Product Description
Methyl Red generally exists as glossy purple crystals or a reddish-brown powder. It is almost insoluble in water but readily dissolves in ethanol, chloroform, and acetic acid. Its main use is in acid–base titrations, where it acts as a pH indicator by changing color to signal the endpoint of the titration.
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Chemical Properties
| Melting point | 179-182 °C (lit.) |
| Boiling point | 412.44°C (rough estimate) |
| Density | 0.839 g/mL at 25 °C |
| Bulk density | 300-500kg/m3 |
| Vapor density | 9.3 (vs air) |
| Refractive index | 1.5930 (estimate) |
| Fp | 11 °C |
| Storage temp. | Store at +5°C to +30°C. |
| Solubility | ethanol: soluble1mg/mL |
| Form | Solid |
| Pka | 4.95(at 25℃) |
| Colour Index | 13020 |
| Color | Reddish-violet |
| PH Range | 4.4(red)-6.3(yellow) |
| Odor | Odorless |
| Water Solubility | Practically insoluble in water. Soluble in alcohol, acetic acidSoluble in ethanol. Insoluble in water. |
| λmax | 410nm, 530nm, 427nm, 519nm |
| ε(extinction coefficient) | ≥10000 at 282-288nm in methanol ≥20000 at 509-519nm in methanol ≥7000 at 329-335nm in methanol |
| Merck | 14,6119 |
| BRN | 750102 |
| Stability | Stable. Incompatible with strong oxidizing agents. |
| Major Application | Waveguides, LED sensors, photoresists, liquid crystals, sol-gel matrix, optical sensors, paints, toys, detection of thiols, food freshness sensors, dental product, saliva sampling method, detecting lactic acid, carbohydrates |
| InChIKey | CEQFOVLGLXCDCX-MSUUIHNZSA-N |
| CAS DataBase Reference | 493-52-7 |
| NIST Chemistry Reference | Benzoic acid, 2-[[4-(dimethylamino)phenyl]azo]-(493-52-7) |
| IARC | 3 (Vol. 8, Sup 7) 1987 |
| EPA Substance Registry System | Methyl red (493-52-7) |
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Product Application
Methyl red is commonly used as an indicator in a 0.1% alcoholic solution, appearing red at pH 4.4 and changing to yellow at pH 6.2. It is suitable for titrating ammonia and weak organic bases such as alkaloids, but it is generally unsuitable for most organic acids, except for oxalic acid and picric acid. Because it can be easily reduced and lose its color, readings should be taken promptly. Increasingly, methyl red is being replaced by sulfonphthalein indicators such as bromocresol green, which are more stable and provide a clearer color change.
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