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J. Am. Chem. Soc. 1997, 119, 5469-5470
5469
(CPMAS) NMR spectroscopy.15 Samples were weighed, placed
in shallow beds in one-half inch horizontal glass tubes on a
vacuum manifold, and outgassed at 700 K until the pressure
returned to the background value of less than 1.0 × 10-5 Torr,
∼6 h. After the samples were cooled to liquid nitrogen
temperature, some samples were dosed with controlled volumes
of unlabeled benzene and controlled pressures of 13C-labeled
carbon monoxide (Cambridge Isotopes Labs). Other samples
were cooled to room temperature and were dosed with controlled
volumes of carbonyl 13C-labeled benzaldehyde or benzoic acid
(Cambridge Isotopes Labs). The samples were sealed in glass
tubes and kept in liquid nitrogen until being warmed to room
temperature and transferred to NMR rotors under an inert
atmosphere.
Figure 1a is the result obtained after adsorption of benzene
and 13C-labeled carbon monoxide to sulfated zirconia and
warming to room temperature for 5 days inside the sealed glass
tube. The figure shows the presence of spectral features at 206
and 176 ppm (from TMS) that we interpret as being due to the
formation of benzaldehyde and benzoic acid, respectively. A
possible mechanism of the reaction is outlined in Scheme 1.
We speculate that the acylium cation 1 is formed as an
intermediate,2,16 although it is not observed in the NMR
spectrum. Upon undergoing a hydride shift and loss of a proton,
1 is converted to benzaldehyde 2. Oxidation of benzaldehyde
produces benzoic acid 3. This is not surprising when one
considers earlier studies in which the redox properties of the
sulfated zirconia were examined.17,18 Carbon monoxide19 is not
observed in these experiments, probably due to desorption during
the transfer of the samples to the NMR rotors. The feature at
130 ppm is the natural abundance signal due to unreacted
benzene. We also note here that the pure zirconia sample did
not produce the reaction product features under the conditions
of this experiment.
The assignment of the product features as benzaldehyde and
benzoic acid is substantiated with the results shown in Figure
1b-d. Figure 1b was obtained after adsorption of benzaldehyde
to the sulfated zirconia sample at a coverage of 0.38 molecules
per Brønsted site. This spectrum shows a single feature centered
at 206 ppm from TMS, with spinning sidebands at 126 and 286
ppm. Identical features are observed in the spectrum obtained
at 0.70 molecules per site (Figure 1c). The observed isotropic
chemical shift of 206 ppm is very close to values obtained for
benzaldehyde in magic acid (205.7 ppm),20 while the carbonyl
resonance for benzaldehyde in CDCl3 solution is 192.15 ppm.21
This suggests that the carbonyl carbon in the benzaldehyde
molecule has been substantially deshielded by interactions with
the environment, analogous to those observed in zeolites22-25
13C NMR Study of the Carbonylation of Benzene
with CO in Sulfated Zirconia
T. H. Clingenpeel, T. E. Wessel, and A. I. Biaglow*
Department of Chemistry, United States Military Academy
West Point, New York 10996
ReceiVed March 14, 1997
Friedel-Crafts acylation1 of butene and ethene to form
ketones in the solid acid zeolite H-ZSM-5 at 296 K has recently
been reported.2 An earlier study demonstrated that small olefins
are converted to carboxylic acids (the Koch reaction3) in the
presence of CO and water in H-ZSM-5 at 296 K.4 The
carbonylation of aromatic hydrocarbons with CO is also
feasible,5-7 although requiring more highly acidic conditions.
Addition of metal-halide Lewis acids to enhance the Brønsted
acidity8 of the zeolite H-Y allows the carbonylation of benzene
with CO to proceed readily.9 Another promising family of
materials are the sulfated zirconias.10 These materials are known
to catalyze the isomerization of small alkanes at relatively low
temperature,10 although the exact mechanism for this may
involve trace alkene impurities.11 The use of metal-promoted
sulfated zirconia as a catalyst in the carbonylation of aromatics
with CO has recently been reported,7 although pure sulfated
zirconia was reportedly not active in the reaction. The present
paper extends the previous work2,3,7 to include a direct
spectroscopic measurement of the carbonylation of benzene with
CO, the Gattermann-Koch reaction,5 using sulfated zirconia
as the solid acid catalyst.
Sulfate-doped zirconia and pure zirconia samples were
obtained from Magnesium Electron, Inc. (XZ0682.01 and
XZ0632.03, respectively). The sulfate-doped and pure zirconia
samples were pretreated by heating to 600 °C for 1 h in flowing
dry O2. The number of Brønsted acid sites in each material
was determined with thermogravimetric analysis (TGA) of
isopropylamine from the number of amine molecules which
desorb between 575 and 650 K.12,13 The sulfated zirconia
sample had a site concentration of 80 µmol/g. While the number
of Brønsted sites is known to depend strongly on pretreatment
conditions,14 we observe a significant difference between the
sulfated zirconia and the pure zirconia, which had a site
concentration of <10 µmol/g and was inactive in the carbony-
lation reaction.
The chemistry of benzene and CO in sulfated zirconia was
1
studied with H-13C cross-polarization magic angle spinning
(1) Olah, G. A. Friedel-Crafts Chemistry; Wiley & Sons: New York,
1973.
(2) Luzgin, M. V.; Romannikov, V. N.; Stepanov, A. G.; Zamaraev, K.
I. J. Am. Chem. Soc. 1996, 118, 10890.
(3) Bahrmann, H. In New Syntheses with Carbon Monoxide; Falbe, J.,
Ed.; Springer-Verlag: Berlin, 1980; pp 372-413.
(4) Stepanov, A. G.; Luzgin, M. V.; Romannikov, V. N.; Zamaraev, K.
I. J. Am. Chem. Soc. 1995, 117, 3615-3616.
(5) (a) Gattermann, L.; Koch, J. A. Ber. 1897, 30, 1622. (b) For a review,
see: Olah, G. A.; Kuhn, S. J. In Friedel-Crafts and Related Reactions;
Olah, G. A., Ed.; Wiley: New York, 1964; pp 1153-1256.
(6) Olah, G. A.; Arpad, M. Organic Reactions; Wiley & Sons: New
York, 1995.
(7) Bruce, D. A.; Occelli, M. L.; Schiraldi, D.; Sood, D.; Sullivan, C.
E.; White, M.G. Carbonylation via Solid Acid Catalysis; U.S. Pat. Appl.,
March 1, 1996.
(8) Makarova, M. A.; Bates, S. P.; Dwyer, J. J. Am. Chem. Soc. 1995,
117, 11309.
(9) Clingenpeel, T. H.; Biaglow, A. I. J. Am. Chem. Soc. In press.
(10) (a) Hino, M.; Arata, K. React. Kinet. Catal. Lett. 1982, 19, 101. (b)
Tanabe, K.; Hattori, H.; Yamaguchi, T. Crit. ReV. Surf. Chem. 1990, 1, 1.
(11) Tabora, J.; Davis, R. J. J. Am. Chem. Soc. 1996, 118, 12240.
(12) Farneth, W. E.; Gorte, R. J. Chem. ReV. 1995, 95, 615.
(13) Wan, K. T.; Khouw, C. B.; Davis, M. E. J. Catal. 1996, 158, 311.
(14) Motera, C.; Cerrato, G.; Pinna, F.; and Signoretto, J. J. Phys. Chem.
1994, 98, 12373.
(15) All spectra were acquired on a Bru¨ker MSL 200 with a 13C resonance
frequency of 50.323 MHz. Spectra consisted of 16 384 scans with a
repetition time of 3.0 s, unless otherwise noted. All spectra were obtained
with 1H-13C cross-polarization, with a proton 90° pulse of 5 µs, a contact
time of 3 ms, and a decoupled acquisition time of 40 ms. The magic angle
spinning frequency was 4050 ( 10 Hz. The magnet was shimmed using
adamantane until a spinning line width of less than 2.5 Hz was obtained.
Adamantane was used as an external frequency standard, and showed daily
frequency variations of less than 0.1 Hz. Spectra shown in the figures are
referenced to TMS.
(16) Another pathway involves protonation of CO to form a formyl
cation, reaction of the formyl cation with benzene to form a benzenium
ion, and deprotonation to form benzaldehyde. See ref 5b.
(17) Tanabe, K. Mater. Chem. Phys. 1985, 13, 347.
(18) Farcasiu, D.; Ghenciu, A.; Li, J. Q. J. Catal. 1996, 158, 116.
(19) CO has been reported as a narrow line at 185 ppm. (a) Anderson,
M. W.; Klinowski, J. J. Am. Chem. Soc. 1990, 112, 10. (b) Munson, E. J.;
Lazo, N. D.; Moellenhoff, M. E.; Haw, J. F. J. Am. Chem. Soc. 1991, 113,
2783.
(20) Olah, G. A.; Rasul, G.; York, C.; Surya Prakash, G. K. J. Am. Chem.
Soc. 1995, 117, 11211. See structure 2.
(21) Aldrich Library of 13C and 1H NMR Spectra; Pouchert, C. J., Behnke,
J., Eds.; Aldrich Chemical Company: Milwaukee, WI, 1993; Vol. 2,
(benzaldehyde) p 932, (benzoic acid) p 1063, (aromatic acetals) pp 238-
241.
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