Pyridinium chloroaluminate

Carbonylation of satarated hydrocarbons to oxygenated hydrocarbons is difficult due to the high stability of C—H or C—C bonds. Superadds, which are generally corrosive and volatile, are often used. Imidazohum or pyridinium chloroaluminates have proven to be suitable catalysts [47]. Alkylaromatic compounds (e.g., toluene or xylene) can also react with carbon monoxide in the presence of an acidic chloroaluminate IL to form an alkyl aromatic aldehyde [48]. 

The pyridinium- and the imidazolium-based chloroaluminate ionic liquids share the disadvantage of being reactive with water. In 1990, Mike Zaworotko (Eigure 1.4) took a sabbatical leave at the Air Eorce Academy, where he introduced a new dimension to the growing field of ionic liquid solvents and electrolytes. 

In an attempt to study the behavior and chemistry of coal in ionic liquids, 1,2-diphenylethane was chosen as a model compound and its reaction in acidic pyri-dinium chloroaluminate(III) melts ([PyHjCl/AlCb was investigated [69]. At 40 °C, 1,2-diphenylethane undergoes a series of alkylation and dealkylation reactions to give a mixture of products. Some of the products are shown in Scheme 5.1-40. Newman also investigated the reactions of 1,2-diphenylethane with acylating agents such as acetyl chloride or acetic anhydride in the pyridinium ionic liquid [70] and with alcohols such as isopropanol [71]. 

The use of acidic chloroaluminates as alternative liquid acid catalysts for the allcy-lation of light olefins with isobutane, for the production of high octane number gasoline blending components, is also a challenge. This reaction has been performed in a continuous flow pilot plant operation at IFP [44] in a reactor vessel similar to that used for dimerization. The feed, a mixture of olefin and isobutane, is pumped continuously into the well stirred reactor containing the ionic liquid catalyst. In the case of ethene, which is less reactive than butene, [pyridinium]Cl/AlCl3 (1 2 molar ratio) ionic liquid proved to be the best candidate (Table 5.3-4). 

So far the historical development of ionic liquids has mainly been driven by combining imidazolium, pyridinium, ammonium and phosphonium cations with different classes of anions. Chloroaluminate ionic liquids were the first more detailed studied ionic liquids. As early as 1948 they were synthesized by Hurley and Wier at the Rice Institute in Texas as bath solutions for electroplating aluminum [1], Later in the seventies and eighties, these systems were further developed by the groups of Osteryoung [2], Wilkes [3], Hussey [4] and Seddon [4c, 5], Due to their chemical nature, chloroaluminate ionic liquids must be classified as extremely hygroscopic and labile towards hydrolysis. 

Separation science focuses on room temperature ionic liquids (RTlLs), salts that are liquid at ambient temperature. They have been studied as extracting solvents, stationary and mobile phases, mobile phase additives, and other uses. Common RTILs consist of a bulky nitrogen- or phosphorus-containing organic cation (pyridinium or pyrrolidinium, alkyl-imidazolium, ammonium or phosphonium) and a variety of organic and inorganic anions (triflate, dicyanamide, trifluoroacetate, acetate trifluo-romethylsulfate, nitrate, perchlorate, bromide, chloride, chloroaluminate, tetrafluo-roborate, hexafluorophosphate). 

In bmim BF4 and CIO4 l-butyl-3-methylimidazolium tetrafluoroborate and perchlorate Fischer, T. Sethi, A. Welton, T. Woolf, J. Tetrahedron Lett. 1999, 40, 793. In chloroaluminates Lee, C.W. Tetrahedron Lett 1999, 40, 2461. In phosphonium tosylates Ludley, P Karodia, N. Tetrahedron Lett. 2001, 42, 2011. In pyridinium salts Xiao, Y MaUiotra, S.V. Tetrahedron Lett. 2004, 45, 8339. In HBuIm, hydrogenbutylimidazolium tetrafluoroborate and DiBuIm, 1,3-dibutylimidazolium, tetrafluoroborate Jaegar, D. A. Tucker, C. E. Tetrahedron Lett. 1989, 30, 1785. 

Abstract Room temperature ionic liquids (ILs) have attracted considerable attention as novel reaction media over the last decade. By virtue of their unique properties, ILs have been proposed as alternative solvents. Structurally, most of the ILs that have been investigated to date are based on imidazolium, pyridinium and ammonium cations, associated with polyatomic anions such as chloroaluminates, tetrafluoroborate, hexafluorophoshate and bis-triflimide. Although these salts have positive properties, imidazole, pyridine and halogenoalkanes come from petroleum feedstocks that are neither green nor sustainable. Renewable resources may represent a valid alternative to synthesized new ILs an alternative able to take into accounts both the ecological and economic requirements. 

The room-temperature chloroaluminate(lll) ionic liquids are the most important members of the first generation of ionic liquids, developed in the second half of the last century The room-temperature halogenoaluminate(III) ionic liquids are extremely sensitive to moisture and must be handled imder an inert atmosphere. Preparation of the halogcno-aluminate(III) ionic liquids is simple a quaternary ammonium (QUAT) halide, e.g. an imidazolium or pyridinium halide, is directly mixed with AICI3 in the ratio necessary to generate the composition required. Upon mixing, an exothermic reaction occurs and the two solids melt into a liquid. The first report on the formation of a room temperature liquid salt, based on the combination of 1-butylpyridinium with AICI3 in the relative molar proportions 1 2 (X =... 

The details of two related patents for the alkylation of aromatic compounds with chloroaluminate(iii) or chlorogallate(iii) ionic liquid catalysts have become available. The first by Seddon and coworkers [35] describes the reaction of ethylene with benzene to give ethylbenzene (Scheme 5.2-8). This is carried out in an acidic ionic liquid based on an imidazolium cation and is claimed for ammonium, phosphonium and pyridinium cations. The anion exemplified in the patent is a chloroaluminate(iii) and the claim includes for chlorogallate(iii) anions and various mixtures of anions. 

Johnson and coworkers investigated the cracking and isomerization of various alkanes such as nonane, tetradecane and 2-methylpentane in acidic pyridinium chloride-aluminum chloride ionic liquids. Similar product types to the cracking of hexane (above) were observed and after 15 days some polymerization of the cracked products had occurred [91]. A similar reaction occurs vyith fatty acids (such as stearic acid) or methyl stearate, which undergo isomerization, cracking, dimerization, and oligomerization reactions. This has been used to convert solid stearic acid into the more valuable liquid isostearic acid [92] (Scheme 5.2-41). The isomerization and dimerization of oleic acid and methyl oleate have also been found to occur in chloroaluminate(iii) ionic liquids [93]. 

There followed research into pyridinium and imidazolium chloroaluminate ionic liquids by Hussey, Seddon and Welton (investigation of transition metal complexes... 

Historically, ionic liquids initial advances in electrochemistry were encouraged by difficulties and safety issues in the aluminum deposition process known as SIGAL (Siemens Galvano-Aluminium). Major concerns were related with the flammability of the aluminum precursors and of the volatile organic solvents used. In the search for low melting, nonvolatile, and nonaqueous electrolytes, pyridinium [25] and imidazolium chloroaluminates (III) were investigated [26]. These ionic liquids are able to dissolve various metal salts. Their biocompatibility is questionable due to their potential toxicity and because they are also corrosive and unstable in air and/or... 

Ionic liquids based on chloroaluminates (the most common form of Lewis acidic or basic ionic liquids) are formed by reacting a quaternary ammonium chloride salt [QAm]" with aluminium chloride (AICI3) in various ratios [94]. Common examples are l-ethyl-3-methyl imidazoUum chloride ([EMIm]Cl) and l-(l-butyl)pyridinium chloride ([BuPy]Cl) [95]. A Lewis base, neutral species or acid is formed by varying the ratio of the two components of the ionic liquid. Using the letter N to represent the mole fraction of AICI3 in the melt [96], the following classification is given for these ionic liquids ... 

---