M.p. of 2-methyl-5-nitro-1H-benzimidazole formed on nitration of 2-methyl-1H-benzimidazole is 219 0C, and it is described in 1905 (Ber. vol 36, p 3690). Or I do not understand is this compound that You want to obtain or You have got a mixture of another compound. Tel me what reaction have You done, i"ll say what umpurities You have to looking for.
Synthetic method: In a 50mL Erlenmeyer flask, a mixture of 4-nitro-o-phenylenediamine (1mmol, 0.153g) ,acetic acid (63uL), 3mL ethylene glycol, 1mL HCl was irradiated through unmodified household microwave oven at 100 W with intermittent heating. The reaction temperature was measured through infrared thermometer. The resulting mixture was cooled at room temperature and 20% NaOH was then added drop by drop. The resulting precipitate was filtered and dried.
Ehylene glycol can be oxidate by nitrogroup espessially during iiradation. Formed dialdehyde reacted with phenylenediamine fragment to form another six-member ring. Such a benzimidazole in your conditions it is better to close usind thiethylorthoacetate (Indian Journal of Chemistry - Section B Organic and Medicinal Chemistry, 2008 , vol. 47, # 7 p. 1154 - 1159 this example is espessially for You because of MW iiriadation), or acetic anhydride (Patent: WO2009/90548 A2, 2009, Journal of the Chemical Society, 1930 , p. 1409,1413) Acetylacetone is too possible regent to obtain your target compound (Organic Letters, 2014 , vol. 16, # 3 p. 764 - 767). Malonic acid can be used also (Bulletin des Societes Chimiques Belges, 1991 , vol. 100, # 3 p. 277 - 286). And if You simple reflux started o-phenylenediamine in acetic acid for long time (10-12 h) with a few drops of H2SO4 You can also obtain your target compound in high yield. Real problems begin if you want to close benzimidazile with too long or brancher (t-Bu) substituent in position 2 from corresponding phenylenediamine. In this cases spesial methods needs
224 0C (http://www.chemspider.com/Chemical-Structure.67105.html?rid=6d114309-3df7-41d0-be60-d45d3996bc5f)
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