Reaction Calorimetry and Scale-Up Considerations of Bromo- and Chloro-Boron Subphthalocyanine

The formation mechanism of boron subphthalocyanines (BsubPcs) has thus far evaded researchers, making it nearly impossible to accurately estimate the overall reaction enthalpy─a critical metric for determining chemical process safety for scale-up. To address this gap, reaction calorimetry was used to collect thermokinetic data for a baseline Br-BsubPc reaction at three temperatures and two BBr₃ reagent ratios and a proposed semibatch process for Cl-BsubPc. For the Br-BsubPc process, the magnitude of the enthalpy of reaction (ΔH_r) increased with increasing reaction temperature, from −244.6 kJ/mol-BBr₃ at 25 °C to −332.7 kJ/mol-BBr₃ at 50 °C to −391.3 kJ/mol-BBr₃ at 75 °C. However, this increase in the magnitude of ΔH_r did not result in a noticeable increase in Br-BsubPc yield, achieving 50%, 49%, and 52% yields at 25 °C, 50 °C, and 75 °C, respectively. When the molar equivalence of BBr₃ was increased by 1.5× at 25 °C, the magnitude of ΔH_r increased slightly (−252.2 kJ/mol-BBr₃), but the yield did not improve (47%). Therefore, further attempts were made to try and improve the yield of Br-BsubPc by increasing the molar equivalence of BBr₃. It was found that BBr₃ equivalencies greater than 0.48 resulted in significant reductions in Br-BsubPc yield. The ΔH_r of the semibatch Cl-BsubPc process was −266.5 kJ/mol-BCl₃ with a yield of 33%. These processes were assessed based on criticality criteria and were both found to be “Criticality Class 1”, which is relatively safe for scale-up. Based on the calorimetry measurements, preliminary estimates for process conditions and reactor design for scale-up are provided.