Triphase catalysis: a rigorous mechanistic model for nucleophilic substitution reactions based on a modified Langmuir-Hinshelwood/Eley-Rideal approach

In the present work, a general kinetic model based on the traditional kinet ic mechanisms of the Langmuir-Hinshelwood and Eley-Rideal types has been de veloped for nucleophilic substitution reaction systems involving a triphase catalyst in which the intrinsic reaction rate at the catalyst active site is the rate-limiting step. The present mechanistic model overcomes the limi tation of the commonly used pseudo-first-order model by incorporating the e ffect of the leaving anion on the ion-exchange step, and can be used to det ermine whether a triphase catalytic system is limited by the organic reacti on step, ion-exchange step, or a combination of both the steps. Reactions t o synthesize octyl acetate by using different octyl halides as the organic reactant have been used to show how the parameters values obtained can be u sed to classify systems. These values showed physical relevance since the d ata were in high conformity with trends that could be expected from the phy sical and chemical properties of the halide anions and the corresponding al kyl halides. (C) 2000 Published by Elsevier Science Ltd. All rights reserve d.