Asghar et al.
229
ously (32, 33). Nevertheless, our results (9) do not yield a
7. S. Lakhdar, R. Goumont, F. Terrier, T. Boubaker, J.M. Dust,
value for k for trifluoromethyl sulfinic acid so that a direct
and E. Buncel. Org. Biomol. Chem. 5, 1744 (2007).
el
8
. B.H.M. Asghar and M.R. Crampton. Org. Biomol. Chem. 5,
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02 (2007).
0. R.A. Bartsch and J.F. Bunnett. J. Am. Chem. Soc. 91, 1376
1969).
comparison is not possible.
1
In fact, the elimination process is likely (34) to involve the
E2 mechanism so that factors other than the nucleofugality
of the leaving group are involved. These include steric fac-
tors involving the accessibility to the catalysing base of the
acidic hydrogen to be removed from the reaction centre in
the adducts, such as 10, and possible steric interaction with
the ring nitro-group in the alkene products, such as 11. For
example, the adduct 10, carrying two phenylsulfonyl groups,
is likely to be more sterically demanding than the corre-
sponding adduct produced from the nitromethane carbanion.
It should also be noted that in the elimination process in
methanol, catalysis has been observed only by the
methoxide ion and not by unreacted carbanions, present in
excess, which will be more sterically inhibited.
9
7
1
(
1
1
1. C.J.M. Stirling. Acc. Chem. Res. 12, 198 (1979).
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Boubaker, and R. Goumont. J. Org. Chem. 70, 6242 (2005).
1
1
1
1
Experimental
Nitro-compounds 5a–5c, 6, and 7 were available from
previous work [9]. Bis(phenylsulfonyl)methane was a com-
mercial sample. Solutions of sodium methoxide were pre-
pared by dissolving clean sodium in AnalaR methanol under
nitrogen. Solutions containing very low equilibrium concen-
trations of methoxide ions were prepared using buffers
prepared from 4-bromophenol, whose pKa value (35) in
methanol is 13.61. All other materials and solvents were the
purest available commercial samples.
17. F. Terrier, A.-P. Chatrousse, Y. Soudais, and M. Hlaibi. J. Org.
Chem. 49, 4176 (1984).
18. F. Terrier, A.-P. Chatrousse, and F. Millot. J. Org. Chem. 45,
2
666 (1980).
1
2
2
2
2
9. L. DiNunno, S. Florio, and P.E. Todesco. J. Chem. Soc. Perkin
Trans. 2, 1469 (1975).
0. J.H. Atherton, M.R. Crampton, G.L. Duffield, and J.A.
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1. M. Makosza, O. Lobanova, and A. Kwast. Tetrahedron, 60,
1
2
H NMR spectra in [ H ]-DMSO were recorded with a
6
Bruker Avance 400 MHz instrument, UV-vis spectra and ki-
netic measurements were made at 25 °C with a Shimadzu
UV-2101 PC spectrophotometer or an Applied Photophysics
SX-17 MV stopped-flow instrument. First-order rate
constants, precise to ± 5%, were evaluated using standard
methods.
2
577 (2004).
2. M.R. Crampton, L.M. Pearce, and L.C. Rabbitt. J. Chem. Soc.
Perkin Trans. 2, 257 (2002).
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Acknowledgements
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2
5. A.O. Cohen and R.A. Marcus. J. Phys. Chem. 72, 4249
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BHMA thanks the Ministry of Higher Education, King-
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ety of Chemistry for the award of a J.W.T. Jones Travel
grant to allow him to spend time in Durham University, U.K.
(
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2008 NRC Canada