Synthetic route to tetrazoles from urea & ammonium nitrate

Authors: Engager and Kmet.

Note: I'm not a natural english language speaker, so don't blame me much for spelling errors or bad language. If someone can help to correct and refine spelling, your help would be gladly appericated.

Introduction

Some initial publications related to chemistry of tetrazoles, shown that interesting class of compounds is still not readily accessible for forum members due to unavailability of source compounds. This difficulties made authors of this article to seek for some more simple routes to synthesis of tetrazole based compounds, and such ways has been explored. Source products – urea and ammonium nitrate were selected due to easy availability and cheapness. Synthesis does not require advanced and difficult to obtain lab equipment and should be suitable for anyone. Simplified scheme of synthesis is shown below:

Synthesis steps, used reagents and reaction yields:

1. Preparation of guanidine nitrate from urea and ammonium nitrate by melting with silica gel. Reagents: 340g ammonium nitrate, 320g of urea. Yield: 190-210g of guanidine nitrate or 60% theoretical.
2. Preparation of nitroguanidine from guanidine nitrate (dehydration by conc. sulphuric acid) . Reagents: 200g guanidine nitrate, 510 g of conc. sulphuric acid. Yield: 142.5g of nitroguanidine or 84% from theory.
3. Preparation of aminoguanidine by reduction of nitroguanidine by zinc dust in acetic acid. Reagents: 142.5g of nitroguanidine, 456g of zinc powder, 86g of glacial acetic acid or equal amount of 70% acetic acid, 132g of ammonium chloride, 144g of soda. Yield: 112g of aminoguanidine bicarbonate or 60% theory.
4. Preparation of 5-aminotetrazole by action of nitrous acid on aminoguanidine. Reagents: 112g of aminoguanidine bicarbonate, 710 ml of 15% nitric acid, 56g of sodium nitrite, 95g of soda. Yield: 60g of 5-aminotetrazole monohydrate or 71% theoretical.
5. Preparation of 5-nitrotetrazolate by Sandmeyer reaction from 5-aminotetrazole. Reagents: 60g of 5-aminotetrazole monohydrate, 121g of sodium nitrite, 64g of copper sulphate, 156 ml of 70% nitric acid or equal amount of dilute solution. Yield: 50g of sodium 5-nitrotetrazolate dehydrate or 50% theory.

Data above show that total synthesis of 5-nitrotetrazole from readily available starting material is real and possible. In total 50g of sodium 5-nitrotetrazolate dehydrate can be prepared from 340g of ammonium nitrate and 320g of urea used as starting material, that is pretty much good for such multistage synthesis. Authors of this article believe that this experimental material will be useful for wide range of forum readers and will allow them access to this extremely interesting class of organic nitrogen compounds. If you have any further questions, please place your questions to corresponding forum thread, or to authors personally via e-mail (engager6@mail.ru) or by ICQ 194-993-149. Wish you an interesting reading, Kmet and Engager.

1. Synthesis of guanidine nitrate from urea and ammonium nitrate.

Guanidine nitrate [C(NH2)3]NO3 is colorless plates (in presence of impurities yellowish) with density 1.44 g/cm3 and melting point 214.2C. Compound is stable to boiling in water and on melting, decomposition starts only at 270C. Soluble in water (13% at 20C, 32% at 55C and 128% at 90C) and ethanol (11.5% at 78C). Guanidine nitrate can be prepared by reaction of urea with ammonium nitrate in molten state in presence of powdered silica gel catalyst at temperature about 160C. Reaction equation:

Reactor is open 2 liter stainless steel container placed on oil bath heated by hotplate and equipped by mechanical stirrer. Stirrer was made from small 9V motor (from old tape recorder) with shaft made from radio antenna section and stirring arms made from stainless steel, all open surfaces were covered by P.T.F.E lacquer (Note #1). Reactor is filled with 340g of ammonium nitrate (Note #2), 200g urea and 80g of tempered dry silica gel (Note #3) and heated up on oil bath to 195C. Mixture melts and then stirring is applied for total 2 hour sitting period, then another 120g of urea is added and mixture is allowed to sit for 2.5-3 more hours at this temperature (urea can not be added at start in single portion because it will lead to formation of triazine compounds). After and of this period mixture is cooled, mixed with 250 ml of water and boiled, filtered hot to remove silica gel, then material on filter washed with 150 ml of boiling water. Filtrates are combined and cooled to 0C, precipitated guanidine nitrate is filtered and recrystallized from minimal amount of water. Yield is 190-210g of pure recrystallized product (65-70% theoretical).

Notes:

1. Experimentation in performing the process without stirring (mixing was applied only once – then adding second crop of urea), shown that yield is lowered by 2-3%.
2. Using dry reagent is essential to reduce foaming, especially on first stage.
3. Used silica gel was prepared from liquid glass (sodium metasilicate) using the following procedure. Commercially available liquid glass is diluted 2-3 times, then 10-15% sulphuric acid is added. Solution forms non fluid galantine (it is essential that acid should be added in one portion, and solution should thicken, if H2SiO3 precipitate is formed, solutions must be more diluted and mixed more efficiently) witch is placed to the cold freezer for 2 days. On defrost galantine disperses to fine powder, witch is filtered, carefully washed and tempered to dryness. This silica gel was reused in guanidine nitrate process for 7 times, without loosing activity. Regeneration of silica gel was preformed by washing thoroughly with 1 liter of hot water and tempering.

Photos:

Reaction vessel and pure guanidine nitrate, made by method described above.

2. Preparation of nitroguanidine by dehydration of guanidine nitrate.

Nitroguanidine C(NH)(NH2)NHNO2 is colorless or slightly yellowish fiber like crystals with monocrystalline density 1.71 g/cm3 and melting point 232C (with decomposition). Nitroguanidine is soluble in common organic solvents, good soluble in water (0.44% at 30C, 7.5% at 100C) and perfectly soluble in alkaline solutions. Heat of formation is -893 kJ/kg, heat of explosion 3220 kJ/kg (liquid water) and 2876 kJ/kg (water – gas), trauzl bomb test gives 305 cm3 expansion, volume of detonation products – 1075 l/kg, oxygen balance -30.7%, 54% mass nitrogen. Nitroguanidine is typical “cold” explosive with low explosion temperature, while explosion workability is slightly higher then TNT. High crystal density and low molecular mass of explosion products results in relatively high detonation velocity (7650 m/s at 1.55 g/cm3, 8200 m/s TMD), so nitroguanidine can be referred as high explosive. Sensitivity to external stimulus is quite low (no detonation on usual impact and friction tests).

The silver derivative, CH3N4O2Ag, is precipitated when barium hydroxide is gradually added to a warm aqueous solution containing nitroguanidine and silver nitrate in molecular proportion; it is a colorless compound, almost insoluble in water, but readily soluble in acids, ammonia, and ammonium salts ; it separates from a hot solution of ammonium nitrate in microscopic needles. It turns yellow when treated with alkalis, and darkens on exposure to the air or on prolonged washing with water; it has an alkaline reaction, and explodes when heated. A yellow precipitate, which seems to have the composition CH2N4O2Ag2, is formed when soda or barium hydroxide is added to a solution of nitroguanidine in ammoniacal silver nitrate; it is very hygroscopic, and decomposes very readily when dried at a moderate temperature. The nitrate, CH4N4O2*HNO3, crystallizes from hot concentrated nitric acid in nacreous plates, and melts at 147°C. The hydrochloride, CH4N4O2*HCI, crystallizes in plates or prisms. When nitroguanidine is treated with soda and zinc-dust, and then with a solution of a ferrous salt, a beautiful red coloration is produced; attempts to prepare alkyl and acidyl derivatives of nitroguanidine were unsuccessful.

Nitroguanidine can be prepared by dehydration of guanidine nitrate with concentrated sulphuric acid, followed by dilution by water and filtering:

Aging period depends from temperature, at 40C 5min period is suitable, 30C requires 10 min and 20C require 30 min of aging. Dehydration uses 2.5-3 times mass quantity of concentrated H2SO4. 500g of 93-95 sulphuric acid is placed on water/ice bath and cooled to 10C, then guanidine nitrate (~200g) is added by portions with stirring (~5-10g at a time) in such rate that at the end of addition temperature should reach 30C (temperature rises relatively slowly, but cooling is still required), then mixture is aged for 10 minutes and poured into 300g of water/ice mixture. Fine precipitate of nitroguanidine is filtered, washed with strongly diluted water solution of ammonia, with cold water and finally with alcohol. Yield is about 142g (85% theory).

Photos:

Crude nitroguanidine made by method above and product recrystallized from water.

3. Synthesis of aminoguanidine by reduction of nitroguanidine with zinc in acetic acid.

Aminoguanidine is crystalline compound unstable in free state, perfectly soluble in water and insoluble in alcohol, melting point not determined because heat causes decomposition before melting point. Aminoguanidine shows basic properties and forms stable salts with strong acids via amino group, many from them form yellowish solutions in water. Free aminoguanidine and alkaline solutions of it’s salts are unstable to heat and oxidation by air oxygen, oxidized products provide such solutions with intense red coloration.

Aminoguanidine hydrochloride, NH2C(=NH)NHNH2*HCl, can be obtained by gradually adding glacial acetic acid (124 grams) diluted with an equal volume of water, to a mixture of nitroguanidine (208 grams) and zinc-dust (700 grams) which has been previously rubbed to a thick paste with ice and water; during the addition of the acid, which occupies 2-3 minutes, the mixture is constantly stirred, and the temperature kept at 0°C by adding ice. The temperature of the mixture is then allowed to rise slowly to 40-45°C, and, as soon as a portion givers no coloration with soda and a ferrous salt, reduction is at an end; the filtered solution is then mixed with excess of hydrochloric acid, concentrated on the water-bath, taken up with alcohol, and evaporated to dryness; the residue consists of aminoguanidine hydrochloride, guanidine hydrochloride, and a little ammonium chloride, which are separated by means of alcohol. Aminoguanidine hydrochloride crystallizes from dilute alcohol in large, thick prisms, melts at 163°, and is very readily soluble in water, but insoluble in ether. The platinochloride, (CH6N4)2*H2PtCl6, is a yellow substance melting at 145 - 146°C.

The nitrate, NH2C(=NH)NHNH2*HNO3, crystallizes from water in large plates, from alcohol in needles, and melts at 144°C; it is only sparingly soluble (12 parts in 100) in water at 16°C. The sulphate, (CH6N4)2*H2SO4*4H2O, crystallizes in needles, loses its water at 110°C, and melts at 207-208°C with decomposition ; it is very readily soluble in water, but insoluble in alcohol. The acid sulphate, CH6N4*H2SO4, crystallizes from water, in which it is only sparingly soluble, in small, yellow needles. When a solution of the sulphate is treated with the theoretical quantity of barium hydroxide, a solution of aminoguanidine is obtained; this solution gradually turns reddish on exposure to the air, and decomposes, with evolution of ammonia, when evaporated at a moderate temperature; on evaporation under reduced pressure, it yields a reddish, crystalline substance which has an alkaline reaction, and is soluble in alcohol, but insoluble in ether. A compound of the composition (CH5N4)2Cu*2HNO3, is obtained as a violet, crystalline precipitate when a solution of aminoguanidine nitrate is treated with copper nitrate and sodium acetate; it crystallizes in microscopic plates or prisms, and is only very sparingly soluble in cold water, yielding a violet solution; it is decomposed by boiling water with separation of copper, and also by ammonia and nitric acid. The corresponding sulphate, (CH5N4)2Cu*H2SO4, prepared in like manner, is a violet, crystalline, sparingly soluble powder.

Aminoguanidine can be prepared by many routes, for example by action of hydrazine on cyanamide or methylisothiourea and by reduction of nitroguanidine by hydrogen. Reduction by hydrogen in chemical or electrochemical process proceeds through formation of nitrosoguanidines and readily proceeds in presence of catalysts such as Raney nickel or zinc acetates. In acid conditions then solution contains more then 1 mole of acid per mol of nitroguanidine reduction proceeds directly to aminoguanidine, without formation of nitrosoguanidines. Probably the best practical method of reduction is reduction of nitroguanidine by zinc dust in acetic acid, since it does not require additional catalysts and is very simple. This method offers 15.6g of aminoguanidine-bicarbonate from per 20g of nitroguanidine (60% from theory).

Procedure of reduction:

20g (0.19 mol) of nitroguanidine, 68g (1.04 mol) of zinc dust and 6 ml water are mixed in mortar and rubbed to thick paste. Reaction weasel (thin-wall glass) is filled with 12 ml of glacial acetic acid + 12 ml water and placed to ice/water bath, then cold nitroguanidine/zinc paste is added in small portions with gentle stirring (note #1). Addition rate is adjusted to hold reaction temperature within 5-15C, care should be taken not to allow temperature to rise to 35C even for a single moment. If mixture becomes too thick or temperature rise to rapidly pieces of ice are added (total 90g). Paste addition takes about 3-4 hours, after this reaction mixture is allowed to sit in ice/water bath for 1 more hour, then mixture is removed from bath and is allowed to heat slowly to room temperature, final mixture volume is about 130-140 ml (note #2). After 1 hour at room temperature mixture is placed on water bath, heated to 25 and stirred for 30 minutes, then to 32-35C and stirred for 30 more minutes and finally heated to 40C and stirred at this temperature for 15 minutes (note #3). Then reduction is complete solution is immediately filtered on vacuum funnel, taking effort to filter solid product to dryness (note #4). Solid is washed with 90 ml of water, filtered and discarded, filtrates are combined, 18.5g of ammonium chloride is added, and mixture is stirred until all ammonium chloride is dissolved (note #5), and on continuous stirring 20.2g of soda is dissolved in reaction mixture. Several minutes from addition aminoguanidine-bicarbonate starts to precipitate. Mixture is placed to cold place and allowed to stand for one night, and precipitated aminoguanidine bicarbonate is filtered, washed with ethanol and dried. Yield is 15.6g (60% theory) of aminoguanidine bicarbonate in form of dense white powder, melting with decomposition at 172C.

Notes:

1. Addition of several first crops of paste is accompanied by virgeous reaction and strong heating. On addition of later portions of paste reaction begins to cool down, and strong heating is slowly ceased. Then reaction becomes calmer larger portions of paste could be added, while taking care to not allow to fast temperature elevation. After addition is near completion reaction slows down and exotherm occurs not permanently, but some time after the addition. If temperature is rising too fast due to inefficient stirring of too thick mixture or if added paste portion was too large it is convenient to add some crushed ice to lower mixture temperature and make stirring easier.
2. To rapid heating of reaction mixture should be avoided, because reaction proceeds faster and becomes exothermic. It should be remembered that aminoguanidine is unstable to heat and to much heat will cause decreased yield of product.
3. Precise timings may be varied from run to run. To determine completion of reduction it is convenient to use qualitive test for nitroguanidine witch is preformed as follows. 3 drops sample of reaction mixture is added to test tube with 5 ml of 10% sodium hydroxide, and 5 ml of fresh saturated solution of Mohr's Salt (Ammonium iron(II) sulfate, or just mixture of NH4SO4 + FeSO4 solutions) is added. Red coloration shows presence of unreduced nitroguanidine. If reduction is complete same test results in formation of greenish precipitate without coloration of solution. As soon as test shows complete reduction, reaction mixture should no longer be heated and must be filtered as soon as possible.
4. Reaction mixture is quite thick and filters not readily. To force filtering to dryness, solid on filter should be trampled down with spoon in effort to fill all cracks forming while solid changes volume to prevent easy entry of air through the filter funnel. Good filtered solid should be almost dry. Filtering after later washing of precipitate goes without any difficulties.
5. Presence of ammonium chloride prevents joint precipitation of zinc salts then sodium hydrocarbonate is added to precipitate aminoguanidine as weak soluble bicarbonate. If on this stage solution is not transparent it should be filtered. Ammonium compounds transform zinc salts to soluble ammoniacal complexes, allowing to precipitate pure aminoguanidine bicarbonate.

Photos:

Source products – zinc and nitroguanidine and thick zinc/nitroguanidine paste used in reaction.

At beginning of addition reaction mixture tend to heat vigorously, so temperature should be controlled carefully. During this period paste should be added in small portions with efficient stirring, fortunately thickness of mixture is still low so this could be done with relative ease.

While new portions of paste are added, mixture becomes thicker and heat exchange becomes more and more difficult, local overheating is possible. If stirring is not efficient enough temperature difference in some places of mixture can be as high as 10-15C. Stirring and heat exchange can be cured by adding portions of crushed ice.

Then paste addition is complete, reaction mixture is allowed to stand at room temperature, giving time for exothermic reaction to finish and heated in water bath as described above. To keep temperature in required interval it is convenient to use hot water stream with temperature 2-3C higher then required.

Left photo shows qualitive reaction for nitroguanidine. Then few drop sample of reaction mixture is added to alkaline solution of iron (II) salt or iron-ammonium complexes nitroguanidine forms beautiful red coloration, while aminoguanidine in absence of nitroguanidine forms greenish precipitate shown on right photo.

Reaction mixture is quite thick and can not be filtered easily, it is highly recommended to use wide vacuum funnel to ease filtering. Filtrate has characteristic yellow color showing presence of aminoguanidine salt and also contains impurities - guanidine and zinc salts.

To exclude cooperative precipitation of zinc salts on addition of soda, required amount of ammonium chloride is added in order to bind zinc in soluble zinc-ammonium complexes. After addition of ammonium chloride and soda aminoguanidine bicarbonate begins to precipitate in form of dense white powder.

4. Preparation of 5-aminotetrazole from aminoguanidine-bicarbonate.

5-Aminotetrazole was first prepared by Thiele, by diazotation of aminoguanidine with sodium nitrite in hydrochloric acid environment. 5-Aminotetrazole crystallizes from water solution in the form of the monohydrate, which are colorless prisms or leaflets, losing water above 100°С and melting with decomposition at 200-203°С. 5-Aminotetrazole is badly soluble in alcohol and more readily in ether. It is also soluble in water solutions of bases and strong acids, and has good solubility in hot and poor solubility in cold water. 5-aminotetrazole's heat of combustion is 246.2 kcal/mol, standard enthalpy of formation is -49.7 kcal/mol. 5-Aminotetrazole shows weak acid properties, and in the anhydrous state is extremely hygroscopic. It is stable to heat, and its dissociation constant is about 1*10-4. Besides its acid properties, upon reaction with strong mineral acids 5-aminotetrazole can act as base, as can many organic amines. In general 5-aminotetrazole acts as an amphoteric substance, with behavior similar to that of amino acids. The high chemical stability of the tetrazole ring in addition to fact that substituents on the tetrazole ring are usually entered during ring formation, leaves the amino group as the only reasonable target for chemical manipulations. The amino group of 5-aminotetrazole has all the common properties of that functional group, and can be related in chemical behavior to the amino group of aniline.

5-Aminotetrazole forms salts with metallic cations, some of them are explosive. The cobalt salt Co(CN5H2)2*H2O, exists as pink water soluble crystals which explode upon heating to 228°С. The nickel salt Ni(CN5H2)2*H2O exists as blue water soluble crystals which explode upon heating at 290°С. The lead salt Pb(CN5H2)2 , exists as colorless crystals which deflagrate upon heating to 303°С. The mercury salt Hg(CN5H2)2 exists as white water insoluble crystals, they explode when dropped on a hot plate heated to 256°С. The Hg salt's shock sensitivity in the lead weight test is 50% explosions using a 2.5 kg weight and 38 cm drop height. The copper salt Сu(CN5H2)2*H2O exists as green very slightly water soluble crystals. A 2.5 kg weight with an drop height of 68 cm gives 50% of explosions when the copper salt is tested and it deflagrates when heated to 164°С. Aminotetrazole in the presence of copper sulfate and sodium acetate produces a green amorphous precipitate, which can be used as a diagnostic test for aminotetrazole. This precipitate is insoluble in acetic acid, and is soluble in hydrochloric acid.

34g (0.25 mol) of aminoguanidine bicarbonate is added to 217 ml of 15% nitric acid (0.561 mol), and mixed until evolution of carbon dioxide is stopped and resulted aminoguanidine nitrate is fully dissolved in solution. Yellow transparent solution is diazotized by slow addition of 17.2g sodium nitrite (0.25 mol) in 35 ml of water. Addition is accompanied by stirring, and temperature during all addition period is kept between 20-25°С by using water bath if needed (note #1). After completion of reaction the diazotation mixture is allowed to sit for 20 minutes at room temperature, and 29g of sodium carbonate is added (or 46g of sodium bicarbonate). Mixture is then heated on a water bath and refluxed for 4 hours. The solution is then neutralized by 30% sulphuric acid to pH=4, cooled to room temperature and allowed to sit over night (note#2). The precipitated crystals of 5-aminotetrazole monohydrate are filtered, washed with cold water and dried. Yield is about 70-74% based on aminoguanidine.

Notes:

1. Diazotation proceeds smoothly with little exotherm. If reaction mixtures begins to foam (this is the result of decomposition of nitrous acid), mixture must be stirred until form is settled before adding new a portion of nitrite solution. If reaction is carried put in the right way, it takes time about 10-15 minutes and proceeds with negligible evolution of nitrogen oxides.
2. 5-Aminotetrazole has an affinity to form supersaturated solutions. Often it does not begin crystallization even after full cooling, in that case crystallization should be assisted by introduction of a seed crystal, or by rigorous friction of a glass rod on side wall of reaction vessel (below liquid). Crystallization is generally fully complete after 12 hours from start.

Photos:

5. Synthesis of 5-nitrotetrazole from 5-aminotetrazole.

Free 5-nitrotetrazole is colorless very hygroscopic crystalline plates, with melting point 101°С, violently exploding then heated above 115-120°С. Measured heats of formation are +62.3 kj/mol in solid state and +89.2 kj/mol in gas. Extremely sensitive to external stimulus – impact, friction or fast heating. 5-Nitrotetrazole is strong monobasic N-H acid (pKa = -0.8) and weak base (рКbн+ = -9.2). Impact sensitivity (K-44-II) is 100%, sensitivity to friction (K-44-III) has lower limit at 250 kg/cm3, detonation velocity at density 1.73 g/cm3 is 8900 m/sec, crystal density is 1.77 g/cm3. Forms stable salts with yellow color in solution, witch transforms to lime green on standing, without any visible change of properties.

Salts of alkali, alkaline earth and ammonium are readily soluble in water, salts of cobalt, nickel, mercury, lead, silver and copper are very badly insoluble[3]. Mercury salt is more soluble then silver salt, lead and copper salts are soluble in hot water. Sodium salt is soluble in acetone. Salts are stable on storage in usual conditions, water and carbon dioxide not affect them in any visible amount. Many salts form hydrates, witch are less sensitive then anhydrous salts. In wet state salts are relatively safe, but then dry they explode on shock, friction and fast heating. Many salts have excellent initiating power and strong brisance.

5-Nitrotetrazole is chemically stable to action of oxidizers and prolonged heating of solution, is readily acylated on atom N-2 forming numerous organic derivatives, reaction is regioselective N-1 derivatives are found only in trace amounts. Electron density in 5-nitrotetrazolate anion is deeply common with one of it’s isoelectronic analogue – cyclopentadienyl cation, and forms sandwich type complexes with Fe (II) in same way. 5-nitrotetrazole forms complexes with copper, iron, cobalt and nickel, witch are usualy not volatile, insoluble in most of solvents and can form polymers.

5-Nitrotetrazole can be successfully obtained, by original Herz method, but method is dangerous in terms of “micro explosion” hazard. Later Gilligan and Kamlet, reviewed original Herz procedure to eliminate minor detonations, increase yield and ease filtration of product, this method is shown below.

Preparation of sodium 5-nitrotetrazolate dehydrate. Place solution 104g (1.5 mol) sodium nitrite and 55g (0.22 mol) copper sulphate pentahydrate in 300 ml water in a 2L beaker and cool to 5°C. Add solution of 51.5g (0.5 mol) 5-aminotetrazole monohydrate, 2g copper sulphate pentahydrate and 64 ml 70% nitric acid in 700 ml water to solution of sodium nitrite/copper sulphate, dropwise with efficient stirring over a period of about 90 minutes holding the temperature at 15° to 18°C (watch hazard notes below). Stir for 15 minutes, add solution 70 ml 70% nitric acid in 30 ml water dropwise and then stir for an additional 30 minutes. Filter with suction and wash the copper acid salt with 250 ml 1.8 N nitric acid and three times with 250 ml of water. Do not allow the cake to dry during the filtration and washing. Transfer the wet cake to a 1500 ml beaker and adjust the volume to about 600 ml with water. Adjust the pH of the slurry to ca 9 with 50% sodium hydroxide solution to precipitate copper hydroxide and then heat the efficiently stirred slurry to 100°C on water bath and digest for 30 minutes (Note 1). Allow the precipitate to partially settle and filter with suction through a packed layer of "celite" (Note 2). Wash the precipitate twice with 100 ml of water. Adjust the pH of the combined filtrate and washes to 4, with concentrated nitric acid. Reduce the volume to ca 350 ml using slow evaporation on water bath. Cool to 2°C and filter the sodium 5-nitrotetrazole (Note 3). Reduce the filtrate to 200 ml and take a second crop...etc. Combine the crops, redissolve in water and recrystallize a second time. Air dry the product. Dissolve the sodium 5-nitrotetrazole in acetone on a steam bath and filter to remove inorganic salts. Cool the filtrate in an ice bath and remove the sodium 5-nitrotetrazole by filtration. Recrystallize a second time from acetone and air dry (Note 4). The yield is about 45-55% of theory based on 5-aminotetrazole. Reaction scheme:

Notes:

1. The blue hydrated cupric hydroxide is converted to the brownish-black cupric oxide at temperatures above 70°C.
2. Without, "celite" the filtration and washing requires several hours since the finely divided cupric oxide clogs the filter.
3. Sodium 5-nitrotetrazole crystallizes from water as a voluminous hydrated mass. After air drying, the salt contains two to five moles of water of crystallization depending on ambient humidity.
4. Sodium 5-nitrotetrazole crystallizes from acetone as a dihydrate. This appears to be stable at ambient conditions.

Hazard notes:

During the diazotization of 5-aminotetrazole nitrogen oxide fumes are given off from the reaction solution. This step should be carried out in an efficient hood. Reaction goes through extremely unstable diazotetrazolium intermediate, witch can spontaneously detonate in solution then the concentration exceeds 1%, causing so called “minor detonations” , which while not harmful in themselves, were pschologically disturbing and did on occasion break glassware. There was the possibility that the potentially dangerous (in the dry state) acid copper nitrotetrazole salt would be spilled over adjacent surfaces. Minor detonations occurring during the diazotization were caused by nitrogen oxide fumes arising from the reaction solution and reacting with droplets of 5-aminotetrazole solution on various surfaces of the apparatus. Since copper salts catalyze the reaction of 5-diazotetrazole with nucleophiles, it was felt that the addition of small amounts of copper sulfate to the 5-aminotetrazole solution would eliminate any build-up of the diazotetrazole by catalyzing its conversion to 5-hydroxytetrazole. This proved to be the case since the addition of small amounts (~2g) of copper sulphate to the 5-aminotetrazole solution completely eliminated the detonations previously experxenced. However one should remember that minor detonations can still take place occasionously in some cases.

The copper acid salt of 5-nitrotetrazole, CuHNT*(NT)2, can be handled safely in the wet state; however in the dry state, it is very sensitive to shock and electrostatic discharge. Air dried sodium 5-nitrotetrazole containing two or more mole-equivalents of water of crystallization is relatively insensitive to shock; it cannot be detonated with a hammer blow. However when completely dry, it is also a sensitive explosive. Both compounds will detonate violently if dropped on a hot plate. All precautions consistent with the handling of potentially dangerous explosive materials should be observed throughout this operation.

Photos:

Reaction is carried out with intense cooling in ice bath, during reaction mixture thickens from microcrystalline acid copper 5-nitrotetrazolate precipitate.

After addition of nitric acid, reaction mixture is allowed to sit for a while, after this period reaction product is filtered by means of vacuum funnel.

After removal of copper salts by boiling in alkali solution and subsequent filtration of insoluble copper oxide, pure solution of sodium 5-nitrotetrazolate is obtained, solution has characteristic yellow coloration. This solution is concentrated on water bath, precipitated salt is filtered and recrystallized from acetone forming transparent plates of sodium 5-nitrotetrazolate dehydrate.

[Edited on 14-10-2009 by Engager]

[Edited on 15-10-2009 by Engager]

Beautiful!!!

Thanks a lot for sharing and for such a nicely written report.

But where are the references? It looks like you lost them in the transfer from the text editor. It would be a shame if the sources of so many interesting information would remain unavailable. Can you please fix this?

"I'm not a natural english language speaker..."
Neither am I, but there seems to be only minor syntax/spelling errors, not worth pointing out. However some sentences I'm unsure if I understand correctly, for example:
"Reduction by hydrogen in chemical or electrochemical process proceeds through formation of nitrosoguanidines and readily proceeds in presence of catalysts such as Raney nickel or zinc acetates."
I understand the use of Raney nickel in a hydrogenation, but how is zinc acetate supposed to catalyse the reduction. Maybe you mean "zinc in acetic acid"?


Also related is the alternative preparation of guanidine and nitroguanidine by Axt:
Nitroguanidine from Sulphamic acid and Urea

Quote: Originally posted by Nicodem

Beautiful!!! Thanks a lot for sharing and for such a nicely written report. But where are the references? It looks like you lost them in the transfer from the text editor. It would be a shame if the sources of so many interesting information would remain unavailable. Can you please fix this? "I'm not a natural english language speaker..." Neither am I, but there seems to be only minor syntax/spelling errors, not worth pointing out. However some sentences I'm unsure if I understand correctly, for example: "Reduction by hydrogen in chemical or electrochemical process proceeds through formation of nitrosoguanidines and readily proceeds in presence of catalysts such as Raney nickel or zinc acetates." I understand the use of Raney nickel in a hydrogenation, but how is zinc acetate supposed to catalyse the reduction. Maybe you mean "zinc in acetic acid"? Also related is the alternative preparation of guanidine and nitroguanidine by Axt: Nitroguanidine from Sulphamic acid and Urea

Quote: Originally posted by 497

Very nice! Thank you for the great writeup! Hopefully I'll be able to try it out soon. P.S I noticed in one place you say 510ml of conc. H2SO4, then later in the detailed description of the reaction you say 500g. I assume you meant grams the first time also? [Edited on 14-10-2009 by 497]

Quote: Originally posted by Formatik

I'm with the praise, that's spectacular work. But a concern I have is heating the ammonium nitrate with urea. Some references in Gmelin were stating it is an explosion risk and it dedicated some references to this. I don't have it now or I'd post it right here, but two references were: J.F. Anderson (Saftey Air Ammonia Plants 9 [1967] 70/2, C.A. 68 [1968] Nr. 41755); L.G. Croysdale, W.E. Samuels, J.A. Wagner (Chem. Eng. Progr. 61 Nr. 1 [1965] 72/7) concerning an explosion accident that happened with a urea-NH4NO3-soln. (35% urea, 45% NH4NO3, 20% H2O). Alternatively, there are other methods using other NH4 salts like the chloride or bromide instead (thread on this forum).

"5. Presence of ammonium chloride prevents joint precipitation of zinc salts then sodium hydrocarbonate is added to precipitate aminoguanidine as weak soluble bicarbonate. If on this stage solution is not transparent it should be filtered. Ammonium compounds transform zinc salts to soluble ammoniacal complexes, allowing to precipitate pure aminoguanidine bicarbonate."

In other preparations of aminoguanidine, complexation of Zn(II) is achieved by addition of NH3 which forms some kind of soluble ammine. This certainly works. However upon reading Engager's writeup I stumbled across this section which suggests that the ammonium ion would form similar complexes. I dont understand what compound is formed by this reaction. Can someone please enlighten me?

Quote: Originally posted by maxidastier

I've some Nitroguanidin now, but it dries very slowly. Can I put it in the oven, or is it not normal that it dries that slowly?

I did it the same way, but: 1. They send out (NOx)gases in my room, so that the room becomes dusty
2. They do not all like in the picture above: Some are flat like in the pic, some are very solid.

Quote: Originally posted by maxidastier

I tried it with: 170 g Ammonium Nitrate, 100+60g Urea and 40 g Silical Gel. Yield should have been 100 g, but it was only 30g. Except the Guanidinitrate another product was formed, which was hard as stone and not soluble in water.Reaction temperature was between 160 and 210 C and 5 hours. Can anyone tell me what's wrong?

Quote: Originally posted by maxidastier

I did it the same way, but: 1. They send out (NOx)gases in my room, so that the room becomes dusty 2. They do not all like in the picture above: Some are flat like in the pic, some are very solid.

Quote: Originally posted by maxidastier

Sry, I have to add another point: You say: 340g of ammonium nitrate (Note #2), 200g urea and 80g of tempered dry silica gel The patent says: urea:AN 1:2, because this is the best method to avoid byproducts. So it would be e.g. 120 g:240 g. Because convertion to Guanidinitrate at the beginning of the reaction is higher, after an hour on has to add 20 g urea to keep the 2:1 ratio. At the end of 3,5-4,5 hours reaction the ratio will change to 1:6, urea stopping to be converted. So you have alot of AN to reuse or to slurry it with the catalyst.

Quote: Originally posted by maxidastier

Another point is the preparation of Nitroguanidin which you claim to be finished in ca. 15 mins. A description I read says, it needs to be aged at least 15 hours to convert all Guanidinitrate. I tried both ways and strongly recommend to age your mix at least 8 hours (over night).

Timings of aging in H2SO4 are widely described in explosive related literature and found to be appropriate on practice. Watch this:



This is actually from Russian book on chemistry and technology of high explosives and it says that at 30C 10 min is ideal timing, while higher temperatures and longer time causes increased decomposition of nitroguanidine.

[Edited on 29-7-2010 by Engager]

Quote: Originally posted by Taoiseach

@497 There's several problems: Reducing 100g NQ would take over 40h at 5 amps. Higher currents are possible but they're operating at quite high a voltage (to overcome additional resistance of the diaphragm I guess) which produces considerable heat. The 300A cell was operated with active cooling. Temperature has to be kept below 30°C otherwise only nitrosoguanidine is formed. The best yield is obtained at 5°C cell temp. At such temperature solubility of NQ is neglible (only 4.4g dissolve in 1000cc water at 25°C) This is probably why they're using rotating electrodes. Near the cathode, concentration of NQ will drop due to reduction to well soluble aminoguanidine. The rotation helps to quickly supply NQ and minimize the gradient in concentration. I dont see how such electrodes could be improvised easily. [Edited on 26-10-2009 by Taoiseach]

Quote: Originally posted by Engager

Calcium cyanamide is not readily available in many countries, for example here in Russia mass production of cyanamide was stopped many years ago and chemical is actually banned one. If you can get your hands on calcium cyanamide it can be converted to aminoguanidine in single step by reaction with hydrazine sulphate or to 5-ATZ by reaction with hydrogen azide. I know this route for a long time and some people tried it, production of calcium cyanamide require access to high temperatures, but source products are very cheap - urea and lime. I was experimenting with cyanamide production for quite a while and will post article on this route some time soon.

It can be inconvenient if there is a need for a banned chemical

It may be possible to use any guanidine salt and react with hydrazine sulfate in corresponding molar proportion to produce either mono aminoguanidine, di-aminoguanidine, or tri-aminoguanidine derivatives. The reaction is similar to the reaction of nitroguanidine with hydrazine to produce nitroaminoguanidine. The mechanism is mentioned in a patent primarily related to production of triaminoguanidine salts. I will have to look it up, but it is posted in the tetrazole thread.

Your interest regarding cyanamide is parallel to some isolated discussions which were taking place here, about experiments for producing pure calcium cyanamide to be used for synthesis of guanidine and aminoguanidine derivatives including tetrazoles. Calcium cyanurate can be thermally decomposed in the absence of air, by moderately high temperature, a low red heat, to produce 100% pure calcium cyanamide as the result. The precursor is easily made by precipitation from calcium chloride solution and sodium cyanurate. Cyanuric acid is available as a chlorine stabilizer for swimming pools, or may be easily synthesized from heating together urea and ammonium chloride. Alternately, reaction between urea and ammonium chloride at different temperature and in the presence of silica gel catalyst produces guanidine hydrochloride instead, and this involves no explosive danger as would occur with ammonium nitrate conversion to guanidine nitrate. The guanidine nitrate can (probably) subsequently be gotten from the guanidine hydrochloride, via double decomposition. Certainly guanidine perchlorate can be gotten easily enough from double decomposition of guanidine hydrochloride and sodium perchlorate, or probably from sodium perchlorate formed in situ from a basification of ammonium perchlorate with sodium hydroxide or sodium bicarbonate, with boiling away of the ammonia. Guanidine perchlorate should nicely crystallize out from the residual byproduct sodium chloride solution.

These interesting materials and methods certainly make urea an interesting subject for experiments. Attached are a couple of relevant patents.


Attachment: US2783276_SUBSTITUTED_GUANIDINE_SALTS.pdf (129kB)
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Attachment: US2527316 Cyanuric Acid via Urea and Ammonium Chloride.pdf (129kB)
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[Edited on 3-8-2010 by Rosco Bodine]