Methyl red

• 2 - (4' -dimethylamino- phenylazo ) benzoic acid
• 4- dimethylaminoazobenzene -2' -carboxylic acid

• 493-52-7 (acid)
• 845-10-3 (sodium salt)

Red - violet solid with a faint odor

Fixed

178-182 ° C

• Poorly in water
• 2.5 g · l-1 in ethanol

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Methyl, and 4' -dimethylamino -azobenzene - 2-carboxylic acid, is a water-insoluble dye selected from the group of azo dyes. The water-soluble sodium salt is an acid-base indicator.

Properties

Methyl red is a red - purple solid with a faint odor.

The color of aqueous Methylrotlösungen proposes at a pH value of less than 4.4 and from 6.2 to red to yellow. Between pH 4.4 and 6.2, the solution is orange.

Synthesis

The synthesis proceeds through an azo coupling. For this, the amino group of the anthranilic acid using sodium nitrite and hydrochloric acid is converted into a diazonium group and this is reacted with N, N- dimethylaniline. This reaction must take place in the cold due to the instability of the diazo compound.

Use

In the analytical chemistry of methyl red is an important indicator in the titration of strong acids with weak bases.

In microbiology, methyl is used to identify bacteria produce organic acids by the fermentation of glucose.