O-Cresolphthalein
o-Cresolphthalein is a phthalein dye used as a pH indicator in titrations. 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.
Production
o-Cresolphthalein is not produced industrially, rather, it is commercially available. To be produced, the method generally used to synthesize phthalein dyes is effective. This method is used to synthesize phenolphthalein and thymolphthalein. To begin, a 2M equivalent of a phenol or a substituted phenol should be combined with a 1M equivalent of a phthalic anhydride.Uses
The compound has uses ranging from medicine to laboratory syntheses of chemically similar compounds. o-Cresophthalein has been used to derive polyamides and polyimides, colorimetrically estimate calcium in serum, and predict amount of time to wait before blood collection after a patient receives gadodiamide.Deriving Polyamides and Polyimides
Aromatic polyamides and polyamides are practical compounds due to their temperature resistance, electrical or insulating characteristics, and their mechanical strength. Some of the polyamides and polyimides that can be synthesized by o-Cresophthalein are polycarbonate, polyacrylate, and epoxy-resin.The diether-diamine 3,3-bisphthalide, or BNMP, is synthesized by 12 g o-cresophthalein, 11.5 g p-chloronitrobenzene, 5.1 g anhydrous potassium carbonate, and 55 mL of DMF. The compounds should be refluxed together at 160 °C for eight hours. Once it is done and has cooled, it should be mixed with 0.3 L methanol. A precipitate should form and be vacuum filtered to obtain a solid. It should then be washed with water and dried, yielding a yellow product. It should then be recrystallized from glacial acetic acid to yield yellow needles. The product is BNMP. The reaction can go further by combining 15.5 g of BNMP with 0.18 g 10% Pd/C and 50 mL ethanol. They should be stirred at 80 °C. 7 mL of hydrazine monohydrate should be added drop by drop for one hour. The solution should then be mixed for eight hours. It should then be filtered to separated from the Pd/C and concentrated. The concentrated solution should be added to water, and a precipitate should be formed. It should then be vacuum filtered to isolate the solid, yelding 3,3-Bispthalide, or BAMP, as a white solid. It should then be purified by water and ethanol.