Ionic liquids are salts melting at temperatures below 100°C. Various inorganic materials can be synthesized in ionic liquids (ILs) under favorable conditions, i.e. near ambient temperature. This approach enables an enormous reduction of energy usage and technical efforts compared to the commonly applied high-temperature processes. Syntheses in ionic liquids also provide great opportunities to discover completely new compounds with potentially outstanding and useful chemical and physical properties. Continuous reaction monitoring is necessary for the understanding of reaction processes. Combination of liquid- and solid-state NMR spectroscopy is a valuable method for these purposes. The reaction of red phosphorus with iodine in [BMIm]Cl 2AlCl3 as ionic liquid was studied in detail [1]. A combination of 31P liquid- and solid-state NMR spectroscopy was used to monitor the reaction process (semi)continuously and to characterize the formed products. Depending on the ratio of red phosphorus and iodine in the starting solution, P2I4 and PI3 appear as main final products at different concentrations. Depending on reaction temperatures and ratios of educts, different phosphorus halides and even nano-sized phosphorus particles were observed. We also varied the cation as well as the anion of the ionic liquid. Variation of the cation had no influence on the reaction, but product formation was crucially dependent on the anion of the ionic liquid. To further understand the reaction of red phosphorus with iodine, we chose [HMIm][X] (X = Cl, Br, I) as ionic liquid because its handling during sample preparation is favorable. In order to assign all obtained signals of the reaction of phosphorus (III) halides PX3 (X = Cl, Br, I) in these ILs, detailed studies were carried out. Combining NMR and Raman spectroscopy, it could finally be demonstrated that phosphorus (III) halides undergo fast anion exchange [2]. Based on these fundamental studies, it became possible to synthesize materials such as copper phosphides from red phosphorous in ionic liquids [3]. Solid-state 31P NMR spectroscopy turned out to be useful for the characterization of such compounds.

Red phosphorous as an educt in near-room-temperature synthesis reactions in ionic liquids: Reaction monitoring by NMR spectroscopy

256th National Meeting (2018)

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