ATR-IR Spectroscopy for the Investigation of Solution Reaction Kinetics: Hydrolysis of Trimethyl Phosphate

Abstract

ATR-IR spectroscopy is proposed as a versatile technique for the investigation of reaction kinetics in solution, particularly in aqueous solution. Subtraction of the solvent spectrum and thus quantitative absorption measurements are possible. In contrast to thin-film transmission spectroscopy, thermostatting is feasible. The high information content of IR spectra demands high-resolution spectra measured at many wave-numbers, and, for kinetic investigations, series of spectra are measured. A multivariate nonlinear least-squares fit is proposed that effectively overcomes the difficulties related to large numbers of data and parameters. As a test for the method, the base-catalyzed hydrolysis of trimethyl phosphate in aqueous solution was investigated. The rate constant is 1.6 × 10−1 s−1 at 40°C and pH 13.