Cresol Red

CAS Number:  1733-12-6
Molecular Weight: 382.43
MDL number: MFCD00005878
EC Index Number: 217-064-2

General description

Cresol Red, also known as o-cresol red, belongs to the phthalein and sulphonphthalein group of dyes. Cresol red changes color from orange to yellow at pH between 0.2-1.8 and yellow to violet at pH between 7.0-8.8. In alkaline solutions, cresol red is present as a hydrophilic dianion. The dianion is small and is violet in color, possessing a larger conjugated system than the yellow hydroxyquinone.


Cresol Red is a widely used pH indicator for routine pH assessments like microbial culture media preparations. In addition, Cresol red is a suitable constituent of PCR reagent systems. Cresol Red is used as a tracking dye in DNA, RNA (agarose), and protein (polyacrylamide) electrophoresis.


grade indicator grade
Quality Level 200
form powder or crystals
composition Dye content, 95%
technique(s) titration: suitable
pH 7.2-8.8, yellow to red
useful pH range 1.8-2.0, orange to yellow(acid)

7.0-8.8, yellow to violet(alkaline)

mp 290 °C
density 0.998 g/cm3
λmax 367 nm (2nd) 570 nm
application(s) diagnostic assay manufacturing



storage temp. room temp
SMILES string Cc1cc(ccc1O)C2(OS(=O)(=O)c3ccccc23)c4ccc(O)c(C)c4
InChI 1S/C21H18O5S/c1-13-11-15(7-9-18(13)22)21(16-8-10-19(23)14(2)12-16)17-5-3-4-6-20(17)27(24,25)26-21/h3-12,22-23H,1-2H3