Metüülpunanes

Metüülpunanes, also known as methyl red, is a pH indicator that exhibits a color change in a specific pH range. It is a weakly acidic compound that turns red in acidic solutions and yellow in alkaline solutions. The transition range for methyl red is approximately pH 4.4 to 6.2. This means that solutions with a pH below 4.4 will appear red, solutions with a pH above 6.2 will appear yellow, and solutions within this range will show intermediate shades of orange.

Chemically, methyl red is an azo dye with the formula C15H14N3NaO2. Its systematic name is sodium 2-(N,N-dimethylamino)phenylazo)benzoate. It is typically used in titrations where the endpoint falls within its pH transition range. For example, it is commonly employed in the titration of strong acids with weak bases, or weak acids with strong bases, where the equivalence point is expected to be in the acidic to slightly acidic range.

In addition to its use as a titration indicator, methyl red is also a component of the Voges-Proskauer (VP) test, a biochemical test used to detect the production of acetoin by bacteria. In this test, methyl red is added to a culture medium after incubation. If acetoin is present, it is converted to diacetyl, which reacts with reagents to produce a red color, indicating a positive VP test. Methyl red itself can also be used in a separate test, the Methyl Red test, to determine if a microorganism produces large amounts of mixed acids during glucose fermentation.