Imidazoles, nitro-, bromination

For many years it was not possible to introduce two nitro groups into the imidazole ring [159], By the use of a somewhat unusual nitration condition (by heating the substrate first with nitric add and then with the sulfuric-nitric acid mixture) it was possible to obtain 4,5-dinitroimidazole [79], The method has now also been used for the production of 4,5-dinitroimidazoles [84, 93, 160], It was also shown that C-polynitrobisimidazoles [79] and not /V-nitroimidazolcs, as considered earlier [161], are formed during the nitration of 2,2 -bisimidazole and its bromine derivatives. As already mentioned earlier, during the nitration of ethyl l-methylimidazole-2-carboxylate the 4,5-dinitro derivative was also isolated together with the other nitration products [128], Increase in the reaction time increases the amount of the dinitro derivative. 

Fluoride converts 1,2-dimethyl-4-trimethylammonio-5-nitroimidazole into the 4-fluoro derivative <87JMC150>. The 2-nitro group of 1-methyl-2,4-dinitroimidazole is replaced by bromine or chlorine when treated with 2-bromoethanol or 2-chloropropanenitrile respectively <84UC(B)363>. When benz-imidazole-2-nitrosamine is treated with dry HCl or HBr with copper metal in acetonitrile the corresponding 2-halogenobenzimidazoles are formed in 71% and 63% yields respectively <87CHE1090>. 

Bromination of (115) with bromine or iodination with iodine monochloride gave the respective 3-bromo (116) and 3-iodo (117) derivatives, while nitration with nitric and sulfuric acids in glacial acetic acid led to the formation of the corresponding 3-nitro (118) derivative <92BCJ3419>. Nitration of (98) with nitric and sulfuric acids gave a mixture of the nitroso (119, 85%) and nitro (120, 15%) derivatives. No nitration occurred on the imidazole ring <84JCR(S)28>. 

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