Methyl Red Chemical Properties

Melting point:

179-182 °C (lit.)

Boiling point:

412.44°C (rough estimate)

Density 

0.839 g/mL at 25 °C

vapor density 

9.3 (vs air)

refractive index 

1.5930 (estimate)

Flash point:

11 °C

storage temp. 

Store at +5°C to +30°C.

solubility 

ethanol: soluble1mg/mL

form 

Solid

pka

4.95(at 25℃)

Colour Index 

13020

color 

Reddish-violet

PH Range

4.4(red)-6.3(yellow)

Odor

Odorless

Water Solubility 

Practically insoluble in water. Soluble in alcohol, acetic acidSoluble in ethanol. Insoluble in water.

λmax

410nm, 530nm, 427nm, 519nm

Merck 

14,6119

BRN 

750102

Stability:

Stable. Incompatible with strong oxidizing agents.

Major Application

Waveguides, LED sensors, photoresists, liquid crystals, sol-gel matrix, optical sensors, paints, toys, detection of thiols, food freshness sensors, dental product, saliva sampling method, detecting lactic acid, carbohydrates

InChIKey

CEQFOVLGLXCDCX-MSUUIHNZSA-N

CAS DataBase Reference

493-52-7

NIST Chemistry Reference

Benzoic acid, 2-[[4-(dimethylamino)phenyl]azo]-(493-52-7)

IARC

3 (Vol. 8, Sup 7) 1987

EPA Substance Registry System

Methyl red (493-52-7)

Safety Information

Hazard Codes 

Xn,T,F,Xi,C,N

Risk Statements 

10-20/21/22-68/20/21/22-68-36/38-23/25-11-36/37/38-34-51/53-39/23/24/25-23/24/25

Safety Statements 

36/37-24/25-22-45-33-24-16-7-36-26-36/37/39-61

RIDADR 

UN 1170 3/PG 2

WGK Germany 

1

RTECS 

DG8960000

TSCA 

Yes

HazardClass 

3

PackingGroup 

II

HS Code 

29270000

Hazardous Substances Data

493-52-7(Hazardous Substances Data)

MSDS

• Language:English Provider:Acid Red 2
• Language:English Provider:ACROS
• Language:English Provider:SigmaAldrich
• Language:English Provider:ALFA

Methyl Red Usage And Synthesis

Description

Methyl red is a commonly used indicator for acid-base titrations. This chemical is usually yellow but turns red below pH 4.0. Bacteria exhibiting mixed acids fermentation will accumulate acids in the medium, resulting in a color change. Approximately five drops of methyl red reagent are added to an overnight culture grown in MRVP broth to determine the test result.
Different bacteria convert dextrose and glucose to pyruvate using different metabolic pathways. Some of these pathways produce unstable acidic products which quickly convert to neutral compounds. Some organisms use the butylene glycol pathway, which produces neutral end products, including acetoin and 2,3-butanediol. Other organisms use the mixed acid pathway, which produces acidic end products such as lactic, acetic, and formic acid. These acidic end products are stable and will remain acidic.
The Methyl Red test involves adding the pH indicator methyl red to an inoculated tube of MR-VP broth. If the organism uses the mixed acid fermentation pathway and produces stable acidic end-products, the acids will overcome the buffers in the medium and produce an acidic environment in the medium. When methyl red is added, if acidic end products are present, the methyl red will stay red.

Chemical Properties

dark red crystalline powder

Uses

Used as pH indicator.

Uses

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.

Uses

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

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

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.

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.

Properties and Applications

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

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.]

Methyl Red(493-52-7)Related Product Information

• Thiophanate-methyl
• 4-Dimethylaminobenzoic acid
• 4-AMINOAZOBENZENE
• Methylparaben
• Kresoxim-methyl
• Methyl acetate
• Chlorodimethylphenylsilane
• Sulforhodamine B
• Ethyl 2-(Chlorosulfonyl)acetate
• Methyl acrylate
• ACID RED 88
• Solvent Yellow 2
• 4-Dimethylaminobenzaldehyde
• Bensulfuron methyl
• METHYL THIOPHENE-2-CARBOXYLATE
• N,N-Dimethyl-1,4-phenylenediamine
• Folic acid
• Bromocresol green