COOH
╱
Calculated for the formula C_{6}H_{4} = 15·84% S.
╲
SO_{2}OH
[Illustration]
A crystallographic examination of the acid showed it to belong to the
orthorhombic system. Axial ratio: a: b: c = ·8507: 1: ·8121.
Planes. Ρ and αΡὰ.
┌─
┌─ │ Edge X = 131° 8'
│ Ρ ^ Ρ ─┤ ” Y = 82° 18'
│ │ ” Z = 118° 40'
Angles measured ─┤ └─
│
│ Ρ ^ αΡὰ = 114° 38'
└─
The crystals are up to 8 mm in length. The pyramidal faces are
generally etched so that the image is poor.
Sulphonfluoresceïn.
Several attempts had already been made to obtain from the action
of o-sulphobenzoic acid and resorcin a substance analogous to the
fluoresceïn obtained by Baeyer[1] from phthalic anhydride and
resorcin but while a strongly fluorescent substance was easily
obtained, no definite compound could be separated from it. Thus
Palmer obtained, by heating together the above named substances to
160°(?) a solid mass, part soluble in water and part insoluble as a
dark brown amorphous powder. Both parts gave a strong fluorescence
with alkalis. He was unable however to obtain the substance itself or
any derivative in a crystalline form.
[1] Annalin. No. 183. S. 1. No. 202. S. 36 & S. 153.
Berichte. No. IV. S. 457. 555. 658. 662.
” ” VIII. S. 66. 146.
The first experiments in this series gave the same negative results.
The mixture of acid and resorcin was heated in a sulphuric acid
both for several hours to 150°-170°, and as it showed no sign of
solidification the temperature was raised to 200° and then to 235°
where it was kept several hours longer. The black viscous mass
obtained in this way became vitreous on cooling, and in all respects
resembled that described by Palmer. This however is not the normal
course of the reaction as shown later but is probably due to a
decomposition of the normal product produced by too high heating.
An experiment was made with the acid salt of ortho-sulphobenzoic acid.
COOH
╱
C_{6}H_{4}
╲
SO_{2}OK,
resorcin and H_{2}SO_{4} heating the mixture to 150°-170°. A solid
black mass was obtained strongly fluorescent in alkaline solution and
in all other respects like the substance obtained above.
Preparation of Sulphonfluoresceïn.
As the result of a number of experiments the following method of
preparing and purifying the sulphonfluoresceïn was found to give the
best results.
The free acid is mixed with resorcin in the proportion of 1 part acid
to 1.2 parts resorcin, or a slight excess over two molecules of the
latter to one of the former. The mixture is placed in a deep vessel,
a test tube or beaker, which is placed in a sulphuric acid bath, a
thermometer being suspended in the mixture. The bath is heated and at
about 100° the resorcin melts and the acid slowly dissolves in the
liquid. No action appears to take place till the temperature reaches
175° where water begins to be given off and the liquid slowly assumes
a darker color. White crystals of resorcin collect on the sides of
the vessel. After the heating has been continued for about seven
hours at 178°-185° the liquid has a clear deep red color but shows no
signs of becoming viscous. At length lustrous yellow crystalline
plates appear in the liquid and soon the whole mass becomes a thick
nearly solid yellow paste. Continuous heating at the same temperature
causes no further apparent change. This mass, which on cooling is
made up of yellow crystals imbedded in a red vitreous matrix, is then
dissolved in hot water forming a clear red solution or at most one
containing but a small quantity of a brown flocculent precipitate.
This solution is filtered if necessary and evaporated to a small
volume from which the substance separates on cooling in reddish
yellow radial crystals. These are filtered and washed with ether
till the washings are perfectly colorless. The substance on repeated
crystallization from water has a pale straw yellow color and when
deposited slowly forms transparent crystal blocks from 2·6 mm long,
arranged in radial groups.
A considerable amount of resorcin is lost by sublimation during
the reaction especially if the operation is carried on in a beaker
so that some excess should be added. But even when the resorcin
is present in excess at the end of the reaction some free acid is
always left which may be obtained from the mother liquid in the
characteristic colorless orthorhombic crystals.
The water of crystallization and sulphur were determined in the
new compound. In estimating the water, the substance was heated to
106°-123° for about ten hours till it attained a constant weight.
On standing in the air it quickly regains its original weight. When
heated to 130°-140° for some time it turns slightly reddish and loses
over 10% of its weight which is not regained by standing in the air.
Estimation No. I. was made by fusion with KOH and KNO_{3}. Nos. II
and III were made by Mr. Mindileff by Morse’s method, oxidizing with
KMnO_{4} in KOH solution.
·3882 gr. heated to 106°-123° lost ·0302 gr. = 8·5%
Calculation for 2H_{2}O - C_{19}H_{12}O_{6}S+2H_{2}O = 8·9% water.
I. ·2007 gr sub. gave ·1286 gr BaSO_{4} = 8·77% S.
II. gr ” ” ” gr ” = 7·91” ”
III. gr ” ” ” gr ” = 7·89” ”
Calculation for C_{19}H_{12}O_{6}S+2H_{2}O = 7·92% S.
These analyses show with but little doubt that the substance has the
composition indicated above i.e. C_{19}H_{12}O_{6}S+2H_{2}O. The
reaction therefore which takes place between ortho-sulpho benzoic
acid and resorcin from its analogy to that taking place between
phthalic anhydride and resorcin may be represented thus, as shown by
Baeyer in his second paper (Ann. 202. S. 43)
Representing the formation of the anhydride as the first action.
COOH CO
╱ ╱ ╲
C_{6}H_{4} = C_{6}H_{4} O + H_{2}O
\ ╲ ╱
SO_{2}OH(o) SO_{2}
and the action of resorcin on this anhydride thus.
CO OH
╱ ╲ ╱
C_{6}H_{4} O + 2C_{6}H_{4}
╲ ╱ ╲
SO_{2} OH (m)
O
╱ ╲
(HO)H_{4}C_{6} C_{6}H_{4}(OH)
╲ ╱
= C + 2H_{2}O
╱ ╲
C_{6}H_{4} O
╲ ╱
SO_{2}
The substance thus formed would naturally receive the name
Sulphonfluoresceïn from its analogy with Fluoresceïn.
┌─
│ OH
│ ╱
│ C_{6}H_{3}
│ ╲
│ O
│ ╱
C ─┤ C_{6}H_{3}
│ ╲
│ OH
│
│ C_{6}H_{4}SO_{2}
│ ╱
│ O
└─
Sulphonfluoresceïn.
┌─
│ OH
│ ╱
│ C_{6}H_{3}
│ ╲
│ O
│ ╱
C ─┤ C_{6}H_{3}
│ ╲
│ OH
│
│ C_{6}H_{4}CO
│ ╱
│ O
└─
Fluoresceïn.
Properties of S.fluoresceïn.
This compound shows a marked similarity to the fluoresceïn described
by Baeyer as would naturally be expected from its great similarity of
composition and constitution, but it also shows decided differences
which may be attributed to the replacement of CO by SO_{2}.
Dissolved in water it shows a weak green fluorescence which in
alkaline solution becomes much deeper but not by any means so strong
as that of fluoresceïn. The dilute alkaline solution by transmitted
light is almost perfectly colorless and by reflected light a clear
green. Unlike fluoresceïn it is extremely soluble in water, about
one part in two or three of hot and five or six of cold water. It
is also soluble in absolute alcohol forming a yellow solution with
weak fluorescence. It is soluble with difficulty in ether but when in
solution is deposited only on evaporating to a small volume.
It does not melt at 250° but if held at a lower temperature for a
long time becomes red undergoing some decomposition. If quickly
heated somewhat above 300° it melts to a deep red liquid and then
solidifies. If the mass is treated with water it partly dissolves
leaving a dark brown flocculent precipitate which dissolves on the
addition of an alkali, the solution having an intense fluorescence,
nearly if not quite equaling that of fluoresceïn. This change
produced by heating was not further studied.
The crystals are very thin blades, apparently monoclinic, showing the
clinopinacoid αΡὰ and a very narrow prism αΡ and clinodome Ρὰ. The
angle β = 75° and the extinction angle against the ϲ axis = 20°.
The axial ratio could not be accurately determined.
Salts of sulphonfluoresceïn.
The influence of the SO_{2} group is shown by the fact that the
substance acts as an acid decomposing carbonates and forming salts
which is not the case with fluoresceïn.
Barium salt.
The substance was boiled with an excess of carefully purified
BaCO_{3} for two hours. The filtrate from the BaCO_{3} evaporated
to a small volume deposited yellow crystals resembling the original
substance but in shorter and thicker prisms. These were twice
recrystallized and had then a light straw yellow color.
A determination of the Ba gave the following results. The salt was
dried in the air.
[Transcriber’s Note:
The following table was crossed out on the original.
A note on the previous page beside the table was:
All these calculations are wrong.
J.R.]
I ·1078 gr salt gave ·0304 gr BaSO_{4} = 15·73% Ba.
II ·1641 ” ” ” ·0457 ” ” = 15·53” ”
III ·2425 ” ” ” ·0680 ” ” = 15·65” ”
IV ·2860 ” ” ” ·0798 ” ” = 15·54” ”
V ·1843 ” ” ” ·0498 ” ” = 15·08” ”
VI ·2620 ” ” ” ·0708 ” ” = 15·08” ”
VII ·3230 ” ” ” ·0906 ” ” = 15·65” ”
VIII ·2875 ” ” ” ·0807 ” ” = 15·66” ”
Calculated for C_{19}H_{13}O_{7}SBa = 15·10% Ba.
In the above determinations the salt analysed was taken from
specimens made at three different times and purified in slightly
different ways, Nos 1, 2, & 3 being washed with absolute alcohol. Nos
V and V were made by precipitating the Ba with H_{2}SO_{4} from a
solution of the salt.
The water was determined by heating at 110° till constant weight was
reached. Part only of the weight lost was regained on standing in the
air.
·3943 gr salt lost at 110° ·0286 gr = 7.25%