Process Safety Evaluation of a Magnesium−Iodine Exchange Reaction

Abstract

An unexpected highly exothermic decomposition was observed during routine safety analysis of the magnesium−iodine exchange reaction of 2-iodo-4-fluorotoluene (3) with commercially available i-PrMgCl (2.0 M solution in THF). When the reaction mixture was scanned in an adiabatic calorimeter with the use of a 2 °C/min temperature ramp, a rapid exothermic decomposition with an onset temperature of approximately 80 °C was observed. The system temperature rapidly rose to 210 °C at a peak rate of 200 °C/min. Subsequent testing of three simplified substrates showed the same type of exothermic decomposition for all cases. Control experiments indicated that the decomposition requires both aryl iodide and i-PrMgCl (or arylMgCl and i-PrI). While the onset temperatures for all cases studied were generally well above the typical operating temperature for these reactions (0−10 °C), it is nonetheless important to cautiously evaluate these types of processes and install proper engineering controls for analogous decomposit...