Part 3

Ber. XXVI-2231; XXVIII-2281

The only effective method of separating this colored substance was found to be to pass to the neutral salt of paranitroorthosulphobenzoic acid, by making the solution slightly alkaline. The salt of this colored substance is also formed and the two can be separated by a few recrystallizations in a fairly satisfactory manner.

The yield in both of the transformations involved in the preparation of paranitroorthosulphobenzoic acid does not fall far short of the theoretical.

III. Preparation of the Symmetrical Chloride of Paranitroorthosulphobenzoic Acid.

This chloride was first separated from its unsymmetrical isomer by Gray. It was obtained by allowing a chloroform solution of the mixed chlorides to evaporate until the chloroform had almost entirely disappeared. In the thick liquid so obtained, crystals of the symmetrical chloride were formed. It was also obtained by applying the method devised by Bucher in connection with the corresponding chloride of orthosulphobenzoic acid—i.e. by the action of dilute ammonia on the mixed chlorides. Gray also found that the best conditions for securing a relatively large proportion of the symmetrical chloride were, the employment of as low a temperature as possible in the formation of the chlorides, and of as small an excess of phosphorus pentachloride as would suffice for the reaction.

Inaug. Diss. J. H. Univ. 1895.

After many experiments, under widely differing conditions, the following method of procedure, embodying the results of Gray’s work, was adopted.

Dehydrated acid potassium salt of paranitroorthosulphobenzoic acid, and phosphorus pentachloride, in the ratio of 40: 55 grams, are brought together in a mortar and intimately mixed. The mixture is put into an evaporating dish, and placed on a sulphuric acid bath, previously heated to 150°. As soon as the action has been well started, the dish is removed, and the reaction allowed to proceed without further heating. When it is complete, and the contents of the dish has cooled down to the temperature of the room, the oily product is poured slowly into a salts bottle containing ice water, the bottle being frequently shaken during the process. The shaking is continued with renewed portions of water, as long as the wash water is cloudy. The water is then poured off, the brownish gummy chloride dissolved in chloroform, and the solution placed in a good-sized separating funnel. Ice water is then added, and the contents of the funnel treated with successive portions of ammonia (desk ammonia diluted one half). Shaking is continued after each addition until the odor of ammonia has disappeared, and ice is added from time to time as may be required.

When it is found that the odor of ammonia persists after several minutes’ shaking, the chloroform layer, which is usually filled with a solid substance that has separated during the process, is drawn off, filtered, and dried with calcium chloride.

By this process all of the unsymmetrical chloride is converted into the ammonium salt of paranitroorthocyanbenzenesulphonic acid, according to the equation:

CCl₂ / \ / O CN / / / C₆H₃——SO₂ + 4NH₃ = C₆H₃——SO₃NH₄ + 2NH₄Cl. \ \ NO₂ NO₂

while the symmetrical chloride remains for the most part unchanged, though some of it is converted into the ammonium salt of paranitrobenzoic sulphinide:

CO / \ COCl / N.NH₄ / / / C₆H₃——SO₂Cl + 4NH₃ = C₆H₃——SO₂ + 2NH₄Cl. \ \ NO₂ NO₂

It was found that working in this way the symmetrical chloride could be prepared in pure condition, free from its isomer. The chloroform completely evaporates in a short time leaving fine crystals of the symmetrical chloride. In case the evaporation is slow and incomplete, it may be concluded that not all of the unsymmetrical chloride has been removed. The yield was uniformly about 40 per cent of the theoretical.

From the water used to wash the chlorides a considerable amount of the original salt can be recovered, as the reaction under the conditions employed, is never complete.

An examination was made of the substance mentioned as separating in the chloroform solution of the chlorides, during the treatment with ammonia, and it was found to possess the following properties. It is insoluble in benzene, chloroform, acetone, ether and ligroin; soluble in glacial acetic acid, from which it separates on cooling in colorless, crystalline condition; insoluble in the cold in water, alcohol and ammonia, but by boiling with these reagents, or by long standing in the cold, it is dissolved with decomposition. It was dissolved in hot water and the solution, which was acid in reaction, was neutralized with potassium carbonate. On adding an excess of hydrochloric acid to the solution, and allowing it to cool, characteristic crystals of acid potassium salt of paranitroorthosulphobenzoic acid separated. These properties identify the substance as the anhydride of this acid.

The formation of the corresponding anhydride of orthosulphobenzoic acid by the action of phosphorus pentachloride upon its acid potassium salt was observed by Sohon, who made use of the reaction to prepare this anhydride in quantity.

Inaug. Diss. J. H. Univ. 1896.

IV. Properties of the Symmetrical Chloride of Paranitroorthosulphobenzoic Acid.

As first obtained, the crystals of the symmetrical chloride resemble irregularly shaped pieces of amber, both in color, and in lustre. On recrystallization from chloroform or ether, they may be obtained perfectly colorless, and are often of very simple crystallographic form. The chloride crystallizes in the monoclinic system, and possesses a very remarkable crystallizing power, in which respect it differs noticeably form its isomer. Even in chloroform solution that is far from dry, crystals appear with the greatest ease.

The habit of the crystals differs very much according to the conditions of crystallization. Not infrequently almost perfectly formed crystals of the simplest form—the oblique octahedron—were obtained though for the most part the form was much more complicated, pinacoid and dome faces, together with basal planes being prominent. As a rule, the crystals were not suitable for crystallographic work, as the faces are usually uneven and the edges rounded. By proper precautions however, good ones were obtained, and measurements of these will be found in this dissertation when it appears in print.

The size of some of the crystals obtained was unusual for substances of this class. One crystal obtained with no special precautions, save letting a solution of the chloride stand undisturbed for several days, in a rather cool place measured 3 × 2.5 × 1.5 cm., and weighed 11.2 grams. The crystals are quite compact, their density being abut 1.85. They melt at 98° (uncorr.) The chloride is quite stable in crystalline condition. Even in moist air the crystals were unchanged, and retained their lustre as long as they were in my possession.

An analysis for chlorine gave the following results.

.2200 gram gave .2212 gram AgCl.

COCl / Cal. for C₆H₃——SO₂Cl \ NO₂ Found. Cl = 24.94 24.83

V. The Action of Benzene and Aluminium Chloride on the Symmetrical Chloride of Paranitroorthosulphobenzoic Acid.

Hollis in his study of the action of these reagents upon the unsymmetrical chloride, tested their action upon one portion of the symmetrical chloride, and found the products to be identical in the two cases. A few experiments were made in confirmation of these results, and the same products, in general, were obtained. It was observed however that the reactions differ in the relative ease with which they are brought about. In the case of the symmetrical chloride, the reaction is a much more vigorous one. On adding aluminium chloride to a solution of the symmetrical chloride, in benzene, action begins at once the temperature of the hand, and very little external heat, and that only in the latter stages of the operation, is needful for the completion of the reaction. The application of much heat converts all of the product into thick tarry substances from which nothing satisfactory could be obtained.

Inaug. Diss. J. H. Univ. 1896.