Imidazolium betaines

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. 

With isothiocyanates, 57 generally yields the isothiazolium betaines 66 (Scheme 18). However, when R is bulky an equilibrium exists with the carbodiimide 67, which gives the imidazolium betaine 68 on heating for R = /Pr or spontaneously for R = Ph. Alternative mechanisms have been discussed. 

Amine oxide zwitterionics are not strongly DR effective. At low temperatures oleyl dihydroxyethyl amine oxide (OHAO) shows weak drag reduction from 5 to 15°C. At high temperatures, behenyl dihydroxyethylamine oxide (BMAO) is weakly DR from 60 to 80°C. However, when 2-lauryl carboxymethyl hydroxyethyl imidazolium betaine was added to OHAO at a ratio of 1 to 1.5, at 15°C DR was increased from 55% to 70%. The surfactant also increased drag reduction from 10% to 88% at 80°C when added to BMAO [Nobuchika et al., 2000]. 

Diphenyl-imidazolium-perchlorat addiert in Gegenwart von Kalium-tert.-butanolat Phe-nylisothiocyanat zum Betain I (49%), das durch Iodmethan zum 1,3-Diphenyl-2-[methylthio-phenylimino-methyl -imidazolium-iodid (II) methyliert wird696. 

Heterocyclic Betaines Pyridinium (Imidazolium) Azolate Inner Salts with Several Interannular Linkages ... 

B. Pyridinium (Imidazolium) Azolate Betaines from Azolylpyridinium... 

Methods of synthesis leading to pyridinium (imidazolium) azolate inner salts and related compounds with a betaine character 1 can be varied. In almost all cases, their protonated compounds azolylpyridinium (imidazolium) salts with several interannular linkages 2 are useful as synthetic intermediates (Scheme 1). These quaternary salts of nitrogen heteroaromatic compounds 2 allow us to deepen the study of classical reactions and seek suitable alternatives for their preparation. 

PVRIDINIUM (IMIDAZOLIUM) AzOLATE BETAINES AND COMPOUNDS WITH A BeTAINE Character 10-27 Obtained from the Corresponding Quaternary Heteroaromatic Salts 29-40... 

Pyridinium(imidazolium) inner azolate salts and molecules with a betaine character of general type 1 are attractive substrates from the viewpoint of structural chemistry, as mentioned in the Introduction. This ensemble of compounds offers the possibility of two terminal heterocyclic rings, joined through several spacers, with extreme characteristics within heteroaromatic systems a 7r-deficient nucleus (cation) and a 7r-excessive nucleus (anion). The high dipolar character is the distinctive feature offered by these compounds and has a powerful influence on their physical and chemical properties. 

The reported IR spectra were recorded for solid samples of compound pairs 1 and 2. The azolylpyridinium(imidazolium) salts with several inter-annular linkages 2 have shown absorptions in the ranges 3500-3200 cm (r-NH) and 2800-2490 cm" (hydrochlorides) or 1100-1000 cm" (tetraflu-oroborates). These bands were absent for the corresponding inner salts and compounds with a betaine character 1. Practically all reported information concerning IR spectra and elemental analysis are included in the references quoted in Tables II to V (II,A and II,B). 

Scheme 5. ASH Observed proton chemical shift difference (ppm DMSO-rf ) between selected examples of betaines of type (10) (i.e., 55), (11), (22), (23), (25) and (27), and their corresponding precursors the benzimida-zolylpyridinium (imidazolium) salts of type (29) (i.e., 54), (30), (41), (42), (44), and (46) (87JOC5009 91JOC4223 92CL2357, 92JOC4829, 92MI3, 92UP1).

Measurement of the dipolar moments of the mesomeric betaines of azolium azolate 11 was extremely difficult. Of the various assays performed (extreme dilution, dioxane, 25°C), the best measurements were chosen. However, these quasi coplanar structures are highly associated when ti> > 0.0003, and the effect of self-association could not be eliminated completely. For example, for 2-(3-methyl-l-imidazolium)benzimidazolate 117 the was 11.35 D and the antiparallel orientation of 117 was confirmed by X-ray diffraction analysis (III,C). 

The chemistry of transition metal carbene complexes with NHC derived from purines or xanthines has its roots in the synthesis of xanthinium betaines [75], the xanthine analogues of imidazolium salts. The synthesis is sttaightforward and involves the methylation of the xanthine with methyl tosylate (see Figure 6.32). 

Reactive betaine intermediates are almost certainly involved in many reactions of imidazoles, e.g. base catalyzed deuterium exchange, acylation at C-2, etc. Begtrup (B-76MI40600, p. 143) has implicated betaines in his studies of the nucleophilic hydroxylation of triazolium salts, and one might expect an extension of these researches into the imidazolium series. 

New types of cross-conjugated, heterocyclic betaines such as 7-oxido-l-methyl-5-oxo-6-phenyl-pyrrolo[l,2-fl]imidazolium (53) have been obtained by reaction of 7V-methylimidazole with chloro-carbonylphenylketene in THF at room temperature in presence of triethylamine (Scheme 7)... 

Synonyms Cocoamphoacetate Cocoamphoglycinate Cocoimidazoline betaine Coconut imidazoline betaine Imidazolium compds., 1-(carboxymethyl)-4,5-dihydro-1-(hydroxyethyl)-2-norcoco alkyl, hydroxides, inner salts Classification Amphoteric organic compd. 

Ylides derived from imidazolium- and triazolium-substituted indole anions belong to the class of conjugated mesomeric betaines. Their tautomers are N-heterocyclic carbenes, which undergo trapping reactions with sulfur, selenium, and triethylborane, respectively. Deprotonation of the salts 45a—c with NaOH/EtOH produces the ylides 46a—c which are in tautomeric equihbrium with carbenes 47a—c (Scheme 36) (2014T8672). 

Several photophysical and ultrafast spectroscopic studies were undertaken in these RTILs [20-69]. Aki et al. [20] determined the polarity of the imidazolium-andpyiidinium-based RTILs using UV-Vis absorption and fluorescence spectroscopy. Muldoon et al. [21] determined the polarity of the RTILs using solvato-chromic probes. Carmichael et al. [22] determined the polarity of several neat l-aIkyl-3-methylimidazolium-based RTILs using the solvatochromic dye Nile red. Using Prodan, pyrene, 1-pyrenecarboxaldehyde, Reichardt s betain dye, and Rhodamine 6G as the solvatochromic probes various bulk properties and polarity of various RTILs-cosolvents mixtures were determined [23-26]. Recently, one excellent review article was published by Reichardt to determine the polarity of RTILs by means of solvatochromic betaine dyes [27]. Femtosecond optical Kerr effect... 

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