Thermal hazards and safe scale-up of reactions containing dimethyl sulfoxide

Extensive thermal analysis has shown that DMSO-containing reaction mixtures can be more energetic and decompose at lower temperatures than pure DMSO. Several processes at Merck using DMSO as a solvent were found to have the onset temperatures of decompositions reduced to the point where it became a thermal and operational hazard. The onset temperature depended on the reagents in the reaction mixture and the thermal history of the mixture. The case studies presented in this paper will include discussion on what process hazards were identified, how the process hazards differ from the pure DMSO hazards, and how to scale up these processes safely.