Silicon tetraazide

Structural formula
General
Surname	Silicon tetraazide
other names	Tetraazidosilane
Molecular formula	Si (N 3 ) 4
Brief description	white crystalline solid
External identifiers / databases
CAS number 27890-58-0 PubChem 57461327 ChemSpider 35764491 Wikidata Q424947
properties
Molar mass	196.17 g mol −1
solubility	soluble in diethyl ether and benzene
safety instructions
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Silicon tetraazide is a thermally unstable silicon - nitrogen compound with a nitrogen content of 85.7%. The high-energy substance tends to decompose spontaneously and could only be characterized in solution. Further coordination to the six-coordinate structure as in hexaazidosilicates [Si (N ₃ ) ₆ ] ²⁻ or in adducts with divalent ligands Si (N ₃ ) ₄ L ₂ leads to relatively stable, crystalline solids that can be handled normally at room temperature.

Presentation and extraction

The synthesis of silicon tetraazide is achieved by reacting silicon tetrachloride with sodium azide in a benzene solution.

The reaction of silicon tetrachloride with an excess of sodium azide at room temperature in acetonitrile initially leads to sodium hexaazidosilicate , which can be converted into stable silicon tetraazide adducts by adding divalent ligands such as 2,2'-bipyridine and 1,10- phenanthroline . Other bases such as pyridine and tetramethylethylenediamine do not react with the hexaazidosilicate anion.

Another preparation of a bis (triphenylphosphine) iminium hexaazidosilicate salt ((PPN) ₂ Si (N ₃ ) ₆ , [Ph ₃ P = NPPh ₃ ] [Si (N ₃ ) ₆ ]) takes place through the reaction of bis (triphenylphosphine) iminium azide (PPNN ₃ , [Ph ₃ P = NPPh ₃ ] ⁺ N ₃ ^- ) with silicon tetrachloride in acetonitrile.

properties

Silicon tetraazide is a white crystalline substance which tends to decompose explosively at 0 ° C. The pure substance, but also samples contaminated with silicon chloride triazide and silicon dichloride diazide can apparently without any external cause z. B. explode spontaneously in storage. The compound is sensitive to hydrolysis . The substance is soluble in diethyl ether and benzene .

The addition compound with 2,2'-bipyridine is much more stable. A melting point of 212 ° C with a melting enthalpy of 110 J · g ^{−1 is} observed here. The DSC measurement shows a strongly exothermic decomposition from 265 ° C with a heat of decomposition of −2400 J g ⁻¹ . The addition compound with 1,10-phenanthroline shows a similar behavior. The compound obtained as hemiacetonitrile solvate releases the bound solvent around 100 ° C, then shows in a DSC measurement from 240 ° C a strongly exothermic decomposition with a heat of decomposition of −2300 Jg ⁻¹ . The heat of decomposition is higher than that of sodium azide with −800 J · g ⁻¹ , but still below the values ​​for classic explosives such as RDX with −4500 J · g ⁻¹ . The addition compounds are stable in solution. The IR and ¹ H-NMR spectroscopic data show no dissociation in silicon tetraazide and 2,2'-bipyridine or 1,10-phenanthroline. The bis (triphenylphosphine) iminium hexaazidosilicate salt ((PPN) ₂ Si (N ₃ ) ₆ ) is also relatively stable. The compound melts at 214 ° C and shows a decomposition reaction from 250 ° C in a DSC measurement. One with a mass spectrometer coupled thermogravimetric investigation revealed as decomposition products of nitrogen , silicon tetraazide and hydrazoic acid .

use

A practical use of free silicon tetraazide is excluded because of the high instability. In solution, the substance can still be used as a starting material for the synthesis of nitrogen-rich compounds. An application as an adjuvant in the manufacture of polyolefin polymers has been patented. The much more stable adducts can serve as energetic compounds or as initial explosives as a substitute for the lead azide .

Individual evidence

1. ↑ ^{a b c d e f} Wilberg, E .; Michaud, H .: On Knowledge of a Silicon Terazide Si (N ₃ ) ₄ . In: Journal of Nature Research B . 9, 1954, p. 500 ( online ).
2. ↑ ^{a b c} Gmelins Handbook of Inorganic Chemistry, 8th Edition, Silicon Supplement Volume B4, Springer-Verlag 1989, p. 46.
3. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
4. ↑ ^{a b c d e f g h i j} Portius, P .; Filippou, AC; Schnakenburg, G .; Davis, M .; Wehrstedt, K.-D .: Neutral Lewis Base Adducts of Silicon Tetraazide in Angew. Chem. 122 (2010) pp. 8185-8189, doi : 10.1002 / anie.201001826
5. ↑ ^{a b c d} Filippou, AC; Portius, P .; Schnakenburg, G .: The Hexaazidosilicate (IV) Ion: Synthesis, Properties, and Molecular Structure in J. Am. Chem. Soc. 124 (2002) pp. 12396-12397, doi : 10.1021 / ja0273187
6. ↑ Bretherick's Handbook of Reactive Chemical Hazards, 7th revised edition, Academic Press 2006, ISBN 978-0123725639 .
7. ↑ T. Grewer: Thermal Hazards of Chemical Reactions , Industrial Safety Series 4, Elsevier 1994th
8. ↑ Nomura, M .; Tomomatsu, R .; Shimazaki, T .: EP 206 034 (1985) PDF download