Anion sources

The price of ionic liquids is determined by many parameters, such as personnel, overheads, and real production costs. One can imagine that production on a small scale would be mostly determined by the personnel cost and little by the material cost. On a large scale, the material cost should become more important and mainly determine the price of an ionic liquid. This means that the price of a large-scale commercial ionic liquid should be dictated by the price of the cation and anion source. 

This table illustrates pretty well that the large-scale ionic liquid will probably not comprise a diallcylimidazolium cation and a [CE3S02)2N] anion. Over a medium-term timescale, we would expect a range of ionic liquids to become commercially available for 25-50 per liter on a ton scale. Halogen-free systems made from cheap anion sources are expected to meet this target first. 

The synthesis of T8[OSiMe2H]8 was first reported by Hoebbel et al. from the reaction between TgLONMeJs and chlorodimethylsilane in dimethylformamide (DMF)/heptane (Table 18, entry 1). Other authors have modified the procedure by changing the solvents to tetrahydrofuran (THF) or hexane, or by using TslONMes (C2H40H)]g as the silicate anion source, but without significant improvement in the yield (Table 18). 

Similarly, reactions which are substantially enhanced by the use of PTC can be carried out even with reduced use of PTC with substantial enhanced rates of reaction as has been demonstrated by Sivakumar and Pandit (2000) in the case of conversion of benzamide to benzonitrile. In the case of A-alkylation of diphenylamine with benzyl bromide, in the presence of KOH as the anion source and PEG methyl ether as the PTC, some improvement in the rate has been observed. (Cains et al., 1998). Metal catalysed hydrogenations, such as those based on Ni, Pd/C, and Ru/C also benefit from ultra-sound. 

Anionic polymerization can be initiated by a variety of anionic sources such as metal alkoxides, aryls, and alkyls. Alkyllithium initiators are among the most useful, being employed commercially in the polymerization of 1,3-butadiene and isoprene, due to their solubility in hydrocarbon solvents. Initiation involves addition of alkyl anion to monomer... 

Strecker reactions provide one of the most efficient methods for the synthesis of a-amino nitriles, which are useful intermediates in the synthesis of amino acids and nitrogen-containing heterocycles. Although classical Strecker reactions have some limitations, use of trimethylsilyl cyanide (TMSCN) as a cyano anion source provides promising and safer routes to these compounds.133-351 Consequently, we focused our attention on tributyltin cyanide (Bu3SnCN), because Bu3SnCN is stable in water and is also a potential cyano anion source. Indeed, the Strecker-type reactions of aldehydes, amines, and Bu3SnCN proceeded smoothly in water (Eq. 9).1361 It should be noted that no surfactants are required in this reaction. Furthermore, Complete recovery of the toxic tin compounds is also possible in the form of bis(tributyltin) oxide after the reaction is over. Since conversion of bis(tributyltin) oxide to tributyltin cyanide is known in the literature, this procedure provides a solution to the problem associated with toxicity of tin compounds. 

Fluorosilylsubstituted aryl derivatives were found to be useful reagents for carbon-carbon bond formation via palladium-catalyzed cross-coupling with aryl halides in the presence of fluoride anions as Si—C bond activator in dimethylformamide (DMF), as well as rhodium-catalyzed 1,4-addition to a, 3-unsaturated ketones in the presence of a fluoride anion source (Equation 14.11) [66, 69, 70],... 

ILs can be immobilized on a functionalized support which contains one component of the IL or a precursor to such a component. The IL may be immobilized via the anion by treating a support with an anion source, e.g., an inorganic halide, before the IL is applied or formed. Alternatively, the IL may be immobilized by having the cation covalently bound to the support, e.g., through silyl groups, or incorporated in the support by synthesizing the support in the presence of a suitable base. The immobilized ILs are of use as catalysts, for example for the Friedel-Crafts reaction. 

The onium carbanion formed under phase-transfer conditions is unstable depending on the anion source, and in the absence of an electrophilic reaction partner, degradation of the accumulated onium carbanion in the organic phase may be observed. This is known to proceed via Hoffman elimination, nucleophilic substitution and/or Stevens rearrangement (Scheme 1.4) [4f,6,7]. The direct decomposition of onium salt, as influenced by the strong inorganic base at the interface, may be also operative. 

Asymmetric phase-transfer catalyzed oxidation of olefin using sodium hypochlorite or potassium permanganate as metal anion sources is the typical example of this category. 

Anions and anion sources Cations and cation sources... 

Another common strategy for addition of metal fragments to a cluster is the combination of a cluster anion source with an organometallic metal cation source. Numerous examples exist, several of which have already been mentioned in Section III,A. The addition of [R3PMX]A (M = Cu, Ag, Au) is perhaps one of the most common. Further examples are given in Eqs. (108)350 and (109).373 Equation (108) is interesting in that the reaction is a simple addition to form a weak adduct based on the Au --Au interactions. 

Figure 21-14. The mass spectrum of the cytidine parent anion which was brought into the gas phase by our pulsed infrared desorption/pulsed photoelectron emission anion source...

Tominaga and coworkers [82,83] reported a thiirane synthesis starting from 2-mercapto-l,3-thiazole derivative 180 bearing a trimethylsilyl group (Scheme 56). Treatment of 180 with CsF in acetonitrile and then with an aldehyde provided adducts 182 that fragmented via the spiro-isomer 183. Interestingly, the use of TASF as the fluorine anion source provided alcohols 185. The latter products were slowly transformed into the respective thiiranes 184 and thiazolidinone on storage (Table 9). 

It was also demonstrated that organosilylstannanes can be used as the trimethylsilyl anion source. In this case, the acid chlorides gave poor results and it was found that aryl iodides were suitable substrates. Reaction of buta-1,3-diene with Phi and BujSnSiMej gave the 1,4-carbosilylation product in 50% yield as an E/Z 84 16 mixture. The use of phenyl triflate as the aryl source did not give the desired 1,4-addition product but afforded the 2 1 telomerization product from two molecules of diene and one trimethylsilyl group, in good yield. 

Synthesis of trifluoromethylated compounds 152 has been achieved via ester-enolate [2,3]-Wittig and [3,3]-lreland-Claisen rearrangements. Perfluorocyclo-butane phosphonium ylides, e.g. 153, have been used as a masked fluoride anion source in their reactions with alcohols and carboxylic acids which lead to alkyl-and acyl-fluorides. Ylides 153 are also reported to cleave Si-C and Si-O bonds, cause dimerisation of fluoro-olefins, and also react with acid chlorides or other activated aromatic compounds under halogen exchange. ... 

Despite the mature nature of this field [22], Huang and Caulton [70] have also discovered some unusual chemistry of the trifluoromethyl group bound to a co-ordinatively unsaturated Ru(II) phosphine complex. As shown below, treatment of RuHF(CO)L2 (L=PlBu2Me) with the trifluormethyl anion source Me3SiCF3/ CsF affords a difluorocarbene complex by a-fluoro migration. 

In the presence of boron trifluoride etherate, 39 (R=H and Ar==C6H5) reacts smoothly with silyl enol ethers (the achiral anion source) at low temperatures ( — 80 to — 30 °C) to provide a chromatographically separable mixture of diastereomeric acids from which either 40 or 41 can be obtained in good yield. Oxidative decarboxylation of the chiral auxiliary with freshly crystallized lead tetraacetate occurs without racemization of the newly formed chiral center to provide either 42 or 43 with 98% ee. Noteworthy is the fact that if pure cis isomers are used, such as 39, they undergo facile isomerization to a 65 35 cis trans mixture at the low reaction... 

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