An Investigation into the Unexpected Corrosion of Nickel Alloy Vessels with Selectfluor

Selectfluor is one of the most widely used fluorinating agents in the pharmaceutical industry. These reactions are often scaled up in reactors made with corrosion-resistant metals such as Hastelloy because of the presence of fluoride in Selectfluor. Herein we report an investigation into the variable performance of a fluorination reaction in the belzutifan synthesis, which initially focused on the unexpected corrosiveness of the reaction toward the high-nickel alloys Hastelloy C-276 (N10276) and Hastelloy C-22 (N06022). This investigation identified that the corrosion, rather than being inherent to the reaction, was associated with the particular lot of Selectfluor used and could be correlated with elevated levels of chloride and iron in the lot of Selectfluor. Further investigation found that the increased aggressiveness was associated with the elevated chloride level (some chloride can be found in nearly all lots of Selectfluor), and the presence of metals does not impact the level of corrosion. A corrosion-reaction pathway involving the presence of an oxidized chloride species is proposed which accounts for both the poor reaction performance and the corrosion observed.