(b) They have been shown to be chemically easier to handle than the corresponding sulphur compounds. (c) Selenium, in the nucleus of cyclic compounds, has been shown to be instrumental for a positive coloration at least equal to the --NH-- or --S-- groupings. The selenocarbonyl, :C:Se, has been shown to be a more powerful chromophore than thiocarbonyl, :C:S, or carbonyl itself, :C:O. (d) Two series of azo dyes of selenium have been prepared and have been shown to possess a marked tinctorial value. (e) The following new compounds have been prepared: 2-methyl-4-selenoquinazolone 2-phenylbenzoselenazole[A] 6-nitro-2-phenylbenzoselenazole 6-amino-2-phenylbenzoselenazole 6-acetylamino-2-phenylbenzoselenazole 6-benzylideneamino-2-phenylbenzoselenazole (B-naphthyl)-6-azo-(2-phenylbenzoselenazole) Dinitro-2-phenylbenzoselenazole Diamino-2-phenylbenzoselenazole Diacetyldiamino-2-phenylbenzoselenazole Dibenzylidenediamino-2-phenylbenzoselenazole PURPOSE OF THE RESEARCH Since Berzelius published the first resume of the chemistry of selenium, in 1818(1), many articles have appeared in this field. Several reviews(2) of its compounds, including references, have been published, besides the resumes in the chemical dictionaries. These reviews are confined mainly to the inorganic side. No attempt has ever been made to compile a bibliography of selenium organic compounds. From time to time, articles have appeared, but the field is still a promising one, with many alluring possibilities. In the perusal of the organic records of the metal, distributed over the span of a century, there are indications of the value of selenium compounds for pharmaceutical and tinctorial uses. An effort has been made to collect these scattered data for critical examination with other analogues and sulphur compounds in particular, and to prepare and study some new organic compounds containing selenium, for the purpose of gaining additional light upon the chemistry of such substances, and in the hope of discovering some which may be of practical service in medicine or elsewhere. Synthesis of 2-methyl-4-selenoquinalozone, 2-phenylbenzoselenazole and Its Derivatives INTRODUCTION