1- alkylpyridinium cation

Room-temperature ionic liquids, salts with V-alkylpyridinium cations in synthesis and catalysis 99CRV2071. 

A particularly interesting system for the epoxidation of propylene to propylene oxide, working under pseudo-heterogeneous conditions, was reported by Zuwei and coworkers [61]. The catalyst, which was based on the Venturello anion combined with long-chained alkylpyridinium cations, showed unique solubility properties. I11 the presence of hydrogen peroxide the catalyst was fully soluble in the solvent, a 4 3 mixture of toluene and tributyl phosphate, but when no more oxidant was left, the tungsten catalyst precipitated and could simply be removed from the... 

In recent years ionic liquids have also been employed as media for reactions catalyzed both by isolated enzymes and by whole cells, and excellent reviews on this topic are already available [47]. Biocatalysis has been mainly conducted in those room-temperature ionic liquids that are composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a noncoordinating anion [47aj. 

Solid state electrodes selective for alkylpyridinium cations are used to study the binding of these surfactants cations, with Cq 2> and alkyl chainlengths,... 

As mentioned earlier, much attention was being given to the formation of ion-radical conductors in the appropriate crystalline form. Meanwhile, Ziolkovskiy et al. (2004) reported data on high conductivity at 77-300 K of the methyl-TCNQ anion-radical salts with A-alkylpyridinium cations that keep their conductivity after crystallization from the melted forms. The melting temperatures of the salts described are rather low and the melting proceeds without salt destruction. This feature opens a possibility to create definite, much essential constructive elements directly from the liquid phase. Importantly, these salts also possess affinity to metals due to the metal-nitrogen coordina-tive ability. The authors notice that such ion-radical salts are promising for use in electronics and microelectronics. 

K. Hayakawa and J.C.T. Kwak Surfacatant-Polyelectrolyte Interactions. 4. Surfactant Chain Length Dependence on the Binding of Alkylpyridinium Cations to Dextran Sulfate. J. Phys. Chem. 88, 1930 (1984). 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

The alkylpyridinium cations suffer from being relatively easy to reduce, both chemically and electrochemically. Charles Hussey (Figure 1.3) and I set out a program to predict cations more resistant to reduction, to synthesize ionic liquids on the basis of those predictions, and to characterize them electrochemically for use as battery electrolytes. 

Biocatalysis in ionic liquids was first reported in 2000 [7, 8, 9]. The early work involved ionic liquids composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a weakly-coordinating anion (Figure 10.1). More recently, attention is shifting toward new structural types. A number of reviews of this rapidly expanding subject have appeared [10, 11, 12, 13, 14]. 

Bronich, T.K., Kabanov, A.V., Kabanov, V.A, Yu, K. and Eisenberg, A. (1997) Soluble complexes from poly(ethylene oxide)-block-polymethacrylate anions and N-alkylpyridinium cations. Macromolecules, 30, 3519-3525. 

The specific proposal is that the hydroxide attacks the 2- or the 4-position of the co-ordinated pyridine to form a hydroxy-substituted 1,2- or 1,4-dihydropyridine (Fig. 8-17). These hydroxy species are known as pseudo-bases. This behaviour is fully in accord with the known behaviour of A-alkylpyridinium cations. Although the pseudo-bases of simple A-alkylpyridinium cations are not dominant solution species under aqueous conditions, those derived from a variety of other nitrogen heterocycles are readily formed and are well-known. The suggestions had the advantage of linking the apparently divergent fields of heterocyclic and co-ordination chemistry by explaining some well-documented anomalies in the reactivity of pyridine complexes. 

Pyridinium hydrobromide perbromide salt was introduced by Djerassi and Scholz as an alternative brominating agent to bromine in 1948. Salazar and Dorta rationalized that since alkylpyridinium salts are well documented and commercially available room temperature ionic liquids, a combination of an alkylpyridinium cation with tribromide anion 1 should therefore lead to a room temperature ionic liquid bromine analogue (Equation 1). 

Alkylpyridinium cations. 1-Methylpyridinium ions 201 react reversibly with hydroxide to form a small proportion of the pseudo-base 202. The term pseudo is used to designate bases that react with acids measurably slowly, not instantaneously as for normal acidbase reactions. Fused benzene rings reduce the loss of resonance energy when the hetero ring loses its aromaticity and hence pseudo-bases are formed somewhat more readily by 1-methylquinolinium, 2-methylisoquinolinium, and 10-methylphenanthridinium, and much more readily by 10-methylacridinium ions. Pseudo-bases carrying the hydroxy group in the -position are usually formed preferentially, but acridinium ions react at the -position. 

Neve and co-workers have also made use of hydrogen-bonded perhalometallate ions, but in this case using salts mononuclear ions hnked by weak charge-assisted C-H---X(M) hydrogen bonds from alkylpyridinium cations [128]. The use of cations with long-chain alkyl substituents leads to hquid crystalline behaviour in these salts [128a-c]. 

Malovikova A, Hayakawa K, Kwak JCT. Binding of alkylpyridinium cations by anionic polysaccharides. ACS Symposium Series 1984 253 225-239. 

The mechanism suggested on the basis of H NMR and ESR studies of the reaction mixtures and kinetic measurements involves the formation of intermediate radical species 6 (Scheme 7). The reaction is very fast in comparison with dequaternization of A -alkylpyridinium cations. Indeed, the observed pseudo-first-order rate constants iobs. for dequaternization of a number of l-alkyl-l,2,4-triazinium salts proved to be approximately 10 s at 25 °C, while A -alkylpyridinium salts are dequaternized much more slowly (iobs. = 10 s at 100 °C) <1995MC104>. 

Other polymerization processes. Polyisobutene, traditionally prepared by the Cosden process, is a valuable lubricant, and also a route to higher value-added materials. In general it was observed that the catalytic activity of the ionic liquids increases towards higher degrees of polymerization from short-chain ohgomers as the alkylchain length of the l-alkyl-3-methylimidazohum or N-alkylpyridinium cation is increased. ... 

DAG-lactones containing 4-alkylpyridinium cations in the alpha-arylidene position Evaluation of their interaction with protein kinase C (PKC) and membranes... 

Alkylpyridinium cations can be used instead of akylammonium for the fabrication of LB films. For example, docosyl- and tetradecylpyridinium[Ni(dmit)2] (abbreviated as C22PyNi(dmit)2 and Ci4PyNi(dmit)2, respectively) LB films mixed 1 1 with arachidic acid showed conductivities of 0.3 and 1.2 S/cm after electrochemical oxidation [203]. 

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