Although these analyses show a per cent. of Ba somewhat above that
required by a compound having the formula C_{19}H_{13}O_{7}SBa still
this appears to be the most probable formula which can be assigned to
the substance. If this is the true composition of the salt, then in
sulphonfluoresceïn the anhydride condition must be broken up by
boiling with BaCO_{3} forming the salt thus.
┌── ──┐ ┌── ──┐
│ │ │ │
│ ┌─ OH │ │ ┌─ OH │
│ │ / │ │ │ / │
│ │ C_{6}H_{3} │ │ │ C_{6}H_{3} │
│ │ \ │ │ │ \ │
│ │ O │ │ │ O │
│ │ / │ │ │ / │
│ C ┤ C_{6}H_{3} │ │ │ C_{6}H_{3} │
│ │ \ │ + H_{2}O = │ C ┤ \ │
│ │ OH │ │ │ OH │
│ │ │ │ │ │
│ │ C_{6}H_{4}SO_{2} │ │ │ C_{6}H_{4}SO_{2}OH │
│ │ / │ │ │ │
│ └─ O │ │ └─ OH │
│ │ │ │
└── ──┘ └── ──┘
┌── ──┐ ┌── ──┐
│ │ │ │
│ ┌ OH │ │ ┌ OH │
│ │ / │ │ │ / │
│ │ C_{6}H_{3} │ │ │ C_{6}H_{3} │
│ │ \ │ │ │ \ │
│ │ O │ │ │ O │
│ │ / │ │ │ / │
│ │ C_{6}H_{3} │ │ │ C_{6}H_{3} │
2 │ C ┤ \ │ + BaCO_{3} = │ C ┤ \ │ Ba.
│ │ OH │ │ │ OH │
│ │ │ │ │ │
│ │C_{6}H_{4}SO_{2}OH │ │ │ C_{6}H_{4}SO_{2}O │
│ │ │ │ │ │
│ └ OH │ │ └ OH │
│ │ │ │
└── ──┘ └── ──┘_{2}
By treating the salt with H_{2}SO_{4} the original
substance is reformed.
Calcium Salt.
Attempts were made to prepare the calcium salt but without success.
The S-fluoresceïn was boiled several hours with very finely powdered
calcite, and some salt was formed as shown by the CO_{2} evolved
but on evaporating the solution and recrystallizing the substance
deposited it was found to be the unchanged S-fluoresceïn. Some Ca.
salt was in the mother liquors but its extreme solubility prevented a
separation being made.
Acetyl derivative of S.fluoresceïn.
S.fluoresceïn was boiled with an excess of acetic anhydride for about
three hours. The solution became quite dark and when evaporated on
the water bath left a black tarry residue. This was treated with
water which dissolved a part leaving a dark flocculent precipitate.
The solution was boiled with animal charcoal and evaporated nearly
to dryness. On cooling there separated a light yellow flocculent
precipitate very soluble in hot water and but slightly less so in
cold. This was dissolved in a small quantity of alcohol from which
it separated on evaporation in small radial crystals having a light
lavender color & satiny luster. They also have a peculiar odor
resembling slippery elm which is not removed by recrystallization.
They show a tendency to decompose, becoming yellow on exposure to
the air. The substance does not melt or change in appearance under
245°. With alkalis it gives a slight greenish fluorescence. From the
method of its formation this was taken to be an acetyl derivative
of S.fluoresceïn but whether the mono-or di-acetyl could not be
determined without analysis for which the substance did not suffice.
Bromine substitution products of S-fluoresceïn.
It was especially interesting to see what influence the SO_{2} group
would exert upon the introduction of Bromine into the compound. In
the case of fluoresceïn four Bromine atoms enter easily and special
precautions are necessary to obtain a product containing a smaller
number. The case however is different with S.fluoresceïn.
The latter was dissolved in glacial acetic acid in which it is
soluble with some difficulty and to the solution was added a 20%
solution of bromine in acetic acid, in sufficient quantity to make
eight atoms of bromine to one molecule of S.fluoresceïn. This
solution was evaporated on the water bath and while still having a
considerable volume, small, red, sharply defined crystals began to
separate. The solution was evaporated to a small volume and allowed
to cool but nothing further separated. These crystals are difficultly
soluble in water, alcohol and ether. The alkaline solution shows a
green fluorescence and slight red color by transmitted light. These
crystals were dissolved in a large quantity of alcohol which on
evaporation gradually deposited very small yellow crystals, which
were dried in the air and taken for analysis. The Br. was determined
by Carius method.
I. ·2345 gr sub. gave ·1718 gr AgBr = 31·17% Br.
II. ·2786 gr ” ” ·1815 gr ” = 27·72% Br.
Calculated for C_{19}H_{10}Br_{2}O_{6}S = 30·42% Br.
These results, though not conclusive, indicate that under the
given conditions it is the di-bromsulphonfluoresceïn which is
formed. Whether this is due to the presence in the compound of the
SO_{2} group or simply to the greater insolubility of the di-than
of the tetra-brom product cannot be definitely stated. When the
original acetic acid mother liquor was evaporated to dryness, a red
non-crystalline substance remained which more closely resembled rosin
than the crystals. The concentrated alkaline solution had a deep red
color without fluorescence and acted as a red dye stuff. The dilute
alkaline solution showed the characteristic delicate pink of rosin.
Action of H_{2}SO_{4} on S.fluoresceïn.
A test tube in which S.fluoresceïn was being made just at the end
of the reaction broke and allowed the contents to run out into the
sulphuric acid bath, which had a temperature of 175°. On standing
several days the solution deposited a heavy precipitate which was
separated by filtering through glass wool. When dry it formed a light
yellow powder extremely soluble in water, alcohol and ether.
The alkaline solution had an intense green fluorescence with
delicate shades of pink by transmitted light. On account of its
great solubility it was impossible to purify it by crystallization,
hence the Ba salt was made. The substance decomposed BaCO_{3} with
great ease forming an easily soluble salt. When it was attempted to
evaporate the solution of this salt to crystallization the latter
came out in a hard insoluble granular form and on continuous boiling
of the solution turned brown. To avoid this undesirable form it was
converted into the Ca. salt by treatment with H_{2}SO_{4} and then
CaCO_{3}. This also formed a hard granular insoluble mass on boiling
but did not change in color. As there was no guarantee as to its
purity and only a small quantity was obtained it was not analyzed.
Action of HCl on S.fluoresceïn.
Hydrochloric acid does not dissolve S.fluoresceïn but converts it
into a light yellow granular powder. When recrystallized from water
in which it is quite easily soluble it melts partially at 130°
apparently with some decomposition. This compound was not further
studied.
Reduction of S.fluoresceïn.
When treated with zinc dust in a strong alkaline solution
sulphonfluoresceïn is reduced to a colorless substance probably
analogous to fluoresceïn which is formed in the same manner. On
account of its great solubility it could not be obtained in the free
state. It is quickly oxidized to s.fluoresceïn by oxidizing agents
as KMnO_{4} and HNO_{3} and passes back spontaneously on standing in
the air. The latter action is however much slower than in case of
fluoresceïn.
Conclusion.
The principal results relating to s.fluoresceïn which have been
reached in this work may be briefly summarized as follows.
Orthosulphobenzoic acid acts on resorcin at a temperature of
about 180° giving off water and forming a substance analogous
to fluoresceïn but having the CO group replaced by SO_{2}.
This substance sulphonfluoresceïn crystallizes from water
in light yellow monoclinic crystals having the composition
C_{19}H_{12}O_{6}S+2H_{2}O. It is very soluble in alcohol and water
and with difficulty in ether. It does not melt under 250° but above
300° melts with decomposition. It shows in alkaline solution
a clear green fluorescence. It acts as an acid, decomposing
carbonates and forming salts, the Ba salt having the composition
C_{19}H_{13}O_{7}SBa. It forms an acetyl compound when boiled
with acetic anhydride. It forms substitution products with Br,
probably the dibrom-product most easily. It forms a compound with
H_{2}SO_{4}, probably a substitution product, whose composition was
not determined. It is reduced by zinc dust and KOH to a colorless
substance analogous to fluoresceïn.
Finally in terms of the prevalent theory the substance itself may be
represented thus--
H H ┌─
C O C │
╱ ╲ ╱ ╲ ╱ ╲ │ OH
(HO)C C C C(HO) │ ╱
│ │ │ │ │ C_{6}H_{3}
HC C C CH │ ╲
╲ ╱ ╲ ╱ ╲ ╱ │ O
C C C = C ──┤ ╱
H ╱ ╲ H │ C_{6}H_{3}
HC ╱ ╲ │ ╲
╱ ╲ ╱ ╲ │ OH
HC C O │
│ │ ╱ │ C_{6}H_{4}SO_{2}
HC C ╱ │ ╱
╲ ╱ ╲ ╱ │ O
C SO_{2} │
H └─