Methyl Red known as C.I. Acid Red 2 is an azo dye that acts as a pH indicator. It occurs as a dark red crystalline powder. It changes color based on pH: red in acidic solutions (pH below 4.4), orange around its pKa of 5.1, and yellow in alkaline solutions (pH above 6.2). This color change is due to protonation affecting methyl red to acquire a hydrazone/quinone structure. As an azo dye, it can be prepared by diazotization of anthranilic acid followed by a reaction with dimethylaniline. Methyl red is fluorescent in a 1:1 water solution (pH 7.0), with an emission maximum at 375 nm when excited with 310 nm light.
CAS No.: 493-52-7
Synonyms: C.I. Acid Red 2; Acid Red 2; 2-Carboxy-4′-(dimethylamino)azobenzene; 4-Dimethylamino-2′-carboxylazobenzene; p-(Dimethylamino)azobenzene-o-carboxylic acid; Cerven methylova; 2-(4-Dimethylaminophenylazo)benzoic acid; o-((p-(Dimethylamino)phenyl)azo)benzoic acid; Benzoic acid, 2-[[4-(dimethylamino)phenyl]azo] -2-((4-Dimethylamino)phenylazo)benzoic acid
| Physical Properties | |
| Chemical formula | C15H15N3O2 |
| IUPAC Name | 2-{[4-(Dimethylamino)phenyl]diazenyl} benzoic acid |
| Molecular weight | 269.30 g/mol |
| Solubility | Soluble in Organic solvents, glacial acetic acid, hot acetone, benzene, chloroform, ethanol, formic acid, and lipids Insoluble in Water |
| Flash Point | 11°C (51.8°F) |
| Density | 0.791 g/cm³ |
| Chemical Properties | |
| Colour | Dark Red |
| State | Crystalline powder |
| Melting point | 181-182 °C |
| Vapour Pressure | 0.0±1.6 mmHg at 25°C |
| pKa | 0.0004 mmHg at 25°C |
| Pictograms : |
|
| Hazard Statements : | H225: Highly flammable liquid and vapour |
| Precautionary statements : | P210: Keep away from heat/sparks/open flames/hot surfaces |
Methyl Red known as C.I. Acid Red 2 is an azo dye that acts as a pH indicator. It occurs as a dark red crystalline powder. It changes color based on pH: red in acidic solutions (pH below 4.4), orange around its pKa of 5.1, and yellow in alkaline solutions (pH above 6.2). This color change is due to protonation affecting methyl red to acquire a hydrazone/quinone structure. As an azo dye, it can be prepared by diazotization of anthranilic acid followed by a reaction with dimethylaniline. Methyl red is fluorescent in a 1:1 water solution (pH 7.0), with an emission maximum at 375 nm when excited with 310 nm light.
CAS No.: 493-52-7
Synonyms: C.I. Acid Red 2; Acid Red 2; 2-Carboxy-4′-(dimethylamino)azobenzene; 4-Dimethylamino-2′-carboxylazobenzene; p-(Dimethylamino)azobenzene-o-carboxylic acid; Cerven methylova; 2-(4-Dimethylaminophenylazo)benzoic acid; o-((p-(Dimethylamino)phenyl)azo)benzoic acid; Benzoic acid, 2-[[4-(dimethylamino)phenyl]azo] -2-((4-Dimethylamino)phenylazo)benzoic acid
| Physical Properties | |
| Chemical formula | C15H15N3O2 |
| IUPAC Name | 2-{[4-(Dimethylamino)phenyl]diazenyl} benzoic acid |
| Molecular weight | 269.30 g/mol |
| Solubility | Soluble in Organic solvents, glacial acetic acid, hot acetone, benzene, chloroform, ethanol, formic acid, and lipids Insoluble in Water |
| Flash Point | 11°C (51.8°F) |
| Density | 0.791 g/cm³ |
| Chemical Properties | |
| Colour | Dark Red |
| State | Crystalline powder |
| Melting point | 181-182 °C |
| Vapour Pressure | 0.0±1.6 mmHg at 25°C |
| pKa | 0.0004 mmHg at 25°C |
| Pictograms : |
|
| Hazard Statements : | H225: Highly flammable liquid and vapour |
| Precautionary statements : | P210: Keep away from heat/sparks/open flames/hot surfaces |
The methyl red test detects the production of stable acids from glucose fermentation, helping to identify bacteria that produce mixed acids as metabolic end products.
A positive methyl red test indicates that the bacteria have produced stable acids from glucose fermentation, resulting in a low pH (red color) in the medium.
Bacteria that are positive for the methyl red test include Escherichia coli and Proteus vulgaris. These bacteria produce stable acids through mixed acid fermentation of glucose.
Methyl red has a pH range of 4.4 to 6.2. In this range, it transitions from red (at pH below 4.4) to yellow (at pH above 6.2), with orange in between.
The shelf life of methyl red is typically 2 to 3 years when stored properly in a cool, dry place and protected from light. However, it’s important to check the manufacturer’s guidelines for specific storage conditions and expiration dates.
