Methylene-bridged Bisimidazolium Energetic Ionic Salts:Synthesis And Properties

Energetic ionic salts are a kind of new energetic material.Compared with the traditional explosives such as TNT,RDX and HMX,energetic ionic salts have several advatages such as low vapor press,environment friendly,and high thermal stability.What is more,energetic ionic salts are insensitive to external stimuli such as friction,impact,and static electricity.In addtion,energetic ionic salts have great research values and practical application potentials in new explosive formulations and green dual-component propellants.Imidazolium energetic ionic salts,with imidazolium cations and different energetic anions,are one of the most important energetic salts.Compared with their energetic anions,imidazolium cations are limited due to the absence of nitro,nitrate,or-N3 energetic groups.In this paper,several methylene-bridged dicationic imidazolium energetic ionic salts(5,6,9a-9c and 10a-10d)with an energetic group in the side chains of imidazolium cations were synthesized starting from imidazole,2-methylimidazole,methyl bromide,and 2-chloroethanol via bridging,quaternization,nitration,and metathesis reactions.All the dicationic energetic ionic salts and intermidiates were characterized by UV-Vis,IR,MS,NMR,and elemental analysis.Moisture absorption tests show that compound 1,1’-methylenebis(3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)dinitrate(5)and 1,1’-methylenebis(2-methyl-3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)dinitrate(6)are very hygroscopic with waterabsorption ratios up to 36%.Comparatively,other compounds have low waterabsorption ratios less than 2%.TGA shows that the ionic salts have good thermostabilities with decomposition temperatures from 160 oC to 300 oC,and first stage decomposition temperatures above 200 oC.DSC shows that compound 1,1’-methylenebis(3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)bis-dinitramide(9b)has a melting point below 100 oC,and other compounds have melting points between 100 oC and 200 oC.The standard enthalpies of formation and detonation properties of the energetic salts were estimated by Kamlet-Jacobs equation,showing that the energetic salts have good detonation performances.Compounds 1,1’-methylenebis(3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)dipicrate(9a),1,1’-methylenebis(3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)bis(3,5-dinitro-1,2,4-triazolate)(9c),1,1’-methylenebis(2-methyl-3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)bis(3,5-dinitro-1,2,4-triazolate)(10c),and 1,1’-methylenebis(2-methyl-3-(2-(nitrooxy)ethyl)-1H-imidazol-3-ium)bis(5-nitrotetrazolate)(10d)have good detonation performances,which have calculated values of detonation pressure and calculated velocitie between those of TNT and RDX.Compounds 10 c and 10 d have calculated detonation velocities of 8.14 km/s and 8.06 km/s,and calculated detonation pressures of 31.51 Gpa and 29.52 Gpa,which are close to those of RDX.