Ionic reactions organic halides

Acidic chloroaluminate ionic liquids have already been described as both solvents and catalysts for reactions conventionally catalyzed by AICI3, such as catalytic Friedel-Crafts alkylation [35] or stoichiometric Friedel-Crafts acylation [36], in Section 5.1. In a very similar manner, Lewis-acidic transition metal complexes can form complex anions by reaction with organic halide salts. Seddon and co-workers, for example, patented a Friedel-Crafts acylation process based on an acidic chloro-ferrate ionic liquid catalyst [37]. 

In some cases, the Q ions have such a low solubility in water that virtually all remain in the organic phase. ° In such cases, the exchange of ions (equilibrium 3) takes place across the interface. Still another mechanism the interfacial mechanism) can operate where OH extracts a proton from an organic substrate. In this mechanism, the OH ions remain in the aqueous phase and the substrate in the organic phase the deprotonation takes place at the interface. Thermal stability of the quaternary ammonium salt is a problem, limiting the use of some catalysts. The trialkylacyl ammonium halide 95 is thermally stable, however, even at high reaction temperatures." The use of molten quaternary ammonium salts as ionic reaction media for substitution reactions has also been reported. " " ... 

Every organic reaction can be classified into one of three, more or less exclusive categories—ionic, radical and pericyclic. Ionic reactions involve pairs of electrons moving in one direction. In a unimolecular reaction, like the ionization of a tertiary alkyl halide, the carbon-halogen bond cleaves with... 

This simple example may illustrate that in general the reaction of an organic halide salt [cation]X with an excess of a Lewis-acid MXy can result in new catalytic materials even if other Lewis-acids are applied than AICI3. In contrast, the use of other Lewis-acids to form the ionic liquid of type [cation][MXy+i] + excess MXy (the excess of MXy may be dissolved in the neutral ionic liquid or may form acidic anionic species such as e.g. [M2X2y+i]-) gives access to new combinations of properties (e.g. a liquid, less oxophilic, Lewis-acidic catalyst with defined solubility and acidity properties). In Table 2 other examples of ionic liquids are presented which are formed by the reaction of an organic halide salt with different Lewis-acids. All these systems should be in principle useful acidic catalysts for synthetic organic chemistry even if not all displayed examples have been already discribed in the literature for this application. 

However, the formation of Lewis-acidic ionic liquids is not restricted to those systems obtained by reaction of an organic halide salt with an excess of Lewis-acid. 

Bis(r 6-aryl) derivatives of molybdenum have been prepared by the co-condensation of the arene and molybdenum atoms at 77 K.305 Friedel-Crafts reactions catalysed by [(r 6-arene)Mo(CO)3] complexes have been developed further, and such reactions with organic halides shown to proceed via an ionic mechanism.306... 

Binary ionic or covalent hydride reduction of organic halides is important in organic syntheses . Reactions of metal hydrides with alkyl halides in ethers occur ... 

To ensure that reaction occurs in homogeneous solution, solvents are chosen that dissolve both the alkyl halide and the ionic salt. Alkyl halides are soluble in organic solvents, but the salts often are not. Inorganic salts are soluble in water, but alkyl halides are not. Mixed solvents such as ethanol-water mixtures that can dissolve enough of both the substrate and the nucleophile to give fairly concentrated solutions are frequently used. 

Ionic End Groups. Telechelics with quaternary ammonium end groups are prepared by quatemization of telechelic tertiary amines with organic halides (184). Unstable salts are formed by the reaction of living polymers with boron and aluminum alkyls. Only the triphenylboron derivatives are stable enough to be examined spectroscopically. 

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