Kinetic Study of α-Bromo-o-toluic Acid Using Raman Spectroscopy

Abstract

In this study,Raman technique has been utilized to demonstrate its feasibility for studying the kinetics of organic reactions in aqueous solution. The solvolytic reaction of a-bromo-otoluic acid in 80% aqueous ethanol has been selected as a model system. Due to a moderate reaction rate and a detection possibility of Raman signal, the solvolytic reaction of a-bromo-o-toluic acid1 is considered as a very good model system for the present Raman study. The major problem in measuring reactions with Raman spectroscopy consists in extracting small vibrational peaks of reactant or product from the strong Raman backgrounds of solvent.2 In this work, we have successfully monitored the disappearance of the C-Br stretching peak for the reactant, a-bromoo-toluic acid, and the appearance of the vibrational peak for the product, phthalide. The solvolysis rates of a-bromo-otoluic acid in 80% aqueous ethanol have been determined by measuring the disappearance rate of the C-Br stretching Raman peak at 619 cm-1 normalized to a C-H stretching peak at 2978 cm-1 as an internal standard. Here we report the kinetic analysis for the solvolytic reaction of a-bromo-otoluic acid using Raman spectroscopy.