Functional materials: Chemically active domains in liquids
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Ionic liquids or deep eutectic solvents can act as functional materials. Depending on the chemical nature of the liquids’ components, special structural motives emerge on the molecular level, while macroscopically the system remains a homogeneous liquid. This is for example the case if alkyl chain functionalizations at the molecular compounds are introduced. The liquid reveals a segregation into polar and nonpolar domains, which allow for the development of new reaction routes in these solvents.
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Paper examples:
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The catalytic effect of domain formation in the bulk and at interfaces (207, 180)
1,1,1,1,3,3,3-Hexafluoropropan-2-ol (HFIP) has recently become a very popular solvent or additive for a variety of chemical applications. It raised interest especially for the activation of hydrogen peroxide or in the organic electrosynthesis of phenol cross-coupling. Earlier epoxidation of olefins suggested the use of HFIP in combination with transition metals. However, recent work showed the electrophilic activation of H2O2 by HFIP without the use of transition metals, which led to the epoxidation of alkenes and the Baeyer-Villiger oxidation of ketones. In this context, it is interesting to note that HFIP-H2O mixtures are homogeneous at the macroscopic level, whereas current molecular dynamics simulations of olefins (nonpolar), aqueous H2O2 (polar) and HFIP (fluorus) suggest the formation of a microheterogeneous structure with triphilic character. The substrate is surrounded by the fluorous phase so that the H2O2 must pass through this domain to react with the unsaturated olefins. Hence, the reaction has to be described as a phase transfer or interfacial reaction rather than a homogeneous liquid phase process. In the case of phenol cross-coupling on boron-doped diamond anodes, the reaction is solvent-controlled via HFIP mixtures and governed by their specific microheterogeneous structure.
Keywords: Microheterogeneous structure, triphilicity, catalytically active domains -
Template effects in ionic liquids (188)
The template or structure-directing effect has been invoked several times for ionic liquids (ILs) to explain the different geometrical outcome of materials synthesized in these solvents. Thus, understanding and controlling the interactions and structural motives that lead to such effects could help to develop new strategies for the material synthesis in ionic liquids and related solvents.
By simulating simple model systems composed of [CxC1Im][NTf2] (x = 2,4,6,8) mixed with either n-butanol or n-dodecanol, we provide detailed molecular level insight and could reveal a strong connection to the complex microstructure being present in the IL itself: The ILs nanosegregation into polar and nonpolar phases, denoted as microheterogeneity, is accompanied by a distinct structural order, which is transferred to the alcohol molecules. This offers the possibility to access alternative reaction channels that would have not been accessible without the IL functioning as template.
Keywords: Ionic liquids, microheterogeneity, template effect
