Yadav, P.H. Mehta and B.V. Haldavanekar

Department of Chemical Technology, University of Bombay, Matunga, Bombay -400 019, India. 

Selectivity of multiphase reactions catalysed by phase transfer catalysts can be greatly improved by the use of the so called capsule membrane - PTC (CM-PTC) technique. We report here the theoretical and experimental analysis of the CM-PTC and Inverse CM-PTC for exclusively selective formation of benzyl alcohol and benzaldehyde from the alkaline hydrolysis and oxidation of benzyl chloride, respectively. The theoretical analysis shows that it is possible to simultaneously measure rate constant and equilibrium constant under certain conditions. The effects of speed of agitation, catalyst concentration, substrate concentration, nature of catalyst cation, membrane structure, nucleophile concentration, surface area for mass transfer and temperature on the rate of reaction are discussed. 

Selectivity engineering is a new term that is coined with the engineering aspects of multiphase reactions that could be manipulated through the use of several techniques such as use of an additional immiscible liquid phase, porous inert solids, particles smaller than diffusion film thickness, etc. in order not only to intensify the rates of reaction but also to improve greatly the selectivity of the desired product. We are particularly concerned in this paper with the selectivity engineering aspects of the capsule membrane phase transfer catalysis, which has interesting attributes, for the preparation of benzyl alcohol and benzaldehyde by selective alkaline hydrolysis and oxidation, respectively, of benzyl chloride. 

In the industrial process, benzyl alcohol is normally manufactured by refluxing benzyl chloride with an alkali over a very long period ( 24 hrs). However, this process leads to significant formation of the byproduct benzyl ether [1]. Several attempts have been reported in the literature to suppress the yields of the ether. Thus, it was thought 

Selective oxidation of benzyl chloride to benzaldehyde is another reaction of great commercial importance. There exist several methods to prepare benzaldehyde, both commercially and synthetically, but the oxidation of benzyl chloride directly to benzaldehyde in a single pot by using CM-PTC merits special attention. We have studied in our laboratory [3] the kinedcsand mechanism of the liquid-liquid and solid-liquid phase transfer oxidation by using chromate and hypochlorite s ts and it was thought desirable to study the selectivity engineering aspects of this reaction. 

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