NO₂ NH NO₂ NH NO₂ (I) /\ /\ /\ / \ /\ /\ / \ /\ | |NH₂ Cl| | | | | | | | | | | | | | = | | | | = | | | | | |SeH NC| |NO₂ | |SeH | |NO₂ | | | |NO₂ \/ \/ \/ / \/ \/ \ / \/ O₂N Se Formula (I) is known, as 1, 3-dinitrobenzoselenazine(21), which was obtained by the action of picryl chloride on the zinc salt of o-aminoselenophenol; the product (picrylaminoselenophenol) being then treated with alkali and thus converted to the dye, which upon experimentation showed marked effects upon protozoa and bacteria. N /\ / \ /\ N | | | | NH₂ /\ // \ /\ (II) | | | | /\ | | | | \/ \ / \/ + | | = | | | | Se | | \/ \\ / \/ Cl \/ Se HO₃As \ NH /\ | | | | \/ HO₃As Formula (II), known as 3-(p-phenylarsonic)-aminoselenazine, is red in dilute alkali and green in mineral acid, and is a typical dye in a series from the coupling of selenodiphenylamine with arsenic compounds. All possess similar toxicity as the thiazine dyes(20). Other selenazines are listed in the bibliography(22). No less than half dozen thioureas are commonly used as drugs. Thiourea itself paralyzes the nerve centers, and is employed commercially for photograph fixing and for removing stains from negatives; thiuret, C₆H₇N₃S₂, serves as a substitute for iodoform; thiosinamine-ethyliodide, or tiodine, IH₅C₂H₂NCSNHC₃H₅, is used for relief of lesions of the central nervous system; allylthiourea or thiosinamine, (NH₂)SC.NHCH₂CH:CH₂, for aiding the absorption of connective tissues, for treatment of burns, keloids, urethral diseases, sclerotic conditions of the ear(23). Selenocarbamide and a number of its derivatives have been prepared and studied. One class of seleno ureas has been patented as pharmaceutical products by Chem. Fabrik von Heyden(24), and are prepared by the action of hydrogen selenide on alkylcyanamides, RNH.CHN + H₂Se = RNH.CSe.NH₂ They possess pronounced therapeutic value and, serve as intermediate products in the production of more stable alkyl halide additive compounds. Other carbamides ranging from seleno urea itself(25), (III) and a cyclic urea(26) (IV) are described in the literature: NH₂ CH₂-Se / | \ Se:C (III) | C:NH (IV) \ | / NH₂ CH₂-NH The latter, known as ethylene-selenourea, may be classified also in the azole group as 2-iminotetrahydroselenazole (V).