Methyl Red

Chemical properties

dark red crystalline powder

The Uses of Methyl Red

As indicator in 0.1% alcoholic solution; pH: 4.4 red, 6.2 yellow. Used for titrating NH3, weak organic bases, e.g., alkaloids; not suitable for organic acids, except oxalic and picric acid. Methyl red is easily reduced, thereby losing its color, and readings should be made promptly. It is gradually being replaced by sulfonphthalein indicators, such as bromcresol green, which are more stable and exhibit a sharper change in color.

The Uses of Methyl Red

Used as pH indicator.

The Uses of Methyl Red

pH indicator in pH range 4.2 - 6.3Methyl red is used as a pH indicator. It is red in pH less than 4.4 and yellow in pH over 6.2. It is used to study its degradation using Fenton's reagent. In microbiology, it is used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation of glucose.

Definition

An acid–base indicator that is red in solutions below a pH of 4.2 and yellow above a pH of 6.3. It is often used for the same types of titration as methyl orange but the transition range of methyl red is nearer neutral (pH7) than that of methyl orange. The two molecules are structurally similar.

Definition

methyl red: An organic dye similarin structure and use to methyl orange.It changes from red below pH4.4 to yellow above pH 6.0 (at 25°C).

Preparation

2-Aminobenzoic acid?diazo, and N,N-dimethylaniline coupling.

What are the applications of Application

Methyl Red is a small molecule azo dye

Definition

ChEBI: An azo dye consisting of benzoic acid substituted at position 2 by a 4-[(dimethylamino)phenyl]diazenyl group.

General Description

Methyl red solution is an azo dye which turns to red when pH is below 4.4 (yellow pH < 6.2, orange pH 4.4-6.2). Some bacteria utilize glucose to form large amounts of acid with the result that the pH value of the medium falls distinct. Other species produce no or less free acid. This difference can be visualized by using methyl red. This test is used to differentiate enteric bacteria.

Hazard

Questionable carcinogen.

Biochem/physiol Actions

Methyl Red is a maroon red crystal azo dye. Methyl Red is a pH indicator and changes color at a pH of 5.5. Methyl Red is widely used in saliva sampling method. In addition, it is also employed in carbohydrate and lactic acid detection. Methyl Red has been effectively used for intrageneric differentiation of Enterobacteriaceae.

Safety Profile

Questionable carcinogen with experimental tumorigenic data. Mutation data reported. When heated to decomposition it emits toxic fumes of NOx.

Purification Methods

The acid is extracted with boiling toluene using a Soxhlet apparatus. The crystals which separate on slow cooling to room temperature are filtered off, washed with a little toluene and recrystallised from glacial acetic acid, *benzene or toluene followed by pyridine/water. Alternatively, dissolve it in aqueous 5% NaHCO3 solution, and precipitate it from a hot solution by dropwise addition of aqueous HCl. Repeat this until the extinction coefficients do not increase. [Beilstein 16 IV 504.]

Properties and Applications

moderate soluble in ethanol, insoluble in water. Alcohol solution to join hydrochloric acid for purple; Add sodium hydroxide to dim yellow.