HC============ CH
/ \
C₆H₃——SO₂OK KOO₂S——C₆H₃
\ /
NO₂ O₂N
It was no doubt the formation of substances of this nature that
occasioned the color observed in some of the oxidations.
[11] Ber. XXVI-2231; XXVIII-2281
The only effective method of separating this colored substance was
found to be to pass to the neutral salt of paranitroorthosulphobenzoic
acid, by making the solution slightly alkaline. The salt of this
colored substance is also formed and the two can be separated by a few
recrystallizations in a fairly satisfactory manner.
The yield in both of the transformations involved in the preparation
of paranitroorthosulphobenzoic acid does not fall far short of the
theoretical.
III. Preparation of the Symmetrical Chloride of
Paranitroorthosulphobenzoic Acid.
This chloride was first separated from its unsymmetrical isomer
by Gray[12]. It was obtained by allowing a chloroform solution of
the mixed chlorides to evaporate until the chloroform had almost
entirely disappeared. In the thick liquid so obtained, crystals of the
symmetrical chloride were formed. It was also obtained by applying the
method devised by Bucher in connection with the corresponding chloride
of orthosulphobenzoic acid—i.e. by the action of dilute ammonia on the
mixed chlorides. Gray also found that the best conditions for securing
a relatively large proportion of the symmetrical chloride were, the
employment of as low a temperature as possible in the formation of the
chlorides, and of as small an excess of phosphorus pentachloride as
would suffice for the reaction.
[12] Inaug. Diss. J. H. Univ. 1895.
After many experiments, under widely differing conditions, the
following method of procedure, embodying the results of Gray’s work,
was adopted.
Dehydrated acid potassium salt of paranitroorthosulphobenzoic acid,
and phosphorus pentachloride, in the ratio of 40: 55 grams, are
brought together in a mortar and intimately mixed. The mixture is
put into an evaporating dish, and placed on a sulphuric acid bath,
previously heated to 150°. As soon as the action has been well started,
the dish is removed, and the reaction allowed to proceed without
further heating. When it is complete, and the contents of the dish
has cooled down to the temperature of the room, the oily product is
poured slowly into a salts bottle containing ice water, the bottle
being frequently shaken during the process. The shaking is continued
with renewed portions of water, as long as the wash water is cloudy.
The water is then poured off, the brownish gummy chloride dissolved
in chloroform, and the solution placed in a good-sized separating
funnel. Ice water is then added, and the contents of the funnel treated
with successive portions of ammonia (desk ammonia diluted one half).
Shaking is continued after each addition until the odor of ammonia has
disappeared, and ice is added from time to time as may be required.
When it is found that the odor of ammonia persists after several
minutes’ shaking, the chloroform layer, which is usually filled with a
solid substance that has separated during the process, is drawn off,
filtered, and dried with calcium chloride.
By this process all of the unsymmetrical chloride is converted into the
ammonium salt of paranitroorthocyanbenzenesulphonic acid, according to
the equation:
CCl₂
/ \
/ O CN
/ / /
C₆H₃——SO₂ + 4NH₃ = C₆H₃——SO₃NH₄ + 2NH₄Cl.
\ \
NO₂ NO₂
while the symmetrical chloride remains for the most part unchanged,
though some of it is converted into the ammonium salt of
paranitrobenzoic sulphinide:
CO
/ \
COCl / N.NH₄
/ / /
C₆H₃——SO₂Cl + 4NH₃ = C₆H₃——SO₂ + 2NH₄Cl.
\ \
NO₂ NO₂
It was found that working in this way the symmetrical chloride could
be prepared in pure condition, free from its isomer. The chloroform
completely evaporates in a short time leaving fine crystals of the
symmetrical chloride. In case the evaporation is slow and incomplete,
it may be concluded that not all of the unsymmetrical chloride has been
removed. The yield was uniformly about 40 per cent of the theoretical.
From the water used to wash the chlorides a considerable amount of the
original salt can be recovered, as the reaction under the conditions
employed, is never complete.
An examination was made of the substance mentioned as separating in
the chloroform solution of the chlorides, during the treatment with
ammonia, and it was found to possess the following properties. It
is insoluble in benzene, chloroform, acetone, ether and ligroin;
soluble in glacial acetic acid, from which it separates on cooling
in colorless, crystalline condition; insoluble in the cold in
water, alcohol and ammonia, but by boiling with these reagents, or
by long standing in the cold, it is dissolved with decomposition.
It was dissolved in hot water and the solution, which was acid
in reaction, was neutralized with potassium carbonate. On adding
an excess of hydrochloric acid to the solution, and allowing
it to cool, characteristic crystals of acid potassium salt of
paranitroorthosulphobenzoic acid separated. These properties identify
the substance as the anhydride of this acid.
The formation of the corresponding anhydride of orthosulphobenzoic acid
by the action of phosphorus pentachloride upon its acid potassium salt
was observed by Sohon[13], who made use of the reaction to prepare this
anhydride in quantity.
[13] Inaug. Diss. J. H. Univ. 1896.
IV. Properties of the Symmetrical Chloride of
Paranitroorthosulphobenzoic Acid.
As first obtained, the crystals of the symmetrical chloride resemble
irregularly shaped pieces of amber, both in color, and in lustre.
On recrystallization from chloroform or ether, they may be obtained
perfectly colorless, and are often of very simple crystallographic
form. The chloride crystallizes in the monoclinic system, and possesses
a very remarkable crystallizing power, in which respect it differs
noticeably form its isomer. Even in chloroform solution that is far
from dry, crystals appear with the greatest ease.
The habit of the crystals differs very much according to the
conditions of crystallization. Not infrequently almost perfectly
formed crystals of the simplest form—the oblique octahedron—were
obtained though for the most part the form was much more complicated,
pinacoid and dome faces, together with basal planes being prominent.
As a rule, the crystals were not suitable for crystallographic work,
as the faces are usually uneven and the edges rounded. By proper
precautions however, good ones were obtained, and measurements of these
will be found in this dissertation when it appears in print.
The size of some of the crystals obtained was unusual for substances
of this class. One crystal obtained with no special precautions, save
letting a solution of the chloride stand undisturbed for several days,
in a rather cool place measured 3 × 2.5 × 1.5 cm., and weighed 11.2
grams. The crystals are quite compact, their density being abut 1.85.
They melt at 98° (uncorr.) The chloride is quite stable in crystalline
condition. Even in moist air the crystals were unchanged, and retained
their lustre as long as they were in my possession.
An analysis for chlorine gave the following results.
.2200 gram gave .2212 gram AgCl.
COCl
/
Cal. for C₆H₃——SO₂Cl
\
NO₂
Found.
Cl = 24.94 24.83
V. The Action of Benzene and Aluminium Chloride on the Symmetrical
Chloride of Paranitroorthosulphobenzoic Acid.
Hollis[14] in his study of the action of these reagents upon the
unsymmetrical chloride, tested their action upon one portion of the
symmetrical chloride, and found the products to be identical in the two
cases. A few experiments were made in confirmation of these results,
and the same products, in general, were obtained. It was observed
however that the reactions differ in the relative ease with which
they are brought about. In the case of the symmetrical chloride, the
reaction is a much more vigorous one. On adding aluminium chloride to
a solution of the symmetrical chloride, in benzene, action begins
at once the temperature of the hand, and very little external heat,
and that only in the latter stages of the operation, is needful for
the completion of the reaction. The application of much heat converts
all of the product into thick tarry substances from which nothing
satisfactory could be obtained.
[14] Inaug. Diss. J. H. Univ. 1896.
When the reaction was complete, the resulting product was isolated and
purified in accordance with the directions given by Hollis. Repeated
trials showed that, as in the case of the unsymmetrical chloride, only
one phenyl group could be introduced by this method. The resulting
compound, paranitroorthobenzoylbenzenesulphon chloride, was identical
with that derived from the unsymmetrical chloride. Owing, however,
to the fact that so much more decomposition occurs in the reaction
with the symmetrical chloride, in paranitroorthobenzoylbenzene sulphon
chloride could not be obtained in perfectly pure condition. In
appearance it agreed closely with that described by Hollis, forming
very characteristic greenish, rhombic crystals. These melted, not very
sharply, at 174° instead of 177° as observed by Hollis.
Accordingly, to establish the identity of the two compounds beyond
any doubt, the material on hand was converted into the barium salt of
paranitroorthobenzoylbenzene sulphonic acid. This was done by boiling
the sulphon chloride with dilute hydrochloric acid until complete
solution had been effected; evaporating to dryness on a water-bath;
dissolving the residue in hot water, and neutralizing with barium
carbonate. On filtering the hot solution from the excess of carbonate,
and allowing it to cool, the barium salt separated.
The solution was somewhat colored by impurities, and the long needles
in which the salt crystallized were also somewhat colored. They were
analysed with the expectation that they would prove to be specimens
of the salt described by Hollis as having three, or three and a half
molecules of water of crystallization, in as much as the conditions
under which they were formed were favorable to the formation of salts
with these ratios of water of crystallization. Hollis found that this
salt could be obtained with at least four different ratios of water
of crystallization viz. three, three and a half, six and seven
molecules respectively. The analysis was as follows, the amount of
barium being calculated on the basis of the anhydrous salt.
0.3087 gram lost 0.064 gram at 210°, and gave 0.0759 gram BaSO₄.
Cal. for (C₁₃H₈O₆NS)₂Ba + 11H₂O Found.
H₂O = 20.90 20.73
Ba = 18.29 18.23
The mother-liquor, in which the crystals remaining from analysis were
redissolved, was warmed, but not boiled, with boneblack, to remove
impurities. When filtered, the solution was perfectly colorless, and
on standing for some time, well formed colorless, rhombic crystals
appeared. On analysis they gave results as follows.
0.2804 gram lost 0.0405 gram at 210°, and gave 0.0759 gram BaSO₄.
Cal. for (C₁₃H₈O₆NS)₂Ba + 7H₂O. Found.
H₂O = 14.40 14.44.
Ba = 18.29 18.03.
In making a further supply of the salt it was found that if the
solution, after filtering from the barium carbonate, was diluted to
such an extent that no crystals separated on cooling, then on slow
evaporation under a bell-jar the first crystals to appear were very
long slender needles. As evaporation proceeded, these needles became
much thicker assuming prismatic proportions, and corresponded in
appearance to the salt described by Hollis as having six molecules of
crystal water.
As growth proceeded, the crystals became dark in color, and the
mother-liquor correspondingly clearer, the crystals evidently absorbing
the impurity in their growth.
When the solution had become quite colorless, rhombic crystals of the
salt containing seven molecules of water of crystallization appeared.
The larger prismatic crystals were carefully removed, and redissolved
in water in order to see if the same phenomena would repeat themselves.
This in fact was the case, crystals of both types appearing in the
same way as described. Without separating the crystals in this second
experiment, water was added, and the crystals dissolved. The solution
was then warmed briskly with boneblack, and filtered. From the
filtrate, which was colorless, nothing but rhombic crystals having
seven molecules of water of crystallization could be obtained,
although a great many variations in the conditions were tried. Analysis
of these last crystals was as follows:
0.2400 gram lost 0.035 gram at 210°, and gave 0.0637 gram BaSO₄.
Cal. for (C₁₃H₈O₆NS)₂Ba + 7H₂O. Found.
H₂O = 14.40 14.58
Ba = 18.29 18.27
Hollis states that treatment with boneblack decomposes this salt,
and hence he did not purify it prior to crystallization. From the
experiments just described it seems probable that the impurities
present affect the crystalline habit, and the degree of hydration of
this salt in a very striking manner. By careful warming with boneblack
no decomposition was observed, and the crystals so obtained have
constantly seven molecules of crystal water.
VI. The Action of Alcohols upon the Symmetrical Chloride of
Paranitroorthosulphobenzoic Acid.
Kastle[15] found that when the chlorides of paranitroorthosulphobenzoic
acid (which he supposed to be an individual) were dissolved in alcohol,
and the solution boiled for some time, the acid etherial salt of
paranitroorthosulphobenzoic acid was the final product. The reactions
were shown to be:
COCl COOC₂H₅
/ /
I. C₆H₃——SO₂Cl + C₂H₅OH = C₆H₃——SO₂Cl + HCl.
\ \
NO₂ NO₂
COOC₂H₅ COOC₂H₅
/ /
II. C₆H₃——SO₂Cl + C₂H₅OH = C₆H₃——SO₂OC₂H₅ + HCl
\ \
NO₂ NO₂
COOC₂H₅ COOC₂H₅
/ /
III. C₆H₃——SO₂OC₂H₅ + C₂H₅OH = C₆H₃——SO₂OH + (C₂H₅)₂O
\ \
NO₂ NO₂
[15] Am. Ch. Journ. XI--281.
Kastle, it will be observed, gave the symmetrical formula to this
mixture of chlorides. Several acid etherial salts were made, and a
series of the neutral salts of various metals described by him.
The action of pure symmetrical chloride was studied in the same general
manner to see if the resulting products would be the same as those
formed from the mixed chlorides.