24696-60-4Relevant academic research and scientific papers
Understanding the unexpected effect of frequency on the kinetics of a covalent reaction under ball-milling conditions
Belenguer, Ana M.,Michalchuk, Adam A. L.,Lampronti, Giulio I.,Sanders, Jeremy K. M.
, p. 1226 - 1235 (2019)
We here explore how ball-mill-grinding frequency affects the kinetics of a disulfide exchange reaction. Our kinetic data show that the reaction progress is similar at all the frequencies studied (15-30 Hz), including a significant induction time before the nucleation and growth process starts. This indicates that to start the reaction an initial energy accumulation is necessary. Other than mixing, the energy supplied by the mechanical treatment has two effects: (i) reducing the crystal size and (ii) creating defects in the structure. The crystal-breaking process is likely to be dominant at first becoming less important later in the process when the energy supplied is stored at the molecular level as local crystal defects. This accumulation is taken here to be the rate-determining step. We suggest that the local defects accumulate preferentially at or near the crystal surface. Since the total area increases exponentially when the crystal size is reduced by the crystal-breaking process, this can further explain the exponential dependence of the onset time on the milling frequency.
Dynamic Covalent Chemistry under High-Pressure:A New Route to Disulfide Metathesis
Sobczak, Szymon,Dro?d?, Wojciech,Lampronti, Giulio I.,Belenguer, Ana M.,Katrusiak, Andrzej,Stefankiewicz, Artur R.
, p. 8769 - 8773 (2018)
This work describes, for the first time, the application of combined pressure and temperature stimuli in disulfide metathesis reactions. In the system studied, above a pressure of 0.2 GPa, equimolar amounts of symmetric disulfides bis 4-chlorophenyl disulfide [(4-ClPhS)2] and bis 2-nitrophenyl disulfide [(2-NO2PhS)2] react to give the heterodimeric product 4-Cl-PhSSPh-2-NO2. In contrast to experiments conducted in solution at atmospheric pressure or in mechanochemical experiments under ball-mill grinding conditions, there is no necessity to use a base or thiolate anion as a catalyst for the exchange reaction under investigated conditions. Single-crystal and powder X-ray diffraction revealed also that, despite the high-pressure conditions of this reaction, the heterodimeric-disulfide product unexpectedly crystallizes into the low-density polymorph A. This counterintuitive result contrasts with the high-pressure stability of the higher-density polymorph B, confirmed by its compression up to 2.8 GPa with no signs of a phase transition.
Direct observation of intermediates in a thermodynamically controlled solid-state dynamic covalent reaction
Belenguer, Ana M.,Lampronti, Giulio I.,Wales, David J.,Sanders, Jeremy K. M.
, p. 16156 - 16166 (2014)
We present the first polymorph interconversion study that uses solid-state dynamic covalent chemistry (DCC). This system exhibits unexpected and rich behavior, including the observation that under appropriate conditions the polymorph interconversion of a heterodimer proceeds through reversible covalent chemistry intermediates, and this route is facilitated by one of the two disulfide homodimers involved in the reaction. Furthermore, we demonstrate experimentally that in all cases a dynamic equilibrium is reached, meaning that changing the milling conditions affects the free energy difference between the two polymorphs and thus their relative stability. We suggest that this effect is due to the surface solvation energy combined with the high surface to volume ratio of the nanocrystalline powder.
Using Solid Catalysts in Disulfide-Based Dynamic Combinatorial Solution- and Mechanochemistry
Belenguer, Ana M.,Michalchuk, Adam A. L.,Lampronti, Giulio I.,Sanders, Jeremy K. M.
, (2021/12/27)
It was shown for the first time that solid amines can act as catalysts for disulfide-based dynamic combinatorial chemistry (DCC) by ball mill grinding. The mechanochemical equilibrium for the two disulfide reactions studied was reached within 1–3 h using ten different amine catalysts. This contrasts with the weeks to months to achieve solution equilibrium for most solid amine catalysts at 2 %mol mol?1 concentration in a 2 mMolar disulfide dynamic combinatorial library in a suitable solvent. The final mechanochemical equilibrium was independent of the catalyst used but varied with other ball mill grinding factors such as the presence of traces of solvent. The different efficiencies of the amines tested were discussed.
