A second method employed consists in starting with p-nitro-toluene.
This when treated with H_{2}SO_{4} forms toluene p-nitro o-sulphonic
acid. If now a method could be obtained for removing the nitro group
the desired result would be attained.
The attempt was made by Remsen and Palmer (A.G.) to accomplish this
by (a) reducing the nitro compound to the amide, (b) making the diazo
compound and (c) boiling this with absolute alcohol. According to
generally accepted views this should effect the removal of the diazo
group and its replacement by hydrogen.
Experiments however showed that the replacement was made not by
hydrogen but by the ethoxy group -OC_{2}H_{5}. This method was
therefore impracticable.
A modification of this method was suggested by an observation of
Baeyer and Liebermann that if phenyl hydrazine be boiled with a
dilute solution of copper sulphate the hydrazine group is replaced
by hydrogen and benzene thus formed. Hence it was believed that if
the hydrazine compound should be made from diazo compound mentioned
above, the corresponding hydrocarbon, i.e. toluene o-sulphonic acid
could be obtained. The results of experiments showed that this
afforded a practicable method of preparing toluene ortho-sulphonic
acid.
After experimenting with various modifications of the method the
following was found to be the best adapted to the purpose.
The potassium salt of toluene p-nitro-o-sulphonic acid is easily
obtained, as already stated, by heating p-nitro toluene on the water
bath with three times its weight of fuming H_{2}SO_{4}, neutralizing
with chalk and to the solution of calcium salt thus obtained adding
a slight excess of K_{2}CO_{3}. On filtering from. the precipitated
CaCO_{3} and evaporating slightly, the salt is obtained in long
needle shaped crystals of a pale straw yellow color. This is
┌─
│CH_{3}
C_{6}H_{3}┤SO_{2}OH (o)
│NO_{2} (p).
└─
The reduction of the nitro group is best effected by means of tin and
HCl, in the proportion, salt 5 parts, tin 6 parts and concentrated
HCl 30 parts.
The amido acid forms a compound with tin which crystallizes from the
HCl together with stannous chloride. This compound may be broken up
and the tin removed by continued boiling with water.
A better method of removing the tin is by dissolving the compound in
Na_{2}CO_{3}. This forms a salt with the amido acid and throws down
the tin as Sn(OH)_{2}, a white flocculent precipitate. On filtering
and adding to the solution conc. HCl, the free amido acid is
deposited in characteristic colorless, rhombic crystals, having the
formula
┌─
│CH_{3}
C_{6}H_{3}┤SO_{2}OH (o)
│NH_{2} (p)
└─
The method at first employed for preparing the hydrazine compound
consisted in treating the amido acid, suspended in HCl, with
potassium nitrite and then with stannous chloride. The tin was then
removed from the solution by the addition of sodium carbonate and the
hydrazine compound thrown down with HCl. This method however gave
poor results the yield being only about 50% of the theoretical.
Another method was accordingly substituted for the above, namely that
of Strecker and Römer (Ber. IV. s 784.) By this the diazo compound
is made first and isolated. This is done by suspending the finely
powdered acid in absolute alcohol, cooling and passing a current of
the oxides of nitrogen through in the ordinary way. The acid changes
in appearance, becoming more crystalline and slightly darker and
settles quickly on being shaken. The reaction here may be expressed
thus--
┌─ ┌─
│ CH_{3} │ CH_{3}
C_{6}H_{3} ┤ SO_{2}OH + HNO_{2} = C_{6}H_{3} ┤ SO_{3} + 2H_{2}O
│ NH_{2} │ \
└─ │ N=N
└─
When the reaction is completed as shown by the appearance of the
suspended powder it is filtered and while still fresh is added to a
solution of acid sodium sulphite as long as it continues to dissolve
readily.
To this solution there is added a quantity of solution of acid
sodium sulphite equivalent to that already used and the solution is
then boiled. It has at first a deep red color but in a few moments
becomes light reddish yellow. The reaction of HNaSO_{3} on the diazo
compound may be represented in two stages, the first portion forming
an addition product and the second acting as a reducing agent. Thus,
┌─ ┌─
│ CH_{3} │ CH_{3}
1. C_{6}H_{3} ┤ SO_{3} + HNaSO_{3} = C_{6}H_{3}┤ SO_{2}ONa
│ \ │
│ N═N │ N═NSO_{3}H
└─ └─
┌─
│ CH_{3}
2. C_{6}H_{3} ┤ SO_{2}ONa + HNaSO_{3} + H_{2}O
│ N═NSO_{3}H
└─ ┌─
│ CH_{3}
= C_{6}H_{3} ┤ SO_{2}ONa + HNaSO_{4}.
│ NH-NHSO_{3}H
└─
To the hot solution an excess of conc. HCl is added when the
hydrazine compound separates in a few moments in lustrous yellow
scales which completely fill the solution. On the addition of the HCl
a large amount of SO_{2} is given off from the excess of HNaSO_{3} and
the solution becomes deep red. When the hydrazine has separated the
mother liquor is again yellow.
The reaction is represented as follows:
┌─
│CH_{3}
C_{6}H_{6}┤SO_{2}ONa + HCl + H_{2}O
│NH-NHSO_{3}H
└─
┌─
│CH_{3}
= C_{6}H_{3}┤SO_{2}OH + H_{2}SO_{4} + NaCl
│NH-NH_{2}
└─
The yield of hydrazine when both the diazo and the NaHSO_{3} are
freshly prepared is practically quantitative.
The hydrazine thus prepared was treated with a hot 10% solution of
copper sulphate till a permanent blue color was obtained in the
solution. Nitrogen is evolved and the copper sulphate is reduced to
cuprous oxide which is precipitated as a red powder. The reaction is
as follows.
┌─
│CH_{3}
C_{6}H_{3}┤SO_{2}OH + 2CuSO_{4} + H_{2}O
│NH-NH_{2}
└─
┌─
= C_{6}H_{4}┤CH_{3} + Cu_{2}O + N_{2} + 2H_{2}SO_{4}
│SO_{2}OH
└─
Chalk was added to the solution to precipitate the H_{2}SO_{4} and
form a calcium salt of toluene-o-sulphonic acid. From this the
sodium salt was made by adding a slight excess of Na_{2}SO_{3} and
evaporating to dryness. The salt is very soluble being deliquescent
in the air while the corresponding potassium salt is not. From 1538
gr. of para-nitro-toluene, 655 gr. of toluene ortho-sodium sulphonate
were obtained.
Having thus obtained the toluene ortho-sulphonic acid the next
step in the problem was to find a convenient method for converting
this into ortho-sulph-benzoic acid. Two ways present themselves
for accomplishing this end. (1) direct oxidation of this salt and
(2) conversion into benzoic sulphinide from which the acid may be
obtained. Both of these methods were tried.
Oxidation of toluene-o-sodium sulphonate.
┌─
C_{6}H_{4}─┤CH_{3}
│SO_{2}ONa
└─
The sodium salt of toluene-o-sulphonic acid is oxidized to
ortho-sulphobenzoic acid with considerable difficulty by KMnO_{4} in
neutral solution.
Thus two experiments showed that the oxidation was not complete after
24 hours boiling with excess of permanganate. If the solution be made
alkaline however, the oxidation is completed in a few hours, yet the
greatest difficulty still remains in the separation of the free acid
from the products of oxidation in the solution. If HCl be added to
the solution the acid salt
COOH
╱
C_{6}H_{4}
╲
SO_{2}OK
is formed and this has nearly the same solubility as the KCl also
present. A better method therefore is to add a slight excess of
H_{2}SO_{4} and evaporate nearly to dryness. In this way are formed
sulphates and the free acid presumably. The mixture is heated with
alcohol (95%) which extracts the acid leaving the greater part of
the manganese salts. This extract is evaporated and reextracted
with alcohol. To this solution BaCO_{3} is added to precipitate the
H_{2}SO_{4} and form the Barium salt of the o-sulphobenzoic acid. The
solution is filtered from the BaSO_{4} and just enough H_{2}SO_{4}
is added to exactly precipitate the barium. The solution should
thus contain only the free acid sought, which crystallizes out on
evaporating to a small volume. While the method is theoretically
possible it presents so many difficulties that it is practically
useless. The yield is extremely small; only enough acid being
obtained in this way to show that it was possible.
Formation of Sulphinide from toluene-o-sodium sulphonate.
The second method for obtaining free o-sulphobenzoic acid from
toluene-ortho-sulphonic acid is by the conversion of the latter first
into benzoic sulphinide and then into the free acid. The sulphinide
was made essentially as described by Remsen (Am. Ch. Jour. Vol. I.
p. 428) with a few changes in the details as follows.
┌─
The salt C_{6}H_{4}┤CH_{3} finely pulverized and in portions
│SO_{2}ONa
└─
of from 10 to 50 gr. was placed in a Florence flask; an equivalent
quantity of PCl_{5} added; An inverted condenser was then attached
and the flask shaken. The action takes place at once and involves
sufficient heat to distill off the oxychloride formed in the
reaction. This being returned to the flask by the condenser furnishes
a liquid medium in which the reaction takes place more readily and
completely than when it is not present. It is best to cool the flask
at first and afterwards heat gently on the water bath. The reaction
which takes place may be represented as follows.
┌─ ┌─
│CH_{3} │CH_{3}
C_{6}H_{4}┤SO_{2}ONa + PCl_{5} = C_{6}H_{4}┤SO_{2}Cl + POCl_{3} + NaCl.
└─ └─
On the addition of water the chloride separates as a light yellow
oil. This is washed with water and concentrated aqueous ammonia
added, which forms toluene-o-sulphonamide thus.
CH_{3} CH_{3}
╱ ╱
C_{6}H_{4} + NH_{3} = C_{6}H_{4} + HCl.
╲ ╲
SO_{2}Cl SO_{2}NH_{2}
The reaction is accompanied by a slight evolution of heat and the
formation, apparently, of an intermediate product having a yellowish
color, which passes over on longer standing into the white amide.
After standing several hours the excess of ammonia was driven off
by very gentle heating on the water bath. If the heat is too high
a large amount of a tarry product is formed and the yield of amide
is correspondingly small. In any case some of this tarry product is
formed. When nearly all the ammonia had been driven off the mass was
boiled with water which dissolves everything except the tar. The
hot solution was filtered through charcoal and on cooling the amide
separated in white feathery crystals which melt at 155°-156°.
The amide thus obtained was oxidized as described by Remsen (loc. cit.)
with potassium permanganate in neutral solution. The proportions are
10 gr amide. 40 gr KMnO_{4} and 1 L. water. The oxidation was usually
effected in from four to six hours.
To obtain the sulphinide from this solution after oxidation, the
latter, after filtration from the precipitated oxides of manganese,
was slightly acidified with HCl and evaporated to about one fourth
its original volume. On the addition of concentrated HCl to this
solution, the sulphinide separated out in white or slightly yellowish
feather shaped crystals melting at 212° and having the characteristic
intensely sweet taste.
Formation of Sulphinide from Toluene by means
of the chlorsulphonic acid reaction.
Before passing on to the methods used for converting the sulphinide
into free acid another method should be described by which
the former was obtained in larger quantities and much more easily
than by the one above described.
Beckurts and Otto (Ber. XI. 2061) found that by treatment of toluene
with sulphuryl hydroxy-chloride or chlorsulphonic acid, ClSO_{2}OH,
both o- and p- and as they supposed also m-toluene sulphonchlorides
were formed together with the corresponding sulphonic acid.
Claesson and Wallin (Ber. XII. p. 1848) repeated the work reaching
practically the same results and finally Noyes (Am. Ch. Jour. Vol.
VIII. p. 176) employed the reaction as a convenient method for
obtaining toluene o-sulphon-chloride.
Chlorsulphonic acid is made by passing dry HCl over solid sulphuric
acid so long as it continues to be absorbed. Since no solid sulphuric
acid was at hand, ordinary fuming Nordhausen acid was taken and
from one of two equal portions the SO_{3} was driven over into
the other. HCl was passed into the latter and the resulting
chlorsulphonic acid distilled off at about 156°.
This was placed in a flask, provided with a drop funnel and exit
tube, in portions of 150 gr. and to each portion 60 gr. of toluene
was added, very slowly, with constant shaking, the temperature
being kept near 10°. The action is violent and if any toluene is
allowed to collect on the surface of the liquid it is apt to produce
disastrous results. Large quantities of HCl are given off and the
liquid in the flask assumes a brown color. When all the toluene has
been added, it is poured into a large quantity of ice water, when
the sulphon-chlorides separate out, the ortho- as a heavy oil and
the para- as a white crystalline solid. After allowing to stand some
time in order that as much of the para-chloride might crystallize as
possible the ortho- was drawn off and subjected to a freezing
temperature for several hours. By this means more of the p-chloride
was removed and the operation was replicated as long as any crystals
continued to form, generally two or three times. In this way the
greater part of the para- may be removed, though some still remains
dissolved in the liquid chloride, which cannot be removed by repeated
freezings.
The chloride thus obtained was treated with strong aqueous ammonia.
The conversion to the sulphamide does not take place so readily as
in case of the pure o-chloride obtained from the sulphonic acid and
phosphorus pentachloride.
After standing about two days the whole of the oily chloride had
solidified to a yellowish brown mass. The excess of ammonia was
driven off by gentle heating on the water bath and the mass then
boiled with water. Not enough water was added at first for complete
solution but when the first portion was saturated it was poured
off through a filter and from it the amide separated in yellowish
feathery crystals which melted at 105°-125° and consisted therefore
as shown by Fahlberg (Am. Ch. Jour. Vol. I. p. 170) of a mixture
of o- and p-sulphonamides. It was recrystallized and from it was
obtained a portion melting at 153°-5° and one at 108°-20°.
Since this mixture cannot be completely separated by
recrystallization another method was suggested. Remsen has shown that
K_{2}Cr_{2}O_{7} in acid solution does not oxidize the methyl group in
CH_{3}
╱
C_{6}H_{4}
╲
SO_{2}NH_{2} (o)
but does oxidize that in
CH_{3}
╱
C_{6}H_{4}
╲
SO_{2}NH_{2} (p).
It was thought that in a mixture of the two the former might be left
unchanged while the latter was oxidized to p-sulphamine benzoic acid.
To test this 15 gr of the mixture, melting at 105°-125°, was heated
with 40 gr K_{2}Cr_{2}O_{7}, 55 gr H_{2}SO_{4} and 2 vols. of water
for about two hours. It was then tested and shown to be still a
mixture of p-& o-amides, since it was again heated for several
hours with half the original quantity of oxidizing mixture, then
diluted, filtered and washed. The white crystalline residue was
treated with sodium carbonate to dissolve the benzoic para-sulphamide
and the residue was found to be pure toluene o-sulphonamide melting
at 153°-155°. The small quantity remaining, 3 gr., indicated that
part of the o-amide had been completely broken down by the strong
oxidizing agent, though the proportion of o-& p-amides in the
original mixtures was known only approximately. The evolution of gas
during the oxidation would point to the same conclusion.
Although this effects a complete separation it is hardly economical
since it will be shown later that a separation can be conveniently
effected after the oxidation with KMnO_{4} so that the o-amide
contained in the mixture need not be lost.
The original mass was treated with successive portions of water
till nothing remained but a black tarry substance. The amide which
separated from these extracts was perfectly white and melted at
153-5°. It was therefore regarded as practically pure o-amide. The
yield in amide melting above 153° was a little over one sixth the
weight of toluene used.
The amide obtained in this way was oxidized in the manner already
described. It was found however that there was always some benzoic
p-sulphamide in the solution of the oxidation, due to the slight
admixture of p- with the o-amide used. This is thrown down with
the sulphinide on acidifying the solution and may be removed by
re-crystallization since it is somewhat less soluble in hot and cold
water than sulphinide.
A better way to effect the separation, however, was found to be
the following. After having evaporated the solution containing the
products of oxidation, nearly neutralized with HCl, to about one
fifth its original volume, it is made very slightly acid and allowed
to cool. In this way very nearly all the benzoic p-sulphamide is
separated from the solution and none of the sulphinide. After
filtering, strong HCl is added and the sulphinide then separates
in its characteristic form. This indicates that sulphinide forms
an alkaline salt which is not decomposed by diluted HCl while the
p-sulphamide does not.
The mixture of amides meeting at 105°-120° was oxidized and the
products separated in this way gave about equal quantities of
sulphinide and benzoic p-sulphamide.
When toluene is treated with chlorsulphonic acid there are formed
besides the ortho- and para- chlorides also ortho and para sulphonic
acids. These of course are in solution in the water from which the
chlorides separated. In order to recover the ortho-acid, the solution
was neutralized with chalk forming the calcium salt: this converted
into the potassium salt which by evaporating the solution to dryness
was obtained as a white crystalline powder. When treated with PCl_{5}
in the manner already described this gave a mixture of ortho and para
sulphonchlorides consisting of about ⅓ ortho and ⅔ para.
Formation of Orthosulphobenzoic acid from Sulphinide.
Benzoic sulphinide may be converted into a sulpho-benzoic
acid (1) by boiling with Ba(OH)_{2}, (2) by heating in a closed tube
with conc. HCl or (3) by evaporating on the water bath with HCl.
1. Three gramms of sulphinide were boiled in a flask connected
with an inverted condenser for about two days with an excess of
Ba(OH)_{2}. There was formed in the flask a hard mineral-like mass
which was insoluble in water and cold diluted HCl but dissolved in
hot HCl with effervesence. This was a Barium salt, probably basic (?)
of ortho sulphobenzoic acid. There was also formed an easily soluble
barium salt of that acid. The former was dissolved in H_{2}SO_{4}
and treated with BaCO_{3}; the filtrate from the BaSO_{4} which
contained a soluble barium salt was added to that above mentioned and
the barium exactly precipitated with H_{2}SO_{4} and the filtrate
evaporated to dryness giving the free acid but not in a perfectly
pure condition.
2. 2.75 gr. of sulphinide was sealed up in a tube with pure conc. HCl
and heated two hours to 150°. On cooling nothing separated; the liquid
was evaporated to dryness giving 3.2 gr of acid and ammonium
chloride. The reaction taking place here may be represented thus:
CO COOH
╱ ╲ ╱
C_{6}H_{4} NH + 2H_{2}O + HCl = C_{6}H_{4} + NH_{4}Cl.
╲ ╱ ╲
SO_{2} SO_{2}OH
3. A more convenient method for obtaining the acid than either of
the above, is to heat the sulphinide with conc. HCl on the water
bath for two days. Then evaporate to dryness and dissolve the
residue in a small quantity of water. If the sulphinide contained
any para-sulphamide, as is usually the case, this will be left
undissolved and most of the NH_{4}Cl will crystallize on standing.
This solution by slow evaporation deposits large colorless crystals
of the free acid.
This acid is soluble in about two parts of cold water, very
difficultly soluble in absolute alcohol and almost completely
insoluble in ether. It does not melt under 250° but considerably
above that it melts, at first apparently without change and then
with slight sublimation of a very deliquescent substance, probably
the anhydride.
Two determinations of the S. made by Mr. A. F. Linn, gave the
following results.