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      Decoupling the Arrhenius equation via mechanochemistry†

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      a , a ,
      Chemical Science
      Royal Society of Chemistry

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          Abstract

          We identified three different energetic regions that we believe are defining characteristics of most, if not all mechanochemical reactions. For a given ball mill's region, 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. Modifications granted control of the locations of Regions I, II, and III.

          Abstract

          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. This revealed three different energetic regions that we believe are defining characteristics of most, if not all, mechanochemical reactors. Relative to the locations of a given ball mill's regions, activation energy determines whether a reaction is energetically easy (Region I), challenging (Region II), or unreasonable (Region III) in a given timeframe. It is in Region II, that great sensitivity to mechanochemical conditions such as vial material and oscillation frequency emerge. Our unique modifications granted control of reaction vessel temperature, which in turn allowed control of the locations of Regions I, II, and III for our mill. Taken together, 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, but gives mechanochemistry the unique opportunity to influence either half of the equation. In light of this, we discuss a strategy for translating solvent-based reaction conditions to ball milling conditions. Lastly, we posit that the extra control via frequency factor grants mechanochemistry the potential for greater selectivity than conventional solution reactions.

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          Most cited references44

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          Mechanochemistry: opportunities for new and cleaner synthesis.

          The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal-organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references). This journal is © The Royal Society of Chemistry 2012
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            Mechanochemical organic synthesis.

            Recently, mechanical milling using a mixer mill or planetary mill has been fruitfully utilized in organic synthesis under solvent-free conditions. This review article provides a comprehensive overview of various solvent-free mechanochemical organic reactions, including metal-mediated or -catalyzed reactions, condensation reactions, nucleophilic additions, cascade reactions, Diels-Alder reactions, oxidations, reductions, halogenation/aminohalogenation, etc. The ball milling technique has also been applied to the synthesis of calixarenes, rotaxanes and cage compounds, asymmetric synthesis as well as the transformation of biologically active compounds.
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              Mechanochemistry: A Force of Synthesis

              The past decade has seen a reawakening of solid-state approaches to chemical synthesis, driven by the search for new, cleaner synthetic methodologies. Mechanochemistry, i.e., chemical transformations initiated or sustained by mechanical force, has been advancing particularly rapidly, from a laboratory curiosity to a widely applicable technique that not only enables a cleaner route to chemical transformations but offers completely new opportunities in making and screening for molecules and materials. This Outlook provides a brief overview of the recent achievements and opportunities created by mechanochemistry, including access to materials, molecular targets, and synthetic strategies that are hard or even impossible to access by conventional means.
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                Author and article information

                Journal
                Chem Sci
                Chem Sci
                Chemical Science
                Royal Society of Chemistry
                2041-6520
                2041-6539
                1 August 2017
                30 May 2017
                : 8
                : 8
                : 5447-5453
                Affiliations
                [a ] Department of Chemistry , University of Cincinnati , 301 Clifton Court , Cincinnati , Ohio 45221-0172 , USA . Email: james.mack@ 123456uc.edu
                Author information
                http://orcid.org/0000-0001-5717-8916
                Article
                c7sc00538e
                10.1039/c7sc00538e
                5609516
                28970924
                f5694d49-eca0-412d-b08e-487b343ad160
                This journal is © The Royal Society of Chemistry 2017

                This is an Open Access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 5 February 2017
                : 28 May 2017
                Categories
                Chemistry

                Notes

                †Electronic supplementary information (ESI) available: Details regarding apparatus design, experimental procedures, and software computations. See DOI: 10.1039/c7sc00538e


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