Catalysis Science & Technology
Paper
P25 with a specific surface area of 62.5 m2 g−1 (Brunauer–
Emmett–Teller surface area (BET)) commercialized under the
name AEROXIDE TiO2 P25 was obtained from Nippon
Aerosil, Evonik Industries. Aluminium oxide (Al2O3) with a
specific surface area of 198.7 m2 g−1 (BET) was obtained from
Nikki Universal Co., Ltd. (JCS-ALO-6, a reference catalyst in
Catalysis Society of Japan (CSJ)). Silicon dioxide (SiO2) with a
specific surface area of 105.5 m2 g−1 (BET) was obtained from
CSJ (JCS-SIO-1, a reference catalyst in CSJ). Various reactant
alcohols such as allyl alcohol, 1-hexanol, 1-octanol, 1-decanol,
1,4-butanediol monomethyl ether, 2-octanol, benzyl alcohol,
2-phenyl-1-cyclohexanol, 2-(phenylthio)ethanol, 3-buten-2-ol,
1-octanethiol and 2-buten-1-ol (mixture of (E) and (Z) isomers)
were obtained from Tokyo Chemical Industry Co., Ltd. Phe-
nol, MoO3, tungsten oxide (WO3), vanadium oxide (V2O5),
(NH4)6Mo7O24IJH2O)4, acetonitrile, biphenyl, hexane and
CDCl3 (containing 0.05 wt% of tetramethylsilane (TMS)) were
obtained from Wako Pure Chemical Industries, Ltd. Cyclo-
hexanol was obtained from Kanto Chemical Co., Inc. All the
materials above were used as received without any further pu-
rification step. H-ZSM-5 was prepared by the calcination of
NH4-ZSM-5 (JRC-Z5-30NH4IJ1), a reference catalyst in Catalysis
Society of Japan (CSJ)) at 500 °C for 3 h.
the Experimental section). When either MoO3 or TiO2 was
used as a catalyst, the etherification of alcohols with 1 did
not proceed at all (entries 1 and 2). We found that the combi-
nation of MoO3 and TiO2 afforded the desired allyl ether 4 in
9% yield (Table 1, entry 3). The yield depended on the
amount of MoO3: when 1, 5, 15, and 20 mg of MoO3 were
added, 4 was obtained in 9, 69, 84, and 77% yields, respec-
tively (Table 1, entries 3, 4, 6, and 7, respectively). The use of
MoO3 and TiO2 at a ratio of 1 : 10 showed the best reactivity,
giving 4 in 86% yield (Table 1, entry 5).
The reaction was optimized at an oil bath temperature of
140 °C (inside temperature 103 °C, Table S1†). The tempera-
ture inside the reaction vessel did not rise to the temperature
in the oil bath since the boiling point of 1 is 97 °C. When the
oil bath temperature was set to 130 °C, 140 °C, and 150 °C,
the temperature inside the reaction vessel rose to 101 °C, 103
°C, and 107 °C, respectively, and the corresponding yields of
4 were 65%, 86%, and 81% (92%, 93%, and 88% selectivity,
respectively) (Table S1†). The over-heating of the reaction ves-
sel gave undesired side products such as 1-octene and its de-
rivatives. In Table 1, entry 5, a medium amount of the side
product was observed as diallyl ether from the homo-
etherification of 1 in 30% yield on the basis of 1; otherwise
dioctyl ether was not detected at all. When the reaction was
carried out using 3 in the absence of 1 under the same condi-
tions as those in Table 1, entry 5, the corresponding dioctyl
ether was given in only 2% yield. These results showed the
necessity of forming the oxy-σ-allyl molybdenum intermedi-
ate to give 4. When the reaction was carried out from 1 and 3
in a ratio of 1 : 1, the conversions of 1 and 3 were 30% and
49%, respectively, and the yields of 4 and diallyl ether were
9% and 1%, respectively. Various kinds of unidentified poly-
merized side products were formed under the conditions
employed. The selectivity and reactivity were improved by in-
creasing the ratio of 1 to 3, and the yield of 4 increased to
86% with almost no unidentified products when 1 and 3 were
used in a ratio of 4 : 1 (Table 1, entry 5). Further optimization
of the catalyst and substrate loading (1 : 3 = 6 : 1) allowed the
production of 4 in 91% yield (Table 1, entry 8).
Methods. GC analyses were performed on a Shimadzu GC-
2014 using a WAX column (0.25 mm × 30 m, GL Sciences Inc).
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
recorded on a JEOL ECX-400P spectrometer at 25 °C. Chemical
shifts (δ) are in parts per million relative to TMS at 0.00 ppm
1
for H and relative to residual CHCl3 at 77.0 ppm for 13C un-
less otherwise noted. X-ray fluorescence analysis (XRF) was
performed on a Rigaku EDXL 300. N2 adsorption–desorption
measurements were conducted at −196 °C on a MicrotracBEL
BELSORP MAX to obtain information on the micro- and meso-
porosities. The BET surface area was calculated from the ad-
sorption data in the relative pressure range from 0.04 to 0.2.
Prior to each adsorption measurement, the sample was evacu-
ated at 200 °C for 6 h. NH3-TPD spectra were recorded on a
MicrotracBEL BELCAT B to obtain information on the acidity
of the catalysts. X-ray diffraction (XRD) patterns were collected
using a Rigaku MiniFlex 600 diffractometer with Cu-Kα radia-
tion. All powder samples were scanned over the 2θ range of 5°
to 60° with a ratio of 0.02° s−1. High-angle annular dark field
scanning-mode transmission electron microscopy (HAADF-
STEM) images were observed and STEM-energy dispersive
spectroscopy (EDS) analyses were carried out using an FEI
Company Tecnai Osiris. X-ray photoelectron spectroscopy
(XPS) measurements were conducted on a VG ESCALab 250
spectrometer fitted with an Al Kα X-ray source. Binding energy
was based on C 1s (284.3 eV).
The catalyst was reused for at least five cycles without any
decrease in the reactivity, and each cycle yielded 4 in the
range of 85–88% (Table 2).
The catalytic reaction was suggested to proceed on the sur-
face of the solid catalyst, since the reaction was terminated
when the catalyst was removed by hot filtration during the re-
action (Fig. 1). The reaction using WO3, ReO3, and V2O5 in-
stead of MoO3 did not give 4 at all (Table 1, entries 9–11).
The use of Al2O3 and SiO2 instead of TiO2 also showed no re-
activities (Table 1, entries 12 and 13). A strong solid acid cat-
alyst, Nafion NR50, showed a high conversion of 3, albeit
with a low yield of 4 (21% yield, Table 1, entry 14). Solid acid
catalysts such as H-ZSM-5 and montmorillonite K10 gave 4 in
28% yield and 11% yield, respectively (Table 1, entries 15 and
16). Solid acid catalysts facilitate the dehydration of 3 to
1-octene which gives various polymerized compounds as well
as the cross-etherification to 4.
Results and discussion
Screening of catalysts
The reaction of 1 and 3 to give 4 was employed to check the
catalytic activity of various metal oxides as shown in Table 1
(details of the reaction in Table 1, entry 5, can be found in
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Catal. Sci. Technol.