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.

The action of methyl, ethyl, and n-propyl alcohols on diazo compounds has been well studied by the above authors, and it has been shown that the first two at ordinary pressures give the alkoxy reaction either in whole or in part; n-propyl alcohol gives the hydrogen reaction only. Also the first two give the hydrogen reaction in the presence of zinc dust or sodium carbonate, but in these cases form salts of the acid. On account of its rarity n-propyl alcohol was not used, but n-butyl alcohol which is available in large quantities and in a pure condition was employed. Recent advances in fermentation as applied to organic chemistry have made this substance easily obtainable as a byproduct in the production of acetone which was needed in large amounts during the late war. Its use was found to be successful; it boils at 117 and so can be easily distilled off after decomposition has been effected without a great increase in temperature above the boiling point of water, which increase Griffin (loc. cit.) showed to cause carbonization. For this reason i-amyl alcohol although available was not considered,—also higher alcohols because of this fact and because of their rarity.

Of the four amino toluene sulphonic acids theoretically possible in which the sulphonic acid group is in the meta position in reference to the methyl group only two are commonly known, No. 1, and No. 2.

Methods of preparing No. 1 and No. 2 were found but without details, so a method had to be worked out to obtain them easily and in good yield. After a little experimenting No. 1, or ortho toluidine sulphonic acid was readily obtained in good yield and in a fairly pure condition. No. 2, or para toluidine meta sulphonic acid was obtained in only a ten per cent yield and by means of a much more difficult method of procedure. The preparation of this acid was undertaken first and consumed a long time; Griffin did his work starting with this acid and I hoped to get as far as he did earlier. It was then available in the market as was the ortho toluidine sulphonic acid, but now neither are available.

The methods employed by earlier investigators when they wished to isolate their diazo compounds was to suspend the substance to be diazotized in alcohol, and then pass in nitrous fumes generated by dropping concentrated nitric acid onto arsenious oxide. The diazo compound from ortho toluidine sulphonic acid is so nearly insoluble in water that it was found possible to diazotize it in water suspension, and generate the nitrous fumes in the solution itself by adding a solution of sodium nitrite to the water suspension containing hydrochloric acid. After a short time the diazo compound separates out and can be filtered off, washed and dried. It is a very stable substance as compared with other diazo compounds. This method was worked out, there being no mention of it in the literature.