Product Description
Methyl Red (CAS No. 493-52-7) is an organic acid–base indicator typically supplied as a dark red to reddish-purple crystalline powder. It has very low solubility in water but dissolves in selected organic solvents, including ethanol, chloroform, and acetic acid, depending on the solvent composition and preparation conditions.
Methyl Red is widely used in analytical chemistry, particularly in acid–base titrations and pH-related testing. It exhibits a distinct color transition from red to yellow over a pH range of approximately 4.4–6.2, helping users visually identify the endpoint in suitable titration systems. Its clear color response makes it a useful indicator for routine laboratory analysis and chemical education.
Product Parameters
| 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) |
Application Scenarios
Methyl Red is commonly used as an acid–base indicator in alcoholic solutions, including 0.1% formulations. It exhibits a color transition from red at approximately pH 4.4 to yellow at approximately pH 6.2, making it suitable for analytical procedures in which the endpoint falls within this transition range.
In volumetric analysis, Methyl Red may be used for selected titrations involving ammonia and certain weak organic bases, depending on the reaction system and endpoint requirements. Its suitability for titrating organic acids should be assessed individually, as indicator performance depends on the pH change near the equivalence point.
Methyl Red may be susceptible to reduction under certain chemical conditions, which can affect its color response. Indicator solutions should therefore be prepared and stored appropriately, and color changes should be evaluated under the recommended test conditions. For some analytical methods, alternative indicators such as bromocresol green may be preferred when their transition range better matches the required endpoint.
