Elsevier

Thermochimica Acta

Volume 388, Issues 1–2, 18 June 2002, Pages 233-251
Thermochimica Acta

Thermal decomposition of aminotetrazoles

https://doi.org/10.1016/S0040-6031(02)00027-8Get rights and content

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.

Introduction

Aminotetrazoles possess a unique combination of properties. In spite of large positive enthalpies of formation [1], they exhibit surprisingly high thermal stability [2], [3], [4], [5]. Aminotetrazoles have the highest content of nitrogen among all organic substances (e.g. 82.3 wt.% for 5-aminotetrazole (5-AT) and 84.0 wt.% for 1,5-diaminotetrazole (DAT) ). Therefore, aminotetrazoles are prospective materials for generation of gases, as blowing agents, solid propellants and other combustible and thermally decomposing systems [6], [7]. The kinetics and mechanism of thermal decomposition of aminotetrazoles is of high interest. Since aminotetrazoles show the tendency to prototropic, ring-chain and mesoionic isomerization [2], [3], [8], the investigation seemed to be important for revealing and evaluation the role of structural factors in the thermal transformations.

Recently, we have studied the thermal decomposition behavior of tetrazole [9], [10], [11] and some aminotetrazoles [2], [3], [4]. This paper presents an overview of the comprehensive study on kinetics and mechanism of thermal decomposition of a series of aminotetrazoles of the following structures.which include 5-AT, (I, R=H), 1-methyl-5-aminotetrazole (MAT, I, R=CH3), DAT, (I, R=NH2), poly-1-vinyl-aminotetrazole (PVAT, polymer of 1-vinyl-5-aminotetrazole I, R=CHCH2), and 5-aminotetrazole sodium salt (SAT, II), where the tetrazole ring exists in the anionic form.

Section snippets

Experimental

Synthesis and purification of 5-AT, MAT, DAT and PVAT were described elsewhere [2], [3], [4]. The purified 5-AT was reacted with sodium ethylate at equivalent ratio in ethanol to prepare SAT. After completion of the reaction, solvent was distilled out under vacuum. The results of chemical analysis for SAT are as following.

CH2N5Na (107,05)Calc.C 11.21H 0.019N 65.39Na 21.49
FoundC 11.26H 0.021N 66.02Na 21.18

The thermal decomposition of the aminotetrazoles was studied either in the sealed steel

Thermal analysis

As thermogravimetry shows (Fig. 1), 5-AT, PVAT and SAT have two step of weight loss within the temperature interval of 460–900 K, whereas, MAT and DAT decompose in one main step at 470–620 K followed by a slow weight loss till 870 K (Fig. 1). The temperature intervals, heats of decomposition, specific volumes of gas evolved and weight losses for the first step of thermal decomposition of aminotetrazoles are presented in Table 1. The decomposition of 5-AT, MAT and DAT starts right after the

Conclusions

Two mechanisms of splitting of the tetrazole ring are effective in aminotetrazoles: (1) evolution of hydrogen azide from the tautomeric forms with hydrogen atom by nitrogens in the ring and (2) evolution of nitrogen molecule from the amino-tautomeric form. This assumption is based on the composition of volatile products of the thermal decomposition as well as data of the study of amino-imino tautomerism. The ab initio calculations of the total energies and the energies of chemical bonds in 5-AT

References (47)

  • S.V. Levchik et al.

    Thermochim. Acta

    (1992)
  • S.V. Levchik et al.

    Thermochim. Acta

    (1993)
  • S.V. Levchik et al.

    Polym. Degrad. Stability

    (1995)
  • A. Gao et al.

    Combust. Flame

    (1991)
  • A.I. Lesnikovich et al.

    Thermochim. Acta

    (1989)
  • S.V. Vyazovkin et al.

    Thermochim. Acta

    (1990)
  • M.J. Frisch et al.

    Chem. Phys. Lett.

    (1990)
  • G.K. Williams et al.

    Combust. Flame

    (1994)
  • T.B. Brill et al.

    Combust. Flame

    (2000)
  • R.N. Butler

    Adv. Heterocycl. Chem.

    (1977)
  • A.I. Lesnikovich et al.

    Thermochim. Acta

    (1993)
  • A.I. Lesnikovich et al.

    Thermochim. Acta

    (1992)
  • K.Ya. Burshtein et al.

    J. Mol. Struct. (Theochem.)

    (1985)
  • S.V. Vyazovkin et al.

    Thermochim. Acta

    (1988)
  • S.V. Vyazovkin et al.

    Thermochim. Acta

    (1992)
  • A.A. Kozyro et al.

    Zhurn. Fiz. Khim.

    (1990)
  • G.K. Lund, R.J. Blau (to Thiokol Co.), US Patent 5,500,059...
  • C.P. Ramaswamy, C. Grzelczyk (to Breed Automotive Technology), US Patent 5,661,261...
  • W. Koźmiński et al.

    Polish J. Chem.

    (1995)
  • A.I. Lesnikovich et al.

    Thermochim. Acta

    (1990)
  • T. Ozawa

    Bull. Soc. Chem. Jpn.

    (1965)
  • A.I. Lesnikovich et al.

    J. Therm. Anal.

    (1983)
  • A.V. Coats et al.

    Nature

    (1964)
  • Cited by (0)

    1

    Permanent address: Akzo Nobel Functional Chemicals, 1 Livingstone Avenue, Dobbs Ferry, NY 10522, USA.

    View full text