Mechanochemistry continues to reveal new possibilities in chemistry including the opportunity for “greening” reactions. Nevertheless, a clear understanding of the energetic transformations within mechanochemical systems remains elusive. We employed a uniquely modified ball mill and strategically chosen Diels-Alder reactions to evaluate the role of several ball-milling variables. We identified three different energetic regions that we believe are defining characteristics of most, if not all mechanochemical reactions. Relative to the locations a given ball mill’s regions, activation energy determines whether a reaction is energetically easy (Region I), challenging (Region II), or forbidden (Region III). In Region II, yield depends exponentially on oscillation frequency. Our unique modifications granted control of reaction vessel temperature, allowing complete control of the locations of Regions I, II, and III. These results suggest envisioning vibratory mills (and likely other mechanochemical methodologies) as molecular-collision facilitating devices that act upon molecules occupying a thermally-derived energy distribution. This unifies ball-milling energetics with solution-reaction energetics via a common tie to the Arrhenius equation. In light of this, we discuss a strategy for translating solvent-based reaction conditions to equivalent ball milling conditions.

Decoupling the Arrhenius equation via mechanochemistry

254th National Meeting (2017)

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