J . Org. Chem. 1997, 62, 1857-1859
1857
assignment of reaction mechanism.5
-13
Therefore, we
Neigh bor in g Meth oxy Gr ou p Effect in
Solvolysis Rea ction s of Cyclop en tyl a n d
Cycloh exyl p-Tolu en esu lfon a tes
have analyzed the kinetic data of Table 1 in terms of both
the two-parameter and four-parameter Grunwald-Win-
stein-type equations (1) and (2), where, for equation 1, k
Donald D. Roberts
Department of Chemistry, Louisiana Tech University,
Ruston, Louisiana 71272
log k ) mYOTs + log k0
(1)
Received October 16, 1996
refers to the solvolytic rate constant in any solvent, k
refers to the rate constant in 80% v/v ethanol/water, and
0
1
In an earlier paper from this laboratory, we investi-
3
YOTs is a scale of ionizing power for tosylates. For eq 2,
gated the neighboring-group effect of a methoxy sub-
stituent upon the rates of solvolysis of trans-2-methoxy-
cyclopentyl p-toluenesulfonate (1) and trans-2-methoxy-
cyclohexyl p-toluenesulfonate (2). Although we found
that the presence of a trans-2-methoxy group retarded
the rate of solvolysis of both the cyclopentyl and cyclo-
hexyl systems, it was observed that this rate retardation
was insensitive to change from acetic acid (a solvent
N
OTs is a
log k ) lNOTs + mYOTs + log k0
(2)
scale for solvent nucleophilicity.2b For comparison pur-
poses we have carried out similar analyses for tosylates
b,c,14
3
and 4, substrates known1
to solvolyze with signifi-
solvolysis for cyclohexyl tosylate2
a-e
cant nucleophilic-solvent assistance. The results are
summarized in Table 2.
known to promote k
s
)
to trifluoroacetic acid (a solvent known to promote k∆
solvolysis for secondary tosylates2
a-d
Striking differences are obvious between the results
of these two analyses. While the reaction rates of both
cyclopentyl and cyclohexyl tosylate are dispersed into
separate correlation lines for the aqueous ethanol and
carboxylic acid solvent series,15 the reaction rates of both
trans-2-methoxycyclopentyl and trans-2-methoxycyclo-
hexyl tosylate correlate well (r ) 0.99) against YOTs over
a range of solvents varying in ionizing power from -1.75
). On the basis of
this solvolytic behavior, it was suggested, but not clearly
demonstrated, that participation by the neighboring
methoxy group may be involved in the solvolysis of both
1
and 2.
Recently, in our continuing study of neighboring-group
effects upon solvolyses, we became interested in a more
detailed study of the methoxy group. Accordingly, we
have investigated the solvolytic behavior of tosylates 1
and 2 using three probessthe effect of varying solvent
ionizing power upon rate, the effect of added azide ion
upon rate, and the identity of the solvolysis products in
7% aqueous TFEsto determine the absence or presence
of neighboring-group assistance by a trans-2-methoxy
group.
(
ethanol) to 4.57 (trifluoroacetic acid). Another note-
worthy feature of Table 2 is the small response of both 1
and 2 to varying solvent nucleophilicity. As can be seen,
the parent compounds, 3 and 4, have much higher l
values (0.3 and 0.3) than those for 1 and 2 (0.05 and 0.1,
respectively). The relatively low m values for 1 and 2
are in the range for compounds known to solvolyze with
9
1
6a-i
predominantly neighboring group participation.
These
The first-order rate constants for solvolysis of 1 and 2
are summarized in Table 1. Reaction progress was
followed by titrating the liberated p-toluenesulfonic acid,
and strictly first-order kinetics were observed up to at
least 75% conversion furnishing, within experimental
error, 100% of the theoretical amount of acid present. In
Table 2 we have listed the results obtained from correla-
tions of the rate data, given in Table 1 and elsewhere,
results clearly demonstrate that nucleophilic solvent
assistance is not significant in the solvolysis of 1 and only
slightly significant in the solvolysis of 2.
(
(
5) Roberts, D. D.; Hall, E. W. J . Org. Chem. 1988, 53, 2573-2579.
6) (a) Harris, J . M.; Mount, D. L.; Raber, D. J . J . Am. Chem. Soc.
1
978, 100, 3139-3143. (b) Harris, J . M.; Mount, D. L.; Smith, M. R.;
Neal, W. C., J r.; Dukes, M. D.; Raber, D. J . J . Am. Chem. Soc. 1978,
100, 8147-8156 and references cited therein.
3
2b
with YOTs values and with YOTs and NOTs values. The
data showing effect of added azide ion upon rates of
solvolysis of tosylate 1, tosylate 2, cyclopentyl tosylate
(7) For a review of the Winstein solvolysis scheme, see: Bentley, T.
W.; Schleyer, P. v. R. (Gold, V., Bethell, D., Eds.) Adv. Phys. Org. Chem.
1977, 14, 1-67.
(8) Bentley, T. W.; Bowen, C. T.; Morten, D. H.; Schleyer, P. v. R. J .
(
4
3), and cyclohexyl tosylate (4) are given in Tables 3 and
. Product composition data for the solvolysis of 1 and 2
in 97% aqueous trifluoroethanol are given in Table 5.
Am. Chem. Soc. 1981, 103, 5466-5475.
9) Bunton, C. A.; Mhala, M. M.; Moffatt, J . R. J . Org. Chem. 1984,
49, 3639-3641.
10) Bentley, T. W.; Koo, I. S.; Norman, S. J . J . Org. Chem. 1991,
(
(
5
6, 1604-1609.
Discu ssion
(11) Richard, J . P.; J encks, W. P. J . Am. Chem. Soc. 1984, 106,
383-1396.
1
The effect of solvent on the rate of reaction of a
substrate has proven to be a very useful criterion for
(12) Allen, A. D.; Kanagasabapathy, V. M.; Tidwell, T. T. J . Am.
Chem. Soc. 1985, 107, 4513-4519.
(13) Kevill, D. N.; Anderson, S. W. J . Am. Chem. Soc. 1986, 108,
1
579-1585.
(
1) (a) Roberts, D. D.; Hendrickson, W. J . Org. Chem. 1969, 34,
415-2417. (b) Roberts, D. D. J . Org. Chem. 1993, 58, 1269-1272. (c)
Kevill, D. N.; Anderson, S. W. J . Am. Chem. Soc. 1986, 108, 1579-
585. (d) Bentley, T. W.; Bowen, C. T.; Morten, D. H.; Schleyer, P. v.
(14) Roberts, D. D. J . Org. Chem. 1984, 49, 2521-2526.
(15) For a similar correlation of cyclohexyl tosylate involving 18
2
solvents, see ref 1e.
1
(16) (a) Roberts, D. D. J . Org. Chem. 1964, 29, 294-297. (b) Diaz,
A.; Lazdins, I.; Winstein, S. J . Am. Chem. Soc. 1968, 90, 6546-6548.
(c) Roberts, D. D.; Watson, T. M. J . Org. Chem. 1970, 35, 978-981.
(d) Capon, B.; McManus, S. P. In Neighboring Group Participation;
Plenum: New York, 1976; Vol. 1, pp 167-168. (e) Shiner, V. J ., J r.;
Seib, R. C. J . Am. Chem. Soc. 1976, 98, 862-864. (f) Harris, J . M.;
Mount, D. L.; Smith, M. R.; Neal, W. C., J r.; Dukes, M. D.; Raber, D.
J . J . Am. Chem. Soc. 1978, 100, 8147-8156. (g) Raber, D. J .; Neal, W.
C., J r.; Dukes, M. D.; Harris, J . M.; Mount, D. L. J . Am. Chem. Soc.
1978, 100, 8137-8146. (h) Ando, T.; Kim, S.-G.; Matsuda, K.; Yama-
taka, H.; Yukawa, Y.; Fry, A.; Lewis, D. E.; Sims, L. B.; Wilson, J . C.
J . Am. Chem. Soc. 1981, 103, 3505-3516. (i) Roberts, D. D. J . Org.
Chem. 1984, 49, 2521-2526.
R. J . Am. Chem. Soc. 1981, 103, 5466-5475. (e) Kevill, D. N.;
Abduljaber, M. H. Croat. Chem. Acta 1992, 539-546.
(
2) (a) Schleyer, P. v. R.; Fry, J . L.; Lam, L. K. M.; Lancelot, C. J . J .
Am. Chem. Soc. 1970, 92, 2542-2544. (b) Schadt, F. L.; Bentley, T.
W.; Schleyer, P. v. R. J . Am. Chem. Soc. 1976, 98, 7667-7674. (c)
Brown, H. C.; Ravindranathan, M.; Chloupek, F. J .; Rothberg, I. J .
Am. Chem. Soc. 1978, 100, 3143-3149. (d) For leading references
regarding the use of trifluoroacetic acid in solvolysis reactions, see:
Allen, A. D.; Tidwell, T. T. J . Am. Chem. Soc. 1993, 115, 10091-10096.
(
3) Bentley, T. W.; Llewellyn, G. Prog. Phys. Org. Chem. 1990, 17,
21-158.
4) Roberts, D. D. J . Org. Chem. 1991, 56, 5661-5665.
1
(
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