META TOLUENE SULPHONIC ACID and RELATED COMPOUNDS
Theoretically toluene should yield three isomeric mono sulphonic acids, in which the entering sulphonic acid group occupies the positions ortho, meta, or para to the methyl group.
The action of sulphuric acid on toluene was first investigated by Jaworsky, (Ztschr. Chem. 1,272), who described one toluene sulphonic acid as the resulting compound. In 1869 Engelhardt and Latschinoff (Ibid. 617), heated toluene with sulphuric acid and made and studied the potassium salt of the resulting acid. They obtained two forms, and identified them by fusion with caustic potash which converted them into the ortho and para cresols, showing that sulphonation had taken place in the positions ortho and para to the methyl group.
Barth (Ann. chem. (Liebig) 152,91), working similarly but fusing under different conditions which also caused oxidation of the methyl group to a carboxyl group obtained para hydroxy benzoic acid and salicylic acid (ortho hydroxy benzoic acid.) This also proved that the sulphonic acid group had entered in the ortho and para positions.
Anna Wolkow (Ztschr. Chem (1870) 321), confirmed this work but ascribed the meta position to the sulphonic acid that passed into salicylic acid. She also made two acid chlorides and amides and recorded their melting points.
Fittig and Ramsay (Ann. chem. (Liebig) 168,242) studied this result of Anna Wolkow, and to determine and settle the constitutions of the sulphonic acids, carefully prepared and purified their sulphonic acids; they proved definitely that no meta acid was formed, and that the products were only the ortho and para toluene sulphonic acids.
Hubner and Post (Ann. chem. (Liebig) 169,47) worked on pure para brom toluene, and obtained two para brom toluene mono-sulphonic acids, one of which they proved to be the ortho acid by removal of the bromine by metallic sodium, and oxidation to salicylic acid. By exclusion they decided that the other acid must be one containing the sulphonic acid group in meta position to the methyl group.
F.C.G. Müller (same as Hubner and Post) made the barium salt of ortho brom toluene sulphonic acid, and then removed the bromine by treatment with sodium amalgam. The excess of alkali was removed by sulphuric acid, the sodium sulphate removed by evaporation and crystallization, and the residue dried. On treatment with phosphorus pentachloride an oily toluene sulphonchloride was obtained; this was decomposed by heating with water, the hydrochloric acid removed by repeated evaporations, and the syrup thus obtained evaporated to a crystalline condition. Several salts were made and studied. His amide melted at 90-91. Because this acid differed in properties from the two previously mentioned, Müller considered it to be the meta toluene sulphonic acid.
About this time F. Gervor (Ann. chem. (Liebig) 169,383), made ortho diazo toluene sulphonic acid by subjecting ortho toluidine sulphonic acid to nitrous fumes. This was decomposed with alcohol under pressure, and a sodium salt of the acid obtained; this was converted into the chloride and an amide which melted at 148, differing in this and other properties from the amides of the ortho and para toluene sulphonic acids previously known.
In 1874 Pechmann (Ibid., 173,195) obtained a quantity of para toluidine meta sulphonic acid by heating para toluidine with sulphuric acid, and crystallizing out the para toluidine ortho sulphonic acid and disulphonic acids, leaving the meta acid in solution because of its greater solubility. The diazo compound was made by treatment of the acid in alcoholic suspension with nitrous fumes, and decomposed with alcohol under pressure. Various salts of the resulting sulphonic acid were made and studied, also the chloride and amide which melted "somewhere below 100".
In 1875 Pagel (Ann. chem. (Liebig) 176,297) working on ortho toluidine sulphonic acid, made a toluene sulphonic acid which resembled Muller’s. His amide melted at 104.
In 1877 Beckurts (Ber.d.che. Ges. 10, 943), seeking for a good method of obtaining pure ortho toluene sulphonic acid, heated toluene and sulphuric acid in the ordinary way, and made the potassium salts of the resulting acids. By treatment with phosphorus pentachloride he obtained the acid chlorides which he separated by cooling to -15, and filtering off the solid para compound. The remaining liquid was transformed into an amide and purified by fractional crystallization. Two compounds were obtained with sharp melting points of 153 and 104. From this work he concluded that the sulphonation of toluene yielded all the three possible acids.
Fahlberg (Am. Chem. J. 1, 170), doubted Beckurts’ statement, because although his acid showed different properties he neglected to prove its constitution by converting it into the hydroxy benzoic acid. He therefore repeated Beckurts’ work, and identified the amide melting at 154 as coming from ortho toluene sulphonic acid, by conversion into salicylic acid. The other amide with a sharp, constant melting point of 108 was oxidized, and the products separated and identified as para sulphamine benzoic acid, anhydro ortho sulphamine benzoic acid, and acid potassium ortho sulphobenzoate. These were the products one would expect from an oxidation of a mixture of the ortho and para toluene sulphonamides. Further proof that his acid was a mixture was obtained by mixing amounts of pure ortho and para toluene sulphonic acids, and by repeated crystallizations a form was obtained which melted at 108.
F.H.S. Muller (Ber. d. chem. Ges. 13, 1348), mentioned the formation of meta toluene sulphonic acid by the action of sulphurous acid upon the corresponding diazo compound, but gave no details except the melting points of his amide, anilide, and toluide.
Claesson and Wallin in 1879 (Ibid. p. 1848), claimed that they had obtained meta toluene sulphonic acid by the action of chlorsulphonic acid upon toluene. They used very large quantities of materials. They obtained three acids, and identified them as the ortho and para, and called the third the meta acid, despite the fact that they had knowledge of Fahlberg’s work.
The next step was undertaken by R. Otto (Ibid, 13, 1292), at the request of Beckurts. He examined some of the latter’s supposed meta toluene sulphonamide, and found it to be a mixture of the amides of the ortho and para acids.
Nevile and Winther (Ibid. 13, 1940), while investigating the formation of amino sulphonic acids, obtained a toluene sulphonic acid by heating ortho diazo toluene sulphonic acid with alcohol under pressure, and also by reducing brom toluene sulphonic acid with sodium amalgam. It was converted into the chloride and amide,—the latter melting at 106.5-107.5.
In 1886, Valin (Ibid. 2952), convinced by the work of Otto that Fahlberg’s views were correct, and that he and Klason had not obtained meta toluene sulphonic acid, again attacked the problem; an acid was made and salts described.
In 1891, Metcalf (Am. Che. J. 15,301) (Dissertation, 1892), proved that decomposition of para diazo toluene meta sulphonic acid with ethyl alcohol under pressure resulted in the formation of para ethoxy meta toluene sulphonic acid in far greater quantity. Consequently the toluene meta sulphonic acid could not have been obtained by either Pechmann or Valin.
Griffin, (Dissertation, 1895), prepared what he thought was a solution of the meta toluene sulphonic acid from the amide, and made and studied several salts as well as the anilide and toluide. However he did not investigate his solution to find out what it contained, but went ahead on the assumption that he had a solution of this acid. It is on the basis of his lack of investigation that I am working.
The derivatives of para toluene sulphonic acid have been made and studied by Newell, (Dissertation, 1895), and are being investigated further. He prepared para tolyl phenyl sulphone by the Friedal-Crafts reaction, para phenyl sulphone benzoic acid by oxidation of the sulphone with chromic acid, its salts, chloride, amide, and anilide, and para benzoyl diphenyl sulphone from the acid by the Friedal-Crafts reaction, and studied their reactions and properties.
The analogous derivatives of ortho toluene sulphonic acid were made and studied by Canter, (Dissertation, 1900). He prepared ortho tolyl phenyl sulphone by the Friedal-Crafts reaction, ortho phenyl sulphone benzoic acid by oxidation of the sulphone by potassium permanganate, its chloride, amide, and anilide, and ortho benzoyl diphenyl sulphone from the acid by the Friedal-Crafts reaction.
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.