to
noise ratio, 500 spectra were accumulated. IR spectra were meaꢀ
sured in a wide frequency range of 400—6000 cm–1 with a resoluꢀ
tion of 4 cm–1. Carbon monoxide served as a probe molecule and
was adsorbed at ~20 °C and an equilibrium pressure of 15 Torr.
The phase composition of catalyst samples was determined
by Xꢀray diffraction analysis. The XRD patterns were collected on
a Dronꢀ3 instrument using CuꢀKα radiation (λ = 0.1542 nm).
The samples were scanned in the 2θ range of 5—60° at 1° min of scan
speed. The size of coherent scattering region (DCSR, Å) was
determined taking the peak width at half heights for the signal at
38.1 Å corresponding to the metallic silver phase. The diffractograms
were compared with the JCPDSꢀICDD and ICDS references.
Table 1. Characteristics of the supports and conditions of
their preliminary thermal treatment
b
Support
Ta/°C
τ /h
SBET/m2 g–1
γꢀAl2O3
SiO2 KCC No. 3
TiO2
Al2O3(F)
МСМꢀ41
W—ZrO2
600
260
550
550
550
650
2
8
2
2
3
2
140—160
450
15
120
896
120
Results and Discussion
According to the literature data,8—10 the catalytic transꢀ
formations of 2ꢀ(2ꢀphenylethynyl)aniline under the acꢀ
a Temperature of thermal treatment.
b Duration of thermal treatment.

2798
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015
Finashina et al.
tion of Ag+ salts can proceed via two routes (Scheme 1)
with the direction depending on the reaction conditions
(СО2 pressure, nature of the used base).
(see Table 2, entry 5 and Table 3, entry 3). No formation
of the products was observed in the absence of silver salts
in the mixture (see Table 2, entries 2 and 3; Table 3, entry 2).
The catalytic reactions in which the triple bond of the
substrate is activated by silver ions are often carried out in
the presence of inorganic base, cesium carbonate.6,7,11 The
obtained results show that in the studied reactions the
replacement of organic bases DABCO and DBU by
Cs2CO3 lead only to an insignificant decrease in the yield
of the target products (see Table 2, entry 4; Table 3, entry 4).
It was also established that the replacement of silver
nitrate by copper iodide does not result in the formation of
target product 2 (see Table 2, entry 6).
Scheme 1
The choice of the heterogeneous Agꢀcontaining cataꢀ
lysts for the synthesis of compounds 2 and 3 was made on
the basis of our earlier results.11 The study of the direct
carboxylation of phenylacetylene by carbon dioxide
showed that the isolated yields of the targeted phenylꢀ
propionic acid exceeding 50% are achieved on the heteroꢀ
geneous Agꢀcontaining catalysts Ag(5%)/TiO2, Ag(20%)/
SiO2, and Ag(0.5%)/γꢀAl2O3(F). The testing of these three
catalysts in the reaction of formation of benzoxazinꢀ2ꢀone 2
showed that the targeted product was formed only on the
Ag(1%)/Al2O3(F) catalyst (see Table 3).
We assumed that the activity of the Ag(1%)/Al2O3(F)
catalyst in the reactions proceeding through the activation
of the triple bond of the substrate is explained by the presꢀ
ence of acid sites on the support surface. The sites are
formed upon the modification of alumina by fluorine anꢀ
ions. Therefore, we synthesized the Agꢀcontaining cataꢀ
lysts on fairly acidic supports (W—ZrO2, zeolite HꢀBeta).
The use of these catalysts in the reactions producing prodꢀ
i. Ag+, CO2 (10 atm), DABCO, DMSO, ~20 °C; ii. Ag+, CO2
(1 atm), DBU, DMSO, 60 °C.
The both reactions were carried out in the presence of
silver nitrate and bases DABCO or DBU in a DMSO
medium (Table 2, entry 1 and Table 3, entry 1). The isolated
yields of compounds 2 and 3 were 80 and 83%, respectively.
It was established that the reactions in the absence of
bases afforded the products in stoichiometric amounts only
Table 2. Yields of benzoxazinꢀ2ꢀone 2 on the Agꢀcontaining catalystsa
Entry
Catalyst
Base
τ/h
Isolated yield
of target product (%)
1
2
3
4
AgNO3
—
—
AgNO3
AgNO3
DABCO
DABCO
Cs2CO3
Cs2CO3
—
24
44
28
24
80
—
—
70
8
5
24
6
7
8
9
10
11
12b
13c
14
CuI
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
Cs2CO3
45.5
76.5
57
37.5
42.5
50
35
44.5
46
—
Traces
—
—
—
40
—
—
60
Ag(1%)/W–ZrO2
Ag(20%)/SiO2
Ag(5%)/TiO2
Ag(2%)/APTES—MCMꢀ41
Ag(1%)/Al2O3(F)
Ag(1%)/Al2O3(F)
Ag(1%)/Al2O3(F)
Ag(1%)/Al2O3(F)
a Reaction conditions: ~20 °C, Р(СО2) = 10 atm, 0.125 mmole of substrate, 0.0125 mmole of Ag, 0.025 mmole
of base, DMSO as solvent (1 mL).
b Р(СО2) = 20 atm.
c T = 50 °С.

Heterogeneous Agꢀcontaining catalysts
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015 2799
Table 3. Yields of 4ꢀhydroxyquinolinꢀ2(1Н)ꢀone 3 on the Agꢀcontaining catalysts*
Entry
Catalyst
Base
τ/h
Isolated yield of target product (%)
1
2
3
4
5
6
7
8
AgNO3
—
AgNO3
DBU
DBU
—
Cs2CO3
DBU
DBU
DBU
Cs2CO3
24
83
—
7
75
—
8
35.5
45.5
40.0
50
32.5
37.5
38.5
AgNO3
Ag(1%)/HꢀBeta
Ag(2%)/APTES—MCMꢀ41
Ag(1%)/Al2O3(F)
Ag(1%)/Al2O3(F)
10
30
* Reaction conditions: T = 60 °C, P(CO2) = 1 atm, 0.3 mmole of substrate, 0.03 mmole of Ag, 0.3 mmole of
base, DMSO as solvent (2—3 mL).
ucts 2 and 3 showed that benzoxazinꢀ2ꢀone 2 was formed
on the Ag(1%)/W—ZrO2 catalyst in trace amounts (see
Table 2, entry 7), and the Ag(1%)/HꢀBeta catalyst is inꢀ
active in the formation of 4ꢀhydroxyquinolinꢀ2(1Н)ꢀone 3
(see Table 3, entry 5).
Two bands are observed in the spectrum of compound
Ag(1%)/Beta. The band at 3741 cm–1 belongs to stretchꢀ
ing vibrations of isolated ≡Si—O—H groups, whereas the
band at 3610 cm–1 characterizes strong bridged Brönsted
acid sites.
The heterogeneous catalysts Ag(1%)/γꢀAl2O3(F),
Ag(1%)/Beta, and Ag(1%)/W—ZrO2 were studied by
DRIFTS spectroscopy. The IR spectra in the region of
OH groups detected on these catalysts are presented
in Fig. 1.
The bands of OH groups of three types are observed in
the spectrum of the Ag(1%)/Al2O3(F) sample treated
in vacuo at 450 °C for 1 h. The band at 3709 cm–1 characterꢀ
izes stretching vibrations of hydroxyls that function as
strong Brönsted acid sites. The formation of these sites is
associated with the partial substitution of the basic hydrꢀ
oxyl groups of the =Al—O—H fragments by fluorine.12—14
The band at 3663 cm–1 is assigned to stretching vibrations
of the bridging OH groups, whereas the broad band with
the center at ~3569 cm–1 can be ascribed to stretching
vibrations of the hydrogenꢀbonded hydroxyl groups that
act as acid sites.
The spectrum of the sample Ag(1%)/W—ZrO2 conꢀ
tains three lowꢀintensity bands. The band at 3744 cm–1 is
attributed to stretching vibrations of isolated ≡Zr—O—H
groups, the band at 3657 cm–1 corresponds to the bridging
OH groups bonded to several zirconium ions, and the band
at 3569 cm–1 is characteristic of the hydrogenꢀbonded
acid sites.
Experiments on the adsorption of a testing molecule of
carbon monoxide were carried out to determine the charge
state of silver in the catalysts. Adsorption of CO on all the
three samples does not result in any changes in the region
of the spectra that contains vibrations of OH groups.
The spectra recorded during CO adsorption—desorpꢀ
tion on the Ag(1%)/F—Al2O3, Ag(1%)/Beta, and Ag(1%)/
W—ZrO2 catalysts are presented in Figs. 2, 2, a, b, and c.
Two bands at 2215 and 2190 cm–1 appear in the specꢀ
trum of the Ag(1%)/Al2O3(F) after CO adsorption. The
first band disappears completely upon shortꢀterm evacuaꢀ
tion at ~20 °C.
Absorbance (Kubelka—Munk units)
8
It is known12,15 that CO is not adsorbed at ~20 °C on
Ag0 and carbonyls on metallic silver are detected in a viꢀ
cinity of 2060 cm–1 only at low temperatures16 or at 2099
cm–1 at high equilibrium pressures.17 Therefore, the band
at 2190 cm–1 can be assigned to stretching vibrations of
CO molecules adsorbed on the Ag+ cations,12,15 and the
band at 2215 cm–1 can be attributed to vibrations of CO
molecules adsorbed on the coordinatively unsaturated Al3+
ions.12,15
The spectrum of the Ag(1%)/Beta catalyst (see Fig. 2, b)
exhibits a band at 2184 cm–1, whereas the spectrum of the
Ag(1%)/W—ZrO2 catalyst (see Fig. 2, c) contains a band
at 2192 cm–1. The both bands belong to stretching vibraꢀ
tions of CO molecules adsorbed on Ag+ cations.
It is known that size effects are more characteristic of
the Auꢀcontaining catalysts than for the Agꢀcontaining
3741
6
3610
3709
3683
4
2
1
3569
2
0
3657
3569
3744
3
3800
3600
3400
3200 ν/cm–1
Fig. 1. DRIFT spectra in the range of stretching vibrations of OH
groups in the catalysts Ag(1%)/Al2O3(F) (1), Ag(1%)/HꢀBeta (2),
and Ag(1%)/W—ZrO2 (3).

2800
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015
Finashina et al.
Absorbance (Kubelka—Munk units)
2.5
I/pulse s–1
800
a
2190
1
600
400
200
Ag+
2.0
1.5
1.0
0.5
0
2215
Al3+
2
1
35
40
45
2θ/deg
Ag+
Fig. 3. Xꢀray patterns of the samples Ag(1%)/SiO2 (particle size
of metallic silver 15 nm) (1) and Ag(1%)/Al2O3(F) (size of Ag
particles <2 nm) (2).
2
2300
2200
2100
2000 ν/cm–1
Absorbance (Kubelka—Munk units)
b
catalysts. However, the Xꢀray phase analysis of the cataꢀ
lysts (Table 4) showed that only the samples with the silꢀ
ver particle size <2 nm (Ag(1%)/Al2O3(F) and Ag(1%)/
W—ZrO2) were active in the studied reactions.
The Xꢀray patterns of two catalyst samples are preꢀ
sented in Fig. 3: Ag(1%)/SiO2 in which the particle size of
metallic silver is 15 nm, according to the Xꢀray phase
analysis data, and the Ag(1%)/(Al2O3(F) sample with the
metal particle with the size <2 nm.
Taking into account the foregoing results, we syntheꢀ
sized the catalyst Ag(1%)/APTES—MCMꢀ41 in which
the surface of the initial mesoporous silicate was preꢀmodꢀ
ified by amino groups to provide high dispersion of silver.
This made it possible to obtain metal particles with the
size <2 nm (see Table 4, entry 5). However, this catalyst
was inactive in the reactions of interest (see Tables 2 and 3).
Thus, it is established that only the Ag(1%)/γꢀAl2O3(F)
samples has a noticeable catalytic activity in the reactions
of synthesis of benzoxazinꢀ2ꢀone 2 and 4ꢀhydroxyquinoꢀ
linꢀ2(1Н)ꢀone 3 (see Tables 2 and 3).
An increase in temperature and in СО2 pressure to
20 atm during the synthesis of benzoxazinꢀ2ꢀone 2 does
not increase the yield of the target product (see Table 3).
The better yields of both products are achieved when
cesium carbonate is used as a base (see Tables 3 and 4).
To conclude, we succeeded to develop the heteroꢀ
geneous catalysts for the both reactions. The best result
was achieved with the Ag(1%)/Al2O3(F) catalyst. For the
synthesis of benzoxazinꢀ2ꢀone 2, the maximum yield of
the targeted product on this catalyst was 40 or ~60% when
2184
0.8
Ag+
0.6
0.4
0.2
0
1
2
2300
2200
2100
2300 ν/cm–1
Absorbance (Kubelka—Munk units)
c
5
4
3
2
1
2192
Ag+
1
2
2300
2200
2100
2000 ν/cm–1
Fig. 2. DRIFT spectra of the reduced catalysts after CO adsorpꢀ
tion at 20 °C and a pressure of 10 Torr (1) and after evacuation at
20 °C for 1 min (2): Ag(1%)/Al2O3 (a), Ag(1%)/HꢀBeta (b), and
Ag(1%)/W—ZrO2 (c).
Table 4. Size of silver particles and sorption capacity of the heterogeneous Agꢀcontaining catalysts
Entry
Catalyst
Size of Ag0 particles/nm
State of adsorbed CO
1
2
3
4
5
6
Ag(1%)/Al2O3(F)
Ag(20%)/SiO2
Ag(1%)/W—ZrO2
Ag(5%)/TiO2
<2
15
<2
27
<2
25
Complex СО—Ag+
Was not studied
Complex СО—Ag+
Was not studied
No sorption
Ag(2%)/APTES—MCMꢀ41
Ag(1%)/HꢀBeta
Complex СО—Ag+

Heterogeneous Agꢀcontaining catalysts
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015 2801
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the standard base DABCO or sodium carbonate, respecꢀ
tively, were used. The maximum yield of the target prodꢀ
uct in the synthesis of 4ꢀhydroxyquinolinꢀ2(1Н)ꢀone 3
was 10 and ~30% in the presence of the standard base
DBU and cesium carbonate, respectively.
The results of physicochemical studies indicate that
the high activity of the catalysts in the reactions proceedꢀ
ing via triple bond activation is explained by a combinaꢀ
tion of three factors. First, the catalyst contains nanoꢀ
particles of metallic silver <2 nm in size. Second, metallic
silver particles coexist with silver cations. Third, strong
acid sites are present in the support surface.
12. A. Davidov, Molecular Spectroscopy of Oxide Catalyst Surfaces,
Wiley, Chichester, 2003.
13. H. Knozinger, C. Ratnasamy, Catal. Rev.: Sci. Eng., 1978,
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14. C. Fairbridge, V. M. Allenger, J. Galuszka, Stud. Surf. Sci.
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67, 1376.
This work was financially supported by the Russian
Science Foundation (Project No. 14ꢀ33ꢀ00001).
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Received July 17, 2015;
in revised form September 23, 2015