Downs process ionic liquids

Since the Petasis boronic-Michael reaction generally requires prolonged stirring at room temperature for 24 h or more, some studies have been devoted to acceleration of this process. Ionic liquids have been shown to be convenient solvents, shortening the reaction times down to 3-4 h at room temperature [19].The recovered ionic liquid was re-used up to five times without loss of activity. In some cases, microwave activation has been shown to achieve acceptable conversion within short reaction times [20]. 

Alkali metals are produced commercially by reduction of their chloride salts, although the exact procedure differs for each element. Both lithium metal and sodium metal are produced by electrolysis, a process in which an electric current is passed through the molten salt. The details of the process won t be discussed until Sections 18.11 and 18.12, but the fundamental idea is simply to use electrical energy to break down an ionic compound into its elements. A high reaction temperature is necessary to keep the salt liquid. 

The ionic liquid can, for example, be added to the butene effluent from the Dimersol process to obtain octenes by butene dimerization the octene can be carbonylated (Section 4.6) and hydrogenated to wo-nonanol, used to make phthalate plasticizers. In the case of the Phillips trimerization process the use of an ionic liquid allows an easy separation of the trimers and the catalyst for recycling (see also reviews to Section 5.5). However, the industrial use as solvents of ionic liquids, containing halide species (especially anions such as Bp4, PFg, or AlCU ) has the disadvantage that they readily break down to give HX, which can adversely affect the reaction. New types of non-halide containing ionic liquids are being actively researched. 

Self-diffusion coefficients were measured with the NMR spin-echo method and mutual diffusion coefficients by digital image holography. As can be seen from Figure 4.4-3, the diffusion coefficients show the whole bandwidth of diffusion coefficient values, from 10-9 m2s-1 on the methanol-rich side, down to 10 11 m s 1 on the [BMIM][PF6]-rich side. The concentration dependence of the diffusion coefficients on the methanol-rich side is extreme, and shows that special care and attention should be paid in the dimensioning of chemical processes with ionic liquids. 

In order to generalize the definition of the solvent system for the case of ionic media, we shall analyse Franklin s definition. First, it should be noted that the term auto-ionization in this definition should be substituted by auto-dissociation or intrinsic acid-base equilibrium of the solvent , as a more common case of heterolytic break down of the constituent particles of a liquid. Indeed, for molecular solvents or those which are slightly ionized at room temperature, the terms autoionization and intrinsic acid-base equilibrium of the solvent , relate to the same process, whereas for ionic liquids they differ considerably. For example, although sodium nitrate (NaNOs) is subject to practically... 

The use of ionic liquids (also called molten or fused salts) as reaction media is a relatively new area, although molten conditions have been well established in industrial processes (e.g. the Downs process. Figure 10.1) for many years. While some molten salts are hot as the term suggests, others operate at ambient temperatures and the term ionic Uquids is more appropriate. This section provides only a brief introduction to an area which has implications for green chemistry (see Box 8.3). 

Fig. 9-6 Generic flow chart for the ionic liquid-based process. The ionic liquid is acting as an extractant, washing down compound B. Compound A is released and can be distilled as a pure compound at the head of the column. B is removed at the bottom. The ionic liquid is recycled into the process after having removed residual B in a falling film evaporator.

Liquid membranes are ideally suited for this application since they have the potential for removing toxic suhiLances from wastewater down to vety low levels. Both molecular and ionic species (anions, cations, and complex ions) have bean extracted successfully by property constituted liquid membranes. A perlial list of processes reported prior to 1978 is given in Table 19.4-1. These heve all been reviewed.2 3 Recent improvements in thase separations as well as new methods reportnd recently are summerlzed in this section. 

These have the advantage of high membrane flux, which results from the very small thickness of the organic membrane. However, there are a number of operational difficulties. The first of these concerns the osmotic transport of water across the membrane as a result of different ionic concentrations in the two aqueous phases. This causes the membrane drops to swell and ultimately to break down, mixing the strip and feed solutions. Another difficulty arises with the ultimate breaking of the emulsion and separation of the two phases that can give rise to entrainment problems. In addition, the overall process is much more complex than that of the supported liquid membrane. 

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