The Pyrolysis of Azides in the Gas Phase

Abstract

The chemistry of the non-metallic elements has in recent years passed through a period of rapid development, often referred to as its "renaissance". To emphasize just one of the key facets: numerous short-lived molecules containing multiple bonds to elements of the third and higher periods have been discovered, often accompanied by the planned synthesis of derivatives which are sterically shielded by bulky groups and thus kinetically stabilized. Thus today molecules such as silabenzenes HhC6-"Sin and silaethenes H2Si=CH2 or R2Si=CR2, disilenes R2Si=SiR2 and diphosphenes RP=PR, silaphenylisonitrile H,C,-N=Si, or methylidyne-phosphanes R-C=P, are all well-known species. Sandwich compounds with P6 rings or silicon centers demonstrate that there are now hardly any barriers to impede the imagination of the nonmetal chemist. In sharp contrast is our lack of knowledge regarding the "microscopic" pathways of chemical reactions: thus apart from information provided for example by molecular beam experiments, or from exact numerical calculations involving species consisting of only a few atoms, it remains largely unknown from which directions medium-sized molecules must approach each other to successfully collide and form a "reaction complex", in which way their structures are changed in such a process or which role is played by molecular dynamics in the energy transfer.-The pyrolysis o f azides X-N,, i.e. compounds which tend to explode violently when ignited in the condensed phase but can be heated in low-pressure gas flow systems without much risk, illustrates that studies of reactive intermediates are of interest not only because novel molecules may be discovered and isolated, and thereby possibilities for synthesis expanded. Moreover, some aspects of the "microscopic" pathways of these a i d e pyrolyses can be described satisfactorily on the basis of calculated energy hypersurfaces, and the influence of molecular dynamics becomes experimentally visible in the "chemical activation" o f intermediates which leads to their "thermal explosion". "Despite all that is known about reaction behavior, understanding of it is rather shallow . . . " (George C . Pimentel"') mhH. 0-6940 Weinhrini, 1987 OS70-083~/87/0606-OS04 S 02.50/0 Angew. Chem. In!. Ed. Engl 26 (1987) 504-526

The diradical (CH3)2CHN and its isomeric molecule (CH3)2C=HN: Generation and characterization

“…22 The purity of 3 was checked by MS and nuclear magnetic resonance. The PES profile of 3 is very similar to those of CH 3 N 3 and CH 3 CH 2 N 3 which were reported previously, [11][12][13] and did not vary in different experiments.…”

“…[11][12][13]23,24 The ionization energies corresponding to these two bands are 10.54 and 12.42 eV for CH 2 NH. Replacing one of the H atoms by a methyl group lowers the ionization energies to 9.20 and 11.20 eV in the case of CH 3 CHNH.…”

Computational study for the second-stage cracking of the pyrolysis of ethylamine: Decomposition of methanimine, ethenamine, and ethanimine

“…Detailed kinetic models on decomposition of EA included these species [23,24]. (CH 2 =NH) is the simplest imine compound, it has been observed in the pyrolysis of methylamine, ethylamine (amines in general), and azides as a reactive intermediate [25][26][27][28][29][30][31][32][33]. A great deal of research has been carried out to assign the microwave, infrared, and electronic spectrum of this moiety [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

“…(CH 2 =NH) is the simplest imine compound, it has been observed in the pyrolysis of methylamine, ethylamine (amines in general), and azides as a reactive intermediate [25][26][27][28][29][30][31][32][33]. A great deal of research has been carried out to assign the microwave, infrared, and electronic spectrum of this moiety [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. As a reactive species, MI can dissociate by 1,2-elimination of H 2 which has been studied both experimentally and theoretically [44][45][46][47][48][49][50][51][52][53][54][55].…”

Gas phase flash pyrolysis of 3-azido-1,2,4-triazole: generation and ultraviolet photoelectron spectrum of N-cyanomethanimine

“…This compound and its deuterated derivative (14, 15) have been the object of several detailed microwave spectrometry studies. In addition, a very recent photoelectron study (16) showed that the decomposition of trimethylenetetrazole yields N-cyanomethanimine and ethylene.…”