Nitration of pyridine by dinitrogen pentoxide, a study of the reaction mechanism †

Abstract

The nitration of pyridine and substituted pyridines by dinitrogen pentoxide (DNP) has been studied. The reaction of DNP with pyridine in either liquid SO₂ or an organic solvent produces N-nitropyridinium nitrate (4). On reaction of this with aqueous solutions of SO₂ or NaHSO₃ three transient species are formed: N-nitro-1,4-dihydropyridine-4-sulfonic acid (5), N-nitro-1,2-dihydropyridine-2-sulfonic acid (6) and 1,2,3,6-tetrahydro-3-nitropyridine-2,6-disulfonic acid (7). Compounds 6 and 7 may be sulfite esters instead of sulfonic acids. Compound 5 reacts by a first order reaction [ΔH^‡ = 32(1) kcal mol^–1, ΔS^‡ = 31(4) cal K^–1 mol^–1] and 3-nitropyridine is formed. Compound 6 is rapidly transformed to 7 which reacts by a first order pH dependent reaction {k_obs = 1.9(4) × 10^–4 s^–1 + 3.5(2) × 10^–2[H⁺] M^–1 s^–1} to give 3-nitropyridine. From the available evidence the reactions were either intramolecular or took place in a solvent cage. Two mechanisms are found to be in accordance with the reported evidence: the nitro group either migrated as a nitronium ion in a solvent cage or by a sigmatropic shift. The results from the nitration of a series of dimethylpyridines support the sigmatropic shift migration mechanism.

References

1. J. M. Bakke and I. Hegbom, Acta Chem. Scand., 1994, 48, 181; J. M. Bakke, I. Hegbom, E. Øvreeide and K. Aaby, Acta Chem. Scand., 1994, 48, 1001.
2. B. Arnestad, J. M. Bakke, I. Hegbom and E. Ranes, Acta Chem. Scand., 1996, 50, 556.
3. J. M. Bakke and I. Hegbom, J. Chem. Soc., Perkin Trans. 2, 1995, 1211.
4. J. M. Bakke and E. Ranes, Synthesis, 1997, 281.
5. G. A. Olah, J. A. Olah and N. A. Overchuck, J. Org. Chem., 1965, 30, 3373.
6. G. A. Olah, S. C. Narang, J. A. Olah, R. L. Pearson and C. A. Cupas, J. Am. Chem. Soc., 1980, 102, 3507; E. K. Kim, K. Y. Lee and J. K. Kochi, J. Am. Chem. Soc., 1992, 114, 1756.
7. V. Simánek and V. Preininger, Heterocycles, 1977, 6, 475.
8. J. Becher, Synthesis, 1980, 589.
9. E. Andersen, J. M. Bakke, E. Ranes and J. Riha, Acta Chem. Scand., in the press.
10. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, Wiley, New York, 5 edn., 1988.
11. Lange's Handbook of Chemistry, ed. J. A. Dean, McGraw-Hill, New York, 13th edn., 1985, pp. 5–16.
12. See for instance R. A. Y. Jones, Physical and mechanistic organic chemistry, Cambridge University Press, Cambridge, 2nd edn., 1984, p. 165.
13. I. Fleming, Frontier Orbitals and Organic Chemical Reactions, Wiley, Chichester, 1976, p. 66.
14. K. Schofield, Aromatic Nitration, Cambridge University Press, Cambridge, 1980, p. 183.
15. C. W. Spangler, Chem. Rev., 1976, 76, 187 and references cited therein.
16. J. W. A. M. Janssen, C. L. Harbraken and R. Louw, J. Org. Chem., 1976, 41, 1758.
17. K. N. Houk, Y. Li and J. D. Evanseck, Angew. Chem., Int. Ed. Engl., 1992, 31, 682.
18. J. H. Ridd, S. Trevelick and J. P. B. Sandall, J. Chem. Soc., Perkin Trans. 2, 1993, 1073.
19. A. Fischer and C. C. Greig, Can. J. Chem., 1974, 52, 1231.
20. B. Boduszek, Pol. J. Chem., 1992, 66, 787.