Predicting 24 and 8 h Adiabatic Decomposition Temperature for Low Temperature Reactions by Kinetic Fitting of Nonisothermal Heat Data from Reaction Calorimeter (RC1e)

Abstract

A new approach to determine the adiabatic decomposition temperature in 24 or 8 h (ADT 24/ADT 8) using a combination of nonisothermal heat data and kinetic modeling for the low temperature decomposition of a lithiated halogenated aromatic intermediate via the formation of a highly unstable benzyne intermediate is presented here. First order rate equations for the two steps were used for fitting the experimental heat curve generated from the temperature ramp of the lithiated reaction mass in RC1e. A good fit of experimental and predicted heat generation curves was obtained by fitting the kinetic parameters in DynoChem software using the heat data generated from the non-isothermal run in RC1e. The decomposition of a lithiated intermediate to a benzyne intermediate is a slow reaction and is sensitive to temperature, with rate constant (k) and activation energy (Ea) of 4.08 × 10–8 1/s (reference temperature Tref = −67 °C) and 99 kJ/mol, respectively. The decomposition of benzyne is a fast reaction and insensitive to temperature, with rate constant (k) and activation energy (Ea) of 1.34 × 10–3 1/s (Tref = −67 °C) and 2.3 kJ/mol, respectively. The kinetic parameters obtained from the fitting were then used to predict the ADT 24/ADT 8 and determine the maximum safe operating temperature for scale up. Kinetic studies indicate that dilution of the reaction with additional solvent has a minor impact on the predicted ADT 24 and ADT 8 and the decomposition is a strong function of temperature. Through this case-study, the methodology of using the heat curve from a single temperature ramp experiment in RC1e for fitting the low temperature decomposition kinetics and evaluating the criticality of the process step is demonstrated.