Analysis of consecutive pseudo-first-order reactions. II: Calculation of the rate constants from the co-product or co-reactant data.

Abstract

The co-product or co-reactant data for a two-step pseudo-first-order consecutive reaction gives unique shape profiles for the natural logarithm of the concentration versus time plots, based on the ratio of two rate constants (k2/k1), for theoretical data without error. But, in the presence of a +/- 2.0% random error in the simulated data, the ability to distinguish between different shapes disappears. A comprehensive analysis shows that accurate rate constants can be obtained only in a limited range of k2/k1 ratios. Reliable rate constants can be obtained when k2/k1 less than 0.5. Two special cases, k1 approximately 2k2 and k2 much greater than k1, cannot be distinguished from each other and could lead to erroneous conclusions if additional information is not used to identify the correct ratio. When k2/k1 greater than 0.5, the calculated parameters are extremely sensitive to experimental errors, and other techniques involving the concentrations of starting material and intermediate should be used to obtain the rate constants.