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Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals. The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms. We introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. We discuss our recent results investigating the formation of (polymorphic) cocrystals. First investigations of a mechanochemical synthesis under controlled temperature which allow determining the activation barrier are presented.6 Furthermore, X-ray diffraction and in situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases as a result of the reaction heat. Our results indicate that in situ investigation of milling reactions offer a new approach to tune and optimize mechanochemically synthesized compounds.
Real time monitoring of chemical reactions has become a key step in industrial processes due to constantly increasing demands on product performance and environmental compatibility. In contrast to spectroscopic methods that usually require sample pretreatment, mass spectrometry (MS) has been proven as a robust method for multicomponent analysis. As an especially demanding reaction process, we here report successfully on the entirely contactless conduction and interrogation of a chemical reaction inside an acoustically levitated microliter droplet of reaction mixture. The approach represents a proof of concept study for fast reaction optimization approaches with minimal resource consumption. The sampling is done by repeated laser desorption of small fractions of the droplets volume spread over the timescale of the reaction process.
The upscaling from small scale academic reactors to large industrial processes typically suffers from a large change in surface-to-volume ratio. A promising approach is the general avoidance of surfaces as in levitated droplet techniques. However, up to now, no mass spectrometric interface for online reaction monitoring in levitated droplets has been provided.
As model reaction the photoinitiated thiol-ene coupling between N-boc cysteine methyl ester and allyl alcohol was studied. A droplet of 5 µL reactand solution was provisioned into an acoustic trap aligned lateral to the MS inlet. Contactless sampling by laser ablation (LA) is followed by dielectric barrier discharge (DBD) postionization. The latter is needed to address non polar reaction partners.