Reductive Amination Bicarbonate Quench: Gas-Evolving Waste Stream Near-Miss Investigation

The use of sodium triacetoxyborohydride (STAB) as a mild and effective reagent for the reduction of imines is well characterized in the literature. For reduction products that require a nonacidic workup, but cannot tolerate a strongly basic quenching regime, the reaction mixture is typically quenched with bicarbonate solution in excess to neutralize any remaining active reagent. We recently experienced a near-miss incident in our pilot plant operation, where the drummed, aqueous waste stream from a reductive amination process generated unexpected internal pressure, resulting in significant deformation of a mild steel drum during temporary storage. This article details the incident, associated hazard evaluation investigation, and recommendation to prevent future occurrences. The root cause was determined to be the slow reaction (hence slow generation of carbon dioxide) of weekly acidic boric acid, with excess potassium bicarbonate, present in the fully quenched aqueous waste stream.