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.