S.V. Levchik

Thermal decomposition of aminotetrazoles

Abstract The thermal decomposition of 5-aminotetrazole (5-AT), 1-methyl-5-aminotetrazole (MAT), 1,5-diaminotetrazole (DAT), poly-1-vinyl-5-aminotetrazole (PVAT) and sodium salt of 5-aminotetrazole (SAT) have been studied by thermogravimetry, thermal volumetric analysis (TVA), DSC, DTA and evolved gas analysis (EGA). The kinetic parameters of the thermal decomposition of aminotetrazoles were calculated either by the Ozawa method or by the method of invariant kinetic parameters (IKP). The gaseous products, volatile condensed products and solid residues were identified by FTIR and gas chromatography–mass-spectrometry (GS/MS). The total energies and the energies of chemical bonds of various isomeric forms of 5-AT and MAT have been calculated ab initio using MP2/6-31G∗∗ theory level and MNDO approximation. Based on the content of products of thermal decomposition and the kinetic consideration, the mechanism of thermal decomposition of aminotetrazoles has been derived. Two routes of the splitting of tetrazole ring leading either to elimination nitrogen or hydrogen azide are suggested. The contribution of each route is changing upon the advancement of the process. It was assumed, that hydrogen azide splits out from the prothotropic forms of the tetrazole ring, which have hydrogen atoms by nitrogens in the ring. Experimental study as well as literature data on the amino-imino tautomerism are in agreement with the suggested mechanism of the decomposition of the tetrazole ring. It is shown that secondary reactions significantly extend variety of the products of thermal decomposition of aminotetrazoles.

Thermal decomposition of aminotetrazoles: Part 1. 5-Aminotetrazole

The thermal decomposition of 5-aminotetrazole (5-AT) has been studied by thermogravimetry, thermal volumometry, DSC, DTA and EGA. Solid products of thermal decomposition have been identified by IR spectroscopy and gaseous products by IR and mass spectrometry. Theoretical considerations of thermodynamic characteristics and energies of atomic bonding in the 5-AT tautomeric forms and intermediates have been carried out by the MO SCF method in the MNDO approximation. On the basis of IR and available literature data it is shown that dehydrated 5-AT exists mainly in the imino form in the solid state. Thermal treatment leads to increasing content of the amino form. The thermal decomposition of the imino form of 5-AT starts just after melting and results in hydrogen azide and carbodiimide. The linear polymer of carbodiimide and melamine derivatives have been identified in the solid residue. Further increase of temperature in the course of linear heating leads to another route of thermal decomposition involving the amino form of 5-AT accompanied by the evolution of nitrogen. Apparent activation energies of these routes determined from non-isothermal thermogravimetric data amount to 165 and 135 kJ mol−1, respectively.

The thermal decomposition of tetrazoles

Abstract A brief review of the literature on the thermal decomposition of chemical compounds containing a tetrazole heterocycle is given. It is shown that there are two radically different pathways of the tetrazole cycle fragmentation connected with the formation of a molecule of nitrogen or azides. The elimination of nitrogen from 2,5-disubstituted tetrazoles results in a nitrilimine. The elimination of nitrogen from 1,5-disubstituted tetrazoles leads to the formation of a nitrene. The stabilization of active intermediate products depends on the chemical properties of the substituents and the conditions under which the process is carried out, and leads to a wide spectrum of final products for the thermal decomposition of tetrazoles. Kinetic studies of the thermolysis of tetrazoles show that the mechanism of heterocycle fragmentation can vary with varying temperature. The elimination of nitrogen from tetrazoles is preceded by a high-polarity transition state.

The thermal decomposition of aminotetrazoles. Part 2. 1-methyl-5-aminotetrazole and 1,5-diaminotetrazole

Abstract The thermal decompositions of 1-methyl-5-aminotetrazole and of 1,5-diaminotetrazole have been studied using thermogravimetry, differential scanning calorimetry and thermal volumetric analysis. The solid residues, and the high boiling point and gaseous products of the decompositions have been collected and identified using IR spectroscopy and mass spectrometry. Both aminotetrazoles start to decompose just after melting: 1-methyl-5-aminotetrazole at 495 K and 1,5-diaminotetrazole at 460 K. The decomposition is accompanied by elimination of gaseous and high boiling point products, partial evaporation of the original substances and formation of thermally stable residues. Both 1-methyl-5-aminotetrazole and 1,5-diaminotetrazole, in the solid state and probably in the melt, coexist in amino and imino tautomeric forms. Therefore, two competing mechanisms of tetrazole ring-breaking, with elimination of respectively nitrogen or hydrogen azide molecule, are proposed.

Thermal decomposition of tetrazole: Part I. Programmed heating

Abstract The thermolysis of tetrazole was studied using differential scanning calonmetry, differential automatic gas volumetry and complex thermal analysis. The thermoanalytical and kinetic parameters from heat-evolution, gas-release and thermogravimetry data were calculated. The results reveal the complex nature of the tetrazole thermolysis. The mechanisms of thermal decomposition seem to be different in the gas phase and in the liquid state.

Analysis and development of effective invariant kinetic parameters finding method bassd on the non-isothermal data

Abstract The connection of the method of estimating effective invariant kinetic characteristics with the common ways of describing the complicated process by means of multiparametric dependences and the main equation of non-isothermal kinetics is discussed. This method gives the possibility to transform variables, which makes the statement inverse kinetic problem conditions better. The validity of the method has been shown by the experimental data of the butyl rubber decomposition.

Thermal decomposition of tetrazole-containing polymers. I. Poly-5-vinyltetrazole thermolysis

Thermal decomposition of poly-5-vinyltetrazole has been investigated by the methods of chemical and complex thermal analyses under isothermal and nonisothermal conditions, infrared spectroscopy and gas chromatography. Activation parameters of the decomposition process have been evaluated by various methods. The analysis of the obtained data leads to the conclusion that, depending on the conditions of the experiment, decomposition of polymer tetrazole cycles may proceed in two parallel ways: either destruction of the tetrazole rings with elimination of hydrogen azide, or their tautomeric isomerization into the respective azidoazomethine, from which a nitrogen molecule is then ‘chipped off’.

Thermal decomposition of tetrazole Part III. Analysis of decomposition products

Abstract By means of methods of IR and 1H NMR spectroscopy, mass spectrometry, chromatography, elemental and chemical analyses it could be stated that tetrazole thermolysis, both in a melt and in the gaseous state, proceeds mainly through elimination of a nitrogen molecule, but in the melt the nitrogen is eliminated predominantly from the azide structure and in the gaseous state it eliminates from the cyclic 2H- form. When carrying out the process in a melt, ca. 5% of the tetrazole decomposes with hydrogen azide evolution. The intermediates (nitrene or C,N-nitrilimine respectively) are unstable and, depending on the experimental conditions, they are capable of either decomposing, with formation of HCN, N2 and H2, or participation in reactions leading to formation of cyanamide polymers.

Thermal behaviour of ammonium polyphosphate-inorganic compound mixtures. Part 2. Manganese dioxide

The chemical interaction between ammonium polyphosphate (APP) and managanese dioxide (MnO2) was studied by thermogravimetry with linear heating. The products of interaction were collected at successive steps of weight loss and analysed by X-ray diffraction (on crystalline products) or by chemical analysis (on amorphous products). It was found that MnO2 starts to interact with APP at the beginning of the thermal decomposition of APP at 270–280°C. At the onset of weight loss of the APPMnO2 mixtures, manganese(VI) is reduced to manganese(III) and (II) producing MnNH4P2O7 and Mn(NH4)2(PO3)4 respectively. Ammonia, which is partially reduced to nitrogen, is evolved from PP. The formation of MnNH4P3O9 and then Mn2P4O12 is observed on further heating of the mixtures to 560–570°C. The content and ratio of the products of reaction depend on the temperature and the ratio of components in the initial APPMnO2 mixtures. Assignment of the X-ray powder diffraction peaks and an estimation of the lattice parameters have been made on orthorhombic MnNH4P3O9 (a = 7.357(3), b = 12.186(8), c = 9.390(5)A, space group Pmcn).

Thermal behaviour of ammonium polyphosphate-inorganic compound mixtures. Part 1. Talc

Abstract The chemical interaction between ammonium polyphosphate (APP) and talc was studied under dynamic or isothermal heating conditions. The products of interaction were identified by X-ray methods or separated by thin layer chromatography and analysed. It was shown that APP decomposes above 280°C and starts to interact with talc above 300°C, giving binary ammonium silicon tetrapolyphosphate and ammonium magnesium polyphosphate or cyclophosphate depending on the initial APP/talc ratio in the mixture. The formation of magnesium cyclotetraphosphate, magnesium ultraphosphate, silicon oxymonophosphate and silicon diphosphate is observed after further heating at 400–800°C. A glass of magnesium silicon phosphate is formed at 1000°C. The schemes of chemical reactions occurring at different temperatures are proposed for various APP/talc ratios.