New insights into N-tert-butyl-α-phenylnitrone (PBN) as a spin trap. Part 2.¹ The reactivity of PBN and 5,5-dimethyl-4,5-dihydropyrrole N-oxide (DMPO) toward N-heteroaromatic bases

Abstract

The reactions of N-tert-butyl-α-phenylnitrone (PBN) and 5,5-dimethyl-4,5-dihydropyrroline N-oxide (DMPO) with a series of N-heteroaromatic bases have been studied in different solvents (benzene, dichloromethane, acetonitrile) in the presence of such oxidants as PbO₂, chloranil and tetrabutylammonium dodecatungstocobalt(III)ate. In all cases spin adducts were formed and their corresponding EPR signals were recorded. The formation of the spin adducts, which mostly involves nucleophilic addition of a base to the nitrone and subsequent oxidation (Forrester–Hepburn mechanism) is also discussed and compared to conventional spin trapping and to ‘inverted spin trapping'. In order to obtain further evidence for the mechanism involved some reactions were carried out using other oxidants, such as galvinoxyl and 2,2-diphenyl-1-picrylhydrazyl (DPPH).The reaction mechanisms are discussed on the basis of the redox potentials of the studied nucleophiles. Particular attention is given to the benzotriazolyl–DMPO˙ spin adduct, whose generation and decay rates were determined in the presence of some benzoquinones having different redox potentials.

References

1. P. Carloni, L. Eberson, L. Greci, P. Sgarabotto and P. Stipa, J. Chem. Soc., Perkin Trans. 2, 1996, 1297.
2. For reviews, see (a) E. G. Janzen, Acc. Chem. Res., 1971, 4, 31; (b) M. J. Perkins, Adv. Phys. Org. Chem., 1980, 17, 1; (c) V. E. Zubarev, V. N. Belevskii and L. T. Bugaenko, Russ. Chem. Rev., 1979, 48, 729; (d) E. G. Janzen, in Advances In Free Radical Chemistry, ed. D. D. Tanner, vol. 1, JAI Press, London, 1990, ch. 6.
3. (a) S. Kubow, E. G. Janzen and T. M. Bray, J. Biol. Chem., 1984, 259, 4447; (b) E. G. Janzen, J. Magn. Reson., 1973, 510.
4. J. G. Pacifici and H. L. Browíng, J. Am. Chem. Soc., 1970, 92, 5231.
5. L. Ueno, M. Kohono, K. Mitsuta, Y. Mizuta and S. Kanegasaki, J. Biochem., 1989, 105, 905.
6. C. Mottley and R. Mason, in Biological Magnetic Resonance 8, Spin Labeling Theory and Applications, ed. L. Berliner and J. Reuben, Plenum Press, New York, London, 1989, ch. 10.
7. (a) P. Riviere, S. Richelme, M. Riviere-Baudet, J. Satge, M. J. S. Gynane and M. F. Lappert, J. Chem. Res. (S), 1978, 218; (b) L. Grossi, L. Lunazzi and G. Placucci, J. Chem. Soc., Perkin Trans. 2, 1983, 1831; (c) R. G. Gasanov, L. V. Ivanova and R. Kh. Freidlina, Izv. Akad. Nauk SSSR, 1984, 938.
8. (a) L. Eberson, J. Chem. Soc., Perkin Trans. 2, 1992, 1807; (b) L. Eberson and M. Nilsson, Acta Chem. Scand., 1993, 47, 1129; (c) L. Eberson, J. Chem. Soc., Perkin Trans. 2, 1994, 171; (d) L. Eberson, J. Lind and G. Merenyi, J. Chem. Soc., Perkin Trans. 2, 1994, 1181; (e) L. Eberson, M. P. Hartshorn and O. Persson, J. Chem. Soc., Perkin Trans. 2, 1996, 141.
9. V. E. Zubarev and O. Brede, J. Chem. Soc., Perkin Trans. 2, 1994, 1821; 1995, 2183.
10. H. Chandra and M. C. R. Symons, J. Chem. Soc., Chem. Commun., 1986, 1301.
11. A. R. Forrester and S. P. Hepburn, J. Chem. Soc. (C), 1971, 701.
12. (a) F. M. Martens, J. W. Verhoeven, R. A. Gase, U. K. Pandit and Th. J. de Boer, Tetrahedron, 1978, 34, 443; (b) R. Foster, Organic Charge Transfer Complexes, Academic Press, London, 1969.
13. G. L. McIntire, H. N. Blount, H. J. Stronks, R. V. Shetty and E. G. Janzen, J. Phys. Chem., 1980, 84, 916.
14. (a) H. Sayo, S. Ozaki and M. Masui, Chem. Pharm. Bull. Jpn., 1973, 21, 1988; (b) P. E. Iversen and H. Lund, Anal. Chem., 1969, 41, 1322.
15. (a) A. Alberti, L. Greci, P. Stipa, P. Sgarabotto and F. Ugozzoli, Tetrahedron, 1987, 43, 3031; (b) P. Carloni, L. Cardellini, L. Greci, P. Stipa and A. Faucitano, Gazz. Chim. Ital., 1989, 119, 621.
16. A. Katritzky, in Handbook of Heterocyclic Chemistry, Pergamon Press, Oxford, New York, 1985, p. 339.
17. The remote possibility that 18 be in fact the indazol-5-yl adduct of PBN, resulting from attack at the condensed aromatic ring¹⁸ cannot be excluded.
18. M. R. Grimmet, in Comprehensive Organic Chemistry, ed. P. G. Sammes, Pergamon Press, Oxford 1979, vol. 4, p. 357.
19. B. Sabourault, D. Abenhalm and J. Bourdaìs, J. Heterocycl. Chem., 1976, 13, 241.
20. (a) M. Bietti, E. Baciocchi and J. B. F. N. Engberts, J. Chem. Soc., Chem. Commun., 1996, 1307; (b) E. Baciocchi, M. Bietti and S. Steenken, J. Chem. Soc., Perkin Trans. 2, 1996, 1261; (c) E. Baciocchi, M. Bietti and M. Mattioli, J. Org. Chem., 1993, 58, 7106; (d) E. Baciocchi, M. Crescenzi, E. Fasella and M. Mattioli, J. Org. Chem., 1992, 57, 4684; (e) L. Eberson, J. Am. Chem. Soc., 1983, 105, 3192.
21. L. Eberson and P. Carloni, Acta Chem. Scand., 1991, 45, 373 and references reported therein.
22. W. Sümmerman and U. Deffner, Tetrahedron, 1975, 31, 593.
23. C. Berti, M. Colonna, L. Greci and L. Marchetti, J. Heterocycl. Chem., 1979, 16, 17.
24. M. Colonna, L. Greci and M. Poloni, J. Chem. Soc., Perkin Trans. 2, 1981, 628.
25. R. Kunh and I. Hammer, Chem. Ber., 1950, 83, 413.
26. G. A. Russell, E. G. Janzen and E. T. Strom, J. Am. Chem. Soc., 1964, 86, 1806.
27. (a) R. Andruzzi, A. Trazza, L. Greci and A. Marchetti, Ann. Chim. (Rome), 1979, 69, 583; (b) R. Andruzzi and A. Trazza, J. Electroanal. Chem., 1977, 77, 101; 1978, 90, 389.
28. C. Berti, L. Greci, R. Andruzzi and A. Trazza, J. Org. Chem., 1982, 47, 4895.