Cubane explosives

Attempts to dehydrate this to the anhydride were unsuccessful attempting to distil off monomeric products under vacuum at 80°C after a dehydration attempt with ethoxyacetylene led to a violent explosion. This is said to be atypical of cubanes, but ... 

Action of chlorine trifluoride causes incandescence [1]. Manganese dioxide catalytically decomposes powerful oxidising agents, often violently. Dropped into cone, hydrogen peroxide, the powdered oxide may cause explosion [2], Either the massive or the powdered oxide explosively decomposes 92% peroxomonosulfuric acid [3], and mixtures with chlorates ( oxygen mixture , heated to generate the gas) may react with explosive violence [4], Cuban pyrolusite can be used in place of potassium dichromate to promote thermal decomposition of potassium chlorate in match-head formulations [5],... 

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. 

Dinitrocubane (28) has been synthesized by Eaton and co-workers via two routes both starting from cubane-l,4-dicarboxylic acid (25). The first of these routes uses diphenylphos-phoryl azide in the presence of a base and tert-butyl alcohol to effect direct conversion of the carboxylic acid (25) to the tert-butylcarbamate (26). Hydrolysis of (26) with mineral acid, followed by direct oxidation of the diamine (27) with m-CPBA, yields 1,4-diiutrocubane (28). Initial attempts to convert cubane-l,4-dicarboxylic acid (25) to 1,4-diaminocubane (27) via a Curtins rearrangement of the corresponding diacylazide (29) were abandoned due to the extremely explosive nature of the latter. However, subsequent experiments showed that treatment of the acid chloride of cubane-l,4-dicarboxylic acid with trimethylsilyl azide allows the formation of the diisocyanate (30) without prior isolation of the dangerous diacylazide (29) from solution. Oxidation of the diisocyanate (30) to 1,4-dinitrocubane (28) was achieved with dimethyldioxirane in wet acetone. Dimethyldioxirane is also reported to oxidize both the diamine (27) and its hydrochloride salt to 1,4-dinitrocubane (28) in excellent yield. ... 

Nitrocubanes are probably the most powerful explosives with a predicted detonation velocity of >10,000 ms-1. Cubanes were first synthesised at the University of Chicago, USA by Eaton and Cole in 1964. The US Army Armament Research Development Centre (ARDEC) then funded development into the formation of octanitrocubane [(ONC) (C8N8016)] and heptanitrocubane [(HpNC) (C8N7014)]. ONC and HpNC were successfully synthesised in 1997 and 2000 respectively by Eaton and co-workers. The basic structure of ONC is a cubane molecule where all the hydrogens have been replaced by nitro groups (1.6). HpNC is denser than ONC and predicted to be a more powerful, shock-insensitive explosive. 

All cubanes are high energy materials and should be handled with due precautions for potential explosives [ 1]. The ring system has almost 700 kJ/mol strain energy (more, per unit weight, than the detonation energy of TNT) and is under study as a basis for high power explosives [2,3]. Cubane itself explodes spontaneously at 3 GPa pressure, the... 

Prismane is an example of another interesting strained compound. Because it contains three-membered rings fused with four-membered rings, it should be even more strained than cubane. Prismane was prepared in 1973. It is a liquid that is stable at room temperature but explosive under some conditions. In toluene at 90°C its half-life (the time it takes for one-half of the compound to decompose) is 11 h. Note that prismane is isomeric with benzene. In fact, it was one of the structures proposed for benzene in the early days of organic chemistry. 

Although initially of only theoretical interest, the special properties of cubane may eventually lead to its practical use in medicine and in explosives. 

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