V. The Action of Benzene and Aluminium Chloride on the Symmetrical Chloride of Paranitroorthosulphobenzoic Acid.
Reading edition
Hollis[14] 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.
When the reaction was complete, the resulting product was isolated and purified in accordance with the directions given by Hollis. Repeated trials showed that, as in the case of the unsymmetrical chloride, only one phenyl group could be introduced by this method. The resulting compound, paranitroorthobenzoylbenzenesulphon chloride, was identical with that derived from the unsymmetrical chloride. Owing, however, to the fact that so much more decomposition occurs in the reaction with the symmetrical chloride, in paranitroorthobenzoylbenzene sulphon chloride could not be obtained in perfectly pure condition. In appearance it agreed closely with that described by Hollis, forming very characteristic greenish, rhombic crystals. These melted, not very sharply, at 174° instead of 177° as observed by Hollis.
Accordingly, to establish the identity of the two compounds beyond any doubt, the material on hand was converted into the barium salt of paranitroorthobenzoylbenzene sulphonic acid. This was done by boiling the sulphon chloride with dilute hydrochloric acid until complete solution had been effected; evaporating to dryness on a water-bath; dissolving the residue in hot water, and neutralizing with barium carbonate. On filtering the hot solution from the excess of carbonate, and allowing it to cool, the barium salt separated.
The solution was somewhat colored by impurities, and the long needles in which the salt crystallized were also somewhat colored. They were analysed with the expectation that they would prove to be specimens of the salt described by Hollis as having three, or three and a half molecules of water of crystallization, in as much as the conditions under which they were formed were favorable to the formation of salts with these ratios of water of crystallization. Hollis found that this salt could be obtained with at least four different ratios of water of crystallization viz. three, three and a half, six and seven molecules respectively. The analysis was as follows, the amount of barium being calculated on the basis of the anhydrous salt.
0.3087 gram lost 0.064 gram at 210°,
and gave 0.0759 gram BaSO₄.
Cal. for (C₁₃H₈O₆NS)₂Ba + 11H₂O Found.
H₂O = 20.90 20.73
Ba = 18.29 18.23
The mother-liquor, in which the crystals remaining from analysis were redissolved, was warmed, but not boiled, with boneblack, to remove impurities. When filtered, the solution was perfectly colorless, and on standing for some time, well formed colorless, rhombic crystals appeared. On analysis they gave results as follows.
0.2804 gram lost 0.0405 gram at 210°,
and gave 0.0759 gram BaSO₄.
Cal. for (C₁₃H₈O₆NS)₂Ba + 7H₂O. Found.
H₂O = 14.40 14.44.
Ba = 18.29 18.03.
In making a further supply of the salt it was found that if the solution, after filtering from the barium carbonate, was diluted to such an extent that no crystals separated on cooling, then on slow evaporation under a bell-jar the first crystals to appear were very long slender needles. As evaporation proceeded, these needles became much thicker assuming prismatic proportions, and corresponded in appearance to the salt described by Hollis as having six molecules of crystal water.
As growth proceeded, the crystals became dark in color, and the mother-liquor correspondingly clearer, the crystals evidently absorbing the impurity in their growth.
When the solution had become quite colorless, rhombic crystals of the salt containing seven molecules of water of crystallization appeared. The larger prismatic crystals were carefully removed, and redissolved in water in order to see if the same phenomena would repeat themselves. This in fact was the case, crystals of both types appearing in the same way as described. Without separating the crystals in this second experiment, water was added, and the crystals dissolved. The solution was then warmed briskly with boneblack, and filtered. From the filtrate, which was colorless, nothing but rhombic crystals having seven molecules of water of crystallization could be obtained, although a great many variations in the conditions were tried. Analysis of these last crystals was as follows:
0.2400 gram lost 0.035 gram at 210°,
and gave 0.0637 gram BaSO₄.
Cal. for (C₁₃H₈O₆NS)₂Ba + 7H₂O. Found.
H₂O = 14.40 14.58
Ba = 18.29 18.27
Hollis states that treatment with boneblack decomposes this salt, and hence he did not purify it prior to crystallization. From the experiments just described it seems probable that the impurities present affect the crystalline habit, and the degree of hydration of this salt in a very striking manner. By careful warming with boneblack no decomposition was observed, and the crystals so obtained have constantly seven molecules of crystal water.