Nucleophilic solvent participation in the solvolysis of 4-methoxybenzyl bromide and chloride

Abstract

The solvolysis of 4-methoxybenzyl chloride (1) and bromide (3), and 1-(4-methoxyphenyl)ethyl chloride (4) in a variety of solvents were carried out. The observation of linear correlation using the dual-parameter Grunwald–Winstein equation, and the positive azide salt effect indicate significant nucleophilic solvent participation for 1 and 3. A smaller deviation of log k (in 100% 2,2,2-trifluoroethanol) for the bromide 3 than chloride 1 in the log k – Y_BnX plots reveals a lesser extent of nucleophilic participation and is also in harmony with the greater nucleofugality of the bromide ion. The use of a low k_Br/k_Cl ratio as evidence for the presence of solvent participation is discussed. The observed α-deuterium kinetic isotope effect of 1.08 to 1.21 measured for 1 and 3 is inconsistent with the magnitude generally considered for a concerted mechanism.

References

1. S. C. J. Olivier, Rec. Trav. Chim., 1922, 41, 301.
2. For summary of early pertinent work see: A. Streitwieser, Jr., Solvolytic Displacement Reactions, McGraw-Hill, New York, 1962.
3. C. K. Ingold, Structure and Mechanism in Organic Chemistry, Cornell University Press, Ithaca, 1953, p. 325.
4. S. Winstein, E. Grunwald and H. W. Jones, J. Am. Chem. Soc., 1951, 73, 2700.
5. E. Grunwald and S. Winstein, J. Am. Chem. Soc., 1948, 70, 846.
6. J. W. Hill and A. Fry, J. Am. Chem. Soc., 1962, 84, 2763.
7. A. Fry, in Isotope Effects in Chemical Reactions(ACS Monograph 167), ed. C. J. Collins and N. S. Bowman, Van Nostrand, New York, 1971, pp. 377–383.
8. D. G. Graczyk, J. W. Taylor and C. R. Turnquist, J. Am. Chem. Soc., 1978, 100, 7333.
9. For instance: V. F. Raaen, T. Juhlke, F. J. Brown and C. J. Collins, J. Am. Chem. Soc., 1974, 96, 5928.
10. V. J. Shiner, Jr., W. Dowd, R. D. Fisher, S. R. Hartshorn, M. A. Kessick, L. Milakofsky and M. W. Rapp, J. Am. Chem. Soc., 1969, 91, 4838.
11. V. P. Vitullo, J. Graowski and S. Sridharan, J. Chem. Soc., Chem. Commun., 1981, 737.
12. M. Fujio, I. Akasaka, S. H. Kim, M. Mishima, Y. Tsuji and Y. Tsuno, Mem. Fac. Sci., Kyushu Univ., Ser. C, 1991, 18, 131.
13. T. W. Bentley, I. S. Koo and S. J. Norman, J. Org. Chem., 1991, 56, 1604.
14. (a) For examples, see: J. March, Advanced Organic Chemistry, 4th edn., Wiley-Interscience, New York, 1992, p. 306, and references cited therein; (b) D. S. Chung, C. K. Kim, B.-S. Lee and I. Lee, Tetrahedron, 1993, 37, 8359; (c) D. N. Kevill, N. H. J. Ismail and M. J. D'Souza, J. Org. Chem., 1994, 59, 6303.
15. T. L. Amyes and J. P. Richard, J. Am. Chem. Soc., 1990, 112, 9507.
16. (a) G. Kohnstam, A. Queen and B. Shillaker, Proc. Chem. Soc., 1959, 157; (b) A. Queen, Can. J. Chem., 1979, 57, 2646.
17. K. Yatsugi, I. Akasaka, Y. Tsuji, S. H. Kim, S.-D. Yoh, N. Sugiyama, M. Mishima, M. Fujio and Y. Tsuno, Tetrahedron Lett., 1994, 35, 135.
18. K.-T. Liu, L.-W. Chang, D.-G. Yu, P.-S. Chen and J.-D. Fan, J. Phys. Org. Chem., 1997, 10, 879.
19. T. W. Bentley and G. Llewellyn, Progr. Phys. Org. Chem., 1990, 17, 121.
20. K.-T. Liu, J. Chin. Chem. Soc. (Taipei), 1995, 42, 607.
21. M. Fujio, T. Susuki, M. Goto, Y. Tsuji, K. Yatsugi, Y. Saeki, S. H. Kim and Y. Tsuno, Bull. Chem. Soc. Jpn., 1994, 67, 2233.
22. (a) D. N. Kevill and S. W. Anderson, J. Chem. Res. (S), 1991, 356; (b) D. N. Kevill and M. J. D'Souza, J. Chem. Res. (S), 1993, 174.
23. Better linear correlation would be found if more data points were included. Kevill and D'Souza considered “little or no nucleophilic assistance to the ionization process” in the solvolysis of 1 based on the calculated R of 0.986 and l of 0.1 at n= 31, despite scattered log k–Y_Cl plots being observed (J. Phys. Org. Chem., 1992, 5, 287).
24. For pioneering work, see, for examples: (a) D. J. Raber, J. M. Harris, R. E. Hall and P. v. R. Schleyer, J. Am. Chem. Soc., 1971, 93, 4821; (b) D. J. Raber, J. M. Harris and P. v. R. Schleyer, J. Am. Chem. Soc., 1971, 93, 4829; (c) R. A. Sneen, Acc. Chem. Res., 1973, 6, 46.
25. K.-T. Liu, P.-S. Chen, C.-R. Hu and H.-C. Sheu, J. Phys. Org. Chem., 1993, 6, 122, 433.
26. Although in some cases the first 0.02 M of sodium azide was found to exhibit a larger effect than the use of the second 0.02 M of salt (see for instance, ref. 15), other examples, such as 2-propyl tosylate (ref. 24a), indicated the reverse.
27. For discussion, see ref. 2, p. 53 and the literature cited therein.
28. T. W. Bentley, C. T. Bowen, W. Parker and C. I. F. Watt, J. Am. Chem. Soc., 1979, 101, 2486.
29. For a review of early work, see: V. J. Shiner, Jr., in Isotope Effects in Chemical Reactions, ACS Monograph No. 167, ed. J. Collins and N. S. Bowman, Van Nostrand Reinhold, New York, 1970, pp. 104–137.
30. For example of general discussion, see: K. C. Westaway, in Isotopes in Organic Chemistry, vol. 7, ed. E. Buncel and C. C. Lee, Elsevier, Amsterdam, 1987, ch. 5.
31. For an example of recent work, see: K. C. Westaway, T. V. Pharm and Y.-r. Fang, J. Am. Chem. Soc., 1997, 119, 3670.
32. (a) Ref. 2, p. 81; (b) T. H. Lowry and K. S. Richardson, Mechanism and Theory in Organic Chemistry, Harper & Row, New York, 1987, pp. 374–375.
33. D. A. da Roza, L. J. Andrews and R. M. Keefer, J. Am. Chem. Soc., 1973, 95, 7003.
34. A. H. Fainberg and S. Winstein, J. Am. Chem. Soc., 1957, 79, 1608.
35. Y. Marcus, Pure Appl. Chem., 1983, 55, 977.
36. K.-T. Liu and C.-S. Tang, J. Org. Chem., 1996, 61, 1523.
37. K.-T. Liu and H.-C. Sheu, J. Chin. Chem. Soc., 1991, 38, 29.
38. K.-T. Liu and H.-C. Sheu, J. Org. Chem., 1991, 56, 3021.
39. J.-D. Fan, MS Thesis, National Taiwan University, 1996.
40. D. N. Kevill and M. J. D'Souza, J. Chem. Soc., Perkin Trans. 2, 1995, 973.
41. K.-T. Liu, J. Chem. Soc., Perkin Trans. 2, 1996, 327.
42. No analysis for 4 has been performed since it is not meaningful to employ only eight data to a three-term equation.
43. D. D. Perrin and W. L. F. Armarego, Purification of Laboratory Chemicals, 3rd edn., Pergamon Press, New York, 1988.