| Phase transfer catalysis (PTC) finds wide-scale applications in the synthesis of a variety of organic chemicals. Recently, some authors have reported mathematical models that account for the role of mass transfer in PTC reactions carried out in liquid-liquid systems. However, no systematic approach to the modeling of solid-liquid PTC (SLPTC) systems is available. The present research is aimed towards providing a systematic methodology for the analysis and modeling of PTC reactions, with focus on solid-liquid systems. The effect of other rate enhancement techniques like the use of microphase or ultrasound in PTC systems is also briefly studied.;The present study is the first instance involving the use of a microphase in a PTC system. The choice of microphase is found to be crucial in PTC systems. A wrong choice of microphase (silica gel, in the present study) leads to a suppression of the PTC action. For the chosen system, both ultrasound and addition of a suitable microphase (fumed silica) lead to a small but significant increase in the reaction rate, which is attributed to an enhancement in mass transfer. However the PT catalyst is necessary to attain a significantly higher increase in the reaction rate.;A framework has been developed for the analysis and modeling of SLPTC based on two main mechanisms. For the homogeneous solubilization mechanism, solid dissolution, ion-exchange reaction kinetics, and interphase quat transport steps can contribute to the overall rate of the PTC cycle. The concentration of the quat in the organic phase is not constant but builds up with time. Assuming pseudo-first order kinetics based on the assumption of organic reaction control, leads to a gross under-estimate of the time required to attain a specific conversion.;For heterogeneous solubilization, a study of the effect of the solid phase ion-exchange reaction on the conversion of the organic substrate leads to some interesting conclusions. Diffusional limitations within the solid phase surprisingly gives higher RX conversion. The effective diffusivity of the solid particles, which is dependent on the porosity and pore structure of the solid reagent, is the crucial parameter in this case. |
