Safety Evaluation of the Copper-Mediated Cross-Coupling of 2-Bromopyridines with Ethyl Bromodifluoroacetate

The potential safety hazards associated with the copper-mediated cross-coupling of 2-bromopyridines with ethyl bromodifluoroacetate were evaluated. Thermal stability evaluation of the postreaction mixture of 50.6 mmol of 2-bromopyridine with 1.3 equiv of ethyl bromodifluoroacetate in the presence of 2.1 equiv of copper in 40 mL of dimethyl sulfoxide (DMSO) indicated a significant decomposition event with an onset temperature of 115.5 °C by accelerating rate calorimetry, which was significantly lower than that of neat DMSO. In contrast, the reaction mixture in N,N-dimethylformamide did not show any exothermic decomposition up to 400 °C by differential scanning calorimetry. Reaction calorimetry evaluation of this reaction in DMSO revealed a heat output (ΔH) of −13.5 kJ and an adiabatic temperature rise (ΔTad) of 129.5 °C, resulting in a maximum temperature of a synthesis reaction (MTSR) of 189.5 °C. The predicted heat of reaction using density functional theory with the BLYP functional was in good agreement...