Introduction.
The close analogy in composition and structure between phthalic acid and ortho-sulpho-benzoic acid suggests the possibility of obtaining from the latter, by its action on phenols, substances analogous to the phthaleïns. If such compounds could be made they would afford a favorable opportunity of studying the effects produced in the properties of a compound by the replacement of CO by SO2. It was with a view to such study that the following discussed work was undertaken at the suggestion of Prof. Remsen and carried on under his constant guidance.
Some experiments previously performed by Remsen and Palmer (A.G.) indicated the possibility of the formation of a fluorescent substance by the action of ortho-sulpho-benzoic acid on resorcin but they did not succeed in obtaining any definite crystallized compound from the reaction.
The chief obstacle to be overcome in the work is the difficulty in obtaining the o-sulpho-benzoic acid and a large proportion of the work here described was applied in that direction.
Ortho-sulpho-benzoic acid: Methods for its preparation.
1. From toluene and H2SO4.
A method employed by Remsen and Fahlberg (Am. Ch. Jour. Vol. 1. p __ ) for getting the sulphonic acid group in the ortho position to methyl was; (a) treat toluene with fuming H2SO4 forming thus ortho- and para- toluene sulphonic acids, (b) make the calcium salt of the sulphonic acids thus formed and from this the potassium salt. (c) treat this mixture of potassium toluene sulphonates with phosphorous penta-chloride forming the corresponding sulphonchlorides. One of these (para) being a solid and the other (ortho) an oily liquid a nearly complete separation could be effected. The difficulty with this method is however that the larger part of the product is the para and only a comparatively small proportion of the ortho compound is formed.
2. From p-nitro-toluene and H2SO4.
A second method employed consists in starting with p-nitro-toluene. This when treated with H2SO4 forms toluene p-nitro o-sulphonic acid. If now a method could be obtained for removing the nitro group the desired result would be attained.
The attempt was made by Remsen and Palmer (A.G.) to accomplish this by (a) reducing the nitro compound to the amide, (b) making the diazo compound and (c) boiling this with absolute alcohol. According to generally accepted views this should effect the removal of the diazo group and its replacement by hydrogen.
Experiments however showed that the replacement was made not by hydrogen but by the ethoxy group -OC2H5. This method was therefore impracticable.
A modification of this method was suggested by an observation of Baeyer and Liebermann that if phenyl hydrazine be boiled with a dilute solution of copper sulphate the hydrazine group is replaced by hydrogen and benzene thus formed. Hence it was believed that if the hydrazine compound should be made from diazo compound mentioned above, the corresponding hydrocarbon, i.e. toluene o-sulphonic acid could be obtained. The results of experiments showed that this afforded a practicable method of preparing toluene ortho-sulphonic acid.
After experimenting with various modifications of the method the following was found to be the best adapted to the purpose.
The potassium salt of toluene p-nitro-o-sulphonic acid is easily obtained, as already stated, by heating p-nitro toluene on the water bath with three times its weight of fuming H2SO4, neutralizing with chalk and to the solution of calcium salt thus obtained adding a slight excess of K2CO3. On filtering from the precipitated CaCO3 and evaporating slightly, the salt is obtained in long needle shaped crystals of a pale straw yellow color. This is
| ⎧ | CH3 | ||
| C6H3 | ⎨ | SO2OH | (o) |
| ⎩ | NO2 | (p). |
The reduction of the nitro group is best effected by means of tin and HCl, in the proportion, salt 5 parts, tin 6 parts and concentrated HCl 30 parts.
The amido acid forms a compound with tin which crystallizes from the HCl together with stannous chloride. This compound may be broken up and the tin removed by continued boiling with water.
A better method of removing the tin is by dissolving the compound in Na2CO3. This forms a salt with the amido acid and throws down the tin as Sn(OH)2, a white flocculent precipitate. On filtering and adding to the solution conc. HCl, the free amido acid is deposited in characteristic colorless, rhombic crystals, having the formula
| ⎧ | CH3 | |
| C6H3 | ⎨ | SO2OH |
| ⎩ | NH2 |
The method at first employed for preparing the hydrazine compound consisted in treating the amido acid, suspended in HCl, with potassium nitrite and then with stannous chloride. The tin was then removed from the solution by the addition of sodium carbonate and the hydrazine compound thrown down with HCl. This method however gave poor results the yield being only about 50% of the theoretical.
Another method was accordingly substituted for the above, namely that of Strecker and Römer (Ber. IV. s 784.) By this the diazo compound is made first and isolated. This is done by suspending the finely powdered acid in absolute alcohol, cooling and passing a current of the oxides of nitrogen through in the ordinary way. The acid changes in appearance, becoming more crystalline and slightly darker and settles quickly on being shaken. The reaction here may be expressed thus—
| ⎧ | CH3 | ⎧ | CH3 | ||
| C6H3 | ⎨ | SO2OH + HNO2 = | C6H3 | ⎨ | SO3 + 2H2O |
| ⎩ | NH2 | | | ╲ | ||
| ⎩ | N=N |
When the reaction is completed as shown by the appearance of the suspended powder it is filtered and while still fresh is added to a solution of acid sodium sulphite as long as it continues to dissolve readily.
To this solution there is added a quantity of solution of acid sodium sulphite equivalent to that already used and the solution is then boiled. It has at first a deep red color but in a few moments becomes light reddish yellow. The reaction of HNaSO3 on the diazo compound may be represented in two stages, the first portion forming an addition product and the second acting as a reducing agent. Thus,
| ⎧ CH3 | ⎧ CH3 | |||
| 1. C6H3 | ⎨ SO3 + HNaSO3 = | C6H3 | ⎨ SO2ONa | |
| │ ╲ | ⎩ N=NSO3H | |||
| ⎩ N=N |
| ⎧ CH3 | ⎧ CH3 | ||
| 2. C6H3 | ⎨ SO2ONa + HNaSO3 + H2O = | C6H3 | ⎨ SO2ONa |
| ⎩ N=NSO3H | ⎩ NH—NHSO3 | ||
To the hot solution an excess of conc. HCl is added when the hydrazine compound separates in a few moments in lustrous yellow scales which completely fill the solution. On the addition of the HCl a large amount of SO2 is given off from the excess of HNaSO3 and the solution becomes deep red. When the hydrazine has separated the mother liquor is again yellow.
The reaction is represented as follows:
| ⎧ CH3 | ⎧ CH3 | ||
| C6H3 | ⎨ SO2ONa + HCl + H2O = | C6H3 | ⎨ SO2OH + H2SO4 + NaCl |
| ⎩ NH—NHSO3H | ⎩ NH—NH2 |
The yield of hydrazine when both the diazo and the NaHSO3 are freshly prepared is practically quantitative.
The hydrazine thus prepared was treated with a hot 10% solution of copper sulphate till a permanent blue color was obtained in the solution. Nitrogen is evolved and the copper sulphate is reduced to cuprous oxide which is precipitated as a red powder. The reaction is as follows.
| ⎧ CH3 | ⎧ | ||
| C6H3 | ⎨ SO2OH + 2CuSO4 + H2O = | C6H4 | ⎨ CH3 + Cu2O + N2 + 2H2SO4 |
| ⎩ NH—NH2 | ⎩ SO2OH |
Chalk was added to the solution to precipitate the H2SO4 and form a calcium salt of toluene-o-sulphonic acid. From this the sodium salt was made by adding a slight excess of Na2SO3 and evaporating to dryness. The salt is very soluble being deliquescent in the air while the corresponding potassium salt is not. From 1538 gr. of para-nitro-toluene, 655 gr. of toluene ortho-sodium sulphonate were obtained.
Having thus obtained the toluene ortho-sulphonic acid the next step in the problem was to find a convenient method for converting this into ortho-sulph-benzoic acid. Two ways present themselves for accomplishing this end. (1) direct oxidation of this salt and (2) conversion into benzoic sulphinide from which the acid may be obtained. Both of these methods were tried.
Oxidation of toluene-o-sodium sulphonate.
| ⎧ | CH3 | |
| C6H4 | ⎨ | |
| ⎩ | SO2ONa |
The sodium salt of toluene-o-sulphonic acid is oxidized to ortho-sulphobenzoic acid with considerable difficulty by KMnO4 in neutral solution.
Thus two experiments showed that the oxidation was not complete after 24 hours boiling with excess of permanganate. If the solution be made alkaline however, the oxidation is completed in a few hours, yet the greatest difficulty still remains in the separation of the free acid from the products of oxidation in the solution. If HCl be added to the solution the acid salt
| COOH | ||
| ╱ | ||
| C6H4 | ||
| ╲ | ||
| SO2OK |
is formed and this has nearly the same solubility as the KCl also present. A better method therefore is to add a slight excess of H2SO4 and evaporate nearly to dryness. In this way are formed sulphates and the free acid presumably. The mixture is heated with alcohol (95%) which extracts the acid leaving the greater part of the manganese salts. This extract is evaporated and reextracted with alcohol. To this solution BaCO3 is added to precipitate the H2SO4 and form the Barium salt of the o-sulphobenzoic acid. The solution is filtered from the BaSO4 and just enough H2SO4 is added to exactly precipitate the barium. The solution should thus contain only the free acid sought, which crystallizes out on evaporating to a small volume. While the method is theoretically possible it presents so many difficulties that it is practically useless. The yield is extremely small; only enough acid being obtained in this way to show that it was possible.
Formation of Sulphinide from toluene-o-sodium sulphonate.
The second method for obtaining free o-sulphobenzoic acid from toluene-ortho-sulphonic acid is by the conversion of the latter first into benzoic sulphinide and then into the free acid. The sulphinide was made essentially as described by Remsen (Am. Ch. Jour. Vol. I. p. 428) with a few changes in the details as follows.
The salt
| ⎧ | CH3 | |
| C6H4 | ⎨ | |
| ⎩ | SO2ONa |
finely pulverized and in portions of from 10 to 50 gr. was placed in a Florence flask; an equivalent quantity of PCl5 added; An inverted condenser was then attached and the flask shaken. The action takes place at once and involves sufficient heat to distill off the oxychloride formed in the reaction. This being returned to the flask by the condenser furnishes a liquid medium in which the reaction takes place more readily and completely than when it is not present. It is best to cool the flask at first and afterwards heat gently on the water bath. The reaction which takes place may be represented as follows.
| ⎧ | CH3 | ⎧ | CH3 | ||||
| C6H4 | ⎨ | + PCl5 = | C6H4 | ⎨ | + POCl3 + NaCl. | ||
| ⎩ | SO2ONa | ⎩ | SO2Cl |
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.
| CH3 | CH3 | ||||||
| ╱ | ╱ | ||||||
| C6H4 | + NH3 = | C6H4 | + HCl. | ||||
| ╲ | ╲ | ||||||
| SO2Cl | SO2NH2 |
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 KMnO4 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, ClSO2OH, 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 SO3 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 K2Cr2O7 in acid solution does not oxidize the methyl group in
| CH3 | ||
| ╱ | ||
| C6H4 | ||
| ╲ | ||
| SO2NH2 (o) |
but does oxidize that in
| CH3 | ||
| ╱ | ||
| C6H4 | ||
| ╲ | ||
| SO2NH2 (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 K2Cr2O7, 55 gr H2SO4 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 KMnO4 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 PCl5 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 H2SO4 and treated with BaCO3; the filtrate from the BaSO4 which contained a soluble barium salt was added to that above mentioned and the barium exactly precipitated with H2SO4 and the filtrate evaporated to dryness giving the free acid but not in a perfectly pure condition.
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 | |||||||
| ╱ | ╲ | ╱ | ||||||
| C6H4 | NH + 2H2O + HCl = | C6H4 | + NH4Cl. | |||||
| ╲ | ╱ | ╲ | ||||||
| SO2 | SO2OH |
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 NH4Cl 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 BaSO4 representing | 15·72% S. |
| II | ” | ” | ” | ” | ” |
Calculated for the formula
| COOH | |||
| ╱ | |||
| C6H4 | = 15·84% S. | ||
| ╲ | |||
| SO2OH |
 | 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 α Ρ ὰ.
The pyramidal faces are generally etched so that the image is poor. |