Several features of interest emerge from Fig. 1. Within group
1 the yields decrease down the group as the cations become
larger. The larger cations presumably block entry to the pore
system of the zeolite, spoiling its potential as a catalyst. How-
ever, the restriction of the pore size might also be expected to
lead to an increase in para-selectivity, which is apparent with
sodium but tails off thereafter. With the larger cations it may be
that a substantial proportion of the product arises from reac-
tion at the external surface, thereby reducing the regioselectivity
and also limiting the yield because of the relatively small num-
ber of available sites.
quite good yield by use of proton, calcium, barium or cobalt()
exchanged forms of zeolite β. All of these cases provide much
better para-selectivity than the published reaction with alu-
minium chloride and methanesulfonyl chloride and in most
cases the yield is substantially improved too. With the add-
itional advantages of easy catalyst recovery and the lack of a
metal-containing waste stream, this approach should prove
attractive for sulfonylation reactions.
Acknowledgements
For Group 2 the yields are higher than their Group 1 counter-
parts in every case. Presumably the smaller divalent cations
allow easier entry into the pore network, which would be con-
sistent with the increased yields. There is also a general increase
in para-selectivity going down the group as the cations get
larger, but again at the expense of overall yield. Be2ϩβ appears
to be an exception, giving a lower yield and higher selectivity
than the Mg2ϩβ analogue.
We thank Zeneca for financial support to G. M. E., the ESPRC
and the University of Wales for grants that allowed the pur-
chase of NMR equipment used in this study, and PQ zeolites
for a gift of zeolite β.
References
1 K. Smith and K. Fry, Tetrahedron Lett., 1989, 30, 5333.
2 K. Smith, M. Butters and B. Nay, Synthesis, 1985, 1157.
3 K. Smith, A. Musson and G. A. DeBoos, Chem. Commun., 1996,
469.
4 K. Smith and D. Bahzad, Chem. Commun., 1996, 467.
5 R. Q. Kluttz and L. H. Slaugh, US Pat 4 395 372, 1983 (Chem
Abstr., 1983, 99, P139469x).
6 A. Corma, H. Garcia and J. Primo, J. Chem. Res. (S.), 1988, 40.
7 P. Geneste, B. Chiche, A. Finiels and C. Gauthier, J. Org. Chem.,
1986, 51, 2128.
8 H. A. Bouncer, Eur. Pat. 160144, 1985 (Chem. Abstr., 1986, 104,
P148457r).
9 A. Cornélis and P. Laszlo, Synthesis, 1985, 909.
10 P. Laszlo, Chem. Ind. (London), 1994, 53, 429.
11 G. A. Olah, S. Kobayashi and J. Nishimura, J. Am. Chem. Soc.,
1973, 95, 564.
12 Publicity document on Envirocats, Contract Catalysts plc.
13 S. Daley, K. A. Trevor, K. R. Randles and B. D. Gott, PTC Int.
Appl. WO93 18.000, 1993 (Chem. Abstr., 1994, 120, P54320u).
With the exception of In3ϩ, all trivalent and tetravalent cation
cases produced reasonable yields (typically 60–70%) and para-
product proportions in the range 40–50%. This is consistent
with the idea that small cations allow more space for reaction
and the results are fairly similar to those obtained with proton-
exchanged zeolite. The divalent cations of the first transition
series provided rather similar results also, with yields typically
70% and para-proportions typically 50%.
The cases which provided results that were out of line may
have arisen from poor exchange, impurities or pore-blocking,
however the benefits to be gained from more careful scrutiny of
them could not justify the amount of work involved in such a
study. It is clear that overall there is a broad correlation between
cation size and both yield and selectivity. Unfortunately, there is
also a trade-off between the two, with those cases providing
highest para-selectivity also giving rather poor yields. Neverthe-
less, the sodium-exchanged case offers the possibility of very
high para-selectivity if the yield based on the anhydride is not
critical (methanesulfonic acid can be recovered after work-up).
Alternatively, reasonable para-selectivity can be achieved in
Paper 7/01025G
Received 12th February 1997
Accepted 28th February 1997
1086
J. Chem. Soc., Perkin Trans. 1, 1997