The analogous derivatives of the meta toluene sulphonic acid with one or two exceptions have not been made or studied, nor has the acid itself been prepared in a form which could be recognized. The following derivatives of meta toluene sulphonic acid have been made and studied; the amide by Müller, Pechmann, Pagel, Beckurts, F.H.S. Muller, Nevile and Winther, Chase Palmer, Klason, Valin, Noyes and Walker, Metcalf, and Griffin; meta sulphamine benzoic acid by Limpricht and Uslar, and Griffin; meta toluene sulphon anilide and toluide by Muller and Wiesinger, (Ber. d. chem. Ges, 12,1348), and by Griffin; the latter also made and studied several metallic salts.
The literature on the ortho and para toluene sulphonic acids and their derivatives is voluminous, and covers a great many derivatives which have been thoroughly studied and whose structure has been determined. The literature on meta toluene sulphonic acid is very meagre, comparatively, and all that could be found is mentioned in this paper. This would seem to indicate that investigators have avoided this series, and apparently the reason is due to the difficulties encountered in isolating the free acid.
The object of this paper is to prepare a solution of meta toluene sulphonic acid, as probably obtained by Griffin, by the most promising of the investigated methods and to find an acceptable one for isolating the acid in the solid state. After a solution is obtained similar to that found by Griffin, (loc. cit.), the intention is to remove as much water as possible by distillation under diminished pressure and then to precipitate the acid by the method of Kastle, (Amer. Chem. J., Vol. 44, page 483), namely saturate the remaining solution with gaseous hydrochloric acid. It is hoped that in this way the solid acid may be obtained which can then be studied.
As has been proved by previous experimenters and discussed above, no direct method of sulphonating toluene will give any of the meta sulphonic acid. Therefore to get a compound containing a methyl group with a sulphonic acid group in the position meta to it some compound with these already in that position and containing some other group which can be replaced by hydrogen might be used, i.e. a disubstituted toluene. The two groups which can be readily replaced by hydrogen are the amino group and bromine, the former by the diazo reaction and the latter by treatment with metallic sodium; the easier of the two to prepare and replace is the amino group and this is the one made use of in this synthesis. This replacement has been widely studied (Amer. Chem. J., by Palmer 8, 243; Orndorff 9, 387; Graham 11, 319; Dashiell 15, 124; Metcalf 15, 301; Parks 15, 320; Shober 15, 379; Beeson 16, 244; and Dissertations by Weida, Cameron, and Chamberlain, all 1894.), and the various conditions affecting it determined. The foregoing investigators decomposed their diazo compounds with alcohols sometimes using certain substances to cause the alkoxy or hydrogen reactions to take place. Later investigators (Buchka, Berichte 23, 1628, St. Von Niemantowski, Ibid., 34, 3325 (1901), Ullman and Bieleck, Ibid., 34, 2174, and Bigelow, J. Amer. Chem. Soc., Vol. 41, 1566), have shown that this decomposition is greatly increased by the presence of copper powder. As the first method has been more extensively studied it was adopted in this case.