Cresol Red

Title: Cresol Red
CAS Registry Number: 1733-12-6
CAS Name: 4,4¢-(1,1-Dioxido-3H-2,1-benzoxathiol-3-ylidene)bis[2-methylphenol]
Additional Names: a-hydroxy-a,a-bis(4-hydroxy-m-tolyl)-o-toluenesulfonic acid g-sultone; o-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: M. D. Sohon, Am. Chem. J. 20, 257 (1898); and properties: H. A. Lubs, W. M. Clark, J. Wash. Acad. Sci. 6, 481 (1916). Raman spectrum: K. Machida et al., J. Raman Spectrosc. 8, 172 (1979). Ionization and spectral properties: R. Casula et al., Talanta 40, 1781 (1993); M. C. Aragoni et al., ibid. 42, 1157 (1995). Protein dye binding stoichiometry: I. Molnár-Perl et al., Food Chem. 35, 69 (1990). Use in detection of alkaloids via ion-associates: Z. Skalican et al., Anal. Lett. 28, 1223 (1995); as pH indicator for emission of NO2 in museum collections: J. Fenn, Polym. Prepr. 37, 170 (1996); for archived photographic films: J. C. Harthan et al., Imaging Sci. J. 45, 81 (1997); for microbiological media: L. A. Actis et al., J. Microbiol. Methods 39, 79 (1999).
Properties: Reddish-brown cryst powder. Sol in alcohol. pH 0.2: red; pH 1.8 yellow; pH 7.2 yellow; pH 8.8 reddish-purple.
Use: Acid-base indicator.
Cresols CRF Crilanomer Crimidine Croceic Acid

Cresol Red
Structure of cresol red.png
CAS number 1733-12-6 YesY
PubChem 73013
ChemSpider 65818 YesY
Jmol-3D images Image 1
Image 2
Molecular formula C21H17NaO5S
Molar mass 404.41 g/mol
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Cresol Red (full name: o-Cresolsulfonephthalein) is a triarylmethane dye frequently used for monitoring the pH in aquaria.