Table 2 Effect of process parameters on the sulfonation reactiona
sulfonic acid using SO2 as the sulfonating agent and O2 as the
oxidant in the presence of a redox catalyst system comprising
Pd(II) and Cu(II) salts. The reaction is highly selective, and as
much as 20% of the SO2 charged is converted to MSA with only
30 psig SO2, the maximum available pressure. The product
MSA can be isolated from the reaction mixture by distillation
under reduced pressure.
PdCl2/ CuCl2/
% SO2
Entry CH4/psig SO2/psig O2/psig mmol mmol T/°C to MSA
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
200
400
650
30
30
30
30
30
0
30
30
30
30
30
30
30
30
0
10
20
40
30
30
30
30
30
30
30
30
30
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.05
0.1
0.3
0.2
0.2
0.2
0.2
0.2
0.2
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.05
0.1
0.2
0.3
0.3
0.3
85 tr
85
85
85
1
2
8
ATOFINA Chemicals, Inc., North America, funded this
study.
1000
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
1200
85 12
85
85
85
85
85
85
85 10
85
85
85 12
85
85
85 10
65
75
0
3
7
0
6
9
10
20
30
30
30
30
30
30
30
30
30
30
30
30
30
Notes and references
1 (a) C. L. Hill, Activation and functionalization of Alkanes, Wiley, New
York, 1989; (b) M. G. Axelrod, A. M. Gaffney, R. Pitchai and J. A.
Sofranko, Natural Gas Conversion II, Elsevier, Amsterdam, 1994, p. 93;
(c) G. A. Olah and A. Molnar, Hydrocarbon Chemistry, Wiley, New
York, 1995; (d) G. J. Hutchings, M. S. Scurrell and J. R. Woodhouse,
Chem. Soc. Rev., 1989, 18, 251; (e) R. M. Ormerod, Chem. Soc. Rev.,
2003, 32, 17; (f) K. Otsuka and Y. Wang, Appl. Catal., 2001, 222, 145;
(g) A. Ueno, Catalysis, 2000, 15, 185; (h) G. Dyker, Angew. Chem., Int.
Ed., 1999, 38, 1698; R. A. Periana, D. J. Taube, E. R. Evitt, D. G. Loffer,
P. R. Wentrcek, G. Voss and T. Masuda, Science, 1993, 259, 340; (i) R.
A. Periana, D. J. Taube, S. Gamble, H. Taube, T. Satoh and H. Fujii,
Science, 1998, 280, 560; (j) R. A. Periana, O. Mirinov, D. J. Taube and
S. Gamble, Chem. Commun., 2002, 2376.
2 (a) Ullmann’s Encyclopedia of Industrial Chemistry, VCH, Weinheim,
1994, Vol. A25, pp. 503–506; (b) F. M. Beringer and R. A. Falk, J. Am.
Chem. Soc., 1959, 81, 2997; (c) H. A. Young, J. Am. Chem. Soc., 1937,
59, 811; (d) R. C. Murray, J. Chem. Soc., 1933, 739.
3 (a) N. Basickes, T. E. Hogan and A. Sen, J. Am. Chem. Soc., 1996, 118,
13111; (b) L. J. Lobree and A. T. Bell, Ind. Eng. Chem. Res., 2001, 40,
736; (c) S. Mukhopadhyay and A. T. Bell, Ind. Eng. Chem Res., 2002, 41,
5901; (d) S. Mukhopadhyay and A. T. Bell, Org. Process. Res. Dev.,
2003, 7, 161; (e) S. Mukhopadhyay and A. T. Bell, Angew. Chem., Int.
Ed., 2003, 42, 1019; (f) S. Mukhopadhyay and A. T. Bell, Angew. Chem.,
Int. Ed., 2003, in press; (g) S. Mukhopadhyay and A. T. Bell, J. Am.
Chem. Soc., 2003, 125, 4406; (h) Y. Ishii, K. Matsunaka and S.
Sakaguchi, J. Am. Chem. Soc., 2000, 122, 7390.
4 In a 100-ml glass lined high pressure Parr autoclave reactor, 0.2 mmol
PdCl2, 0.3 mmol CuCl2, and 5 ml of trifluoromethanesulfonic acid were
charged together with a small Teflon coated magnetic stir bar. The reactor
was then pressurized with 30 psig SO2, 30 psig O2, and then ultimately
with 1200-psig methane from the adjacent connecting cylinders. The
reactor was then heated to 85 °C under stirring and kept at that
temperature for 12 h. After the stipulated period of time, the reactor was
cooled to room temperature and opened to collect the reaction mixture.
The mixture was then added slowly to 1.0 g of water and then taken for
1H NMR analysis. D2O and methanol were used in a capillary as the lock
references. The corresponding chemical shift for MSA was 2.78 to 2.98
ppm, depending on the concentration of MSA in the mixture.
5 Pd and Cu catalyst combination is used for the carbonylation of methane
to acetic acid in CF3COOH as the solvent, see (a) T. Nishiguchi, K.
Nakata, K. Takaki and Y. Fujiwara, Chem. Lett., 1992, 1141; (b) A. Sen,
Platinum Met. Rev., 1991, 35, 126; (c) L.-C. Kao, A. C. Hutson and A.
Sen, J. Am. Chem. Soc., 1991, 113, 700; (d) Carbene based Pd-catalyst
has been used recently for methane oxidation, see M. Muehlhofer, T.
Strassner and W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41,
1745.
3
7
7
8
2
8
100 13
a Reaction conditions: time, 12 h; solvent, CF3SO3H, 5 ml.
increase in the amount of PdCl2 had no effect on the MSA
conversion (Table 2, entries 13–15).
When the amount of CuCl2 was increased from 0.05 to 0.3
mmol, the SO2 conversion to MSA increased from 7 to 12%
(Table 2, entries 16–18). In the absence of CuCl2, Pd-black
particles were observed in the reaction mixture after 4 h of
reaction, whereas in presence of CuCl2 the appearance of Pd-
black particles was not so prominent. This suggests that CuCl2
enhances the rate of oxidation of Pd(0) to Pd(II) species.
The conversion of SO2 to MSA increased from 2 to 12%
when the temperature was raised from 65 to 85 °C. At 100 °C,
a 13% conversion of SO2 to MSA was achieved and a trace
amount of CF3SO3CH3 was also detected (Table 2, entries
19–21).
The reaction requires a highly acidic solvent. When per-
formed in H2SO4, 5% conversion of SO2 to MSA was observed;
however, no reaction was observed using acetic acid as the
solvent. A 12% conversion of SO2 to MSA was achieved using
CF3SO3H as the solvent. To verify that the solvent CF3SO3H
does not react with CH4 to give CH3SO3H and CHF3 (CH4 +
CF3SO3H ? CH3SO3H + CHF3), a controlled reaction was
performed in presence of O2 and catalysts in CF3SO3H. No SO2
was added. Under these conditions, MSA was not detected after
12 h of reaction. Likewise, no CHF3 was detected by 19F NMR.
A small amount of CF3SO3CH3 was observed as the sole
product.
The mechanism by which Pd(II) and Cu(II) promote the
sulfonation of CH4 to MSA is not understood. It seems plausible
to suggest, though, that the reaction proceeds via an electro-
philic substitution of high valent Pd-species with CH41h–j,5,6 and
subsequent SO2 insertion and oxidation3h to form MSA and
Pd(0). Cu(II) then promotes the reoxidation of Pd(0) to Pd(II) in
presence of O2.7
6 Pt-salt based methane activation by Shilov chemistry, see (a) A. E. Shilov
and G. B. Shul’pin, Activation and Catalytic Reactions of Saturated
Hydrocarbons in the Presence of Metal Complexes, Kluwer Academic
Publishers: Dordrecht, 2000; (b) For a nice mechanistic recent review see
J. A. Labinger and J. E. Bercaw, Nature, 2002, 417, 507.
7 For the role of co-catalysts in PdCl2 catalyzed C–H bond activation in
benzene, see S. Mukhopadhyay, G. Rothenberg, G. Lando, K. Agbaria,
M. Kazanci and Y. Sasson, Adv. Synth. Catal., 2001, 343, 455.
In conclusion, we have developed a highly selective low-
temperature reaction protocol to sulfonate methane to methane-
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