Guide to by-products formed in organic solvents under solvothermal conditions

Solvothermal chemistry is widely applied in research laboratories as well as industry, entailing significant consumptions of organic solvents every year. Yet, there is a very poor understanding of the internal reaction chemistry in solvents under such non-ambient conditions and the organic by-products they incur. This study has sought to elucidate trends in by-product formation under continuous-flow conditions for a range of the most commonly used solvents: Methanol, ethanol, isopropanol, ethylene glycol, acetone and toluene. The impact of binary mixtures (co-solvents) has been studied for the two cases (i) acetone–ethanol and (ii) ethanol–toluene. Additionally, the effect of solvothermal nanoparticle synthesis has been investigated, employing the specific cases of Pt, PtRu (alloy) and Ru metal nanoparticles produced from Pt(acac)2 and Ru(acac)3 precursors in an ethanol/toluene mixture. Finally, the impact of switching to a different reactor system has been tested for three solvents: Ethanol, isopropanol and acetone. All experiments were carried out as flow syntheses. The series were temperature resolved in the 100–450 °C range. By-products have been characterized and selectively quantified by MS and GC–MS. Reaction pathways are unraveled and given for all identified by-products in all solvents and binary mixtures. Quantifications shows conversion rates up to 8.14 wt% of the solvents and formation up to 190 by-products. The intent of this study is to provide a “manual” for the field of solvothermal chemistry which can guide choices between solvents and/or reaction temperatures. Also, it may afford better evaluations of “green footprints” i.e. improve existing and future sustainability analyses in the field.