Aniline Methylation Over Modified Micro- And Mesoporous Catalysts
Methylation of aniline is an industrially important process, aimed at the synthesis of mono-N-methylaniline (NMA), di-N-methylaniline (NNDMA) and toluidines which are useful raw materials for organic syntheses as well as important intermediates in the dye-stuff production and in the pharmaceutical and agrochemical industries. Up till now, industrial processes leading to these products are based on the application of corrosive liquid acids as catalysts [1,2] and should be replaced by environmentally more benign processes using solid catalysts such as oxides, clays and zeolites. It is known that alkylation of aniline may take place on acidic [3, 4, 5, 6] and on basic zeolites [7,8]. Moreover, this reaction was performed even on zeolites with redox properties [3,9,10]. A detailed study of reaction mechanisms over zeolite catalysts pointed to existence of two mechanistic pathways: on acidic catalysts, the reaction proceeds via a methanol dehydration leading to surface methoxy groups as intermediates of N- alkylation, while on basic and redox catalysts, the reaction pathway includes methanol dehydrogenation leading to formaldehyde species, alkylation of aniline with formaldehyde to give N-methyleneaniline and hydrogenation of N- methyleneaniline to N-methylaniline [11, 12]. In this contribution, aniline methylation has been studied on various molecular sieve catalysts. The effects of both catalyst structure and nature of active sites were investigated. The catalyst structures selected covered a broad range of pore sizes from 5.5 Å to 30 Å. The nature of the active sites was altered to obtain acidic, basic and redox materials.
KeywordsClay Porosity Microwave Carbide Zeolite
Unable to display preview. Download preview PDF.
- 2.Doraiswamy, L.K., Venkata Kirshman, G.R., and Mukharjee, S.P.(1981), Chem. Eng.88, 78.Google Scholar
- 4.Chen, P.Y., Chen, M.C., Chen, H.Y., Chang, N.S., and Chuang, T.K. (1986), in Murakami, Y., Iijima, A., and Ward, J.W.(eds). “New Developments in Zeolite Science and Technology, Stud. Surf. Sci Catal”, Elsevier, Amsterdam, Vol. 28, p. 739.Google Scholar
- 8.Hari Prasad Rao, P.R., Massiani, P., and Barthomeuf, D. (1994), inWeitkamp, J., Karge, H.G., Pfeifer, H.,and Hölderich, W., (eds.) “Zeolites and Related Microporous Materials: State of the Art 1994, Stud. Surf. Sci Catal.”, Elsevier, Amsterdam, Vol. 84, p. 1449Google Scholar
- 11.Wei Wang, Seiler, M, Ivanova, I.I., Weitkamp, J., and Hunger, M. (2001) In situ stopped-flow (SF) MAS NMR spectroscopy: A novel NMR technique applied for the study of aniline methylation on a solid base catalyst, Chem.Comm., in press.Google Scholar
- 12.Ivanova, I.I,. Pomakhina E.B,. Rebrov A.I, Hunger, M., Kolyagin Y.G., Weitkamp, J. (2001), Surface species formed during aniline methylation on zeolite HY investigated by in situMAS NMR spectroscopy, J.Catal., in pressGoogle Scholar