Thiele method. 34g aminoguanidine-bicarbonate is dissolved in 217 ml of 15% nitric acid (36ml of 70% HNO3 + 185 ml water). Mixture is stirred until CO2 evolution stops and all solid dissolved. Resulting solution is diazotized by solution of 17.2g sodium nitrite in 35 ml of water. Nitrite solution is added slowly with stirring, while reaction mixture is cooled on ice bath, temperature must all times kept below 20-25C. Diazotation is proceeding smothly with neglible evolution of NOx, if mixture is foaming (result of HNO2 decomposition), addition must be paused and mixture must be well stirred to stop foaming, before new portions of nitrite added. Addition takes time about 10-15 minutes. After addition of nitrite is completed, mixture is allowed to sit for 20 mins at room temperature, and 29g of Na2CO3 (or 46g of baking soda) is added by portions with mixing. Mixture is stirred untill CO2 evolution stops and all excess of bicarbonate fully dissolves. Mixture is placed to round bottom flask with attached reflux condenser and boiled for 4 hours. Resulting solution of 5-aminotetrazole is acidified by 30% H2SO4 to pH=4, and left to cool to room temperature. Usualy crystallization of product starts around 40C, but solution have great tendency to supersaturate. If after cooling to room temperature crystallization is not started, seed crystall of aminotetrazole is introduced (made by placing glass rod with drop of solution to alcohol), or inner side of flask (below solution of course) is rubbed with glass rod with intense friction. After crystallization is started solution is left at room temperature for 12 hours, and cooled to 10C in freezez. Crystalls of 5-aminotetrazole are filtered, slightly washed with ice cold water and dried at room temperature. Yield is 13.6g (64%). Photo of product will be shown at bottom of post.

Schtolle method. Warning!!! This method includes work with exteremely dangerous, explosive and highly toxic hydrogen azide. Concenration of it's solution must be kept below 20% all the times because of severe explosion hazard (<20% are explosion safe). All work must be done with good ventilation, and fumes must not be inhaled in any circumstances (HN3 is very volatile, and is effective protoplasmic poison, causes blood cells decomposition and severe headaches). Never add sodium azide to cold acids solutions - it may result in condensation of drops rel. conc. HN3 on cold walls of flask, and can explode with extreme violence. Method of synthesis is optimized for maximum safety, but precautions must be remembered all times. Dissolve 10.5g of dicyandiamide and 16.25g of sodium azide in 250 ml of water heated to 50C. Mixture is stirred untill all solid dissolve, and 2.15 ml of 36% HCl is added dropwise with stirring, mixture is left at room temperature for 12 hours, then, after heating to 50C 4.3 ml of 36% HCl is added in same way, mixture is left for 6 hours, next 6.45 ml and 2-3 hours, and finaly remaining 8.6 ml of 36% HCl. After addition is completed mixture is left standing at room temperature for 1 week, white crystalls of 5-aminotetrazole must apper, but solution again may be supersaturated and no crystalls are precipitated - in this case crystallization must be started as written in Thiele method above. Yield depends of standing time and puriry of reagents, i have ~50% (10.5g) yield after 2 weeks of standing, but literature sources show yeilds up to 97% after longer standing. Pure snow white crystalls of 5-aminotetrazole are filtered off, washed with ice cold water and dried at room temperature.

Photos of products are shown below. Left photo is ATZ made by Thiele's method, and right one is photo of ATZ made by Schtolle's method:

Prepare solution 20.8g sodium nitrite and 11g of copper sulphate (CuSO4*5H2O) in 60 ml of hot water, resulting solution contains copper nitrite and has dark green color. Prepare solution of 10.3g aminotetrazole (ATZ) and 0.4g CuSO4*5H2O in 12.8 ml 70% nitric acid + 120 ml of water. Diazotetrazole is intermediate in nitrotetrazole synthesis, it can explode in solution if concentration will reach 2% from the slightless stimulus, even at 0C. Microexplosions are not dangerous but acting on nerves. To completely avoid them, slow addition, effective stiring and carefull temperature control are essential. Small adition of copper sulphate to ATZ solution is essential to avoid microexplosions in drops, on contact with nitrogen oxides, escaping from reaction mixture. Copper nitrite solution is placed on ice bath and cooled to 5C, then solution of ATZ in nitric acid, is added slowly with stirring (perfectly drop by drop). During addition temperature of reaction mixture must be kept below 15C all times. If mixture begins to foam, addition is paused and mixture is well stirred until foam dissapears before next portions of ATZ solution are added (foaming is result of HNO2 decomposition to water and NOx if it's concentration is too high). Reaction is proceeding smoothly, without microexplosions, with small evolution of NOx, if conditions are carefully controlled. Whole addition process takes time about 1.5 hours. Close to end of addition mixture becomes thicker, and changes color to green- blue (similar with homemade CuCO3*Cu(OH)2). After addition is completed mixture is left to sit in ice bath for 15 minutes, after that 14 ml of 70% nitric acid + 6 ml of water is added with stirring. Reaction mixture is left for 1 hour, solid precipitate of acid copper salt of nitrotetrazole is filtered off, washed with 5.72 ml HNO3 + 44 ml H2O and with three portions of 50 ml H2O. Yield is about 85%. Product is bluish - green crystals, almost insoluble in cold water.

Warning!!! Acid copper salt of nitrotetrazole is powerfull and sensitive explosive. It is almost completely safe then wet, but in dry state it can explode violently on friction, impact or heating. Safety precautions must be remembered all times.

Below are the photos of process. Left photo shows solutions of copper nitrite (left one) and ATZ in nitric acid with CuSO4 added (right one). Photo in the middle shows ice bath with sitting reaction flask, and termocouple temperature control. Right photo shows reaction product on filter.

Acid copper salt of nitrotetrazole can be easily converted to soluble salts of nitrotetrazole by heating in solution of corresponding hydroxides. For example solution of sodium 5-nitrotetrazolate can be prepared by boiling acid copper salt in NaOH solution: Cu(NT)2*HNT + 3NaOH => 3NaNT + CuO+ 2H2O. Solid black copper oxide is removed by filtering, pure solution of NaNT can be concentrated to separate solid salt, or can be used dirrectly for further reactions.