Kolthoff, I. M. published the artcileThe color changes of sulfonephthaleins, benzeins and phthaleins, Formula: C28H18O4, the publication is Journal of Physical Chemistry (1931), 1433-47, database is CAplus.
In an aqueous solution of phenolphthalein the concentration of the lactone form is of the order of 10,000 times greater than that of the carboxylic acid configuration. The equilibrium between the quinone and the quinone phenolate (anion) forms of the sulfonephthaleins in their alk. range quantitatively governs the color change. Benzeins which are not too little soluble in water have advantages over the corresponding sulfonephthaleins as indicators. α-Naphtholphthalein in aqueous solution is mainly present in the quinoid form. The color change of sulfonephthaleins, benzeins and phthaleins in acid medium is to be attributed to the weakly basic character of the quinone group. Thymol blue forms a hybrid ion in its color change in the acid range. By using the Fajans method of adsorbing cations on negatively charged AgCNS (with excess of CNS ions) or on positively charged AgCNS (if excess of Ag ions) and remembering that if the adsorbed ions are colored the precipitate will usually be colored, the colors of a number of indicator ions were determined By examining the behavior of dyestuffs as adsorption indicators it is possible to decide whether they are present in the form of cations or of anions.
Journal of Physical Chemistry published new progress about 596-01-0. 596-01-0 belongs to benzofurans, auxiliary class Benzofuran,Naphthalene,Alcohol,Ester, name is 3,3-Bis(4-hydroxynaphthalen-1-yl)isobenzofuran-1(3H)-one, and the molecular formula is C28H18O4, Formula: C28H18O4.
Referemce:
https://en.wikipedia.org/wiki/Benzofuran,
Benzofuran | C8H6O – PubChem