2.4.5- trinitroimidazole

Nitro groups on azole rings are often smoothly displaced by nucleophiles even more readily than are halogen atoms in the corresponding position. Thus 2,4,5-trinitroimidazole (450) is converted by HCl successively into (451) and (452) (80AHC(27)24l). 

The direct nitration of imidazole with acidic reagents is difficult due to facile nitrogen protonation (pA aH 7). Nitration of imidazoles proceeds in the 4- and 5-positions with the amidine 2-position being quite inert. Imidazole can be directly nitrated to 4,5-dinitroimidazole but no further. 2,4,5-Trinitroimidazole (TNI) can be prepared from the successive nitration of 2-nitroimidazole the latter synthesized from the diazotization of 2-aminoimidazole in the presence of excess sodium nitrite and a copper salt. The nitrative cleavage of polyiodoimidazoles also provides a route to polynitroimidazoles. " ... 

The substitutive nitration of iodoimidazoles has been described in detail [376-382], However, the structure assigned to the obtained nitro imidazoles proved erroneous [367, 377, 379, 382], The correct structure was established later [140, 141], The error was due to the fact that the initial compound was assigned the structure of 2,4-diiodoimidazole. In fact, 4,5-diiodoimidazole undergoes nitration and is converted into 4,5-dinitroimidazole. 2,4,5-Triiodoimidazole and 1,2,4,5-tetraiodoimidazole are nitrated to 2,4,5-trinitroimidazole by the action of nitric acid [383] (Scheme 51). 

Methyl-2,4,5-trinitroimidazole has been synthesized from 4-nitroimidazole using stepwise nitration and further methylation by dimethylsulfate or from commercially available imidazole. l-Methyl-2,4,5-trinitroimidazole is relatively insensitive to impact, and its thermal stability is excellent. The calculated detonation properties point to the fact that its performance is about 30% better than that of TATB. The data of impact sensitivity, friction sensitivity, time-to-explosion tern-... 

Both 1-methyl-4- and l-methyl-5-chloroimidazoles can be nitrated in sulfuric acid. Exhaustive nitration of imidazole in mixed acids yields in succession 4-mono-, 4,5-di-, and 2,4,5-trinitroimidazole. With dinitrogen tetroxide in acetonitrile 4-substituted imidazoles with electron-withdrawing substituents yield a mixture of 5- and 2-nitro derivatives." Nitrations at C-2 are most unexpected. The nitration of 4-(4 -alkoxyphe-nyl)imidazoles with 3-4 M nitric acid occurs ortho to the alkoxy group and in the imidazole 5-position. With concentrated nitric acid di- and trinitro compounds are formed." ... 

The 3rd nitration to 2,4,5-trinitroimidazole (6) was performed in the mixed acid condition. As the intermediate of potassium 2,4,5-trinitroimidazolate (7), 6 was not stable enough that we could not isolate that. From the extracted ether solution of 6, the solid of 7 was precipitated with the saturated K2CO3/KCI solution in good yield (60 %) [15]. It was reported that 6 could be manufactured via 2,4,5-triiodoimidazole, but we chose the route through 2,4-DNI (5). 

Our target molecule, 1-methyl-2,4,5-trinitroimidazole (MTNI 1) was synthesized (36 %) when 6, which was regenerated from 7 by treating with hydrochloric acid, was reacted with diazomethane (CH2N2) in ether solution [7]. To make the diazomethane, Diazald (/V-methyl-ZV-nitroso-p-toluenesulfonamide) was purchased from the Aldrich and used in situ [16]. When the crude 6, which was prepared from 5 and extracted with ether, was used to make 1 without converting to 7, we failed to separate 1 from the product mixture. It is probably that in the crude 6, there were lots of impurities such as unreacted 5. 

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