As environmental concerns are becoming more prominent in today's society, Green Chemistry has evolved in an effort to reduce the harmful impact of chemical waste. Ideally, Green Chemists would be able to eliminate all hazardous and wasteful components of their experiments. With that lofty goal, the Mack group has adapted a solventless method which uses high speed ball milling. In this system, dry reagents are crushed together in a way which physically breaks up and mixes the materials, allowing them to react in a similar manner to being dissolved in a solution. Because of this lack of solvent, the chemical environment is expected to be unfavorable to the dissociation and stabilization of ions. Therefore, it is expected that SN1-type reactions should not occur due to the carbocation intermediate involved. This suggests that all substitution reactions in the high speed ball mill will undergo SN2-type chemistry; however, as this requires a concerted mechanism with backside attack, sterically hindered electrophiles are unreactive. This leads to a question about limitations within the ball mill. In this study, we attempt to identify whether sterically hindered reagents are able to undergo substitution within the ball mill, and if so, under which mechanism the reaction proceeding. Are the physical impacts of the milling process capable of inducing strain which allows SN2-type substitution, or is there a pseudo-cation formation which can proceed via SN1-type substitution?

Substitution without solution: The effects of a solventless system on the reactivity of sterically hindered reagents

248th National Meeting (2014)

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