Molecular queuing

DNT chemisorbs very strongly, much more than the consecutive intermediates. Over the whole range of DNT concentrations the occupancy with DNT is almost complete up till DNT conversions above 90%. This implies that almost all the DNT must be converted before the conversion of 2-nitro-4-hydroxylaminotoluene and of 2-amino-4-nitrotoluene can start. This is called molecular queuing - the intermediates queue to be adsorbed on the active sites until the DNT has almost completely disappeared. 

In Figure 9.4 the degrees of occupation have been plotted under certain conditions for components A, B and D as a function of the conversion of A. Over almost the whole conversion range the catalyst is almost exclusively occupied by component A. For a conversion below 73% 6b is below 0.10 and for values of below 97% 6 D remains below 0.10. This is known as molecular queuing as the conversion proceeds, the catalyst must first be cleaned of the first component, before the next one can be adsorbed and converted. To this end Figure 9.5 shows for the same conditions RBJRM and RDJRAD as a function of the conversion of A. It is seen that RDE becomes equal to RAD only after 92% of the available A has been converted, and RBC becomes equal to R only after a conversion = 0.96. 

Microporous membranes in general (pore diameter < 2 nm), and zeolite membranes in particular, have pores whose dimensions are similar to those of many molecules. This means that often molecules cannot pass each other in a restrictive pore medium, and single file diffusion occurs. Such a molecular queuing (see Figure 11.24) may provide a new scenario for avoiding secondary reactions, that is, to increase selectivity in consecutive reaction networks with a valuable intermediate... 

Heterocycles Via Pd Catalyzed Molecular Queuing Processes. Relay Switches and the Maximization of Molecular Complexity. 

Grigg, R., Putnikovic, B. and Urch, C.J. (1996) Palladium-catalysed ter- and tetra-molecular queuing processes. One pot routes to 3-spiro-2-oxindoles and 3-sprro-2 (3H)-benzofuranones. Tetrahedron Letters,... 

However, in the queuing processes terminating with stannanes orborane, as anion capture agents, the desired molecular queuing to 57 can be achieved only increasing... 

Conceptually similar palladium-catalyzed cascade reactions have been developed, involving molecular-queuing cycloaddition, cyclocondensation and Diels-Alder reactions [71], cydization-anion-capture-olefin metathesis [72], carbonylation-allene insertion [73], carbonylation/amination/Michael addition [74], sequential Petasis reaction/palladium-catalyzed process [75], supported allenes as substrates [76], and palladium-ruthenium catalysts [77]. 

Grigg, R Liu, A., Shaw, D Suganthan, S Washington, M.L., Woodall, D.E. and Yoganathan, G. (2000) Palladium-catalysed cascade molecular queuing-cycloaddition, cyclocondensation and Diels-Alder reactions. Tetrahedron Letters, 41,... 

---