Monitoring of Liquid‐Phase Organic Reactions by Photoelectron Spectroscopy

Abstract

There are strings attached: after linking the reacting groups to head groups of ionic liquids to drastically lower the vapour pressures of the reactants, ordinary liquid-phase organic reactions can be monitored by in situ X-ray photoelectron spectroscopy. This approach is demonstrated for the nucleophilic substitution of an alkyl amine and an alkyl chloride moiety, which are attached to the cation and anion of ionic liquids, respectively.

Ionic Liquids in Catalysis

“…The first studies by AR-XPS demonstrated that the adsorption and wetting behaviour strongly depend on the particular combination of IL and support, with a strong influence of contaminations [150,156,192]. Furthermore, it was demonstrated that XPS can be also used to study reactions in ILs or at ILsubstrate or IL-electrode interfaces in situ, as a function of time or temperature [148,161,162,173,[193][194][195][196][197][198][199][200].…”

“…This was due to the high vapour pressures of common liquids or solvents, which are not compatible with the required UHV conditions. It was only recently realized that the situation is very different, when studying reactions in ILs, which have an inherently low vapour pressure, and first studies have been performed within the last years [148,161,162,173,[193][194][195][196][197][198][199][200]. Compared to classical spectroscopy techniques used to monitor chemical reactions, the advantage of XPS is that through the analysis of their core levels all relevant elements can be quantified and their chemical state can be analysed under well-defined (ultraclean) conditions.…”

Perspective: Chemical reactions in ionic liquids monitored through the gas (vacuum)/liquid interface

“…Reaction mechanism of the alkylation of an aminefunctionalized IL (N-IL) cation by the chlorinated anion of a second IL (Cl-IL), leading to the formation of an ammonium zwitterion and free chloride (Am-IL). 106 reactions and for deriving a mechanistic understanding. 106 In our approach, we drastically lowered the vapour pressures of the reactants by linking them before-hand to an ionic head group of an IL; notably, these IL head groups do not directly participate in the investigated reaction.…”

“…106 reactions and for deriving a mechanistic understanding. 106 In our approach, we drastically lowered the vapour pressures of the reactants by linking them before-hand to an ionic head group of an IL; notably, these IL head groups do not directly participate in the investigated reaction. 47,106,119 In the following, we discuss the liquid-liquid reaction between an IL with a reactive chloro-functionalized anion The reactive Cl-IL/N-IL mixture was prepared by dissolving both ILs in a 1:1 molar ratio in acetonitrile as a co-solvent to ensure proper mixing and by applying this solution repetitively to the surface of a polycrystalline Au foil that acted as an inert sample support for the following XPS investigation.…”

“…105 The third example deals with the alkylation of an amine under solvent-free conditions by tethering the reactive groups to the cations and anions of an IL; the nucleophilic substitution reaction between the two functionalized ILs is sufficiently slow to allow for ex situ mixing and introduction into the UHV chamber, where the reaction is triggered thermally. 106 The fourth example deals with dehydrogenation of a liquid organic hydrogen carrier (LOHC) tethered to an ionic headgroup of an IL, in a macroscopic film of the functionalized IL. 107 Dehydrogenation occurs at a catalytically active Pt foil, but can be monitored at the IL/vacuum interface, since product diffusion proved to be sufficiently fast.…”