Part 3

On the addition of water the chloride separates as a light yellow oil. This is washed with water and concentrated aqueous ammonia added, which forms toluene-o-sulphonamide thus.

CH{3} CH{3} ╱ ╱ C{6}H{4} + NH{3} = C{6}H{4} + HCl. ╲ ╲ SO{2}Cl SO{2}NH{2}

The reaction is accompanied by a slight evolution of heat and the formation, apparently, of an intermediate product having a yellowish color, which passes over on longer standing into the white amide. After standing several hours the excess of ammonia was driven off by very gentle heating on the water bath. If the heat is too high a large amount of a tarry product is formed and the yield of amide is correspondingly small. In any case some of this tarry product is formed. When nearly all the ammonia had been driven off the mass was boiled with water which dissolves everything except the tar. The hot solution was filtered through charcoal and on cooling the amide separated in white feathery crystals which melt at 155°-156°.

The amide thus obtained was oxidized as described by Remsen (loc. cit.) with potassium permanganate in neutral solution. The proportions are 10 gr amide. 40 gr KMnO_{4} and 1 L. water. The oxidation was usually effected in from four to six hours.

To obtain the sulphinide from this solution after oxidation, the latter, after filtration from the precipitated oxides of manganese, was slightly acidified with HCl and evaporated to about one fourth its original volume. On the addition of concentrated HCl to this solution, the sulphinide separated out in white or slightly yellowish feather shaped crystals melting at 212° and having the characteristic intensely sweet taste.

Formation of Sulphinide from Toluene by means of the chlorsulphonic acid reaction.

Before passing on to the methods used for converting the sulphinide into free acid another method should be described by which the former was obtained in larger quantities and much more easily than by the one above described.

Beckurts and Otto (Ber. XI. 2061) found that by treatment of toluene with sulphuryl hydroxy-chloride or chlorsulphonic acid, ClSO_{2}OH, both o- and p- and as they supposed also m-toluene sulphonchlorides were formed together with the corresponding sulphonic acid.

Claesson and Wallin (Ber. XII. p. 1848) repeated the work reaching practically the same results and finally Noyes (Am. Ch. Jour. Vol. VIII. p. 176) employed the reaction as a convenient method for obtaining toluene o-sulphon-chloride.

Chlorsulphonic acid is made by passing dry HCl over solid sulphuric acid so long as it continues to be absorbed. Since no solid sulphuric acid was at hand, ordinary fuming Nordhausen acid was taken and from one of two equal portions the SO_{3} was driven over into the other. HCl was passed into the latter and the resulting chlorsulphonic acid distilled off at about 156°.

This was placed in a flask, provided with a drop funnel and exit tube, in portions of 150 gr. and to each portion 60 gr. of toluene was added, very slowly, with constant shaking, the temperature being kept near 10°. The action is violent and if any toluene is allowed to collect on the surface of the liquid it is apt to produce disastrous results. Large quantities of HCl are given off and the liquid in the flask assumes a brown color. When all the toluene has been added, it is poured into a large quantity of ice water, when the sulphon-chlorides separate out, the ortho- as a heavy oil and the para- as a white crystalline solid. After allowing to stand some time in order that as much of the para-chloride might crystallize as possible the ortho- was drawn off and subjected to a freezing temperature for several hours. By this means more of the p-chloride was removed and the operation was replicated as long as any crystals continued to form, generally two or three times. In this way the greater part of the para- may be removed, though some still remains dissolved in the liquid chloride, which cannot be removed by repeated freezings.

The chloride thus obtained was treated with strong aqueous ammonia. The conversion to the sulphamide does not take place so readily as in case of the pure o-chloride obtained from the sulphonic acid and phosphorus pentachloride.

After standing about two days the whole of the oily chloride had solidified to a yellowish brown mass. The excess of ammonia was driven off by gentle heating on the water bath and the mass then boiled with water. Not enough water was added at first for complete solution but when the first portion was saturated it was poured off through a filter and from it the amide separated in yellowish feathery crystals which melted at 105°-125° and consisted therefore as shown by Fahlberg (Am. Ch. Jour. Vol. I. p. 170) of a mixture of o- and p-sulphonamides. It was recrystallized and from it was obtained a portion melting at 153°-5° and one at 108°-20°.

Since this mixture cannot be completely separated by recrystallization another method was suggested. Remsen has shown that K{2}Cr{2}O_{7} in acid solution does not oxidize the methyl group in

CH{3} ╱ C{6}H{4} ╲ SO{2}NH_{2} (o)

but does oxidize that in

CH{3} ╱ C{6}H{4} ╲ SO{2}NH_{2} (p).

It was thought that in a mixture of the two the former might be left unchanged while the latter was oxidized to p-sulphamine benzoic acid.

To test this 15 gr of the mixture, melting at 105°-125°, was heated with 40 gr K{2}Cr{2}O{7}, 55 gr H{2}SO_{4} and 2 vols. of water for about two hours. It was then tested and shown to be still a mixture of p-& o-amides, since it was again heated for several hours with half the original quantity of oxidizing mixture, then diluted, filtered and washed. The white crystalline residue was treated with sodium carbonate to dissolve the benzoic para-sulphamide and the residue was found to be pure toluene o-sulphonamide melting at 153°-155°. The small quantity remaining, 3 gr., indicated that part of the o-amide had been completely broken down by the strong oxidizing agent, though the proportion of o-& p-amides in the original mixtures was known only approximately. The evolution of gas during the oxidation would point to the same conclusion.

Although this effects a complete separation it is hardly economical since it will be shown later that a separation can be conveniently effected after the oxidation with KMnO_{4} so that the o-amide contained in the mixture need not be lost.

The original mass was treated with successive portions of water till nothing remained but a black tarry substance. The amide which separated from these extracts was perfectly white and melted at 153-5°. It was therefore regarded as practically pure o-amide. The yield in amide melting above 153° was a little over one sixth the weight of toluene used.

The amide obtained in this way was oxidized in the manner already described. It was found however that there was always some benzoic p-sulphamide in the solution of the oxidation, due to the slight admixture of p- with the o-amide used. This is thrown down with the sulphinide on acidifying the solution and may be removed by re-crystallization since it is somewhat less soluble in hot and cold water than sulphinide.

A better way to effect the separation, however, was found to be the following. After having evaporated the solution containing the products of oxidation, nearly neutralized with HCl, to about one fifth its original volume, it is made very slightly acid and allowed to cool. In this way very nearly all the benzoic p-sulphamide is separated from the solution and none of the sulphinide. After filtering, strong HCl is added and the sulphinide then separates in its characteristic form. This indicates that sulphinide forms an alkaline salt which is not decomposed by diluted HCl while the p-sulphamide does not.

The mixture of amides meeting at 105°-120° was oxidized and the products separated in this way gave about equal quantities of sulphinide and benzoic p-sulphamide.

When toluene is treated with chlorsulphonic acid there are formed besides the ortho- and para- chlorides also ortho and para sulphonic acids. These of course are in solution in the water from which the chlorides separated. In order to recover the ortho-acid, the solution was neutralized with chalk forming the calcium salt: this converted into the potassium salt which by evaporating the solution to dryness was obtained as a white crystalline powder. When treated with PCl_{5} in the manner already described this gave a mixture of ortho and para sulphonchlorides consisting of about ⅓ ortho and ⅔ para.

Formation of Orthosulphobenzoic acid from Sulphinide.

Benzoic sulphinide may be converted into a sulpho-benzoic acid (1) by boiling with Ba(OH)_{2}, (2) by heating in a closed tube with conc. HCl or (3) by evaporating on the water bath with HCl.

1. Three gramms of sulphinide were boiled in a flask connected with an inverted condenser for about two days with an excess of Ba(OH){2}. There was formed in the flask a hard mineral-like mass which was insoluble in water and cold diluted HCl but dissolved in hot HCl with effervesence. This was a Barium salt, probably basic (?) of ortho sulphobenzoic acid. There was also formed an easily soluble barium salt of that acid. The former was dissolved in H{2}SO{4} and treated with BaCO{3}; the filtrate from the BaSO{4} which contained a soluble barium salt was added to that above mentioned and the barium exactly precipitated with H{2}SO_{4} and the filtrate evaporated to dryness giving the free acid but not in a perfectly pure condition.