Direct Visualization of a Mechanochemically Induced Molecular Rearrangement

Abstract

Recent progress in the field of mechanochemistry has expanded the discovery of mechanically induced chemical transformations to several areas of science. However, a general fundamental understanding of how mechanochemical reactions by ball milling occur has remained unreached. For this, we have now implemented in situ monitoring of a mechanochemically induced molecular rearrangement by synchrotron X‐ray powder diffraction, Raman spectroscopy, and real‐time temperature sensing. The results of this study demonstrate that molecular rearrangements can be accomplished in the solid state by ball milling and how in situ monitoring techniques enable the visualization of changes occurring at the exact instant of a molecular migration. The mechanochemical benzil–benzilic acid rearrangement is the focal point of the study.

Sustainability Assessment of Mechanochemistry by Using the Twelve Principles of Green Chemistry

“…Similarly, real-time temperature sensing has allowed understanding the development of thermal effects during ball milling reactions, [115] and the detection of reaction onsets in mechanochemical transformations. [208,209] Other strategies to follow mechanochemical reactions include manometric real-time monitoring to study reaction mechanisms in the mechanosynthesis of zeolitic imidazolate frameworks, [24] palladium-catalyzed carbonylative reactions, [210] and cyclodehydrogenation reactions. [211] Complementarily, formation of volatile products in ball milling reactions has been monitored by gas chromatography (Scheme 10), [168] while online spectroscopic identification of gaseous products generated by ball milling has been achieved by nondispersive infrared spectroscopy.…”

“…a) Setup for synchrotron X-ray powder diffraction, Raman spectroscopy, and real-time temperature sensing. [208] b) Milling jar for pressure and temperature sensing. [210] c) Modified milling vial for online nondispersive infrared spectroscopy monitoring.…”

“… [204] In the case of mechanochemical reactions by ball milling, a breakthrough occurred after the implementation of in situ real‐time monitoring by synchrotron powder X‐ray diffraction (PXRD), [205] Raman spectroscopy [206] or the combination of both, [207] which has permitted the study of solid state changes in crystalline materials as well as structural changes at the molecular level. Similarly, real‐time temperature sensing has allowed understanding the development of thermal effects during ball milling reactions, [115] and the detection of reaction onsets in mechanochemical transformations [208,209] …”

“… Top) Examples of analytical methods for real‐time monitoring of mechanochemical reactions by ball milling and by pulsed ultrasonication. a) Setup for synchrotron X‐ray powder diffraction, Raman spectroscopy, and real‐time temperature sensing [208] . b) Milling jar for pressure and temperature sensing [210] .…”

Epimerization-free C-term Activation of Peptide Fragments by Ball-Milling

“…Temp (°C) t (min) Yield (%) Purity (%) a,b LDL (% Ball-milling is known to induce a slight temperature raise of the milled materials. [39][40][41] As the temperature inside the reactor could have an influence on the reaction course, the temperature of the milled material was measured directly after milling. During the coupling under ball-milling conditions, the temperature reached 33 °C.…”