2- Phenylbenzimidazole

Phenylbenzimidazole is nitrated first at the 5-position with mixed acid, and subsequent reaction produces 5-nitro-2-(4-nitrophenyl)-and 5-nitro-2-(3-nitrophenyl)-benzimidazole. 2-Phenyl-, 2-(4-nitro-phenyl)- and 5-nitro-2-phenyl-benzimidazole are nitrated as their conjugate acids. ... 

The photoaddition reaction of 2-phenylbenzimidazole with Michael acceptors was investigated <96JHC1031> as was the preparation and cycloaddition-reactivity of benzimidazole-2-carbonitrile oxide <96AJC199>. The nitration of 1-methylbenzimidazole was found to give only the 5- and 6-nitrated products as a mixture of isomers in 87% yield... 

The effectiveness of various chemicals such as IH-benzotriazole, 2-methyl-benzotriazole, and 2-phenylbenzimidazole as a corrosion inhibitor for mild steel in 15% HCl was investigated by weight loss and electrochemical techniques [1547]. Among different azoles, 2-phenylbenzimidazole has shown the best performance. A synergism of iodide and 2-phenylbenzimidazole was observed. 

Figure 11-1. Corrosion inhibitors 2-phenylbenzimidazole, 2-methylbenzotri-azole, benzotriazole, and 1,3-dimethyi-2-thiourea.

Very recently, Shinde and colleagues have prepared the interesting amide coupling reagent diethyl 2-phenylbenzimidazol-l-yl phosphonate 110 and demonstrated that it is an efficient reagent for the preparation of 0-alkyl hydroxamic acids too (Scheme 57) ". The 0-alkyl hydroxamic acids of V-protected amino acids were also synthesized. 

The product of reaction between 2,3-diphenylquinoxaline and potassium amide has now been assigned as 2-phenylbenzimidazole,133 rather than 2,2-diphenyl-3-amino-l,2-dihydroquinoxaline, as suggested earlier. 

Selective polarographic reduction of a-C-F bonds in 2,2,2-trifluoro-l-phenylethanone is performed under high pH, while in acidic media the compound is reduced without loss of fluorine to the alcohol and the corresponding pinacol.98 l,2-Dimethyl-2-phenylbenzimidazole, which is a novel and efficient reducing agent, transforms 2,2,2-trifluoro-l-phenylethanone(8) effectively into acetophenone with high yield.99... 

According to the data obtained, such a reaction either does not proceed at all [4] or yields the corresponding f3-amino adduct 2 or 2-phenylbenzimidazole 4 [2], depending on the reaction conditions. These results were treated as a general feature of the interaction between 0-PDA and chalcones [2]. The impossibility of the formation of aromatic dihydrobenzodiazepine derivatives was explained by the essentially lower reactivity of the carbonyl group in chalcone molecules in comparison with that of the C = C bond. 

As noted already, the reactions of oc,(3-unsaturated ketones with or /zo-diamines are often accompanied by various rearrangements and side processes. For instance, the o-PDA condensation with chalcone in the presence of an acid catalyst or during overheating of the reaction mixture produces a final product of 2-phenylbenzimidazole [2, 7] a similar phenomenon is also observed for 2,3-diaminopyridine [54]. Owing to the existence of much more suitable approaches to the synthesis of 2-aryl derivatives of benzimidazole and their heteroannelated analogues (e.g., proceeding from diamines and acids or aldehydes [121]), such a trend in the interaction of chalcones with diamines is unlikely to have any application for this purpose. 

In the case of benzimidazole itself, nitration usually occurs at the 5-position (80MI1). Sterba and co-workers have studied the nitration of some arylbenzimidazoles and have showed that 2-phenyl benzimidazole, when treated with nitric acid sulfuric acid at 10°C, gives 6-nitro-2-phenyl-benzimidazole (75%). The 2-(3-nitrophenyl) and 2-(4-nitro phenyl) benzimidazoles similarly yield the 6-nitro products (57 and 97% respectively), and nitration of 6-nitro-2-phenylbenzimidazole gives the 2-(4-nitrophenyl) and 2-(3-nitrophenyl) products in 44% and 32.5% yields, respectively (65CCC1093). 

It has been noted that in the nitration of 2-phenylbenzimidazole, the rate of nitration into the benzimidazole 5 position is about three orders of magnitude higher than that of the phenyl ring [51]. 

An interesting reaction has been described by Simonov and his colleagues [371], Studying the reaction of some aromatic rnt/zo-dinitro- and trinitrocompounds with benzylamine they have discovered that under special conditions the reaction of substitution of the nitro group with the benzylamine group is accompanied by reduction of the second nitro group and cyclization into 2-phenylbenzimidazole derivatives. In this case benzyl alcohol forming from benzylamine serves as a reducer. By the way it was obtained 4,5-dimethoxy-7-nitro-2-phenylbenzimidazole in 89% yield from 3,4,5-trinitroveratrole [371],... 

The mass spectra of nitro derivatives of 2-phenylbenzimidazoles show the dissociative ionization to be characterized by two trends involving the formation of [M-NO]+ and [M-N02]+ ions (Scheme 3.72) [1342] ... 

Treatment of 211 (R = CH3) with a catalytic amount of sodium 2-ethoxyethoxide gave 22 9 223 while 211 (R = C6H5) also gave 229.228 Acid hydrolysis of 211 (R = CH3 or C6H5) gave acetone and 2-methyl-benzimidazole or acetophenone and 2-phenylbenzimidazole.223 A... 

The reductive cyclization of o-benzoquinonedibenzimide (5) with triphenylphosphine gives l-benzoyl-2-phenylbenzimidazole, perhaps by the mechanism outlined in Scheme 3 (74CRV279). 

Above 170 °C the amidrazone ylide (36) decomposes with loss of triethylamine and concurrent cyclization to give an 85% yield of 2-phenylbenzimidazole (Scheme 19) (B-75M140800). Poorer yields ( 40%) are obtained when N-benzyl-o-nitroaniline is pyrolyzed in the presence of iron oxalate. No doubt this last reaction is similar in many respects to the reactions shown in Scheme 2. Both 2-phenyl-imidazoles and -benzimidazoles (as well as other 2-substituted analogues) can be obtained as a result of thermal rearrangement of the 1-substituted isomers (Section 4.07.1.2.2), by radical substitution methods (Section 4.07.1.7) or via the 2-lithio derivatives (Sections 4.07.1.6, 4.07.3.7). 

A) 2-phenylbenzimidazole-5-sulfonic acid 3% (Eusolex 232), (A) hydroxypropyl-y-cyclodextrin 2%. Source From Ref. 45. 

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