Benzimidazoles confirmation

Only one example in this category has been described in recent years (as of 2003). Treatment of o-phenylenediamine (396) with 3,4,5,6-tetrachloropyridazine (397) in A-methylpyrrolidine at 115°C for 17 h gave a separable mixture of products, one of which was 2,3-bis(benzimidazol-2-yl)quinoxaline (398) (unstated yield). The structure (398) was confirmed by X-ray analysis,and a mechanism for its formation was suggested. ... 

RT Wilson, JM Groneck, AC Henry, LR Rowe. Multiresidue assay for benzimidazole anthelmintics by liquid chromatography and confirmation by gas chromatography/selected-ion monitoring electron impact mass spectrometry. J Assoc Off Anal Chem 74 56-57, 1991. 

Mechanism of the nitration of benzimidazoles has not been studied much, but there are weighty arguments to conclude that they are nitrated as conjugated acids [51, 103], Kinetic studies of the nitration of benzimidazole and some of its 2-substituted derivatives have confirmed that the protonated form is involved in the process [104], Recent results of quantum chemical studies of the nitration of ben-zazoles indicate the importance of the protonated benzimidazolium cations in the nitration process [43],... 

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). 

In similar experimental conditions, some examples of l-alkyl-4-azoliden-l,4-dihydropyridines 12 were measured, the values of which ranged between 9 and 9.7 D. This implies a considerable separation of charges in the ground state, and also a dipolar nature, which was confirmed by X-ray diffraction analysis of 4-(benzimidazol-2-iden)-l-methyl-l,4-dihydropyridine 118 (11I,C). 

Acceptably stable metal complexes also may be prepared, such as the cobalt-cthy-Icnediamine product 156. The reaction on benzimidazole derivatives affording seven-membered rings (158) confirms the tendency to produce cycles larger than the pentaatomic ones, as a molecule containing two fused fivc-membered rings would in principle be expected from this type of substrate (see also the derivatives 130,131,140, 149 described above). 

While the rr-densities predict greater reactivity to electrophilic attack at C-2 in the imidazole anion, localization energies suggest an order of reactivity of C-4 > C-2. Use of the CNDO/2 method predicts the order of electrophilic substitution in benzimidazole to be5= 7>6>4>2, whereas the observed order (for aqueous bromination) is 5>7>6,4,2 (78JCS(P2)865). Predictions of preferential nucleophilic attack at C-2 are confirmed by experiment. Table 2 lists rr-electron densities in benzimidazole. 

Gulland and coworkers recently confirmed the finding that the sugar component of the four mononucleotides of yeast pentosenucleic acid is D-ribose through the isolation of D-ribonic benzimidazole and they also reported that a small amount of L-lyxonic benzimidazole was detected how this latter result is to be interpreted is not yet clear. 

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