Peter Golding

Preparation of di- and polynitrates by ring-opening nitration of oxetanes by dinitrogen pentoxide (N2O5)

Abstract Ten oxetanes bearing various substituents were reacted with N2O5 in chlorinated hydrocarbon solvents to yield 1,3-dinitrate esters (I) by ring-opening nitration. The yields ranged from 73 to 88% for di-/trinitrates derived from oxetanes unsubstituted in the 2-position, to only 15 to 21% for oxetanes bearing such substituents. Although selective ring cleavage of oxetanes bearing non-hydroxylic substituents (epoxy (oxiranyl), spiro-oxetane and alkene) was not, in general, possible, selective nitration of hydroxyalkyloxetanes was achievable under the conditions employed to yield nitrato-methyloxetanes useful as precursors for energetic polyethers. A semi-quantitative reactivity comparison with representative epoxides indicated that the reactivity of oxetanes towards N2O5 was lower, as expected on account of their lower ring strain.

Preparation of nitramine-nitrates by ring-opening nitration of azetidines by dinitrogen pentoxide (N2O5)☆

Abstract Eleven azetidines, bearing various types of substituents on the ring nitrogen, were treated with N2O5 in chlorinated solvents at sub-ambient temperature and in certain cases formed 1,3-nitramine-nitrate products by a novel ring-opening nitration reaction analogous to that established for aziridines. Yields of the nitramine-nitrates, where ring-opening took place, were generally moderate to high (41–88%), but azetidines bearing N-acyl substituents (acetyl, butyryl or carbamyl) instead underwent nitrolysis of the exocyclic substituent to form N-nitroazetidine. Also, azetidines bearing strongly electron-withdrawing groups such as picryl were inert to attack by N2O5. The different reactivity of azetidines compared with aziridines is rationalised in terms of the reduced ring strain of the four-membered ring compounds.

Preparation of Di- and polynitrates by ring-opening nitration of epoxides by dinitrogen pentoxide (N2O5)

Abstract Eighteen epoxides of various kinds were reacted with N2O5 in chlorinated hydrocarbon solvents (principally CH2Cl2) to give vicinal nitrate ester products by a novel ring-opening nitration reaction. The procedure offers easier temperature control and simpler isolation procedures compared with conventional mixed acid nitrations; it also enables selective nitration reactions to be carried out on polyfunctional substrates. The scope and limitations of the reaction, as well as those of an alternative route utilising N2O4 with in situ oxidation of an intermediate nitrite-nitrate, are discussed.

Nitration by oxides of nitrogen, part 4: unexpected behaviour of certain aziridines and azetidines upon reaction with dinitrogen pentoxide

Abstract Seven aziridines and azetidines, either unsubstituted on ring nitrogen or bearing N-acyl (N,N-dimethylcarbamyl or propionyl) groups, were reacted with N2O5 in halogenated solvents with the following results:- the behaviour of the aziridines was highly dependent on the N-substituent, giving respectively dinitrate esters, nitramine-nitrate or predominantly uncharacterisable products, whereas the azetidines gave in all cases N-nitroazetidine. The different behaviour is believed to result from ring strain effects.

Preparation of nitramine-nitrates by ring-opening nitration of aziridines by dinitrogen pentoxide (N2O5☆

Abstract Thirteen aziridines, bearing various types of substituents on the ring nitrogen, were treated with N2O5 in chlorinated solvents at sub-ambient temperature and formed 1,2-nitramine-nitrate products by a novel ring-opening nitration reaction analogous to that established for the corresponding oxygen heterocycles (epoxides). A wide variety of classes of aziridine underwent the reaction (N-alkyl, N-(nitroaryl), N-acyl and N-imidyl), the yields in many cases being high (70-82%), although in one category (the N-(alkylcarbonyl)aziridines) competing deacylation reactions resulted in reduced yields. Also, aziridines bearing groups capable of liberating nitric acid with N2O5 (i.e. those with OH, NH or unsubstituted aryl groups) gave rise to greatly reduced yields of the nitramine-nitrates owing to competing reactions, principally polymerisation/ oligomerisation.