Tomoharu Oku et al.
COMMUNICATIONS
der supercritical conditions resulted in not only a phatic precursors of coke from the catalyst surface
marked increase in the reactivity and methanol efficien- with liquid-like scCH3OH.
cy but also in the selectivity of ortho methylation as list-
In conclusion, we have reported the practical example
ed in Table 1. This selective methylation process is more of the chemoselective methylation of 1, which can be
appealing when ZrO2 was used as a supported material; tuned by using scCH3OH as a methylating agent and a
a combination of Fe-Voxide with ZrO2 caused a signifi- reaction medium. Using scCH3OH can improve the effi-
cant improvement in the catalytic activity with up to ciency of methanol and catalyst lifetime by lowering the
99% conversion from 65% with the silica supported reaction temperature, effectively removing of the depo-
Fe-V catalyst as shown in Scheme 2.
sition of higher molecular weight products from degra-
Thanks to pressure tunable fluid properties, optimum dation of CH3OH and extracting coke precursors from
combinations of the liquid-like density and gas-like dif- the catalyst surface. A suitable choice of a catalyst com-
fusivity can be realized to maintain catalyst activity, bining the weaker acidic and basic properties of solid
leading to an enhancement of the catalyst lifetime.[1]
A
metal oxides allowed the desired chemoselectivity for
continuous flow reaction over the Fe-V mixed oxide the scCH3OH methylation of phenols to be realized.
on a silica catalyst at 3508C and a 1:30 molar ratio under
otherwise identical conditions to those described in Ta-
ble 1revealed that the catalytic activity of Fe-V/SiO 2 did
Experimental Section
not suffer from serious deactivation under supercritical
The magnesium oxide catalyst, MgO, was prepared by calcina-
conditions compared to those attained under gas phase
tion of magnesium carbonate at 5408C under a nitrogen atmos-
conditions as shown in Figure 2. Although the catalyst
phere for 5 hours. ZrO2, prepared by precipitation from the re-
activity of the gas phase reaction deteriorated quickly
action of ZrO(NO3)2 and aqueous ammonium hydroxide fol-
lowed by calcination at 430, 500, 700, 850 and 1,0008C under
a nitrogen atmosphere for 5 hours. The Fe-V mixed oxide on
in several hours and almost reached a steady state within
12 hours, giving 14% conversion, the use of supercritical
conditions caused a significant improvement in the cat- SiO2 was prepared by impregnating a homogenous methanol
solution of Fe(NO3)3 and VOC2O4 into synthesized amorphous
silica powder (Sylysia 350, Fuji Silysia Chemical Ltd.), fol-
lowed by calcination at 7508C under air for 5 hours. Except
for amorphous SiO2, the triclinic FeVO4 phase was detected us-
ing powder X-ray diffraction analysis.
alyst lifetime with an increase in pressure, the activity re-
maining for several days. 13C Magic-angle-spinning
NMR spectroscopy of the deposited materials on the
catalyst surface after 72 hours of reaction showed that
the carbon species on the tested catalysts in scCH3OH
originated from an aromatic carbon, while the gas phase
reaction gave the material consisting of aliphatic com-
pounds, indicating that the deactivation of the Fe-V/
SiO2 catalyst might be caused by deposition of aliphatic
The methylation reaction of 1 in the gas or supercritical
phase was carried out isothermally in a continuous up-flow,
tubular reactor (SUS316 tubular reactor with a Swagelok
VCR joint, 1/2 inchꢀ1 0 mmꢀ135 mm). The reactor, loaded
with catalyst particles, was placed in an oven. A mixture of phe-
carbons originating from methanol degradation.[8] A sig- nol and methanol was supplied to the reactor using an HPLC
pump (PU1580, Jasco Co.) through the preheating coil. The
pressure in the reaction system was controlled with an auto-
matic back pressure regulator (880–81, Jasco Co.) at 0.1 to
15 MPa. Standard reaction conditions were used [5.0 mL cata-
lyst, 3008C, 8.2 MPa, molar ratio of methanol:amine¼13.5:1
or 20:1and the LHSV (mL-liquid/mL-cat·h), which is the
space velocity as normal liquid flow rate of mixed solution of
reactants, is 4 hÀ1). The reaction products were identified by
Agilent 5973N-6890N (Agilent Technologies) GC-MS analy-
sis. The selectivity and chemical yield of the products were de-
termined by gas chromatography analysis (GC-17A; Shimadzu
Co., FID detector and DB-1701 (J&W) capillary column).
nificant improvement in catalyst lifetime could be at-
tained by retarding methanol degradation, reducing re-
action temperature and effectively extracting the ali-
References and Notes
[1] As leading reviews: a) P. E. Savage, S. Gopalan, T. I. Miz-
an, C. J. Martino, E. E. Brock, AIChE J. 1995, 41, 1723–
1778; b) P. E. Savage, in: Handbook of Heterogeneous
Catalysis, Vol. 4, (Eds.: G. Ertl, H. Knçzinger, J. Weit-
kamp), Wiley-VCH, Weinheim, 1997, pp. 1339–1347;
c) A. Baiker, Chem. Rev. 1999, 99, 453–473; d) L. Fan,
K. Fujimoto, in: Chemical Synthesis Using Supercritical
Fluids, (Eds.: P. G. Jessop, W. Leitner), Wiley-VCH,
Figure 2. The catalyst lifetime: Influence of time-on-stream
on the catalytic activity as a function of conversion of or-
tho-methylation of phenol under supercritical and gas phase
conditions for several days.
1556
asc.wiley-vch.de
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2005, 347, 1553 – 1557