1-ethyl-3-methylimidazolium acetate as a reactive solvent for elemental sulfur and poly(sulfur nitride)

Abstract

We investigate the reactive dissolution process of poly(sulfur nitride) (SN)x in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate [EMIm][OAc] in comparison to the process of elemental sulfur in the same IL. It has been known from the literature that during the reaction of S8 with [EMIm][OAc], the respective thione is formed via a radical mechanism. Here, we present new results on the kinetics of the formation of the respective imidazole thione (EMImS) via the hexasulfur dianion [S6]2– and the trisulfur radical anion [S3]•–. We can show that [S6]2– is formed first, which dissociates then to [S3]•–. Also, long-term stable radicals occur, which are necessary side products provided in a reaction scheme. During the reaction of [EMIm][OAc] with (SN)x chains, two further products can be identified, one of which is the corresponding imine. The reactions are followed by time-resolved NMR spectroscopic methods that showed the corresponding product distributions and allowed the assignment of the individual signals. In addition, continuous-wave (CW) EPR and UV/vis spectroscopic measurements show the course of the reactions. Another significant difference in both reactions is the formation of a long-term stable radical in the sulfur–IL system, which remains active over 35 days, while for the (SN)x–IL system, we can determine a radical species only with the spin trap 5,5-dimethyl-1-pyrrolin-N-oxide, which indicates the existence of short-living radicals. Since the molecular dynamics are restricted based on the EPR spectra, these radicals must be large.