Action with hydroquinone occurs at 120°-135°, the mixture at the same time becoming dark colored and viscous.
On cooling, the product was powdered and treated with dilute alkali. It readily dissolved, without residue, forming a dark red solution. In concentrated solution the addition of acid produces a voluminous precipitate, dark brown in color, which when washed, and dried in paper forms an almost black powder. A dilute solution of this powder is dark red when alkaline, orange-yellow when acid.
From the way in which this powder was obtained, and owing to the fact that its solubility prevented repeated washing, it was evident that it would not give close analytical results for a calculated formula. It was thought, however, that analysis would give a general idea of the composition.
Analysis of different specimens gave results for sulphur which averaged about 5.5%. The percentage required for the formula
|
C[C₆H₃(OH)₂]₂ /\ /O // C₆H₃—SO₂ \ NO₂ |
which represents the simplest sulphonfluoresceïn, is 7.43.
The compound could hardly have been so far from pure as to occasion such a discrepancy in results as this. It would appear, therefore, that more than two molecules of hydroquinone enter into the reaction with one molecule of the chloride. Should four molecules be involved in the reaction, leading to a compound of some such formula as
|
C[C₆H₃(OH)₂] /\ /O // C₆H₃—SO[C₆H₃(OH)₂]₂ \ NO₂ |
the theoretical percentage of sulphur would be 6.00 which corresponds much more closely with the results obtained.
This is in accord with the observations of a number of workers in this laboratory—Lyman, Gilpin, Linn and others—who have worked on various sulphonfluoresceïns, and have found that in many cases four, six and even eight phenol residues condense with one molecule of the anhydrous acid. Lyman[22] especially describes a tetra hydroquinone sulphonfluoresceïn derived from orthosulphoparatoluic acid. No etherial salt was observed.