Carbonylation of Nitrobenzene in Methanol
FULL PAPER
with helium as mobile phase. The injector and detector were operated at
2508C. An injection volume of 1 mL was taken with a split ratio of 10:1.
After injection, the column was heated at 1208C for five minutes, where-
Experimental Section
General remarks: All ligands were generously provided by Shell Global
Solutions Amsterdam B.V., where they were synthesized according to lit-
erature procedures.[86–94] All other solids were purchased from Acros or-
ganics and used as received. Methanol, nitrobenzene and aniline were all
of analytical-reagent purity, and were distilled under an argon atmos-
phere over the appropriate drying agent.[95] After distillation, they were
saturated with argon. It was ensured that no water was present by using
an analytical reaction with trimethyl orthoformate according to a modi-
fied literature procedure[96] (see below and also the Supporting Informa-
tion). Carbon monoxide (>99% pure)[51] was purchased from Linde gas
Benelux B.V. and used as received.
1H and 13C NMR spectra were recorded on a Bruker DPX300 (300 MHz)
or a Bruker DMX400 (400 MHZ) machine. High-pressure catalysis ex-
periments were conducted in stainless steel autoclaves (100 mL)
equipped with two inlet/outlet valves, a burst disc, a pressure sensor and
a thermocouple. The autoclaves were heated by a Hel polyBLOCK elec-
trical heating system. Temperatures and pressures where measured with
probes connected to a computer interface making it possible to record
these parameters throughout the course of the reaction. GLC-MS meas-
urements were performed on a Hewlett Packard series 2 type 5890 gas
chromatograph equipped with a Hewlett Packard 5971 mass-selective de-
tector. Depending on the analyte, a polar or an apolar column was used.
Technical details and settings are identical to those used for the quantita-
tive GLC-FID measurements (see below). Mass spectra of the gas phase
were recorded with a Spectra MicroVision plus 24 VDC series K64764,
coupled to a computer for digital readout. Data points were collected
with a resolution of m/z 0.25 in the range of m/z 3–50.
after it was heated to 1758C (108Cminꢃ1
) and then to 3258C
(508Cminꢃ1) for four minutes. This method was used to quantify the fol-
lowing products (tR in minutes): dimethyl carbonate (4.1), dimethyl oxa-
late (5.9), nitrosobenzene (7.8), aniline (8.5), decane (9.7), methyleneben-
zenamine (10.2) nitrobenzene (11.0), methyl phenylcarbamate (13.4),
azobenzene (14.8), and azoxybenzene (15.7).
For the polar column,
a Varian star 3400 CX gas chromatograph
equipped with a Shimadzu integrator was used. A Varian WCOT fused
silica CP-wax 58 (FFAP) column (length: 25 m; diameter: 0.32 mm; film
thickness: 1.20 mm) was used as stationary phase with helium as mobile
phase. The injector and detector were operated at 2508C. An injection
volume of 0.5 mL was taken with a split ratio of 10:1. The temperature of
the column was maintained at 408C throughout the 10 min elution time.
This method was used to quantify the products (tR in minutes): di
ACHTUNGTRENNUNGmeth-
AHCTUNGERTGoNNUN xymethane (1.5), methyl formate (1.9), acetone (2.4), decane (6.4), and
trimethyl orthoformate (7.3). Water was analyzed by adding an amount
of freshly prepared 0.55m p-toluenesulfonic acid in trimethyl orthofor-
mate to the reaction mixture, heating to 708C for 120 min followed by
cooling to laboratory temperature and thereafter analyzing the amount
of methyl formate that is formed. See the Supporting Information for
more details.[96]
Quantification of N,N’-diphenylurea: Because N,N’-diphenylurea (DPU)
is a solid and poorly soluble in methanol, this compound was quantita-
tively analyzed by isolation and determination of its weight. First, a
sample was taken for GLC-FID analysis (see above). Then, 10 mL n-
hexane was added to the reaction mixture to ensure that all DPU precipi-
tated. The reaction mixture was then stirred and carefully filtered by
using a weighed paper filter and a Bꢃchner funnel. The resulting solid
was washed five times with 2 mL portions of n-hexane and dried over-
night in a vacuum oven at 508C. The amount of DPU could then be de-
termined by weight. For each isolated batch, 1H and 13C NMR spectro-
scopic analysis was used to verify the purity of DPU.
Catalytic/high-pressure reactions: In
a typical catalytic experiment,
0.05 mmol Pd(OAc)2 and 0.075 mmol ligand (and, if relevant, another ad-
ACHTUNGTRENNUNG
ditive) were weighed and transferred into an autoclave, together with a
magnetic stirring rod. The autoclave was tightly closed and subsequently
filled with argon by using a Schlenk system that was connected to one of
the valves of the autoclave. Through the other valve 2.50 mL (24.4 mmol)
dried and degassed nitrobenzene was added under a continuous flow of
argon. In a similar fashion, 25.0 mL dried and degassed methanol was
then added. This reaction mixture was allowed to stir at 500 rpm for
about 15 min to ensure that complex formation was complete.[42] The au-
toclave was then inserted into the heating block and pressurized with
50 bar CO gas. The reaction mixture was heated to 1108C (within
30 min) under stirring at 500 rpm. After standing for four hours at this
temperature, the autoclave was cooled to room temperature over about
one hour. The autoclave was then slowly vented to atmospheric pressure
and the reaction mixture was analyzed as described below. To check re-
producibility, all catalytic reactions were performed in quadruplet; the
relative standard deviation was always less than 5% for all products.
Acknowledgements
This research has been financially supported by the Council for Chemical
Sciences of the Netherlands Organization for Scientific Research (CW-
NWO). This work has been performed under the auspices of the joint
NIOK Research Graduate School of Leiden University and six other
Dutch Universities. Dr. A. I. Yanson and Prof. Dr. M. T. M Koper are
kindly acknowledged for their assistance with the mass spectroscopic
measurement equipment. Shell Global Solutions International B.V. is
kindly acknowledged for generously donating phosphane ligands and for
their hospitality during the initial phase of this project.
Trapping experiments with cyclohexane: Cyclohexene (passed through
an alumina column and saturated with argon; 2.7 mL, 25 mmol) was
transferred to a piece of stainless steel tubing (5 mL) that was closed on
both sides by two valves. This piece of tubing was mounted on one of the
gas inlet/outlet valves of an autoclave that was prepared for a normal
high-pressure catalytic reaction (see above). The catalytic reaction was
then started as normal. After the decline in pressure inside the autoclave
was about half of what is usually observed when using a specific catalyst,
cyclohexene was added to the reaction mixture with a small overpressure
of CO. The reaction was then allowed to continue for the usual total of
four hours. After cooling and venting, the reaction mixture was analyzed
by GLC-FID and GLC-MS.
[1] J. Paetsch in Ullmannꢀs Encyclopedia of Industrial Chemistry, Wiley-
VCH, New York, 1975.
[6] R. L. Metcalf in Kirk-Othmer Encyclopedia of Chemical Technology,
(Eds.: J. L. Kroschmitz, M. Howe-Grand.), Wiley, New York, 1995.
[7] N. N. Melinkov, Chemistry of Pesticides, Springer, Berlin, 1971.
[8] M. Jayabalan, P. P. Lizymol, J. Polym. Mater. 2000, 17, 9–12.
[10] K. C. Frisch, Polimery 1996, 41, 257–264.
Quantitative GLC-FID analysis of reaction mixtures: Prior to the work-
up of N,N’-diphenylurea (see below), a sample (0.5 mL, diluted with
1.0 mL methanol) was taken to quantify the other analytes by GLC-FID
analysis with an apolar and a polar column, and decane as internal stan-
dard.
For the apolar column, a Hewlett Packard 6890 series gas chromatograph
equipped with an auto sampler was used. An AT-1 column (length: 30 m;
diameter: 0.25 mm; film thickness: 1.00 mm) was used as stationary phase
Chem. Eur. J. 2011, 17, 13318 – 13333
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