Tetrazole
1H- tetrazole
Colorless, sublimatable Papers (1H- tetrazole )
Fixed
1.406 g · cm -3
157 ° C (1H- tetrazole )
4.89
- Slightly soluble in water and ethanol
- Sparingly soluble in ether ( 1H - tetrazole )
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Tetrazole is a heterocyclic chemical compound, can be formulated for the three isomeric structures.
Tautomerism
Depending on the position of the double bonds, we distinguish between isomeric structures 1H, 2H, and 5H- tetrazole. 1H- and 2H -tetrazol form a tautomeric equilibrium, which is situated on the side of the 1H- tetrazole (Formula in the box). Both the 1H - tetrazole (left ) and the 2H- tetrazole (center) can be seen as 6π - heteroaromatics:
5H- tetrazole (far right ) is a non-aromatic structure.
Representation
1H- tetrazole is formed by the reaction of hydrocyanic acid with hydrazoic acid. This reaction is a 1,3- dipolar cycloaddition reaction. The compound may also be through the commercially available deamination of 5-aminotetrazole, which can be prepared from aminoguanidine easily be obtained.
Properties
1H- tetrazole is a crystalline solid, which occurs in two polymorphic forms. The two crystal forms are enantiotropic each other. Below the transition temperature of -31 ° C prior to the Form II. Above the transition temperature, the form I is the thermodynamically stable crystal form. This has a melting point at 157 ° C. The enthalpy of fusion is 18.4 kJ · mol -1, the enthalpy of transition at the solid-solid phase transition of 14.0 J · mol -1. The vapor pressure function is obtained after August according to ln ( P) = -A / T B (P in Pa, T in K) with A = 10560 ± 168 and B = 31.148 ± 0.458 in the temperature range from 333 K to 404 K. From the vapor pressure function can be a molar sublimation enthalpy of 87.8 kJ · mol -1 derived. The connection is a standard enthalpy of 236 kJ · mol = ΔfHsolid -1 or ΔfHgas = 320 kJ · mol -1 strongly endothermic. The standard enthalpy of -915.5 kJ · mol ΔcHsolid is -1. The aqueous solution of 1H - tetrazole is slightly acidic and has about the same acidity as acetic acid.
Importance
From the derivatives of 1H - tetrazole tetrazolium salts are particularly important in biochemistry. The importance of tetrazoles in pharmacy is the bioisosterism to the carboxyl group. 5R, 1 H- tetrazoles have similar physical properties such as their carboxy analogs, but show a higher stability against metabolism. Pharmaceuticals are known, for example, the losartan or the pentamethylenetetrazole or pentylenetetrazol, an analeptic.
Security
1H - tetrazole by the Federal Institute for Materials Research and Testing ( BAM) in terms of the Explosives Act classified as potentially dangerous substance in the substance group A.