Thymolphthalein

Thymolphthalein is an acid-base (pH) indicator. Its transition range is at approximately pH 9.3-10.5. Below this pH, it is colorless; above this pH, it is blue. Its molecular formula is C₂₈H₃₀O₄, which gives a molecular weight of 430.53. The molar extinction coefficient for the blue thymolphthalein dianion is 38000 M^-1cm^-1 at 595 nm. [cite journal |author=Hahn HH, Cheuk SF, Elfenbein S, Wood WB |title=Studies on the pathogenesis of fever. XIX. Localization of pyrogen in granulocytes |journal=J. Exp. Med. |volume=131 |issue=4 |pages=701–9 |year=1970 |month=April |pmid=5430784 |pmc=2138774 |doi= |url= http://www.jem.org/cgi/reprint/131/4/701.pdf]

It can be used to make a disappearing ink. Dissolve the thymolphthalein in alcohol solution and add sodium hydroxide (NaOH) dropwise until it turns blue. It can then be sprayed onto cloth. After several minutes, it will turn colorless. (Carbon dioxide from the air will react with the basic solution. When the pH drops below 9.3, the thymolphthalein turns colorless.) Such inscription can be turned visible again by submerging it in liquid of pH higher than 10.5. A similar pH indicator is phenolphthalein, which is colorless in acidic and neutral pH ranges and bright fuchsia at high (basic) pH.

CAS Registry Number 125-20-2

SMILES formula SMILES|S=CC(C)c1cc(c(C)cc1O)C2(OC(=O)c3ccccc23)c4cc(C(C)C)c(O)cc4C

References