Studies On The Synthesis And Separation Processes Of N₅^- Salts

Pentazolate energetic materials have become one research hotspot of energetic materials.Metal pentazolates are the basic raw materials of new pentazolate energetic materials.However,the synthesis of metal pentazolates still suffers some problems such as high cost,low efficiency,as well as difficulties in separation,purification and process scale-up.In this paper,the process optimization and scale-up of metal pentazolates,the separation and purification method of metal pentazolates,and the synthesis of non-metallic pentazolates were studied.（1）Process optimization and scale-up of sodium pentazolateThe synthesis of 4-amino-2,6-dimethylphenol（2）was studied via reduction of azo or nitrous groups,starting from 2,6-dimethylphenol（1）.Data show that the reduction of azo group is more concise,giving compound 2 with a better purity and a yield up to 82.7%.Studies on the synthesis and process optimization of sodium pentazolate（4）were carried out via amination,diazotization,cyclization and C-N cleavage reactions starting from compound2.Reaction condition studies indicate that it would have a negative effect on the yield of sodium pentazolate（4）if hydrochloric acid was added before cyclization,and have a positive effect on the yield of sodium pentazolate（4）if sodium bicarbonate was added before cyclization.A suitable sodium bicarbonate dosage is 0.28 eq of HCl with a sodium pentazolate yield of 18.7%.The C-N cleavage of arylpentazole 3 was studied with different C-N cleavage reagents.It was found that only m-CPBA/Fe（Gly）₂and m-CPBA/Fe（acac）₂could selectively cleave the C-N of arylpentazole 3,and m-CPBA/Fe（Gly）₂has a better efficiency.Experiments show that the brands and batches of Fe（Gly）₂have a significant effect on the C-N bond cleavage.Based on the process optimization,the synthesis process of sodium pentazolate（4）was studied by scaling up gradually,and the synthesis process of 10 g sodium pentazolate per batch was obtained.The product was characterized by mass spectrometry（MS）,ion chromatography（IC）and infrared（IR）.IC data show that the purity of sodium pentazolate is up to 94.61%.（2）The separation and purification method of metal pentazolatesThe separation and purification methods of metal pentazolates were studied by C18column chromatography,recrystallization and precipitation based on the aqueous solution of sodium pentazolate,which was obtained via C-N cleavage reaction of arylpentazole,but they were unsuccessful.The probable reason is that there are large amounts of organic and inorganic impurities such as sodium m-chlorobenzoate,sodium chloride and sodium nitrate in the crude sodium pentazolates（4）,as shown by IR and ion chromatography analysis.IR data show that organic acid radical is more likely to precipitate with metal ions,resulting in the failure of metal pentazolates separation by precipitation method.Interestingly,cobalt pentazolate（11）was successfully precipitated from the aqueous solution of sodium pentazolate via acidification,removel of organic acid salts by extraction,and then addition of cobalt chloride.It is found that the lower the p H is,the higher the removal efficiency of organic acid salts is and the better the purity of cobalt pentazolate（11）is.The suitable synthesis conditions of cobalt pentazolate are as follows:the p H is 3,and the molar ratio of cobalt chloride to 2,6-dimethyl-4-aminophenol（2）is 0.26:1.Ion chromatography shows that the purity of cobalt pentazolate（11）is up to 97.9%after simple recrystallization.Besides,the applicability of this precipitation method to other metal pentazolates were also studied.Results show that it is also suitable for synthesizing the pentazolates of iron,ferrous and copper.After removing the organic acid salt,the separation of pentazolate（4）was further studied via extraction method.It was found that sodium pentazolate（4）could be effectively separated with a purity of 96.7%after recrystallization.Generally,the precipitation and extraction methods avoid column chromatography,featuring simplicity,high efficiency and low cost,which would be helpful for the synthesis and process scale up of related metal pentazolates.（3）The synthesis of non-metallic pentazolatesSarting from imidazole（15）,3’,3-methylene bis（1-hydroxyethylimidazolium）dibromide（17）was synthesized by bridging reaction and hydroxyethylation.Besides,silver pentazolate（12）was successfully obtained by the metathesis reaction of Ag NO₃with cobalt pentazolate（11）or sodium pentazolate（4）.Finally,hydrazine pentazolate（14）in 87.90%yield and3’,3-methylene bis（1-hydroxyethylimidazolium）dipentazolate（18）in 71.24%yield were successfully synthesized via the metathesis reaction of silver pentazole（12）with hydrazine hydrochloride（14）or compound 17.The target products and intermediates were characterized by IR,MS,NMR and TG-DSC.TG-DSC data show that the decomposition temperatures of compound 14 are 113.5℃and compound 18 are 97.6℃respectively.