Communications
Under the best reaction conditions with 650 psig methane
and using 0.41 to 0.6 mmol of CaO as the radical initiator, a
temperature accelerates the kinetics of MSA formation.
When temperature is raised above that for the maximum
conversion of SO to MSA, a rapid decomposition of CaO or
2
8
9 to 91% conversion of SO to MSA was observed (Table 2,
3
3
2
entries 19 and 20). The methane conversion to MSA under
these conditions was 11%. Remarkably, 18% of the methane,
H O2 generated in situ occurs and the O2 thus released
inhibits the free-radical processes leading to MSA.
2
and correspondingly 10% of the SO , was converted to MSA
In conclusion, we have demonstrated a synthetic approach
for the direct, liquid-phase sulfonation of methane with
30 wt% SO3 in sulfuric acid. Under the best reaction
3
at 708C with a methane pressure of only 30 psig using CaO as
2
the initiator (Table 2, entry 21).
The acidity of the solvent media has a marked influence
on the rate of MSA formation (Table 3). Thus, in trifluoro-
conditions, 91% conversion of SO to MSA was achieved.
The respective methane conversion to MSA was 11–18%.
3
acetic acid, a 19% conversion of SO to MSA was attained,
CaO is an effective radical initiator even at low reaction
3
2
temperatures and CH pressures.
4
Table 3: Effect of solvent media on the conversion of SO to MSA[
a]
3
Received: August 8, 2002
Solvent
t [h]
Conv. of SO to MSA [%]
Revised: December 3, 2002 [Z19922]
3
CF COOH
3
1019
H SO4
CF SO H
3
5
5
89
53
2
3
[
1] a) C. L. Hill, Activation and Functionalization of Alkanes, Wiley,
New York, 1989; b) M. G. Axelrod, A. M. Gaffney, R. Pitchai,
J. A. Sofranko, Natural Gas Conversion II, Elsevier, Amsterdam,
1994, p. 93; c) C. Starr, M. F. Searl, S. Alpert, Science 1992, 256,
[a] Reaction conditions unless otherwise stated: methane: 650psig;
CaO : 0.4 mmol; SO : 1.7 g; molar ratio of methane to SO : 8.4:1;
2
3
3
fuming sulfuric acid: 5.67 g; time: 5 h; temperature: 658C.
981; d) A. E. Shilov, Activation of Saturated Hydrocarbons by
Transition Metal Complexes (Ed.: D. Reidel), Dordrecht, 1984;
e) G. A. Olah, A. Molnar, Hydrocarbon Chemistry, Wiley, New
York, 1995; f) M. Lin, A. Sen, Nature 1994, 368, 613; g) A. Sen,
Acc. Chem. Res. 1998, 31, 550; h) J. A. Labinger, Fuel Process.
Technol. 1995, 42, 325; i) R. H. Crabtree, Chem. Rev. 1995, 95,
whereas in sulfuric acid the conversion rose to 89%. Triflic
acid was not as effective as sulfuric acid due possibly to the
consumption of SO to form polysulfonic acids of the general
3
987; j) A. E. Shilov, G. B. Shul'pin, Chem. Rev. 1997, 97, 2879;
formula CF (SO ) H by the reaction of triflic acid and SO .
3
3
n
3
k) G. Dyker, Angew. Chem. 1999, 111, 1808; Angew. Chem. Int.
Ed. 1999, 38, 1698; l) H. D. Gesser, N. R. Hunter, Catal. Today
The mechanism by which CH reacts with SO to form
4
3
MSA is not understood; however, it is reasonable to suggest
that the reaction proceeds by a mechanism inovolving free
radicals, since the presence of molecular oxygen inhibits the
formation of MSA. It is conceivable that methane activation
1998, 42, 183; m) J. A. Labinger, J. E. Bercaw, Nature 2002, 417,
507.
[
2] a) M. Asadullah, T. Kitamura, Y. Fujiwara, Angew. Chem. 2000,
112, 2609; Angew. Chem. Int. Ed. 2000, 39, 2475; b) E. G.
Chepaikin, A. P. Bezruchenko, A. A. Leshcheva, G. N. Boyko,
I. V. Kuzmenkov, E. H. Grigoryan, A. E. Shilov, J. Mol. Catal. A
+
2
involves Ca ions and H O generated by the reaction of
2
2
CaO and H SO . Once CH C radicals are generated they can
2
2
4
3
2
001, 169, 89; c) R. A. Periana, D. J. Taube, E. R. Evitt, D. G.
Loffer, P. R. Wentrcek, G. Voss, T. Masuda, Science 1993, 259,
40; d) R. A. Periana, D. J. Taube, S. Gamble, H. Taube, T. Satoh,
react with SO to form CH SO C radicals, which can in turn,
3
3
3
abstract hydrogen from methane to form MSA.[ To assess
5]
3
whether H O generated by the reaction of CaO and H SO
2
2
2
2
4
H. Fujii, Science 1998, 280, 560; e) R. A. Periana, O. Mirinov, D. J.
Taube, S. Gamble, Chem. Commun. 2002, 2376.
might be solely responsible for the activation of CH , an
4
experiment was conducted in which 0.6 mmol of H O was
[3] a) Ullmann's Encyclopedia of Industrial Chemistry, Vol. A25,
VCH, Weinheim, 1994, pp. 503 – 506; b) F. M. Beringer, 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.
2
2
used as the initiator.[ A SO conversion to MSA of 9% was
9]
3
obtained in this experiment. If CaCl (0.6 mmol) was added to
2
the synthesis mixture containing H O , while keeping the
2
2
[
4] N. Basickes, T. E. Hogan, A. Sen, J. Am. Chem. Soc. 1996, 118,
3111.
amount of free SO the same, the conversion of SO to MSA
3
3
1
rose to 16%. This is considerably lower than the 72%
[
5] a) L. J. Lobree, A. T. Bell, Ind. Eng. Chem. Res. 2001, 40, 736;
b) S. Mukhopadhyay, A. T. Bell, Ind. Eng. Chem. Res. 2002, 41,
5901.
conversion of SO to MSA observed when 0.6 mmol of CaO2
3
was used in place of CaCl and H O , which suggests that
2
2
2
[
[
[
6] Sulfur Trioxide and Oleum: Storage and Handling, Dupont
Corporation, Wilmington, DE.
7] Y. Ishii, K. Matsunaka, S. Sakaguchi, J. Am. Chem. Soc. 2000, 122,
CaO has a unique role in the activation of methane.
2
The observed lowering in the conversion of SO to MSA
3
(
Table 2, entries 13 and 14) when more than 0.6 mmol of
metal peroxide was used in the synthesis mixture can be
attributed to the high rate of decomposition of H O to O ,
7390.
8] In a 100-mL glass-lined Parr autoclave, CaO (0.6 mmol), and SO3
2
2
2
2
(1.7 g) and H SO (3.99 g) were charged, together with a small
2
4
which can act as a free radical scavenger,[ thereby inhibiting
the formation of MSA. This interpretation is consistent with
the failure to observe any MSA when the reaction was carried
out in the presence of 30 psig of O2.
4]
teflon-coated magnetic stirring bar. The reactor was purged with
to expel the air out of the system and sealed. The autoclave was
then pressurized with 650 psig methane and heated to 708C for
h while stirred. After the stipulated period of time, the reactor
N
2
5
was quenched with ice and opened to collect the reaction mixture.
The observation of a maximum in the conversion of SO to
3
The reaction mixture was then added slowly to water (0.5 g) and
MSA with increasing temperature, such as that seen in entries
1
analyzed by H NMR spectroscopy. D O and methanol, contained
2
1
5–18 in Table 2, can be interpreted as follows: For temper-
in a capillary placed adjacent to the NMR tube containing the
sample, were used as the lock and references. The corresponding
atures lower than that for the best conversion, increasing the
1
020
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Angew. Chem. Int. Ed. 2003, 42, No. 9