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 |