Process for preparing 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane

A process for preparing 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, which comprises the step of reacting an N-acylated-1,3,5,7-tetraazacyclooctane of the following formula ##EQU2## wherein R is an alkyl radical of 1 to 6 carbon atoms, and M in both cases is the same and is either a nitro group or an acyl radical of the formula RCO--, wherein R has the aforesaid definition, with nitrogen pentoxide in the presence of a liquid diluent from the group consisting of a nitroparaffin, methylene chloride, chloroform, 100% nitric acid, polyphosphoric acid containing more than 75% by weight of phosphorus pentoxide and a liquid system for producing nitrogen pentoxide consisting essentially of a mixture of 100% nitriacid and a material of the group consisting of trifluoroacetic anhydride, sulfur trioxide, phosphorus pentoxide and polyphosphoric acid containing more than 75% by weight of phosphorus pentoxide.