CAS No 2303-01-7 , 4-[3-(4-hydroxy-2-methylphenyl)-1,1-dioxo-2,
1λ

Title: Cresol Purple
CAS Registry Number: 2303-01-7
CAS Name: 4,4￠-(1,1-Dioxido-3H-2,1-benzoxathiol-3-ylidene)bis[3-methylphenol]
Synonyms: m-cresolsulfonphthalein
Molecular Formula: C21H18O5S
Molecular Weight: 382.43
Percent Composition: C 65.95%, H 4.74%, O 20.92%, S 8.38%
Literature References: pH sensitive dye. Prepn: W. R. Orndorff, A. C. Purdy, J. Am. Chem. Soc. 48, 2212 (1926). Solvent effects: J. Barbosa et al., Mikrochim. Acta 106, 327 (1992). Ionization and spectral properties: R. Casula et al., Talanta 40, 1781 (1993); M. C. Aragoni et al., ibid. 42, 1157 (1995). Titrimetric determn: K. Vytras et al., Analyst 114, 479 (1989). Use as pH indicator for emission of NO2 in museum collections: J. Fenn, Polym. Prepr. 37, 170 (1996); in wine: E. N. Gaiao et al., Analyst 124, 1727 (1999); in buffered solns: S. Paula et al., Biochemistry 38, 3025 (1999).
Properties: Slightly sol in ethanol; sol in ethanol denatured with 10% methanol. pH 1.2 red; pH 2.8 yellow; pH 7.4 yellow; pH 9.0 purple.
Use: Acid-base indicator.