Complexities of mechanochemistry: elucidation of processes occurring in mechanical activators via implementation of a simple organic system

Abstract

There is, at present, a substantial lack of mechanistic-level understanding of mechanochemical processes, despite their current widespread use. The system α-glycine + β-malonic acid was previously shown to adhere to divergent reaction pathways under mechanical treatment. In the present study, this system's complexity was further amplified when mechanical treatment was observed to yield yet another divergent reaction path, producing either a known salt, glycinium semi-malonate (GSM), or what is at present an unidentified phase. Isolating the two major mechanical “actions” – impact and shear – it was observed that each of these treatments favours a different product; shear yielding GSM and impact inducing production of the novel phase. Combination of isolated treatments with milling studies demonstrated two distinct regions within the milling jar, the jar ends and the jar shaft. While sample located in the latter undergoes larger amounts of shear treatment, sample located in the former is privy to both shearing and impact, depending on both its ability to tablet and the geometry with which this tablet forms. Following tablet formation, in which the major stress appears to be shear, sample located in the milling jar ends is subsequently treated by pure impact. This study offers unique insights towards a mechanistic understanding of mechanochemistry and its processes.