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.
CH_{3} CH_{3} CH_{3} CH_{3}
/ \ / \ / \ / \
/ \ / \ / \ / \
/ \NH_{2} / \ / \NH_{2} / \
| | | | | | | |
| | | | | | | |
HSO_{3} \ / \ / HSO_{3} \ / NH_{2} \ / HSO_{3}
\ / \ / \ / \ /
\ / \ / \ / \ /
NH_{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.