Part 4

2. 2.75 gr. of sulphinide was sealed up in a tube with pure conc. HCl and heated two hours to 150°. On cooling nothing separated; the liquid was evaporated to dryness giving 3.2 gr of acid and ammonium chloride. The reaction taking place here may be represented thus:

CO COOH ╱ ╲ ╱ C{6}H{4} NH + 2H{2}O + HCl = C{6}H{4} + NH{4}Cl. ╲ ╱ ╲ SO{2} SO{2}OH

3. A more convenient method for obtaining the acid than either of the above, is to heat the sulphinide with conc. HCl on the water bath for two days. Then evaporate to dryness and dissolve the residue in a small quantity of water. If the sulphinide contained any para-sulphamide, as is usually the case, this will be left undissolved and most of the NH_{4}Cl will crystallize on standing. This solution by slow evaporation deposits large colorless crystals of the free acid.

This acid is soluble in about two parts of cold water, very difficultly soluble in absolute alcohol and almost completely insoluble in ether. It does not melt under 250° but considerably above that it melts, at first apparently without change and then with slight sublimation of a very deliquescent substance, probably the anhydride.

Two determinations of the S. made by Mr. A. F. Linn, gave the following results.

I ·1358 gr substance gave ·1855 gr BaSO_{4} representing 15·72% S.

II ” ” ” ” ” ”

COOH ╱ Calculated for the formula C{6}H{4} = 15·84% S. ╲ SO_{2}OH

A crystallographic examination of the acid showed it to belong to the orthorhombic system. Axial ratio: a: b: c = ·8507: 1: ·8121. Planes. Ρ and αΡὰ.

┌─ ┌─ │ Edge X = 131° 8' │ Ρ ^ Ρ ─┤ ” Y = 82° 18' │ │ ” Z = 118° 40' Angles measured ─┤ └─ │ │ Ρ ^ αΡὰ = 114° 38' └─

The crystals are up to 8 mm in length. The pyramidal faces are generally etched so that the image is poor.

Sulphonfluoresceïn.

Several attempts had already been made to obtain from the action of o-sulphobenzoic acid and resorcin a substance analogous to the fluoresceïn obtained by Baeyer from phthalic anhydride and resorcin but while a strongly fluorescent substance was easily obtained, no definite compound could be separated from it. Thus Palmer obtained, by heating together the above named substances to 160°(?) a solid mass, part soluble in water and part insoluble as a dark brown amorphous powder. Both parts gave a strong fluorescence with alkalis. He was unable however to obtain the substance itself or any derivative in a crystalline form.

Annalin. No. 183. S. 1. No. 202. S. 36 & S. 153. Berichte. No. IV. S. 457. 555. 658. 662. ” ” VIII. S. 66. 146.

The first experiments in this series gave the same negative results. The mixture of acid and resorcin was heated in a sulphuric acid both for several hours to 150°-170°, and as it showed no sign of solidification the temperature was raised to 200° and then to 235° where it was kept several hours longer. The black viscous mass obtained in this way became vitreous on cooling, and in all respects resembled that described by Palmer. This however is not the normal course of the reaction as shown later but is probably due to a decomposition of the normal product produced by too high heating.

An experiment was made with the acid salt of ortho-sulphobenzoic acid.

COOH ╱ C{6}H{4} ╲ SO_{2}OK,

resorcin and H{2}SO{4} heating the mixture to 150°-170°. A solid black mass was obtained strongly fluorescent in alkaline solution and in all other respects like the substance obtained above.

Preparation of Sulphonfluoresceïn.

As the result of a number of experiments the following method of preparing and purifying the sulphonfluoresceïn was found to give the best results.

The free acid is mixed with resorcin in the proportion of 1 part acid to 1.2 parts resorcin, or a slight excess over two molecules of the latter to one of the former. The mixture is placed in a deep vessel, a test tube or beaker, which is placed in a sulphuric acid bath, a thermometer being suspended in the mixture. The bath is heated and at about 100° the resorcin melts and the acid slowly dissolves in the liquid. No action appears to take place till the temperature reaches 175° where water begins to be given off and the liquid slowly assumes a darker color. White crystals of resorcin collect on the sides of the vessel. After the heating has been continued for about seven hours at 178°-185° the liquid has a clear deep red color but shows no signs of becoming viscous. At length lustrous yellow crystalline plates appear in the liquid and soon the whole mass becomes a thick nearly solid yellow paste. Continuous heating at the same temperature causes no further apparent change. This mass, which on cooling is made up of yellow crystals imbedded in a red vitreous matrix, is then dissolved in hot water forming a clear red solution or at most one containing but a small quantity of a brown flocculent precipitate. This solution is filtered if necessary and evaporated to a small volume from which the substance separates on cooling in reddish yellow radial crystals. These are filtered and washed with ether till the washings are perfectly colorless. The substance on repeated crystallization from water has a pale straw yellow color and when deposited slowly forms transparent crystal blocks from 2·6 mm long, arranged in radial groups.

A considerable amount of resorcin is lost by sublimation during the reaction especially if the operation is carried on in a beaker so that some excess should be added. But even when the resorcin is present in excess at the end of the reaction some free acid is always left which may be obtained from the mother liquid in the characteristic colorless orthorhombic crystals.

The water of crystallization and sulphur were determined in the new compound. In estimating the water, the substance was heated to 106°-123° for about ten hours till it attained a constant weight. On standing in the air it quickly regains its original weight. When heated to 130°-140° for some time it turns slightly reddish and loses over 10% of its weight which is not regained by standing in the air.

Estimation No. I. was made by fusion with KOH and KNO{3}. Nos. II and III were made by Mr. Mindileff by Morse’s method, oxidizing with KMnO{4} in KOH solution.

·3882 gr. heated to 106°-123° lost ·0302 gr. = 8·5%

Calculation for 2H{2}O - C{19}H{12}O{6}S+2H_{2}O = 8·9% water.

I. ·2007 gr sub. gave ·1286 gr BaSO_{4} = 8·77% S. II. gr ” ” ” gr ” = 7·91” ” III. gr ” ” ” gr ” = 7·89” ”

Calculation for C{19}H{12}O{6}S+2H{2}O = 7·92% S.