1911 Encyclopædia Britannica/Tetrazines

TETRAZINES, in organic chemistry, a group of compounds containing the ring system

C·N·N C·N·N C·N·C

Ċ·N·Ṅ, Ṅ·N·Ċ, Ṅ·N·Ṅ;

only derivatives of the first two types are known. The members of the first series may be prepared by oxidizing osazones (i.e. dihydrazones of α-diketones), dihydrotetrazines resulting. Dihydro-derivatives of the second type are formed from hydrazine and imino-ethers (A. Pinner, Ber., 1893, 26, p. 2126; 1894, 27, p. 984); these easily oxidize to the corresponding tetra zines, which are stable towards acids; their dihydro-derivatives, however, are decomposed, the group—NH-NH-being eliminated as hydrazine and replaced by oxygen, with consequent formation of the five membered oxybiazole ring. Concentrated acids convert the dihydro-tetra zines into isodihydrotetrazines, thus:—

R·C·NH·NH > R·C·NH·N

N̈·N :C̈·R N̈-NH-C-R,

the N-alkyl derivatives of which type may be prepared by the action of alcoholic potash and chloroform on aromatic hydrazines. I .

Much discussion has circulated about the decomposition of diazo-acetic ester, from which A. Hantzsch and O. Silberrad (Bern, 1900, 33, p. 58) obtained what they considered to be a dihydrotetrazine, thus:—

CH·CO₂R > HO₂C-CH-Nzlf g Hc-NH-151-IQ

N=N -CH-CO₂H N-NH-CH.

C. Bülow (Ber., 1906, 39, pp. 2618, 4106), however, showed this substance to be an N-aminotriazole, which necessitates the first decomposition product being an acid (I.), the conversion into the (I.) HO2C-(; ~NH~NH 9 (H) HOQC-ge-NZNH,

N-N: C-COQH ' N~N:C-CO2H

triazole derivative (II.) being due to the ring opening on the addition of the elements of water and then closing again to the five-membered ring with elimination of water again. The decompositions of diazoacetic ester were then again examined by T. Curtius and his students (Ber., 1907, 40, pp. 262, 350, 450, &c.), who showed that both triazole and tetra zine derivatives could be obtained from the Vbisdiazo-acetic acid which is formed by the action of alkali on diazo-acetic ester.