Oleg A. Ivashkevich

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.

1,5-Diamino-1H-1,2,3,4-tetrazolium picrate: X-ray molecular and crystal structures and ab initio MO calculations

The crystal and molecular structures of 1,5-diamino-1H-1,2,3,4-tetrazolium picrate (DATP) were determined by X-ray diffraction analysis. The tetrazolium cation in DATP has a structure with protonated N4 atom of the ring. Two amino groups in the cation are found to be rather different. The 5-amino group lies in the plane of the tetrazole ring and valence angles around the N atom are close to 1208, which indicates sp 2 hybridization of atomic orbital of the nitrogen atom. In contrast, valence angles around the N atom of the 1-amino group are close to tetrahedral angle, which suggests sp 3 hybridization. The exocyclic C– N bond in the cation is substantially shorter than that in 1,5-diaminotetrazole. The obtained results indicate a conjugation between the p-system of the tetrazole ring and the 5-amino group. The results of ab initio calculations of electronic structure and relative stability for various tautomeric forms of protonated 1,5-diaminotetrazole using MP2/6-31G* and B3LYP/6-31G* levels of theory are in a good agreement with X-ray data and show that there are differences in s-electron overlap populations for the C– N bonds in the cation in DATP, while p-electrons are delocalized. q 2003 Elsevier Science B.V. All rights reserved.

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.

Deprotonative Metalation of Chloro‐ and Bromopyridines Using Amido‐Based Bimetallic Species and Regioselectivity‐Computed CH Acidity Relationships

A series of chloro- and bromopyridines have been deprotometalated by using a range of 2,2,6,6-tetramethylpiperidino-based mixed lithium-metal combinations. Whereas lithium-zinc and lithium-cadmium bases afforded different mono- and diiodides after subsequent interception with iodine, complete regioselectivities were observed with the corresponding lithium-copper combination, as demonstrated by subsequent trapping with benzoyl chlorides. The obtained selectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase and as a solution in THF by using the DFT B3LYP method.

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.

N-aryl pyrazoles: DFT calculations of CH acidity and deprotonative metallation using a combination of lithium and zinc amides

A series of N-aryl and N-heteroaryl pyrazoles have been deproto-metallated using a 2,2,6,6-tetramethylpiperidino-based mixed lithium-zinc combination. Mono-, di-, and tri-iodides have been obtained after subsequent trapping with iodine, depending on the substrate and on the quantity of base used. The results have been discussed in the light of the CH acidities of the substrates, determined both in the gas phase and in THF solution using the DFT B3LYP method.

Effect of nitrogen doping on the electromagnetic properties of carbon nanotube-based composites

Nitrogen-doped and pure carbon nanotube (CNT) based composites were fabricated for investigating their dielectric properties in static regime as well as electromagnetic response properties in microwave frequency range (Ka-band). Two classes of host matrix—polystyrene and phosphate unfired ceramics—have been used for composites fabrication. The study reveals miscellaneous effect of nitrogen doping on the dielectric permittivity, dc conductivity and electromagnetic interference shielding efficiency of CNT-based composites, produced with both polymer and ceramic matrices. The high-frequency polarizability, estimated for different-length CNTs, and static polarizability, calculated for nitrogen-containing CNT models using a quantum-chemical approach, show that this effect results from a decrease of the nanotube defect-free-length and deterioration of the polarizability with incorporation of nitrogen in pyridinic form.

Computed CH Acidity of Biaryl Compounds and Their Deprotonative Metalation by Using a Mixed Lithium/Zinc‐TMP Base

With the aim of synthesizing biaryl compounds, several aromatic iodides were prepared by the deprotonative metalation of methoxybenzenes, 3-substituted naphthalenes, isoquinoline, and methoxypyridines by using a mixed lithium/zinc-TMP (TMP=2,2,6,6-tetramethylpiperidino) base and subsequent iodolysis. The halides thus obtained, as well as commercial compounds, were cross-coupled under palladium catalysis (e.g., Suzuki coupling with 2,4-dimethoxy-5-pyrimidylboronic acid) to afford various representative biaryl compounds. Deprotometalation of the latter compounds was performed by using the lithium/zinc-TMP base and evaluated by subsequent iodolysis. The outcome of these reactions has been discussed in light of the CH acidities of these substrates, as determined in THF solution by using the DFT B3LYP method. Except for in the presence of decidedly lower pKa values, the regioselectivities of the deprotometalation reactions tend to be governed by nearby coordinating atoms rather than by site acidities. In particular, azine and diazine nitrogen atoms have been shown to be efficient in inducing the reactions with the lithium/zinc-TMP base at adjacent sites (e.g., by using 1-(2-methoxyphenyl)isoquinoline, 4-(2,5-dimethoxyphenyl)-3-methoxypyridine, or 5-(2,5-dimethoxyphenyl)-2,4-dimethoxypyrimidine as the substrate), a behavior that has already been observed upon treatment with lithium amides under kinetic conditions. Finally, the iodinated biaryl derivatives were involved in palladium-catalyzed reactions.

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.