Products / pH Indicators


C.A.S. No. 4430-20-0
M.F. C19H12Cl2O5S
M.W. 423.32gm/mole


Dye Content (by Spectrophotometry) >93%
Solubility 0.1% (95% EtOH) Clear solution
Transition Range pH 4.8-7.0
Absorption maximum (0.1N NaOH) ?max 573-579nm
Absorptivity (A1%1cm ,in 0.1NaOH at ?max) >1550
Loss On Drying (110°C) <7%

Chemical Name

Phenol, 4,4'-(3H-2,1-benzoxathiol-3-ylidene)bis[2-chloro-, S,S-dioxide

InChI Key



Soluble in water (30 mg/ml), ethanol (80 mg/ml), and methyl cellusolve (50 mg/ml).

Product Description:

Chlorophenol red is an indicator dye that changes color from yellow to violet in the pH range 4. 8 to 6. 7.


Chlorophenol red is used in the frozen food industry for monitoring storage temperature changes. Chlorophenol red is a pH indicator that can also detect chlorine dioxide in drinking water. Chlorophenol red has a narrow pH range (5.2-6.8 or so) when the solution is applied to dry paper, and somewhat broader (4.8-6.4 or so; different suppliers give different figures) when the solution is in a beaker to which solutions or slurries are added. Chlorophenol Red was tested many naturally aged book papers using a chlorophenol red solution, and reported a visual transition interval of pH 6.0 to 6.7.In the presence of chlorophenol red (CPR) and H2O2, the absorption maximum at 435 nm decreased upon addition of Fe2+, resulting in a significant color change of the CPR solution from yellow to colorless. The chemosensor system did not show significant responses to a series of other metal ions including Al3+, Zn2+, Cd2+, Hg2+, Mn2+, Co2+, Fe3+, Ni2+, Cu2+, La3+, Ce4+, Th4+, Pd2+, Pb2+, Sb3+, Cr3+, Au3+, Ag+, Nd3+, Sm3+, alkali and alkaline earth metal cations, allowing for highly selective naked-eye detection of Fe2+. Quantitative analysis was carried out kinetically for practicable the Fe2+ assay when either fixed time method or the initial rate method was applied. When the detecting time was set, the decrease of absorbance signal was linear with Fe2+ concentration in the range of 0 to 7.50 × 10-5 mol L-1 and the regression equation was ?A = 0.00759 + 0.00593CFe with a correlation coefficient r = 0.9953. The chemodosimetric system has employed an irreversible Fenton reagent-promoted oxidation of the CPR free chromophore and the hydroxyl radicals were generated in the presence of both Fe2+ and hydrogen peroxide. The mechanistic interpretation of the signaling process was partially confirmed by the radical scavenging experiment and the FT-IR analysis of the intermediates formed at different reaction periods.

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