Aniline Methylation Over Modified Micro- And Mesoporous Catalysts

Abstract

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 [3–6] 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.