Kinetics of protonation of anthracene and phenanthrene radical anions in DMF by a series of substituted phenols. Comparison of Brønsted and Hammett plots

Abstract

The rate constants k_H for the proton transfer from a series of substituted phenols to anthracene and phenanthrene radical anions formed in DMF have been measured by the voltammetric method. The quadratic Brønsted dependencies of RT ln k_H against pK_a of phenols for both radical anions were observed. For the conjugate acid ArH˙ of the anthracene radical anion pK_a is known and the intrinsic activation barrier ΔG_o^‡ = 59 kJ mol^–1 was calculated. The homolytic bond dissociation energy D for ArH˙→Ar + H˙ was evaluated and the obtained value of D/4 = 51 kJ mol^–1 is in good agreement with the theoretical prediction ΔG_o^‡ = (D + λ_o)/4 (where λ_o is the solvent reorganization energy) based on a recent theory of the deprotonation of radical cations described as a concerted electron and H atom transfer. However, linear Hammett plots of log k_H against σ were observed for both radical anions and the lack of a quadratic effect was explained as a result of a through-resonance contribution. On the other hand, the application of normalized substituent constants σ^o resulted in the quadratic Hammett plots in accordance with the Reactivity Selectivity Principle.

References

1. V. D. Parker, M. Tilset and O. Hammerich, J. Am. Chem. Soc., 1987, 109, 7905.
2. D. Griller, J. A. Martinho Simões, P. Mulder, B. A. Sim and D. D. M. Wayner, J. Am. Chem. Soc., 1989, 111, 7872.
3. Y. Zhao and F. G. Bordwell, J. Org. Chem., 1996, 61, 2530 and 6623; F. G. Bordwell and W. Liu, J. Phys. Org. Chem., 1998, 11, 397.
4. (a) S. Hayano and M. Fujihira, Bull. Chem. Soc. Jpn., 1971, 44, 2046; (b) M. Fujihira, H. Suzuki and S. Hayano, J. Electroanal. Chem., 1971, 33, 393.
5. C. Amatore and J. M. Savéant, J. Electroanal. Chem., 1980, 107, 353.
6. (a) B. Aalstad and V. D. Parker, J. Electroanal. Chem., 1980, 112, 163; (b) E. Ahlberg and V. D. Parker, J. Electroanal. Chem., 1981, 121, 73.
7. C. Amatore, M. Gareil and J. M. Savéant, J. Electroanal. Chem., 1983, 147, 1.
8. J. M. Savéant, in Techniques of Chemistry, Investigation of Rates and Mechanisms of Reactions, ed. F. A. Bernasconi, vol. 6, part II, 4th edn., Wiley-Interscience, New York, 1986, 305–390.
9. V. D. Parker, Acta Chem. Scan, Ser. B, 1981, 35, 349 and 373.
10. M. F. Nielsen, O. Hammerich and V. D. Parker, Acta Chem. Scand., Ser. B, 1986, 40, 101.
11. M. F. Nielsen, O. Hammerich and V. D. Parker, Acta Chem. Scand., Ser. B, 1987, 41, 50.
12. M. F. Nielsen and O. Hammerich, Acta Chem. Scand., Ser. B, 1987, 41, 668.
13. M. F. Nielsen and O. Hammerich, Acta Chem. Scand., 1989, 43, 269.
14. M. F. Nielsen and O. Hammerich, Acta Chem. Scand., 1992, 46, 883.
15. (a) M. F. Nielsen, Z. Porat, H. Eggert and O. Hammerich, Acta Chem. Scand., Ser. B, 1986, 40, 652; (b) M. F. Nielsen, H. Eggert and O. Hammerich, Acta Chem. Scand., 1991, 45, 292.
16. R. A. Marcus, J. Phys. Chem., 1968, 72, 891.
17. A. Anne, P. Hapiot, J. Moiroux, P. Neta and J. M. Savéant, J. Am. Chem. Soc., 1992, 114, 4694.
18. A. Anne, S. Fraoua, P. Hapiot, J. Moiroux and J. M. Savéant, J. Am. Chem. Soc., 1995, 117, 7412.
19. A. Anne, S. Fraoua, V. Grass, J. Moiroux and J. M. Savéant, J. Am. Chem. Soc., 1998, 118, 2951.
20. A. Pross, Adv. Phys. Org. Chem., 1977, 14, 69.
21. S. J. Formosinho, J. Chem. Soc., Perkin. Trans. 2, 1988, 839.
22. S. J. Formosinho, J. Chem. Soc., Perkin. Trans. 2, 1987, 61.
23. C. P. Andrieux, G. Delgado and J. M. Savéant, J. Electroanal. Chem., 1993, 348, 123.
24. J. S. Jaworski, P. Leszczyński and J. Tykarski, J. Chem. Res. (S), 1995, 510.
25. M. F. Nielsen, Acta Chem. Scand., 1992, 46, 533.
26. F. Maran, D. Celadon, M. G. Severin and E. Vianello, J. Am. Chem. Soc., 1991, 113, 9320.
27. F. G. Bordwell and J. Cheng, J. Am. Chem. Soc., 1991, 113, 1736.
28. K. Izutsu, Acid-Base Dissociation Constants in Dipolar Aprotic Solvents, IUPAC Chem. Data Series No. 35, Blackwell, Oxford, 1990.
29. J. Magoñski, Z. Pawlak and T. Jasiñski, J. Chem. Soc., Faraday Trans., 1993, 89, 119.
30. C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165.
31. C. Hansch and A. J. Leo, Substituent Constants for Correlation Analysis in Chemistry and Biology, J. Wiley, New York, 1979, p. 3.
32. J. Czermiński, A. Iwasiewicz, Z. Paszek and A. Sikorski, Statistical Methods in Applied Chemistry, PWN, Warsaw and Elsevier, Amsterdam, 1990, pp. 306–307.
33. M. M. Kreevoy and S. Oh, J. Am. Chem. Soc., 1973, 95, 4805.
34. M. M. Kreevoy and D. E. Konasewich, Adv. Chem. Phys., 1972, 21, 243.
35. D. J. Hupe and D. Wu, J. Am. Chem. Soc., 1977, 99, 7653.
36. (a) A. J. Kresge, Chem. Soc. Rev., 1973, 2, 475; (b) A. J. Kresge, Acc. Chem. Res., 1975, 8, 354.
37. R. P. Bell, in Correlation Analysis in Chemistry, Recent Advances, eds. N. B. Chapman and J. Shorter, Plenum Press, New York, 1978, p. 55.
38. C. J. Schlesener, C. Amatore and J. K. Kochi, J. Phys. Chem., 1986, 90, 3747.
39. A. O. Cohen and R. A. Marcus, J. Phys. Chem., 1968, 72, 4249.
40. (a) J. M. Savéant, J. Am. Chem. Soc., 1987, 109, 6788; (b) J. M. Savéant, J. Am. Chem. Soc., 1992, 114, 10595; (c) J. M. Savéant, Acc. Chem. Res., 1993, 26, 455.
41. F. G. Bordwell, J. E. Bares, J. E. Bartmess, G. J. McCollum, M. Van der Puy, N. R. Vanier and M. S. Mattews, J. Org. Chem., 1977, 42, 321.
42. D. M. Bishop and K. J. Laidler, J. Chem. Phys., 1965, 42, 1688.
43. The free energy of solvation of H● by DMF is not available; for ACN the value of D increases by 13 kJ mol^–1 using¹⁹ a solvation of H₂ instead of H●.
44. Y. Marcus, Ionic Solvation, Wiley, Chichester, 1985, p. 166.
45. C. P. Andrieux, A. Le Gorande and J. M. Savéant, J. Am. Chem. Soc., 1992, 114, 6892.
46. A. M. P. Nicholas and D. R. Arnold, Can. J. Chem., 1982, 60, 2165.
47. H. Kojima and A. J. Bard, J. Am. Chem. Soc., 1975, 97, 6317.
48. O. Exner, Correlation Analysis of Chemical Data, Plenum Press, New York, 1988, pp. 195–206.