The Preparation And Characteristics Research Of Nitrogen-rich Tetrazole Derivatives

Tetrazole is a kind of nitrogen-rich heterocyclic compound containing unsaturated five membered ring, whose ring skeleton is planar construction. Tetrazole derivative not noly has the same structure of tetrazole, but has excellent performance, for example, aromatic properties, high nitrogen content, a large number of N-N, C-N, N=N, C=N bonds in the molecular structure, very high enthalpy of formation, high density, low sensitivity, good thermal stability, its final product of combustion or explosion being the nitrogen, low smoke, no pollution, friendly to environment, reducing the harm to health, all of which makes it be the ideal high energy density materials(HEDMs). It has active chemical properties that can undertake to deprotonation, protonation, substitution and oxidation reaction, every nitrogen atom contain lone pair electrons which is easy to coordinate with metal ions. Therefore, there are varieties of tetrazole derivatives possessing many special physical and chemical properties that can be used in biomedical fields with some antihypertensive, antivirus, antitumor efficacy; used as new green herbicide, growth promoter in the field of agriculture; used as a metal-organic frameworks(MOFs), proton exchange membrane materials, low signature energetic materials, gas generating agent and precursor of superhard materials in the fields of automobile, military defense, aerospace and microelectronics. The exploration and research of tetrazole derivative has become the interesting topics for new special energy and medicine materials.In order to research and develop new rich-nitrogen tetrazole derivatives, the paper systematically summarized the physicochemical properties, application fields, synthesis methods and construction mode of rich-nitrogen tetrazole derivatives.In this paper we synthesized tetrazole with triethyl orthoformate(CH(OEt)3), sodium azide, ammonium chloride and acetic acid as raw materials, explored the effect of the raw material ratio and reaction time on the yield, obtaining the optimal synthesis conditions: a raw material ratio of 1:3:3:4(sodium azide: ammonium chloride: triethyl orthoformate: acetic acid), a reaction time of 10 h, a reaction temperature of 90 °C, affording a 91.55 % yield(higher than other literature reported); we produced tetrazole with 15 N labeled ammonium chloride as the raw material and characterized the product with nuclear magnetic resonance(15N), mass spectrum and isotope ratio mass spectrometer, and proved that the basic synthesis mechanism of tetrazole could be that ammonium cation NH4+connecting azide group N3- attacked CH(OEt)2+(isolated by CH(OEt)3), and there were three ethanol released progressively before obtaining the stable five membered ring structure; ammonium chloride in the reaction plays two roles, not only as a catalyst, and as one of raw materials, the nitrogen atom provider of the tetrazole ring. We then synthesized sodium tetrazolate, ammonium tetrazolate, hydrazinium tetrazolate and guanidine tetrazolate using tetrazole with ammonia, hydrazine and guanidine carbonate, respectively(guanidine tetrazolate hasn’t been reported before) and fully characterized by IR spectroscopy, nuclear magnetic resonance, elemental analyses, thermogravimetry and differential scanning calorimetry(TG/DSC), etc. The result indicated that the decomposition temperature order of the five compounds was sodium tetrazolate(319.45 °C) > guanidine tetrazolate(271.81 °C) > ammonium tetrazolate(226.97 °C) > hydrazinium tetrazolate(219.78 °C) > tetrazole(206.03 °C). We can see that guanidine tetrazolate is the most stable comparing with ammonium tetrazolate and hydrazinium tetrazolate, which was due to larger number of amino which can significantly improve the stability of compound, and ammonium tetrazolate contained crystal water that is conducive to the formation of hydrogen bonds and the stabilization of the structure, so the decomposition temperature of ammonium tetrazolate was higher than hydrazinium. In addition, the highest decomposition temperature of guanidine tetrazolate offers the research theory and basis for being used as nitrogen system flame retardant and has potential application value. Sodium tetrazolate crystal was obtained by recrystallization from ethanol, Crystal Data: CH3N4 Na O, formula weight = 110.06 g·mol-1, Orthorhombic, Pmc2(1), a = 5.847(4)(?), b = 5.605(3)(?), c = 6.387(4)(?), β = 90°, V = 209.3(2) ?3, D c = 1.746 g·cm-3, Z = 2; the sodium ion is coordinated by four different tetrazolate rings and two crystal water, the packing arrangement of sodium tetrazolate was rhombus structure viewed along b axis and long-chain “*” type structure viewed along c axis which leads to highest thermostability.We developed a convenient, simple work-up process and low-cost chlorination protocol: preparing sodium 5-chlorotetrazolate using sodium hypochlorite solution as a halogenating reagent, tetrazole as a raw material and acetic acid as a solvent, investigating optimal organic extracting solvent and reaction process conditions: a raw material ratio of 1:12:12(tetrazole: sodium hypochlorite solution: acetic acid), a reaction time of 6 h, a reaction temperature of 55 °C, affording a 92.76 % yield, acetone was the best extraction solvent. 5-chloro-tetrazole was obtained by the acidification of sodium 5-chlorotetrazolate and reacted with ammonia, hydrazine and guanidine carbonate, yielding ammonium 5-chlorotetrazolate, hydrazinium 5-chlorotetrazolate and guanidine 5-chlorotetrazolate, respectively. The five new compounds were fully characterized by IR spectroscopy, nuclear magnetic resonance, elemental analyses, single-crystal X-ray diffraction, thermogravimetry and differential scanning calorimetry(TG/DSC), etc. All of the five structures have not been investigated. The decomposition reaction of chlorinated tetrazolium nitrogen-rich derivatives is exothermic reaction, and the decomposition temperature order was sodium 5-chlorotetrazolate(241.05 °C) > guanidine 5-chlorotetrazolate(231.52 °C) > hydrazinium 5-chlorotetrazolate(212.86 °C) > ammonium 5-chlorotetrazolate(182.39 °C) > 5-chloro-tetrazole(159.98 °C) which were higher than 100 °C, so they are handled safely and have the potential application in the field of energetic materials; the thermal stability of chlorinated tetrazolium nitrogen-rich derivatives was lower than corresponding tetrazolium nitrogen-rich derivatives that is because the chlorine atom improves the reactivity of compound in some degree; the decomposition temperature variation tendency of different chlorinated tetrazolium nitrogen-rich salts was the same to the tetrazolium nitrogen-rich salts, sodium 5-chlorotetrazolate possessed the highest decomposition temperature(having more amino group), and guanidine 5-chlorotetrazolate took second place, the only difference was that the decomposition temperature of hydrazinium 5-chlorotetrazolate was higher than ammonium 5-chlorotetrazolate, and the amount of residue of ammonium 5-chlorotetrazolate was the most, reaching 37.64 %, its IR spectra contained bands for the stretching vibrations of the N-H, C≡N, C=N and C-N bonds which can be deduced that it may be a type of carbon nitride material, so ammonium 5-chlorotetrazolate could be a promising precursor material for carbon nitride. Crystal Data of Sodium 5-chlorotetrazolate: C0.5H2Cl0.5N2Na0.5O, formula weight = 81.26 g·mol-1, Orthorhombic, Pnma, a = 6.8611(19)(?), b = 6.9243(19)(?), c = 6.387(4)(?), α = β = γ = 90°, V = 583.5(3) ?3, D c = 1.850 g·cm-3, Z = 8; the sodium ion is coordinated by two different tetrazolate rings and four crystal water, the packing arrangement of sodium 5-chlorotetrazolate was diamond structure viewed along c axis, intersecting channel structure viewed along b axis and viewed along a axis, there was a gap between molecules and larger space which can coordinate with nitrogen-rich group and metal ion.We also explored the reactivity of tetrazole, 5-amino-tetrazole with cyanuric chloride, respectively, separated and purified the reaction solution by thin-layer chromatography and column chromatography and fully characterized the products by IR spectroscopy, nuclear magnetic resonance, mass spectrum and TG/DSC. According to the results, the two purified products were only di-substituted products because the third C-Cl bond was less active than other bonds, which was hard to react under usual conditions. The thermal properties of the two products were: the thermostability of tetrazyl triazine di-substituted product was poor, and it was decomposed at the temperature of 150.12 °C and released heat due to the decomposition of the tetrazole ring(the stability of triazine ring is higher than that of tetrazole ring); 5-amino tetrazolyl triazine di-substituted product was decomposed at the temperature of 200.72 °C and 216.07 °C which were caused by the cracking of triazine ring and tetrazole ring, respectively; the decomposition of the amino tetrazole ring was exothermic behavior, and the 5-amino tetrazolyl triazine di-substituted product was more stable than tetrazyl triazine di-substituted product.The non-isothermal kinetic method was adopted to analyze sodium tetrazolate, 5-chloro-tetrazole, sodium 5-chlorotetrazolate, hydrazinium 5-chlorotetrazolate, and guanidine 5-chlorotetrazolate, two formulas Kissinger and Flynn-Wall-Ozawa were used respectively to calculate the kinetic parameters of the five compounds. Testing the thermogravimetry and differential thermal gravity(TG/DTG) curves of the five compounds at a heating rate of 2.5, 5, 10, 20 °C·min-1 in the temperature range from 35-400 °C under a nitrogen flow of 20 m L·min-1; obtaining the value of β and the corresponding thermal decomposition peak T p; calculating ln(β/T P2), lgβ and 1/T P; drawing ln(β/T P2)- 1/T P and lgβ-1/T P and using Origin software to get the linear fitting curves. The activation energy E K(Kissinger), E O(Flynn-Wall-Ozawa) and pre-exponential factor lg A was calculated by the slope and intercept of the linear fitting curves, the value of which were reliable and valuable because that the linear correlation coefficient R2 was close to one and the data relevancy was higher; the result showed that the values of E K and E O were similar that indicated the thermal decomposition kinetic method was reasonable; the value of E K order was: sodium 5-chlorotetrazolate(271.66 k J·mol-1) > sodium tetrazolate(209.03 k J·mol-1) > guanidine 5-chlorotetrazolate(162.05 k J·mol-1) > hydrazinium 5-chlorotetrazolate(156.87 k J·mol-1) > 5-chloro-tetrazole(82.32 k J·mol-1). The larger the activation energy is, the greater the energy of decomposition need, and that is to say the higher the decomposition temperature is; the higher of E K of guanidine 5-chlorotetrazolate once again proved that amino group is good for the the stability of compound. However, the E K of sodium 5-chlorotetrazolate was higher than sodium tetrazolate, the decomposition temperature of sodium 5-chlorotetrazolate was lower than sodium tetrazolate which can be explained that the pre-exponential factor lg A of sodium 5-chlorotetrazolate(27.8) was greater than that of sodium tetrazolate(18.2), in other words, sodium 5-chlorotetrazolate had more active sites.