TETRAZOLES  , in organic

chemistry, a group of heterocyclic compounds, capable of existing in two isomeric series (formulae 1 and 2), although the methods of preparation do not always permit discrimination between the possible isomers . They are prepared by the action of nitrous acid on cyanamidrazone (dicyanophenylhydrazine) and hydrolysis of the resulting nitrile, from which J . A . Bladin by elimination of the phenyl group (by nitration, reduction, &c.) and of carbon dioxide obtained free tetrazole, CH4N2; from amidines by the action of nitrous acid, followed by the reduction of the intermediately formed dioxytetrazotic acids with sodium amalgam; from amidoguanidine by diazotization, the diazonium nitrate. on treatment with acetates or carbonates yielding aminotetrazole (J . Thiele, Ann., 1892, 270, p . 1); from the action of nitrous acid on phenylthiosemicarbazide; and by the action of arylazoimides on aldehyde hydrazones (O . Dimroth, Ber., 1907, 40, p . 2402) . The tetrazoles behave as strong monobasic acids, and are exceedingly stable . A series of tetrazolium bases (formula 3) have been obtained by H . V . Pechmann (Ber., 1894, 27, p .

2020) starting from formazyl compounds (formula 4), which are oxidized by means of amyl nitrite and hydrochloric acid . They are strong bases, which in aqueous

solution absorb carbon dioxide readily . The free bases have not been isolated, but their salts are well-crystallized solids . /N:N l/N•NH /N:CH RHN-N:CH HN\N:CH or N\N:CH RN\N:N RN:N HO (1) , (2) . (3) , (4) .