Action of H2SO4 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 BaCO3 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 H2SO4 and then CaCO3. 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 KMnO4 and HNO3 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 SO2. This substance sulphonfluoresceïn crystallizes from water in light yellow monoclinic crystals having the composition C19H12O6S + 2H2O. 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 C19H13O7SBa. 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 H2SO4, 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—