| 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.