1.3.5.7- tetranitrocubane

The sodium salts of 1,3,5,7-tetranitrocubane and 1,2,3,5,7-pentanitrocubane can be nitrated successfully with N204 in THF at low temperature. These reactions proceed by N204 oxidation of the anion to the radical and its combination with N02 (Eq. 2.23) 43 Such highly nitrated cubanes are predicted to be shock-insensitive, very dense, high-energy compounds with great potential as explosives and propellants. 

Eaton and co-workers also reported the synthesis of 1,3,5-trinitrocubane and 1,3,5,7-tetranitrocubane (39) ° The required tri- and tetra-substituted cubane precursors were initially prepared via stepwise substitution of the cubane core using amide functionality to permit ort/jo-lithiation of adjacent positions. The synthesis of precursors like cubane-1,3,5,7-tetracarboxylic acid was long and inefficient by this method and required the synthesis of toxic organomercury intermediates. Bashir-Hashemi reported an ingenious route to cubane-1,3,5,7-tetracarboxylic acid chloride (35) involving photochemical chlorocarbonylation of cubane carboxylic acid chloride (34) with a mercury lamp and excess oxalyl chloride. Under optimum conditions this reaction is reported to give a 70 8 22 isomeric mixture of 35 36 37... 

The acidity of 1,3,5,7-tetranitrocubane, which features nitro groups on alternate comers of cubane, has been measured (p/C, 21) and reactions of the corresponding o-nitro anion have been explored.183... 

Syntheses have been made of energetically substituted cubanes. For example, 1,3,5,7-tetranitrocubane [10] (shown in Fig. 26) has been synthesized. As noted previously, its density is 1.814 g/cc. Another is the flu-dinitroethy] ester of tetracarboxycubane [36] (Fig. 27). The density is 1.762 g/cc. An energetic ammonium perchlorate substitution of cubone has been made in the form of 1,4-bis-cubanediammonium perchlorate hydrate [40] (Fig. 28). The dashed lines in Fig. 28 represent some of the many hydrogen bonds that occur in the crystal whose density is 1.7S5 g/ce. An estimate of the dry density extrapolated from this work is 1.83 g/cc- It was obtained by subtracting the volume and mass of water from the unit cell contents. The volume of H2O was taken to be the same as that in liquid water. 

The acidity of the unadivated cubyl-H is comparable to NH3 (pKa 38). Cubyl H-atoms are at least 105-106 times more acidic than vinyl and phenyl hydrogens (K. A. Lukin, J. Li, P. E. Eaton, N. Kanomata, J. Hain, E. Pun-zalan, R. Gilardi, Synthesis and chemistry of 1,35,7-tetranitrocubane induding measurement of its acidity, formation of o-nitro anions, and the first preparations of pentanitrocubane and hexanitrocubane , J. Am Chem. Soc, 1997,119, 9591-9602 and the references cited therein). 

Di-, tri- and tetranitrocubanes have been successfully synthesized their observed crystal densities are shown in Table 5. As predicted, the densities of nitrocubanes increase as a function of nitro group content. 

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