The sulphobenzoic acids have been the subject of investigation in this
laboratory for a number of years past. Among the many interesting
facts that have been brought to light in the course of this study,
perhaps no others have been attended with more interest than the
discovery of well characterized isomerism in the case of the chlorides
of orthosulphobenzoic acid, and its paranitro derivative; together
with the preparation of a series of isomeric derivatives of these
substances. The chlorides themselves have been isolated in the
crystalline condition, and have been found to differ markedly, not
only in chemical, but in physical properties as well.
The first evidence that such isomerism existed, was obtained by Remsen
and Coates[1] who, in the course of an investigation of the action of
aniline upon the chloride of orthosulphobenzoic acid, obtained two
isomeric anilids quite different in properties, which they designated
as fusible and infusible respectively. The following year, Remsen and
Kohler[2] obtained one of the chlorides in crystalline form, together
with an oil which they did not succeed in crystallizing.
This however was accomplished the succeeding year by Remsen and
Saunders[3], and a still more satisfactory result was obtained by
Remsen and McKee[4] in 1895. The chloride melting at 79° was found to
yield only the fusible anilid, together with an anil, while from the
lower melting chloride, in addition to these, the infusible anilid was
also formed.
[1] Am. Chem. Journ. XVII, 311.
[2] Ibid XVII, 230.
[3] Ibid XVII, 354.
[4] Ibid XVIII, 794.
In 1895, Gray[5] isolated the two corresponding isomeric chlorides of
paranitroorthosulphobenzoic acid, the lower melting chloride being
obtained in small quantity only. The succeeding year Hollis[6] made a
more careful study of this lower melting chloride, and prepared it in
considerable quantity.
From evidence drawn from the action of ammonia upon these chlorides,
taken in connection with a number of other facts, the higher melting
chloride is identified as the one possessing a symmetrical structure,
while the lower melting chloride possesses an unsymmetrical structure.
The first one, when treated with ammonia is slowly transformed into the
ammonium salt of paranitrobenzoic sulphinide:
[5] Inaug. Diss. J. H. Univ. 1895.
[6] Inaug. Diss. J. H. Univ. 1896.
CO
/ \
COCl / N.NH₄
/ / /
C₆H₃——SO₂Cl + 4NH₃ = C₆H₃——SO₂ + 2NH₄Cl.
\ \
NO₂ NO₂
while the lower melting chloride is quickly transformed into the
ammonium salt of paranitroorthocyanbenzenesulphonic acid:
CCl₂
/ \
/ O CN
/ / /
C₆H₃——SO₂ + 4NH₃ = C₆H₃——SO₂ONH₄ + 2NH₄Cl.
\ \
NO₂ NO₂
Gray’s study of the symmetrical chloride was confined for the most part
to the preparation of a series of salts of this latter acid, and to
an investigation of the action of aniline upon the chloride itself.
It was thought to be of interest to extend this study to a wider
range of reactions, as well as to improve, if possible, the method of
preparing the chloride in pure condition. At the suggestion of Prof.
Remsen this work was accordingly undertaken.