Cyanosilylation of benzaldehyde with TMSCN over perovskite-type oxide catalyst prepared by thermal decomposition of heteronuclear cyano complex precursors

Article abstract of DOI:10.1007/s11164-015-1980-y

The perovskite-type oxide catalyst, SmFeO₃, prepared by decomposition method of heteronuclear cyano complex precursor (CN method) was applied to liquid-phase organic reaction, cyanosilylation of benzaldehyde with TMSCN. The maximum catalytic ac

Full text of DOI:10.1007/s11164-015-1980-y

Res Chem Intermed
DOI 10.1007/s11164-015-1980-y
Cyanosilylation of benzaldehyde with TMSCN
over perovskite-type oxide catalyst prepared
by thermal decomposition of heteronuclear cyano
complex precursors
Syuhei Yamaguchi1 Takahisa Okuwa1
•
•
Hiroki Wada1 Hiroyuki Yamaura1
•
•
Hidenori Yahiro1
Received: 30 June 2014 / Accepted: 21 October 2014
Ó Springer Science+Business Media Dordrecht 2015
Abstract The perovskite-type oxide catalyst, SmFeO3, prepared by decomposi-
tion method of heteronuclear cyano complex precursor (CN method) was applied to
liquid-phase organic reaction, cyanosilylation of benzaldehyde with TMSCN. The
maximum catalytic activity per catalyst weight was achieved at 800 °C of calci-
nation temperature in CN method and it was found that the catalytic activity was
strongly related to the crystallinity of SmFeO3 catalyst. The catalytic reaction
performed in the presence of pyridine and 2,6-di-tert-butylpyridine suggests that the
catalytically active sites are the Brønsted acid sites formed on the SmFeO3 catalyst.
The catalytic activity of SmFeO3 catalyst prepared by CN method was much higher
than those of acid catalysts: SiO2–Al2O3 and Amberlyst.
Keywords Perovskite-type oxide ꢀ Cyano complex ꢀ Cyanosilylation
Introduction
Perovskite-type oxide, ABO3, is one of the attractive compounds due to its adequate
catalytic activity in oxidation processes and its good thermal stability. Numerous
efforts of low-temperature wet-chemical method have been undertaken to prepare
perovskite-type oxides with high surface areas. For example, sol–gel [1–4], co-
precipitation [2, 5, 6], citrate route [1, 5], reverse micelle [7, 8], reverse
homogeneous precipitation [9], and polymeric precursor methods [10, 11], and
flame hydrolysis of aqueous solution of precursor salts [12] have been developed
and designed to prepare nano-sized perovskite-type oxides. Sadaoka and co-workers
&
Hidenori Yahiro
hyahiro@ehime-u.ac.jp
1
Department of Materials Science and Biotechnology, Graduate School of Science and
Engineering, Ehime University, Matsuyama 790-8577, Japan
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S. Yamaguchi et al.
[13–20] reported a new preparation route of perovskite-type oxide via the thermal
decomposition of heteronuclear cyano complex, M[M’(CN)6]ꢀnH2O (abbreviated as
CN method) where M and M0 stand for lanthanide and transition metal ions,
respectively. Recently, we have prepared SmFe0.5Co0.5O3 catalyst by CN method
and found that this catalyst exhibited the highest CO oxidation activity among a
series of SmFexCo1-xO3 catalysts due to high homogeneity in composition [21, 22].
The advantage of the CN method is to prepare perovskite-type oxide catalysts with
high crystallinity at relatively low temperature because of the structure similarity
between cyano complex and perovskite-type oxide [23–25]. Up to date, several
perovskite-type oxides prepared by low-temperature wet-chemical methods have
been reported to show the high catalytic activity for catalytic reaction in gas phase,
such as the complete oxidation of hydrocarbons [26, 27] and CO [28, 29] and the
decomposition of NO [30–33]. However, little is known about the catalytic activity
of perovskite-type oxides for organic reactions in the liquid phase.
The cyanosilylation of carbonyl compounds with trimethylsilyl cyanide
(TMSCN) is one of the very important transformations that allow the formation
of the C–C bond and the protection of a hydroxyl function. Cyanohydrin
trimethylsilyl ethers produced by the cyanosilylation can be further transformed
into important synthetic intermediates such as a-hydroxy acids, a-amino acids, and
b-amino alcohols [34–37], which are widely applied in the chemical industry. Many
researchers have reported this transformation using several catalysts [34–43]. The
reaction was catalyzed by Brønsted [38] and Lewis acids [39–42] as well as Lewis
bases [43]. In the present paper, as a preliminary result of liquid-phase organic
reaction, we wish to report the catalytic activity for cyanosilylation of carbonyl
compounds with TMSCN over perovskite-type oxide, SmFeO3, prepared by CN
method.
Experimental
Catalyst preparation
SmFeO3 catalysts were prepared by three different methods: the CN method [15,
23], decomposition method of polymer precursor (abbreviated as the PP method)
[10, 23], and the reverse homogenous precipitation method (RHP method) [9, 23].
CN method
The heteronuclear cyano complex, Sm[Fe(CN)6]ꢀnH2O, as a precursor of per-
ovskite-type oxide was synthesized at room temperature by mixing aqueous
solutions of appropriate amounts of Sm(NO3)3 (Wako, 99.5 %) and K3Fe(CN)6
(Hayashi, 99.0 %) under continuous stirring, according to the following reaction:
Sm(NO3)3(aq) ? K3Fe(CN)6(aq) ? SmFe(CN)6ꢀnH2O(s) ? 3KNO3(aq). The pre-
cipitate obtained was collected by suction filtration, washed with deionized water,
ethanol, and diethyl ether, and then dried in air at 50 °C. The resulting powder was
calcined at 600–1,000 °C for 1 h in air.
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Cyanosilylation of benzaldehyde with TMSCN
PP method
Sm(NO3)3 and Fe(NO3)3ꢀ9H2O (Wako, 99.0 %) were dissolved in an ethylene
glycol solution (Wako, 99.5 %) at the desired metal molar ratio. Acetylacetone
(acac) (Wako, 99.0 %) was then added (oxide:acac = 1 mol:8 mol) as a chelating
agent and then poly(vinyl alcohol) (PVA) (Wako, 96.0 %) was added as the
polymer additive (7.5 wt%) to form the polymer precursor. The prepared polymer
precursor was decomposed on a heating plate to obtain the powders. The resulting
powder was calcined at 1,000 °C for 1 h in air.
RHP method
Samarium and iron nitrates (0.02 mol for each) were dissolved in 100 ml of
deionized water. The mixed nitrate solution was then dropped through a burette at a
rate of 0.5–1.0 ml min-1 into aq. NH3 (300 ml, pH 13) under vigorous stirring. The
final pH of the reaction medium was adjusted to be about 11. The suspension was
further stirred for 1 h, kept standing for 30 min, and filtrated to collect the solid
precursor (hydroxide). The precursor was dried at 110 °C for 12 h, and then
calcined at 1,000 °C for 1 h in air.
Characterization of catalysts
The crystalline structure of the product was elucidated using the powder XRD (Rint
2000, Rigaku) with Cu-Ka radiation. Sm and Fe contents in samples were measured
by X-ray fluorescence spectrometer (RIX2100 (Rigaku), Rh Ka radiation source).
The specific surface area was determined with BET analysis (Belsorp-mini, BEL
Japan) for the adsorption–desorption measurements using N2 adsorbent at 77 K. The
samples used in the present study and their characteristic data are summarized in
Table 1.
Table 1 Characteristic data of catalysts used in the present study
Sample
Methoda
Calcination
condition
Surface
(area/m2 g-1
Crystallite
(size/nm)b
Atomic
compositionc
Sm/Fe
)
(temp./°C)
Sm[Fe(CN)6]ꢀnH2O
SmFeO3
SmFeO3
SmFeO3
SmFeO3
SmFeO3
SmFeO3
a
CN
CN
CN
CN
CN
PP
–
–
–
0.98
0.98
0.98
0.99
0.97
0.98
0.98
700
8.7
4.0
2.7
1.5
3.3
2.4
27
29
34
40
37
34
800
900
1,000
1,000
1,000
RHP
Preparation method of precursor
b
The average crystallite size in the (110) direction was evaluated from XRD line broadening using
Scherrer’s equation
c
XRF analysis
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S. Yamaguchi et al.
Catalytic reaction for cyanosilylation of benzaldehyde with TMSCN
The chemicals, benzaldehyde (Wako, 98.0 %), trimethylsilyl cyanide (TMSCN)
(TCI, 98.0 %), and a-(trimethylsilyl)phenylacetonitrile (Sigma Aldrich, 98 %),
were used without any purification. The reference materials, SiO2–Al2O3 (JRC-
SAH-1) with 28.61 % of Al2O3 content, SiO2–Al2O3 (JRC-SAL-2) with 13.75 % of
Al2O3 content, and Amberlyst 15 DRY, were supplied by the Catalysis Society of
Japan. A typical procedure for cyanosilylation of benzaldehyde is as follows;
catalyst (25–50 mg), benzaldehyde (0.5 mmol), and dichloromethane (3–12 ml)
were successively placed into a Pylex-glass test tube. The reaction was initiated by
addition of TMSCN (1.0 mmol) and the reaction mixture was vigorously stirred
(800 rpm) at 20–30 °C in air (1 atm). The detailed reaction conditions are shown in
the captions of the figures. The conversion of benzaldehyde and the yield of product,
a-(trimethylsilyl)phenylacetonitrile, were periodically determined by GC analysis.
Results and discussion
Figure 1 shows XRD patterns of the samples prepared by the CN, PP, and RHP
methods. All the samples were finally calcined at 1,000 °C for 1 h. It is clear that
the samples prepared by the CN, PP, and RHP methods provided the XRD patterns
indicating the single phase formation of the perovskite-type structure of SmFeO3
(JCPDS# = 39-1490). Figure 2 shows the amount of product per surface area for
cyanosilylation of benzaldehyde with TMSCN over SmFeO3 catalysts prepared by
CN, PP, and RHP methods, where the specific surface area of SmFeO3 prepared by
CN, PP, and RHP methods were 1.5, 3.3, and 2.4 m2 g-1, respectively, as shown in
Table 1. The catalytic activity per specific surface area decreased in the following
order: CN [ PP [ RHP method; SmFeO3 catalyst prepared by CN method
exhibited the highest catalytic activity. Therefore, the SmFeO3 catalysts prepared
by the CN method were investigated in more detail. The catalytic activities for
cyanosilylation of benzaldehyde with TMSCN over SmFeO3 catalysts prepared by
CN method were investigated as a function of calcination temperature. XRD profiles
of the Sm[Fe(CN)6]ꢀnH2O precursors calcined at 600–1,000 °C for 1 h were
depicted in Fig. 3 together with that of as-prepared Sm[Fe(CN)6]ꢀnH2O precursor.
The as-prepared Sm[Fe(CN)6]ꢀnH2O precursor provided the XRD pattern of the
single phase of the heteronuclear metal complex precursor of Sm[Fe(CN)6]ꢀnH2O
(JCPDS# = 39-738) (Fig. 3a). The sample calcined at 600 °C provided no intense
XRD peak, suggesting an amorphous phase (Fig. 3b). The samples calcined at
700–1,000 °C provided the XRD pattern indicating the single phase of the
perovskite-type structure of SmFeO3 (JCPDS# = 39-1490) (Fig. 3c–f). The crys-
tallite diameter of SmFeO3, which was determined by Scherrer’s equation,
decreased as follows: 1,000 (40 nm) [ 900 (34) [ 800 (29) [ 700 °C (27).
Figure 4a shows the catalytic activities per catalyst weight for this reaction over
SmFeO3 catalysts calcined at several temperatures. The catalytic activity per
catalyst weight increased with increasing calcination temperature and reached the
maximum value at 800 °C. With further increasing calcination temperature,
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Cyanosilylation of benzaldehyde with TMSCN
Fig. 1 XRD patterns of SmFeO3 prepared by a CN, b PP, and c RHP methods. These precursors of all
methods were calcined at 1,000 °C for 1 h
Fig. 2 Catalytic activity for cyanosilylation over SmFeO3 catalysts prepared by CN, PP, and RHP
methods. Reaction conditions benzaldehyde (0.5 mmol), TMSCN (1 mmol), catalyst (50 mg), CH2Cl2
(12 ml), 20 °C, and 1 h
catalytic activity slightly decreased. Figure 4b shows the catalytic activities per
specific surface area for this cyanosilylation. The specific surface areas of each
samples calcined at 600, 700, 800, 900, and 1,000 °C were 41.5, 8.7, 4.0, 2.7, and
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S. Yamaguchi et al.
Fig. 3 XRD patterns of SmFe-containing samples. A heteronuclear metal cyano complex precursor,
Sm[Fe(CN)6]ꢀnH2O (a), was calcined at 600 (b), 700 (c), 800 (d), 900 (e), and 1,000 °C (f) for 1 h in air
1.5 m2 g-1, respectively (see Table 1); the specific surface area decreased with
increasing calcination temperature. The result shown in Fig. 4b leads us to conclude
that the catalytic activity per specific surface area monotonously increases with
increasing calcination temperature.
We have already reported that for SmFeO3 catalysts prepared by CN method, an
increment of calcination temperature resulted in a decrement of surface area and an
increment of crystallite diameter [22–24]. The catalytic activities per specific
surface area over SmFeO3 catalysts prepared by CN method with different
calcination temperature were plotted against the crystallite diameter, which was
determined by Scherrer’s equation. The result is shown in Fig. 5. The catalytic
activity per specific surface area seems to be correlated with the crystallite diameter
of SmFeO3 catalysts; the catalytic activity increased with increasing crystallite
diameter accompanying with increasing calcination temperature. This result
suggests that the crystal growth, that is, the long-term ordering of perovskite-type
structure, plays an important role in increasing the catalytic activity for cyanosi-
lylation of benzaldehyde with TMSCN. This is consistent with the result that the
catalytic activity per specific surface area decreased in following order:
CN [ PP [ RHP method, shown in Fig. 2, because the crystallite diameter of
SmFeO3 calcined at 1,000 °C decreased in the same order: CN (40 nm) [ PP
(37) [ RHP (34) method.
As mentioned in the introduction, it has been reported that cyanosilylation
proceeds on acid and base catalysts [38–43]. To clarify an active site of SmFeO3
catalyst, the effect of the addition of pyridine and 2,6-di-tert-butylpyridine on the
catalytic activity for cyanosilylation was investigated. It is reported that pyridine is
strongly adsorbed on both Brønsted and Lewis acid site to inhibit catalytic reaction,
123

Cyanosilylation of benzaldehyde with TMSCN
Fig. 4 Catalytic activities a per catalyst weight and b per specific surface area over SmFeO3 catalysts
calcined at several temperatures (CN method). Reaction conditions benzaldehyde (0.5 mmol), TMSCN
(1 mmol), catalyst (50 mg), CH2Cl2 (12 ml), 20 °C, and 1 h
while 2,6-di-tert-butylpyridine is adsorbed only on the Brønsted acid site because of
steric hindrance [38]. Figure 6 shows catalytic activities for cyanosilylation over
SmFeO3 catalyst prepared by the CN method with calcination at 1,000 °C as a
function of the amount of pyridine derivatives. The catalytic activity gradually
decreased with increasing the amount of pyridine added. Similarly, the small
addition of 2,6-di-tert-butylpyridine resulted in the drastic decrease in the catalytic
activity, although when the amount of 2,6-di-tert-butylpyridine increased, the
catalytic activity slightly increased because 2,6-di-tert-butylpyridine may act as a
stronger base catalyst than pyridine. From these results, it was concluded that the
Brønsted acids formed on SmFeO3 are catalytically active sites for cyanosilylation
of benzaldehyde with TMSCN.
Finally, the catalytic activity of SmFeO3 (CN method, calcination at 1,000 °C)
for cyanosilylation was compared with those of solid acid catalysts: SiO2–Al2O3
(JRC-SAH-1 and JRC-SAL-2) and Amberlyst 15 DRY, with Brønsted acid sites.
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S. Yamaguchi et al.
Fig. 5 Catalytic activities for cyanosilylation as a function of crystallite diameter of SmFeO3 catalysts.
Reaction conditions benzaldehyde (0.5 mmol), TMSCN (1 mmol), catalyst (50 mg), CH2Cl2 (12 ml),
20 °C, and 1 h
Fig. 6 Catalytic activity for cyanosilylation over SmFeO3 catalyst prepared by calcination at 1,000 °C as
a function of the amount of pyridine derivatives (black square pyridine and black circle 2,6-di-tert-
butylpyridine). Reaction conditions benzaldehyde (0.5 mmol), TMSCN (1 mmol), catalyst (25 mg),
CH2Cl2 (6 ml), 20 °C, and 1 h
The result is depicted in Fig. 7. SmFeO3 catalyst exhibited the highest catalyst
activity per catalyst weight among the catalysts shown in Fig. 7, although the
specific surface area of SmFeO3 (1.5 m2 g-1) was much lower than those of SiO2–
Al2O3 (JRC-SAH-1 (511) and JRC-SAL-2 (560)) and Amberlyst 15 DRY (45).
Thus, SmFeO3 catalyst is one of the potential candidates active for cyanosilylation
of benzaldehyde with TMSCN. The reason why SmFeO3 with low surface area
showed high catalytic activity is under investigation.
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Cyanosilylation of benzaldehyde with TMSCN
Fig. 7 Catalytic activities for cyanosilylation over SmFeO3 (CN method, calcination at 1,000 °C), SiO2–
Al2O3, and Amberlyst 15 DRY catalysts. Reaction conditions benzaldehyde (0.5 mmol), TMSCN
(1 mmol), catalyst (50 mg), CH2Cl2 (3 ml), 30 °C, and 1 h
Conclusions
As a model organic reaction in the liquid phase, the cyanosilylation of benzaldehyde
with TMSCN was performed over perovskite-type oxide, SmFeO3. The catalytic
activity per specific surface area over SmFeO3 catalyst prepared by CN method was
higher than those by PP and RHP methods. Among these preparation methods, the
CN method was the best for preparing SmFeO3 catalyst highly active for
cyanosilylation. For SmFeO3 catalyst prepared by CN method, the catalytic activity
per catalyst weight increased with increasing calcination temperature of
Sm[Fe(CN)6] complex precursor, reached maximum value at 800 °C, and slightly
decreased with further increasing calcination temperature. Taking XRD results into
consideration, it was found that the catalytic activity was strongly related to
crystallinity of SmFeO3 catalyst. The cyanosilylation was carried out in the presence
of pyridine and 2,6-di-tert-butylpyridine, which act as a catalyst poison for acid
catalyst. From this result, the catalytically active sites for cyanosilylation were
found to be the Brønsted acid sites formed on SmFeO3 catalyst. It was demonstrated
that the catalytic activity of SmFeO3 catalyst prepared by CN method was much
higher than those of acid catalysts: SiO2–Al2O3 and Amberlyst.
Acknowledgments This work was financially supported by JSPS KAKENHI Grant Nos. 24560948 and
25820394.
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