O CRESOLPHTHALEIN PH INDICATOR
It is insoluble in water but soluble in ethanol. Its solution is colourless below pH 8.2, and purple above 9.8. Its molecular formula is C22H18O4. It is used medically to determine calcium levels in the human body, or to synthesize polyamides or polyimides.
Two kinds of applicable polymeric pH indicators were synthesized by the reaction of phenolphthalein and o-cresolphthalein with formaldehyde under alkaline conditions by a one-pot method. The synthesized products were fully characterized with Fourier transform infrared, 1H NMR, ultraviolet–visible spectroscopy, and gel permeation chromatography.