Tetrachloroaluminate anion

Cumene (isopropylbenzene) is the major intermediate (10.6 Mt/a was the world capacity in 2004) for the manufacture of phenol. It is formed by alkylation of benzene with propylene according to Equation 6. Propylene is believed to react with hydrogen chloride forming the more stable secondary carbocation, which is associated with the tetrachloroaluminate anion. The ion pair reacts further with benzene to give the product. 

A further method for the synthesis of cyclic compounds in the phosphinic acid series, and investigated within the last decade, is the clearly not unrelated cheletropic reaction which takes place between alka-1,3-dienes and phosphenium salts. The latter are based on dicoordinate phosphorus, [R R P ], the commonly encountered counter ion being the tetrachloroaluminate anion. Such salts are obtained in situ through the interaction of AICI3 and a hosphorus(III) chloride R R PCl, for which R = Cl, R = R2N, or R = R =... 

The conclusion as to the preferability of the type XLIXa Tc-complex structure and its fluxionality, at which the calculations [137] arrived, has recently found a strong experimental support. X-ray structural data [142] have been obtained on the durene and hexamethylbenzene Tc-complexes, with nitrosonium cation counter-ioned by the tetrachloroaluminate-anion, showing close similarity to the gas-phase structure XLIXa. Both solution and solid-phase C-NMR spectra... 

The requirements of the counterions are also extreme. Large anions with relatively high inertness toward oxidation and with low basicity through coordination or dissociation to more basic fragments are the more appropriate for stabilizing naked cationic clusters. Best results have been obtained with the tetrachloroaluminate anion [AICI4] " which is normaly generated in situ from the metal halides and aluminum chloride used as solvents. 

It is assumed that NaAlCl4 is dissociated into sodium and tetrachloroaluminate ions. Torsi and Mamantov [35] have investigated a further dissociation of the tetrachloroaluminate ion in molten sodium chloroaluminates by potentiometric studies. For the 50 50 mol% composition of NaCl-AlCl3 the principal anion is A1C14. In acidic melts it was assumed that the reaction A1C13 + A1C14 <-> A12C17 is quantitative. More important is the con-... 

RTILs consist of large, unsymmetrical ions, such as 1,3-dialkyl-imidazolium, 1-alkylpyridinium, 1-alkylpyrazolium, tetralkylammonium or tetralkyl-phosphonium cations and tetrachloroaluminate, tetrafluoroborate, hexafluorophosphate, trifluoromethanesulfonate or bis((trifluoromethyl) sulfonyl)imide anions. 

Ionic hquids are low melting organic salts that are liquids at ambient temperature. They typically contain quaternary ammonium cations such as l-butyl-3-methylimida-zolium- or N-butylpyridinium- with inorganic anions, such as tetrachloroaluminate or tetrafluoroborate (Chauvin and Helene, 1995 Freemantle, 1998). Melting points for these materials can be near -100°C, and the liquids are often thermally stable at temperatures approaching 200°C. 

Pentathiazyl tetrachloroaluminate(l —) and, to a lesser extent, penta-thiazyl tetrachloroferrate(l —) are moisture-sensitive both are soluble in thionyl chloride, anhydrous formic acid, and concentrated sulfuric and nitric acids. On dissolution in acid, hydrogen chloride is evolved because of decomposition of the anion. The solution in anhydrous formic acid can be used to prepare other salts by metathesis.7 The hexachloroantimonate(l —) undergoes almost no reaction when exposed to water or moist air for 24 hr. 

Ethylammonium nitrate (entry 18 in Table 3-1) was shown in 1914 to have m.p. 12 °C and was hence the first room temperature ionic Hquid [156] this was followed in 1967 by tetra- -hexylammonium benzoate with m.p. —50 °C (entry 26) [169], Ambient-temperature ionic liquids based on l-alkyl-3-methylimidazolium salts (entries 19-24) were first reported by Wilkes et al. in 1982 as tetrachloroaluminates [162a], Replacement of this moisture-sensitive anion by the tetrafluoroborate ion and other anions led, in 1992, to air- and water-stable, room temperature ionic liquids [162b], which have since found increasing application as reaction media for various kinds of organic reactions, mainly owing to the work of Seddon [167, 190] and Hussey [187], Suitably selected... 

This method is not only limited to halide-based ionic liquids. Synthesis of ionic liquids containing a tetrafluoroborate anion and imidazolium cation has been performed successfully [16] by use of a modified domestic microwave oven with pulsed irradiation (5 x 30 s). Approximately 90% yields of the desired ionic liquids were usually obtained compared with 36% after the same reaction time using conventional heating. Microwave irradiation has been used in the synthesis of l-ethyl-3-methylimidazolium benzoate and dialkyl imidazolium tetrachloroaluminate ionic liquids [17, 18]. These reactions were again performed in a domestic microwave oven using pulsed irradiation. 

Force fields for [BMIM][PF6] that explicitly treat aU hydrogens (all-atom models) were developed soon after this by Margulis et al. [14], and Morrow and Maginn [11], while Stassen and coworkers [83] published a force field for the [EMIM]+ and [BMIM]+ cations paired with tetrachloroaluminate and tetrafluoroborate anions. The force fields aU have similar functional forms, and parameters were again maiiily developed using literature force field parameters for similar compounds and ab initio calculations of single ions or ion pairs. In these and later studies, repulsion-dispersion parameters were generally adapted from those available from one of three popular force field databases (Amber [114], OPLS [118] and CHARMM [119]). For [BMIM][PF6], the added realism of the all-atom model enabled densities to be predicted vyithin 1% of the experimental value [11]. The first indications of restricted dynamics in these systems were also observed [11,14,15]. 

The most reliable information on the structure of species of a new type is provided by X-ray analysis. It has so far been little applied to arenium ions. One of the few examples is the determination of the structural parameters of the tetrachloroaluminate of the heptamethylbenzenium ion . The anion of this salt is a nearly t ular tetrahedron with the Al—Cl bond equal to 2.12 A. Five sp -hybridized carbon atoms of the cation are lying in the same plane while the sp -hybridi2 d atom C, is deflected from it by 0.07 A (the angle between the planes Cj, C4, Cg and Cj, Ci, Cg is 5.4°). The mean values of the bond lengths (in A) are given in the following diagramme ... 

The anions of the MY type are involved in the formation of hydrogen bonds with the acidic hydrogens of the ammonium- and hydroxonium-type cations The interaction of anions with the cationic part of the arenium ion salts results in decreasing the anion symmetry to be recognized by the splitting of the AICI4 lines in the Raman spectrum of the mesitylenium tetrachloroaluminate. 

Common inoiganic anions (X ) are halide, tetrachloroaluminate (also tetra-chlorofenate and tetiachloioindate), tetrafluoioborate, hexafluoiophosphate, and bis(trifluoromethylsulfonyl)iniide, and common organic anions are derivatives of sulfate or sulfonate esters, trifluoroacetate, lactate, acetate, or dicyanamide. Substituents (R-groups) on the cation are usually alkyl chains, but can contain any of a variety of functional groups such as fluoroalkyl, alkenyl, methoxy, or hydroxyl [67-69], Some typical examples of common anions are BF , PFg, B(CN) , CH-... 

There has been a wide range of anions that have been used for the construction of ionic liquids. Historically, anions such as tetrachloroaluminate, which are highly reactive with water and other hydroxylic species, were involved for the construction of ionic hquids that were reasonably fluid at temperatures below 100°C. Unfortunately, tetrachloroaluminate is... 

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