Transition metal containing zeolites and mesoporous MCM-41 as heterogeneous catalysts for the N-alkylation of 2,4-diaminotoluene with dimethylcarbonate

Two series of catalysts, either zeolites exchanged with transition metal ions (Zn2+, Pb2+ and Sc3+) or mesoporous aluminosilicates containing Lewis acid sites introduced by ion exchange (Zn2+) or forming part of the framework (SnIV, TiIV and ZrIV) have been tested for the reaction of 2,4-diaminotoluene with dimethylcarbonate. The predominant products were those arising from N-methylation, although hard Lewis acid sites (Sc3+ in zeolite Y) and mesoporous catalysts also lead to N-carbamoylation in a significant extent (over 50% for Sc in zeolite Y or Zr in MCM-41 framework). This has been explained as result of the influence of the hardness/softness and the dimensions of the reaction cavity on the reaction selectivity. Overall, these heterogeneous catalysts were more active than NaY that is the zeolite previously studied in the literature for the same process. This enhanced efficiency of transition metal containing aluminosilicates is the consequence of the presence of stronger acid sites compared to Na+.