Research On The Synthesis Of Polynitroadamantanes

High energy density cage compounds have attracted extensive attention for their high energy and low sensitivity which are a result of symmetrical structures,particularly in combination with good thermal stability.Among them,polynitroadamantanes are potential High Energy Density Materials(HEDMs),which were attributed to the good designable structures with numerous C-H bonds on the adamantane skeleton.Herein,recent reviews of the developments of polynitroadamantanes,construction methods of adamantane skeletons and introduction methods of gem-dinitro groups were summarized,and some polynitroadamantanes and their derivates were prepared.The reactions for the construction of adamantane skeleton and introduction of gem-dinitro groups were researched.In addition,several strategies for the synthesis of 2,2,4,4,6,6,8,8-octanitroadamantane were also tried.The adamantane skeletons 4-methyleneadamantan-2,6-dione and 4-hydroxyadamantan-2,6-dione were constructed utilizing acylation followed by intramolecular aldol condensation of bicyclo[3.3.1]nonane-2,6-dione in 76%and 91%yield accordingly,both of which can be converted to the key intermediate 2,2,6,6-bis(ethylenedioxy)adamantan-4-one.Then,2,2,4,4,6,6-hexanitroadamantane was successfully synthesized from the key intermediate via a several steps procedure including oximation,gem-nitration,deketalization,oximation and gem-nitration.The nitration of ketoximes was conducted using N2O5 as the nitration reagent,and 2,2.4,4,6,6-hexanitroadamantane was obtained with 4.7%and 14%overall yield accordingly,with yields of the gem-nitration steps increased from 37%to 65%and 21%to 35%.It provided an efficient synthesis of gem-dinitro compounds from aromatic and aliphaticketones with yields up to 86%,which avoided the use of excess nitric acid and sulfuric acid and formation of large amounts of acidic waste compared to traditional nitration process.TG-DSC curve shows that HNA has good thermal stability,and an exothermic reaction occurs at 256?.The adamantane skeleton 4,8-dihydroxyadamantane-2,6-dione was successfully constructed utilizing formylation and intramolecular aldol condensation of 1.5-cyclooctanedione via a 4 steps procedure in 58%overall yield.Then,a novel high-performance energy compound 4,4,8,8-tetranitroadamantane-2,6-diyl dinitrate was prepared from 4,8-dihydroxyadamantan-2,6-dione with an overall yield of 15.3%via a several steps procedure.TG-DSC curve shows that 4,4.8,8-tetranitroadamantane-2,6-diyl dinitrate has good thermal stability(200?),and an exothermic reaction occurs at the temperature of 220??The calculated detonation velocities(8529 m·s-1)and detonation pressures(33.43 GPa)are comparable to those of conventionally used RDX.2,2,4-trinitroadamantane was synthesized from 2-adamantone with an overall yield of 9.9%via a nine steps process including Bayerer-Villiger oxidation,rearrangement,ketalization,oxidation,oximation and gem-nitration.The high sterically hindered nitration of its sodium salt was studied,and the optimal reaction conditions were determined as:sodium salt/NO2Cl = 1:20,reaction temperature-70 ? and reaction time 2 h.with the yield of 87%.Then,the optimal reaction conditions were applied to the high sterically hindered nitration of sodium salts from different kinds of polynitroadamantanes.The nitration system was found suitable for the high sterically hindered nitration of sodium salts of polynitroadamantanes that containing single nitro group or nitro groups on para-methylenes of the adamantane skeleton,but not suitable for the nitration of those sodium salts of polynitroadamantanes containing nitro groups on ortho-methylenes.Synthesis of 2,2,4,4,6,6.8,8-octanitroadamantane by gem-nitration of oximinoadamantanes or high sterically hindered nitration of sodium salts of polynitroadamantanes were studied.4,4,8,8-tetranitroadamantan-2,6-dione was synthesized from 4,8-dihydroxyadamantan-2,6-dione with an overall yield of 22.6%via a six steps process including ketalization,oxidation,oximation,gem-nitration,deketalization and oximation.The gem-nitration of 4,4,8,8-tetranitro-2,6-dioximidoadamantane was conducted using N2O5 as the nitration reagent,but only deoximation product was obtained due to its high steric hindrance and electron-withdrawing inductive effects of gem-dinitro groups.Deoximation product was also obtained when the nitration conditions was applied to the gem-nitration of 4,4,8-trinitro-2,6-dioximidoadamantane.While,a mono-nitrated product 4,6,6,8-tetranitroadamantan-2-one was obtained in the gem-nitration of 4,8-dinitro-2,6-dioximidoadamantane in 40%yield.A comparation of results of different gem-nitration reactions shows that steric hindrance has strong impact on gem-nitration reaction,and sterically hindered substrates will not undergo gem-nitration reaction.