Part 2

While phenyldisulphide is colorless, when an auxochrome group is added, such as NH₂, the compound is colored. This is the case with o-diaminodiphenyldisulphide(48) which is yellow both in solution and in crystalline form. In other words, an auxochrome in addition to the chromophore group transforms a colorless chromogen into a colored one. Therefore groups like -S.S- and -Se.Se- are chromophores in the same sense as -N:N-. This is in agreement with the chromophore ideas of Hugo Kaufmann. The -Se.Se- is a more powerful chromophore than -S.S-.

This brings one directly to the inquiry as to why 2-phenylbenzo- selenazole, which contains a :Se radical, should be colorless; and that even 6-nitro-2-phenylselenazole, with the addition of a chromophore NO₂, should be only faintly colored. The benzothiazoles, their isomers and derivatives are mostly colorless, and similar causes are probably responsible in the case of the phenylbenzoselenazole, for its lack of color. But when this selenazole is combined with another chromophore, for example an azomethine grouping, the result is a more positively colored compound (in this case benzalaminoselenazole), the crystals being yellow. The corresponding thiazole derivative is light colored.

The tinctorial value of the selenium derivative is further evidenced by the ease with which it forms azo dyes and the deep colors of the latter. This was observed when 6-amino-2-phenylbenzoselenazole was diazotized and coupled with B-naphthol, salicylic acid, etc. The corresponding aminothiazole has been considered difficult to diazotize, on account of its insolubility in hydrochloric acid, cold or hot, but the aminoselenazole dissolves readily and completely, the coupling is almost instantaneous, and the dyes obtained are mostly red and of metallic lustre. In view of the stability of benzoselenazoles toward hot concentrated acids (with the exception of nitric, when nitration ensues) and alkalis, these dyes may prove of some commercial interest.

The azole dyes of the benzoselenazole have been exposed to light for weeks, and also exposed to acids and alkalis, and have been found to be quite fast.

EXPERIMENTAL

Preparation of 2-methyl-4-selenoquinazolone

Busch prepared quinazolines by the action of o-amino or o-nitro benzylamine with phosgene, and thioquinazolines with carbon disulphide(51):

CH₂NH₂ CH₂-NH / / | C₆H₄ + COCl₂ = C₆H₄ | + 2HCl \ \ | NH₂ NH--CO

CH₂NHC₆H₅ CH₂-NC₆H₅ / / | C₆H₄ + CS₂ = C₆H₄ | + H₂S \ \ | NH₂ NH--CS

Accordingly the same reaction was tried with o-nitrobenzylamine, prepared by the method of Lellmann and Stickel(50), using carbon diselenide(51). The reaction seemed to work, but the mixture formed was difficult to extract and it appeared that other reactions took place at the same time, due to the impurity of the carbon diselenide, as the latter has never been prepared in the pure state.

Another method, which is equally attractive because of its simplicity, is that of Gabriel and Stelzner(52),

CHO CH=N / NH₂ / | H₂O C₆H₄ + | = C₆H₄ | + \ H₂N-CO \ | NH₃ NH₂ NH-CO

In accordance with the above reaction o-aminobenzaldehyde should work with equal ease with selenocarbamide, but the initial materials were not available.

The reaction which was used successfully was that of Bogert, Breneman and Hand(53),

NH₂ NHCOR N=CR / / / | C₆H₄ + (RCO)₂O → C₆H₄ → C₆H₄ | \ \ \ | CSNH₂ CS-NH₂ CS-NH

↑ ↑ or

H₂S H₂S N=CR / | + + C₆H₄ | \ | NH₂ NHCOR C=N / / | C₆H₄ + (RCO)₂O → C₆H₄ SH \ \ CN CN

The hydrogen selenide used in the reaction was prepared from FeSe by the action of hydrochloric acid, or by heating paraffin and selenium, in the proportion of four to one respectively, at 335° to 350°C(54).

The selenoquinazoline was prepared from anthranilic nitrile by the following methods--the anthranilic nitrile being prepared from o-nitraniline(57),

(a) 20 grams of acetyl-anthranilic nitrile was dissolved in absolute alcohol, and dry hydrogen selenide and dry ammonia passed into the solution for three hours. The quinazoline crystallized out gradually on cooling was filtered out and recrystallized from dilute alcohol. The yield was about ten per cent.

(b) 10 grams of acetyl-anthranilic nitrile was heated in a sealed tube at 110° with alcohol saturated at zero degrees with dry hydrogen selenide and dry ammonia. After five hours, the tube was taken out and the quinazoline crystallized out on cooling. Yield was about sixteen per cent.

As hydrogen selenide was somewhat unstable and did not dissolve freely in alcohol, freshly prepared sodium selenide was used in the following method and was found to be more satisfactory. It was prepared from sodium hydroxide in absolute alcohol by passing dry hydrogen selenide into the solution for about three hours. In the beginning and end of the reaction, nitrogen was used to exclude the oxygen of the air. The selenide was collected and dried in an atmosphere of nitrogen, and then in a vacuum, in presence of phosphorus pentoxide. When thus prepared, sodium selenide was colorless, but on exposure to air it turns reddish and finally dark colored. The C. P. selenide on the market was black and was found to be entirely useless.

(c) 20 grams of anthranilic nitrile and fifty grams of sodium selenide were mixed and heated in a distilling flask in an atmosphere of nitrogen, and forty grams of acetic anhydride dropped into the flask very slowly. The temperature was kept at 115° for half an hour and then raised to distill off the acetic acid formed in the reaction, as the condensation hardly went to completion in the presence of any trace of acetic acid. The whole process took an hour and a half. The flask was removed from the oil bath and, after cooling, dilute alkali was run in, in successive portions, to dissolve out the quinazoline. Into the clear alkaline extracts carbon dioxide was bubbled for an hour, and common salt then added. The precipitate was recrystallized several times from twenty-five per cent. alcohol. The yield was from twenty to twenty-five per cent.

(d) 10 grams of anthranilic nitrile, twenty grams of acetic anhydride, and twenty-five grams of sodium selenide were mixed in a sealed tube and heated together for three hours and a half at 110°-115°. The condensation product was crystalline when the tube was cooled to room temperature. The contents of the tube were extracted with dilute alkali as before, filtered, precipitated by carbon dioxide, and recrystallized from dilute alcohol. The yield was not over twenty per cent.

(e) An attempt was made to make o-aminobenzoselenamide, and from the latter, by treatment with acetic anhydride, to form the quinazoline, but the yield of the amide was too small to carry the reaction further.

The substance prepared by the above methods crystallizes from dilute alcohol in needles or prisms of dark brown color. It melts at 213.5° (corr.). It dissolves readily in hot alcohol but on concentration sometimes forms a sticky mass with a peculiar but not unpleasant odor. It dissolves readily in alkalis and is slightly soluble in hot benzene and chloroform, but insoluble in hot water. Crystals purified from (a) were analyzed and gave the following results:

Calculated for Found C₉H₈N₂Se I II

Carbon 48.38% 48.45% 48.62% Hydrogen 3.61 3.82 3.52 Nitrogen 12.55 12.51 12.66 Selenium 35.46 35.60 35.42

The crystals on standing in the presence of air and light decomposed with separation of finely divided selenium and methyl quinazolone.

Analysis of Selenium Organic Compounds

In the quantitative determination of selenium in quinazoline the method adapted by Becker and Meyer was found to be quite satisfactory(56). Other methods are listed in the bibliography(57).

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 selenazole 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.

NHCOC₆H₅ N / / \\ C₆H₄ + Se = C₆H₄ C-C₆H₅ + H₂O \ \ / H Se

NHCOC₆H₅ NH₂ / / C₆H₄ + HOH = C₆H₄ + HOOC-C₆H₅ \ \ H H

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.

Mononitro Derivative

The mononitro derivative of the selenazole, 6-nitro-2-phenylbenzo- selenazole, was prepared by nitration with nitric acid at a low temperature:

Twenty-five grams of the selenazole were dissolved in 150 grams of concentrated sulphuric acid, keeping the temperature below the room temperature until complete solution took place. It was then cooled on a freezing mixture and a mixture of sulphuric and nitric acids (previously prepared and cooled by mixing 9.5 grams of nitric and fifteen grams of sulphuric acids) slowly dropped into it in the course of half an hour, using mechanical stirring for four hours. The solution was then poured into two liters of water (ice water), filtered, dried, and recrystallized from acetic acid, and alcohol with the help of animal charcoal. The yield was 95 per cent.

This nitro compound crystallizes in flattened needles of a light yellow color. It melts at 202.4°C. (corr.). It is very insoluble in water; but soluble in hot acetic acid, acetic anhydride, nitrobenzene, nitrotoluene, toluene, benzene, alcohol, and difficultly soluble when cold. The crystals were analyzed and gave the following results,

Calculated for Found C₁₃H₈N₂O₂Se I II

Nitrogen 9.24% 9.36% 9.48%

Monoamino Derivative

The conversion of mononitro compound to 6-amino-2-phenylbenzoselenazole was accomplished by the action of tin and hydrochloric acid as follows:

30.3 grams of nitro compound were mixed with 42 grams of twenty mesh tin in a liter flask, immersing the latter in cold water. 175 cc. of conc. HCl were slowly added to the flask. In some cases it was necessary to apply initial heating but when once the reaction started it took place rapidly. After the effervescence had abated, the flask was heated over a free flame, under a return condenser, for two hours. The solution usually turned to a pasty mass, due to the formation of a tin double salt. The mixture was dissolved in a large volume of water and heated on a water-bath, the precipitate filtered out, washed, and preserved. The clear filtrate was treated with concentrated alkali, in excess, the separated amine collected, washed with water, dried and recrystallized from alcohol, using bone-black. The precipitate set aside was treated with strong alkali, the insoluble residue washed, recrystallized, and added to the main product. The yield was 75 per cent.

This amine crystallizes from alcohol in fine yellowish needles, melting at 201.2°-202.3°C (corr.). It is insoluble in water and ether, difficultly soluble in the hot; and fairly soluble in aniline. A pure sample was analyzed and gave the following results:

Calculated for Found C₁₃H₁₀N₂Se I II

Nitrogen 10.25% 10.34% 10.42% Carbon 57.18 57.17 57.00 Hydrogen 3.69 3.79 3.85

Decomposition of Monoamino Derivative

Five grams of the monoamino compound were mixed with powdered KOH, heated together until the mixture just melted, and maintained in that state for a few minutes. When the latter had cooled down to room temperature, cold water was poured over the mixture. The filtered solution was acidified until no further precipitate was formed. The precipitate was collected and recrystallized from water, m.p. 121°C.

One gram of this solid was placed in a test tube, provided with a cork and a delivery tube, and heated with soda lime; a liquid with the smell of benzene was collected in another test tube cooled with water. When this liquid was treated with a few drops of nitric acid mixture the smell of nitrobenzene was given off. A gram of the crystals was heated with concentrated sulphuric acid and alcohol when the odor of ethyl benzoate was noted.

Monacetyl Derivative

Five grams of the monoamino selenazole were heated on a water-bath with 10 cc. of acetic anhydride until the solution was clear, which took about two hours. 100 cc. of water were poured into the mixture, which was then neutralized with dilute ammonium hydroxide. The precipitate was filtered, decolorized by animal charcoal, and recrystallized from dilute alcohol.

The acetyl compound, 6-acetamino-2-phenylbenzoselenazole, forms colorless crystals, melting at 188.1°-.7°C. (corr.). It is insoluble in ether, benzene, carbon disulphide; slightly soluble in toluene; soluble in alcohol, ethyl acetate, amyl acetate, acetone, and acetic acid. A pure sample was analyzed and gave the following result,

Calculated for C₁₅H₁₂N₂SeO Found

Nitrogen 8.88% 8.92% 8.68%

Monobenzylidene Derivative

Five grams of the monoamino compound were dissolved in 200 cc. absolute alcohol with the addition of 3 cc. of benzaldehyde and the clear solution was boiled on a water-bath, with a return condenser, for two hours. After the solution was boneblacked, the yellow precipitate was recrystallized from carbon disulphide. The yield was 90 per cent.

It crystallizes in yellow plates, melting at 156.7°-157.6°C., soluble in benzene, ether, ethyl alcohol, carbontetrachloride, acetone, but difficultly soluble in ligroin. An analysis of the crystals showed the following result,

Calculated for C₂₀H₁₄N₂Se Found

Nitrogen 7.75% 7.92% 7.68%

An Azo Dye

Five and four tenth grams of the monoamino compound were dissolved in hot conc. HCl, cooled in ice, and diazotized with sodium nitrite solution, until starch iodide paper showed excess nitrous acid. The diazotization was performed in ice, with mechanical stirring, and required about an hour. The diazo solution was poured into a solution of 3 grams B-naphthol in 8 grams of NaOH and 60 cc. of water, while gradually stirring. A very deep red solution formed. This was acidified with excess HCl, salted out by NaCl, and crystallized from aniline-alcohol mixture. In the pure state, it is a deep red powder, with a metallic lustre when rubbed, melting at 284.2°C. An analysis showed the following result,

Calculated for C₂₃H₁₅N₃OSe Found

Nitrogen 9.81% 9.75%

Dinitro Derivative

The nitration for the production of dinitro derivative was at first carried out under the same conditions as in the preparation of mononitro compound and after the latter was formed more nitric acid mixture was added with the addition of heat: conc. sulphuric acid, keeping it below room temperature. It was then cooled in a freezing mixture and half the volume of a nitric acid mixture (prepared and cooled by mixing 19 grams of nitric and 30 grams of sulphuric acids) was introduced very slowly to the selenazole solution through a dropping funnel, maintaining at this temperature for two hours (using mechanical stirring). The remaining half of the nitric acid mixture was then slowly introduced and the flask was heated on a water-bath for two hours. The solution was poured into two liters of water, the precipitate filtered off, dried and recrystallized several times from acetic acid. The yield was 80 per cent.

This dinitro compound crystallizes in fine yellow needles, m. p., 246.8°C. (corr.), very insoluble in water, but soluble in hot acetic acid, acetic anhydride, nitrobenzene, nitrotoluene, ethyl alcohol, and difficultly soluble cold. It was analyzed and the following results were found,

Calculated for Found C₁₃H₇N₃O₄Se I II

Nitrogen 12.07% 12.30% 12.12%

Diamino Derivative

The conversion of the dinitro to diamino derivative was accomplished in the same manner as the reduction of the mononitro derivative excepting that twice as much tin and HCl were used.

This diamino compound crystallizes in yellowish glistening needles from alcohol and pyridine; m. p., 269°-270.5°C.; was analyzed and gave the following results,

Calculated for Found C₁₃H₁₁N₃Se I II

Nitrogen 14.6% 14.4 14.7

Diacetyl and Dibenzylidene Derivatives

The diacetyl and dibenzylidene compounds were also prepared from these diamino derivatives. The former crystallizes in cubes from dilute alcohol; m. p., 307°C (Corr.) and the latter in beautiful yellow plates from carbon disulphide, m. p., 195°-196°C. (Corr.). An analysis of these two compounds showed the following results,

Calc. for Calc. for Found C₁₇H₁₅N₃O₂Se C₂₇H₁₉N₃Se I II

Nitrogen 9.05% 11.21% 9.21% 11.43%

Dyeing with Azo Dyes

Both the monoamino and the diamino derivatives form intensely colored dyes when diazotized and coupled with phenols and aromatic amines. The dyes formed are fast to light. In the following table silk is given to represent the fabrics used. Wool and cotton were dyed similar shades, though with slight variation. Each silk sample was dyed in acid or alkaline baths as indicated and each bath contained 0.01 gram in twenty cc. solution:

Diazo. On Diazo. On Coupler monoamine silk diamine silk

Phenol deep red v. light (alk) yellow (alk) yellow deep red

Dimethylaniline orange light orange-red yellow (acid) yellow (acid)

P-nitraniline light brownish grayish brown (acid) brown (acid)

P-toluidine light brownish brownish brown (acid) (acid)

Pyrogallic dark grayish dark grayish acid brown brown (acid) (alk)

Salicylic reddish light red brown acid (alk) brown (alk)

B-naphthol deep red pink deep red red (alk) (alk)

Sulphanilic light brownish brown brown acid brown (alk) (alk)

A-naphthylamine light brownish yellow yellow brown (acid) (acid)

Resorcinol purple red dark deep red (alk) purple (alk)

BIBLIOGRAPHY

1. Berzelius, Annales de Physique et Chimie (2) 9, 239, 356 (1818).

2. Gmelin-Kraut, “Handbuch der Anorg. Chemie” I (1) 705-804; Roscoe and Schorlemmer, “Treatise on Chemistry” I, 467-82 (1920); Browning, “Introduction to the Rarer Elements,” 144-52 (1917).

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