Selective mono-N-methylation of primary aromatic amines by dimethyl carbonate over faujasite X- and Y-type zeolites

Abstract

The reaction of dimethyl carbonate (DMC) with different primary aromatic amines has been investigated under batch conditions (autoclave) in the presence of Y- and X-type zeolites. Operating at 120–150 °C, highly selective mono-N-methylations are observed for anilines even when they are deactivated by either electronic effects or steric hindrance (G–C₆H₄NH₂, G = p-NO₂, p-CN, o-CO₂CH₃ and 2,6-dimethylaniline); typical selectivities for the formation of the corresponding mono-N-methyl derivatives [ArNH(CH₃)] are in the range 92–98%, at a substrate conversion of 72–93%. A synergic effect between the reactivity of DMC (acting both as a methylating and as a reversible methoxycarbonylating agent) and the dual acid–base properties of zeolites is considered to be responsible for the unusually high selectivity observed; accordingly, a reaction mechanism is discussed, involving carbamates (ArNHCO₂CH₃) and N-methylcarbamates [ArN(CH₃)CO₂CH₃] as intermediates. The reaction is an example of a synthesis with low environmental impact: it couples the use of a non-toxic methylating agent (DMC, in place of the highly toxic methyl halides or dimethyl sulfate) with eco-friendly catalysts (zeolites) in a waste-free process.

References

1. Kirk-Othmer Encyclopedia of Chemical Technology, Wiley, New York, 3rd edn., 1978, vol. 2, pp. 309–321.
2. J. March, in Advanced Organic Chemistry, Wiley, New York, 4th edn., 1991.
3. M. Onaka, K. Ishikawa and Y. Izumi, Chem. Lett., 1982, 1783.
4. M. Onaka, A. Umezono, M. Kawai and Y. Izumi, J. Chem. Soc., Chem. Commun., 1985, 1202.
5. Y. Izumi and M. Onaka, Adv. Catal., 1992, 38, 249.
6. T. M. Wortel, D. Oudlin, C. J. Vleugel, D. P. Roelofsen and H. van Bekkum, J. Catal., 1979, 60, 110.
7. P. Tundo, F. Trotta and G. Moraglio, J. Chem. Soc., Perkin Trans. 1, 1989, 1070.
8. M. Selva, C. A. Marques and P. Tundo, J. Chem. Soc., Perkin Trans. 1, 1994, 1323.
9. P. Tundo and M. Selva, CHEMTECH, 1995, 25(5), 31.
10. A. Bomben, C. A. Marques, M. Selva and P. Tundo, Tetrahedron, 1995, 51, 11573.
11. P. Tundo and M. Selva, in Green Chemistry: Designing Chemistry for the Environment, ed. P. Anastas and T. Williamson, ACS Symposium Series No. 626, 1996, ch. 7, pp. 81–91.
12. F. Trotta, P. Tundo and G. Moraglio, J. Org. Chem., 1987, 52, 1300.
13. M. Lissel, A. R. Rohani-Dezfuli and G. Vogt, J. Chem. Res. (S), 1989, 312.
14. P. R. Hari Prasad Rao, P. Massiani and D. Barthomeuf, Catal. Lett., 1995, 31, 115.
15. Z.-H. Fu and Y. Ono, Catal. Lett., 1993, 22, 277.
16. D. Delledonne, F. Rivetti and U. Romano, J. Organomet. Chem., 1995, 448, C15.
17. P. Tundo, in Continuous Flow Methods in Organic Synthesis, Horwood, Chichester (UK), 1991, ch. 1.
18. N. Bortnick, L. S. Luskin, M. D. Hurwitz and A. Rytina, J. Am. Chem. Soc., 1956, 78, 4358.
19. J. Grimshaw, R. J. Haslett and J. Trocha-Grimshaw, J. Chem. Soc., Perkin Trans. 1, 1977, 2448.
20. R. A. Katritzky and J. M. Lagowski, J. Chem. Soc., 1958, 4155.
21. R. M. Moriarty, C. J. Chany II, R. K. Vaid, O. Prakash and S. M. Tuladhar, J. Org. Chem., 1993, 58, 2478.
22. I. D. Rae, Austr. J. Chem., 1966, 19, 409.
23. C. Wünsche, Org. Mass. Spectrom., 1973, 7, 1253.
24. A. Maquestiau, Y. Van Haverbeke, R. Flammang, M. C. Pardo and J. Elguero, Org. Mass. Spectrom., 1974, 9, 1188.