Imidazoliums

The various fonns of betaines are very important for their charge control functions in diverse applications and include alkylbetaines, amidoalkylbetaines and heterocyclic betaines such as imidazolium betaines. Some surfactants can only be represented as resonance fonns having fonnal charge separation, although the actual atoms bearing the fonnal charge are not ftmctionally ionizable. Such species are mesoionic and an example of a trizaolium thiolate is illustrated in table C2.3.3. 

Given that the p/Ca of imidazolium ion is 7 is a 1 M aqueous solution of imidazolium chloride acidic basic or neutraP What about a 1 M solu tion of imidazole A solution containing equal molar quantities of imidazole and imidazolium chloride ... 

Substituted ammonium ions derived from nitrogen bases with names ending in -amine receive names formed by changing -amine into -ammonium. When known by a name not ending in -amine, the cation name is formed by adding the ending -ium to the name of the base (eliding the final vowel) e.g., anilinium, hydrazinium, imidazolium, acetonium, dioxanium. 

Neither pyrazoles nor pyrazolium salts react by this mechanism which has been described for imidazoles and imidazolium salts (Section 4.01.1.7.4). As exchange rates show (Section 4.04.2.1.7(iii)), it is considerably more difficult to generate an ylide from a pyrazolium salt than from an imidazolium salt (at C-2). 

Imid azolin-2-ones polymers, 1, 296 synthesis, 5, 466, 491 Imidazolium cations, 2-fluoro-nucleophilic substitution, 5, 413 Imidazolium chloride, 4-amino-l-methyl-2,3-diphenyl-... 

Dimroth rearrangement, 5, 438 Imidazolium chloride, 4-chloromethyl-reaction with poly(vinyl alcohol), 1, 306 Imidazolium chloride, 2,4,5-tri(diethylamino)-reduction, 5, 415 Imidazolium complexes, 7, 746... 

Imidazolium halides pyrolysis, 5, 449 Imidazolium ions acylation, 5, 402 H NMR, 5, 352 hydrogen exchange, 5, 417 nucleophilic attack, 5, 375 reactivity, 5, 375 ring opening, S, 375 Imidazolium oxides in pyrrole synthesis, 4, 344 Imidazolium perchlorate, 1,3-diphenyl-acylation, 5, 402 Imidazolium salts 1-acetyl-... 

Chichibabin reaction, 5, 409-410 UV spectra, 5, 356 Naphthimidazoles, 2-amino-tautomerism, 5, 368 Naphth[2,3-h]imidazoles oxidation, 5, 405 Naphth[l,2-d]imidazolium salts nucleophilic substitution, 5, 412 Naphth[l, 2-h]isoquinolines... 

The results supported the proposal of Glu-165 as the general base and suggested the novel possibility of neutral histidine acting as an acid, contrary to the expectation that His-95 was protonated [26,58]. The conclusion that the catalytic His-95 is neutral has been confinned by NMR spectroscopy [60]. The selection of neutral imidazole as the general acid catalyst has been discussed in terms of achieving a pX, balance with the weakly acidic intermediate. This avoids the thermodynamic trap that would result from a too stable enediol intermediate, produced by reaction with the more acidic imidazolium [58]. 

By using imidazole catalysis, it is possible to get a better understanding of the active forms that water takes in enzymatic processes Thus, at low concentrations m the presence of an enzyme, the water may not be fully hydrogen bonded and therefore more reactive [61] The rate of hydrolysis of p-nitrotrifluoroacetanilide in acetonitrile shows a strong dependence on water concentration at low levels in the presence of imidazole The imidazolium complex is the approximate transition state (equation 60)... 

Up to the present the principal interest in heteroaromatic tautomeric systems has been the determination of the position of equilibrium, although methods for studying fast proton-transfer reactions (e.g., fluorescence spectroscopy and proton resonance ) are now becoming available, and more interest is being shown in reactions of this type (see, e.g., references 21 and 22 and the references therein). Thus, the reactions of the imidazolium cation and imidazole with hydroxyl and hydrogen ions, respectively, have recently been demonstrated to be diffusion controlled. ... 

Tlie desulfurization of thiono compounds is another frequently used synthetic approach for the formation of double bonds via carbenoid intermediates. By this methodology, some indigoid 1,3,5,7-tetraazafulvalenes 88 and 90 were synthesized (83BSB781 90JPR949).Tliis dimerization starting from 2,4,5-tris(dimethylamino)imidazolium chloride via the appropriate thione 87 has been realized in the presence of phosphanes or phosphites to... 

One method to transform imidazolium salts (00AGE3773) into carbene ligands, imidazol-2-ylidenes, is by deprotonation with sodium hydride or other suitable hydride in a mixture of THE and liquid ammonia (73JCS(D)514, 96CEJ1627, 98IC6412). 

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