Methyl red (methyl red, p-dimethylaminoazobenzene-2-carboxylic acid) - synthetic aniline, acid-base indicator. This purple-maroon crystals melting at 175 ° C (with decomposition). Poorly soluble in water, soluble in acetic acid, benzene (particularly heated), moderately soluble in ethanol.
In the acidic medium the methyl red turns red in neutral or alkaline - yellow (transition from red to yellow in the range of about pH 4,4 - 6,2).
Also used in the titration of aliphatic amines in 1,4-dioxane and chloroform. Used in argentometry as adsorption indicator (color change from yellow to orange-red). Can be used as a water soluble sodium salt.