Kinetics of homogeneous and heterogeneous reactions in the reductive aminolysis of glucose with dimethylamine

The reductive aminolysis of glucose with dimethylamine (DMA) as aminating agent has been investigated experimentally as well as via kinetic model construction. A fed-batch reactor configuration was used at following conditions: temperatures ranging between 383 K-398 K, total pressures from 6.0 MPa to 7.5 MPa, an overall catalyst to glucose ratio of 9-31 g(cat) mol(-1), an overall DMA to glucose ratio of 12-24 mol mol(-1) and an overall hydrogen to glucose ratio of 5-10 mol mol(-1). Such a reactor configuration, combined with a controlled feeding rate of the sugar, allowed to significantly avoid degradation reactions. The main desired products, i.e., dimethylaminoethanol (DMAE) and tetramethylethylenediamine (TMEDA), were obtained after amination followed by retro-aldol cleavage with maximum selectivity, amounting up to 15% and 60% respectively. Retroaldol cleavage after amination proceeds at lower temperatures, evidenced by an activation energy of 60 kJ mol(-1), than without amination, where activation energies amounting to 140 kJ mol(-1) have been reported. A higher catalyst to glucose ratio leads to more parallel side products such as N,N-dimethylglucamine and 4-dimethylarnino-1,2,3-butanetriol. The effects of temperature and catalyst to glucose ratio were much more pronounced than that of the total pressure or the ratio of the aminating agent to glucose. The developed kinetic model is based on the most prominent homogeneous bulk phase and heterogeneously catalyzed reactions and accounts quantitatively for degradation reactions. A statistically and physically significant model which could satisfactorily reproduce the experimental observations, was thus obtained.