The IUPAC name of o-Cresolsulfonephthalein is 4-[3-(4-hydroxy-3-methylphenyl)-1,1-dioxo-2,1λ6-benzoxathiol-3-yl]-2-methylphenol. With the CAS registry number 1733-12-6, it is also named as Phenol,4,4'-(1,1-dioxido-3H-2,1-benzoxathiol-3-ylidene)bis[2-methyl-; Cresol red. The product's categories are organics; analytical chemistry; indicator (pH); pH indicators. In addition, it is dark green or brown-red powder which is soluble in water and easily soluble in alcohol and dilute sodium hydroxide solution.

The other characteristics of this product can be summarized as: (1)ACD/LogP: 3.94; (2)# of Rule of 5 Violations: 0; (3)ACD/LogD (pH 5.5): 3.94; (4)ACD/LogD (pH 7.4): 3.94; (5)ACD/BCF (pH 5.5): 581.38; (6)ACD/BCF (pH 7.4): 575.63; (7)ACD/KOC (pH 5.5): 3314.28; (8)ACD/KOC (pH 7.4): 3281.47; (9)#H bond acceptors: 5; (10)#H bond donors: 2; (11)#Freely Rotating Bonds: 4; (12)Index of Refraction: 1.669; (13)Molar Refractivity: 101.62 cm³; (14)Molar Volume: 272.3 cm³; (15)Polarizability: 40.28×10^-24 cm³; (16)Surface Tension: 62.9 dyne/cm; (17)Enthalpy of Vaporization: 87.64 kJ/mol; (18)Vapour Pressure: 3.11E-13 mmHg at 25°C; (19)Rotatable Bond Count: 2; (20)Tautomer Count: 5; (21)Exact Mass: 382.087494; (22)MonoIsotopic Mass: 382.087494; (23)Topological Polar Surface Area: 92.2; (24)Heavy Atom Count: 27.

Preparation of o-Cresolsulfonephthalein: Stirring and heating the mixture of benzoic acid anhydride, o-cresol and anhydrous zinc chloride, condensating 7h at 115-120 °C, then using water vapor to clean up the remaining o-cresol . Filtering and dissolving the cake with hot sodium carbonate aqueous solution, filtering again, adding 1:1 hydrochloric acid in the clearest filtrate to neutralize, and vigorous mixing. Filtering out the crystals, washing with a small amount of water, drying, and then we can get the product. Recrystallization with glacial acetic acid when necessary.

Uses of o-Cresolsulfonephthalein: It is a triarylmethane dye frequently used for monitoring the pH in aquaria. The pH color range is 7.2 (yellow) -8.8 (purple) and 2.0 (red) -3.0 (amber). And it can also be used as a color marker to monitor the process of agarose gel electrophoresis and polyacrylamide gel electrophoresis.

When you are using this chemical, please be cautious about it as the following:
It is harmful by inhalation, in contact with skin and if swallowed. And it is also irritating to eyes, respiratory system and skin, so people should avoid contact with skin and eyes. In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. If you want to contact this product, you must wear suitable protective clothing.

People can use the following data to convert to the molecule structure. 
1. SMILES: O=S2(=O)OC(c1ccccc12)(c3ccc(O)c(c3)C)c4ccc(O)c(c4)C;
2. InChI: InChI=1/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.