Synthesis of 2-methyl-4-selenoquinazolone, 2-phenylbenzoselenazole, and its derivatives / Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Faculty of Pure Science of Columbia University

by Yü-Gwan Chen

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.

The selenazole crystallizes in colorless long needles, melting at 117.5°C. (corr.) Fromm and Martin[(58)] gave the melting point as 117°C. It is insoluble in water, and in the following solvents it is lightly soluble in the cold, more easily hot: ether, methyl alcohol, acetone, acetic acid, acetic anhydride, chloroform, and nitrobenzene. It is difficultly soluble in ethyl alcohol, ethyl acetate, and carbon tetrachloride, in the cold, but easily soluble hot.