Interfacial behavior of phase transfer catalysis of the reaction between potassium thiocyanate and p-nitrobenzyl bromide with crown ethers as catalysts

Abstract

A very simple and novel method is devised to study the mechanism of phase transfer catalysis (PTC) for a nucleophilic substitution reaction between potassium thiocyanate and p-nitrobenzyl bromide (p-NB); the mechanism of the nucleophilic substitution reaction is illustrated by characterizing the interfacial dilational viscoelastic properties of the crown ether catalysts and intermediates, which are closely related to the interfacial behavior of the species in the PTC reaction. The results obtained from this study can be used to infer the mechanism of the nucleophilic substitution reaction that uses 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) as phase transfer catalysts. This mechanism begins with formation of the intermediates [K · Crown ether]+ and [K · Crown ether]+SCN− through mutual collisions between crown ethers and KSCN in the aqueous phase near the interface. Then the complex, [K · Crown ether]+Br−, was obtained due to the collision between [K · Crown ether]+SCN− and p-NB in the organic phase near the interface and simultaneously the products were obtained.