The role of the milling environment on the copper-catalysed mechanochemical synthesis of tolbutamide†
Abstract
We provide a systematic investigation of the role of atmospheric oxygen and choice of milling assembly (i.e., the milling jar and ball materials) on a prototypical medicinal mechanochemistry reaction: the copper-catalysed coupling of isocyanate and sulfonamide to form the sulfonylurea tolbutamide. Using in-house developed equipment for work under controlled-atmosphere milling conditions, we reveal that the reaction is in fact catalysed by Cu(II) species, with the conventionally used CuCl acting as a pre-catalyst, which becomes activated via aerobic oxidation during milling. Unexpectedly, the choice of milling jar material was found to have a profound effect on the coupling, with aluminium jars effectively “shutting down” reactivity, most likely by preventing CuCl oxidation. Hence, opposite to direct mechanocatalysis, a term used to describe reactions promoted by the milling jar or ball material, this observation reveals the possibility of direct mechanoinhibition – i.e., the inhibition of a mechanochemical reaction by the jar. These results highlight the importance of systematic investigations of both the milling assembly, as well as atmosphere, in understanding and controlling organic mechanochemical transformations.
Please wait while we load your content...
