Molten salt ionic phase

In this chapter we discuss preparative routes for inorganic materials in three basic types of systems involving the presence of a distinct solid-liquid interface those in which the liquid and solid phases are of the same chemical identity (solidification and vitrification processes), those in which the liquid and solid phases are not of the same chemical identity (crystallization, precipitation), and the special case in which the liquid phase is a pure ionic liquid or molten salt. Ionic liquids can serve as the solvent as well as a templating agent, and the liquid components may or may not become incorporated into the final solid product. We also discuss two areas where the distinct solid-liquid interface becomes somewhat blurred namely, sol-gel and solvothermal processes. 

The field of reaction chemistry in ionic liquids was initially confined to the use of chloroaluminate(III) ionic liquids. With the development of neutral ionic liquids in the mid-1990s, the range of reactions that can be performed has expanded rapidly. In this chapter, reactions in both chloroaluminate(III) ionic liquids and in similar Lewis acidic media are described. In addition, stoichiometric reactions, mostly in neutral ionic liquids, are discussed. Review articles by several authors are available, including Welton [1] (reaction chemistry in ionic liquids), Holbrey [2] (properties and phase behavior), Earle [3] (reaction chemistry in ionic liquids), Pagni [4] (reaction chemistry in molten salts), Rooney [5] (physical properties of ionic liquids), Seddon [6, 7] (chloroaluminate(III) ionic liquids and industrial applications), Wasserscheid [8] (catalysis in ionic liquids), Dupont [9] (catalysis in ionic liquids) and Sheldon [10] (catalysis in ionic liquids). 

Dupont, J., de Souza, R.F. and Suarez, P.A.Z. (2002) Ionic liquid (molten salt) phase organometallic catalysis. Chemical Reviews, 102 (10), 3667-3691. 

Although chemically similar, the inorganic and organic chloroaluminate molten salts or ionic liquids, as some prefer to call them, differ greatly with respect to their melting temperatures and physical properties. Figures 1 and 2 show the phase diagrams... 

One synthesis approach that does not rely on CNT formation from the gas phase is molten salt synthesis. The reactor consists of a vertically oriented quartz tube that contains two graphite electrodes (i.e. anode is also the crucible) and is filled with ionic salts (e.g. LiCl or LiBr). An external furnace keeps the temperature at around 600 °C, which leads to the melting of the salt. Upon applying an electric field the ions penetrate and exfoliate the graphite cathode, producing graphene-type sheets that wrap up into CNTs on the cathode surface. Subsequently, the reactor is allowed to cool down, washed with water, and nanocarbon materials are extracted with toluene [83]. This process typically yields 20-30 % MWCNTs of low purity. 

The reaction of l- -butyl-3-methylimidazolium chloride (BMIC) with sodium tet-rafluoroborate or sodium hexafluorophosphate produced the room temperature-, air-and water-stable molten salts (BMr)(BF4 ) and (BMTXPFg ), respectively in almost quantitative yield. The rhodium complexes RhCKPPhjls and (Rh(cod)2)(BF4 ) are completely soluble in these ionic liquids and they are able to catalyze the hydrogenation of cyclohexene at 10 atm and 25°C in a typical two-phase catalysis with turnovers up to 6000 (see fig. 6.10). 

Ionic liquids (continued) for Heck coupling, 1, 870 for homogeneous-multi-phase catalysis, 1, 856 for hydroformylations, 11, 450 for hydrogenations, 1, 857 for kinetic study monitoring, 1, 517 metalloorganic ILs, 1, 853 and molten salts, 1, 848... 

Excision reactions are sometimes accompanied by redox chemistry. For example, dissolution of the 2D solid Na4Zr6BeCli6 in acetonitrile in the presence of an alkylammonium chloride salt results in simultaneous reduction of the cluster cores (144). Here, the oxidation product remains unidentified, but is presumably the solvent itself. As a means of preventing such redox activity, Hughbanks (6) developed the use of some room temperature molten salts as excision media, specifically with application to centered zirconium-halide cluster phases. A number of these solids have been shown to dissolve in l-ethyl-2-methylimidazolium chloride-aluminum chloride ionic liquids, providing an efficient route to molecular clusters with a full compliments of terminal chloride ligands. Such molten salts are also well suited for electrochemical studies. 

Molten salt electrolyte systems comprise salts in the liquid state (molten), which form ionic phases and are highly ionically conductive, thus reaching specific conductivities comparable to those of room temperature concentrated aqueous solutions (0.1 < X < 10 Q -cur1) [160], These systems can be divided into two classes ... 

Electrode surface area — The area of the - interface between the ionically conducting phase (electrolyte solution, molten salt electrolyte etc.) and the electronically conducting phase (metal, semiconductor etc.) ... 

As Schmickler states [3], Electrochemistiy is the study of structures and processes at the interface between an electronic conductor (the electrode) and an ionic conductor (the electrolyte) or at the interface between two electrolytes . The electrode/electrolyte or electrolyte/electrolyte interface is the region whose properties differ from the two adjoining phases, and/or the place where reactant adsorption and electrochemical reactions occur. Commonly, it is recognized as the interface between an electronic conductor (e.g., metals and semiconductors) and an ionic conductor (e.g., electrolyte solutions, molten salts, and solid electrolytes), known as an electrochemical interface. In a narrow region of an electrode/electrolyte interface, an electrical double layer (EDL) exists. The EDL is believed to be extremely thin, and is an important component of the interface. 

Dupont, J., de Souza, R. F., Suarez, P. A. Z. Ionic Liquid (Molten Salt) Phase Organometallic Catalysis. Chem. Rev. 2002, 102, 3667-3691. Amatore, C., Bahsoun, A. A., Jutand, A., Meyer, G., Ntepe, A. N., Ricard, L. Mechanism of the Stille Reaction Catalyzed by Palladium Ligated to Arsine Ligand PhPdl(AsPh3)(DMF) Is the Species Reacting with Vinylstannane in DMF. J. Am. Chem. Soc. 2003,125,4212-4222. 

Ionic fluids such as molten salts and electrolyte solutions have always been of central interest in Chemical Physics, Physical Chemistry and many applied fields such as electrochemistry, chemical engineering or the geosciences. It is the aim of this review to connect the knowledge about structure and thermodynamic properties of ionic fluids and electrolyte solutions with that of the ILs. Liquid-liquid phase transition of ionic solutions are the main topic of this paper. 

Ionic liquid (molten salt)-phase organometallic catalysis 02CRV3667. 

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