In the ultimate analysis of carbon and hydrogen, the ordinary absolute method was followed with the use of copper oxide, lead chromate, and lead peroxide in the tube. In the determination of nitrogen the ordinary absolute method was also followed excepting that a considerable quantity of specially prepared lead chromate powder was mixed with the sample in a number six porcelain boat. This was found to be desirable when the dinitroselenazole was burned. Selenium dioxide, which is a solid, seems to be formed in the tube and carried away by the current of carbon dioxide with some difficulty. In such a case the analysis usually took four hours after the combustion had actually started. In the carbon and hydrogen determination selenium dioxide was easily absorbed in the presence of oxygen gas.
Preparation of 2-Phenylbenzoselenazole
The first method employed was a modification of the method described by Fromm and Martin[(58)]. Method (b) is an adaptation of the method for preparing benzothiazoles.
(a) Twenty grams of benzanilide was mixed in a pyrex flask with 160 grams of selenium dust and the flask placed in a nitrate bath under an air condenser. After heating for an hour at 220°C., the temperature was raised to 250°C., and kept at 250°-280°C. for sixteen hours. The dark mass was extracted with hot concentrated HCl, the acid extracts filtered through glass wool using a hot water funnel. The combined extracts were poured into a large volume of water when the selenozole precipitated out immediately; it was recrystallized from alcohol. In some cases it was necessary to dissolve in hot HCl again and to recrystallize. The yield was twelve per cent.
The above method has the disadvantage that water is formed in the reaction and this in turn reacts upon benzanilid at the higher temperature necessary (as selenium only melts at 217°C.), decomposing the benzanilid into aniline and benzoic acid.
Furthermore benzanilid boils at 160°C. and at such high temperatures as 250°C. and over some of it is apt to be driven off.
(b) 106 grams of benzaldehyde were heated with 93 grams of redistilled aniline at 120°C., for two hours or until the solution was clear. The clear benzalaniline was then poured into 160 grams of selenium dust in a pyrex flask on a sand bath, the flask being connected with an air condenser as before. In order to distribute the flame to better advantage over the bath, an air space was made between the Meker burner and the bath by introducing a wire gauze. Hydrogen selenide was evolved freely. Complete reaction took three days. The extraction and recrystallization were the same as in the former case. The yield was sixty per cent.