Methyl Red
Precise pH Indicator: Methyl Red serves as a highly reliable acid-base indicator with a well-defined transition range of pH 4.4-6.2, enabling clear differentiation between acidic (red) and basic (yellow) conditions during titrations.
Sharp Endpoint Detection: The compound's vivid color shift at the equivalence point enables precise determination of titration endpoints in analytical procedures.
Organic Solubility Profile: While demonstrating limited aqueous solubility, it readily dissolves in ethanol, chloroform, and acetic acid, providing formulation flexibility in various solvent systems.
Stable Material Characteristics: Supplied as either lustrous purple crystals or reddish-brown powder, the reagent maintains consistent physical and chemical properties under standard laboratory conditions.
Methyl Red is characterized by its lustrous purple crystalline form or reddish-brown powder morphology. The compound demonstrates negligible solubility in aqueous media but exhibits excellent dissolution in ethanol, chloroform, and acetic acid solvent systems. Its principal application resides in acid-base titration analyses, functioning as a reliable pH indicator that undergoes distinct chromatic transition to demarcate titration endpoints with precision.
Methyl Red 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 |
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) |
Methyl red is typically employed as a pH indicator in the form of a 0.1% alcoholic solution, displaying a red coloration at pH 4.4 and transitioning to yellow at pH 6.2. This indicator is appropriate for titrating ammonia and weakly basic organic compounds including alkaloids, though it is generally unsuitable for most organic acids except oxalic and picric acids. Due to its susceptibility to reduction and consequent color loss, readings should be promptly recorded. The compound is gradually being superseded by sulfonphthalein indicators such as bromcresol green, which provide enhanced stability and more distinct chromatic transitions.
