Methyl red

Methyl red

Overview
Methyl red, also called C.I. Acid Red 2, is an indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...

 dye that turns red in acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

ic solutions. It is an azo dye, and is a dark red crystalline powder.

Methyl red is a pH indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...

; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pKa
Acid dissociation constant
An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions...

 of 5.1 .

Murexide
Murexide
Murexide , also called ammonium purpurate or MX, is the ammonium salt of purpuric acid. It may be prepared by heating alloxantin in ammonia gas to 100 °C, or by boiling uramil with mercury oxide. W.N...

 and methyl red are investigated as promising enhancers of sonochemical
Sonochemistry
In chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems. The chemical effects of ultrasound do not come from adirect interaction with molecular species...

 destruction of chlorinated hydrocarbon pollutant
Pollutant
A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...

s.

Methyl red is classed by the IARC
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....

 in group 3 - unclassified as to carcinogenic potential in humans.

As an azo dye, Methyl Red may be prepared by diazotization of anthranilic acid
Anthranilic acid
Anthranilic acid is the organic compound with the formula C6H4COOH. This amino acid is a white solid when pure, although commercial samples may appear yellow. The molecule consists of a benzene ring with two adjacent functional groups, a carboxylic acid and an amine...

, followed by reaction with dimethylaniline
Dimethylaniline
N,N-Dimethylaniline is an organic chemical compound, a substituted derivative of aniline. It consists of a tertiary amine, featuring dimethylamino group attached to a phenyl group. This oily liquid is colourless when pure, but commercial samples are often yellow...

:


In microbiology
Microbiology
Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

, methyl red is used in the Methyl Red (MR) Test, used to identify bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 producing stable acids by mechanisms of mixed acid fermentation
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

 of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 (cf. Voges–Proskauer (VP) test).

The methyl red test is the "M" portion of the four IMViC tests used to characterize enteric bacteria.
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Encyclopedia
Methyl red, also called C.I. Acid Red 2, is an indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...

 dye that turns red in acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

ic solutions. It is an azo dye, and is a dark red crystalline powder.

Methyl red is a pH indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...

; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pKa
Acid dissociation constant
An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions...

 of 5.1 .

Murexide
Murexide
Murexide , also called ammonium purpurate or MX, is the ammonium salt of purpuric acid. It may be prepared by heating alloxantin in ammonia gas to 100 °C, or by boiling uramil with mercury oxide. W.N...

 and methyl red are investigated as promising enhancers of sonochemical
Sonochemistry
In chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems. The chemical effects of ultrasound do not come from adirect interaction with molecular species...

 destruction of chlorinated hydrocarbon pollutant
Pollutant
A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...

s.

Methyl red is classed by the IARC
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....

 in group 3 - unclassified as to carcinogenic potential in humans.

Preparation


As an azo dye, Methyl Red may be prepared by diazotization of anthranilic acid
Anthranilic acid
Anthranilic acid is the organic compound with the formula C6H4COOH. This amino acid is a white solid when pure, although commercial samples may appear yellow. The molecule consists of a benzene ring with two adjacent functional groups, a carboxylic acid and an amine...

, followed by reaction with dimethylaniline
Dimethylaniline
N,N-Dimethylaniline is an organic chemical compound, a substituted derivative of aniline. It consists of a tertiary amine, featuring dimethylamino group attached to a phenyl group. This oily liquid is colourless when pure, but commercial samples are often yellow...

:

Methyl red test


In microbiology
Microbiology
Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

, methyl red is used in the Methyl Red (MR) Test, used to identify bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 producing stable acids by mechanisms of mixed acid fermentation
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

 of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 (cf. Voges–Proskauer (VP) test).

The methyl red test is the "M" portion of the four IMViC tests used to characterize enteric bacteria. The methyl red test is used to identify enteric bacteria based on their pattern of glucose metabolism. All enterics initially produce pyruvic acid from glucose metabolism. Some enteric subsequently use the mixed acid pathway to metabolize pyruvic acid to other acids, such as lactic
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...

, acetic
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

, and formic
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...

 acids. These bacteria are called methyl-red positive and include Escherichia coli and Proteus vulgaris. Other enterics subsequently use the buytylene glycol pathway to metabolize pyruvic acid to neutral end-products. These bacteria are called methyl-red-negative and include Serratia marcescens and Enterobacter aerogenes.

Process


An isolate is inoculated into a tube with a sterile transfer loop. The tube is incubated at 35°C for 2-5 days. After incubation, 2.5ml of the medium is transferred to another tube. Five drops of the pH indicator methyl red is added to this tube. The tube is gently rolled between the palms of the hands to disperse the methyl red.

Expected results


Enterics that subsequently metabolize pyruvic acid to other acids lower the pH of the medium to 4.2. At this pH, methyl red turns red. A red color represents a positive test. Enterics that subsequently metabolize pyruvic acid to neutral end-products lower the pH of the medium to only 6.0. At this pH, methyl red is yellow. A yellow color represents a negative test.

See also

  • Methyl
  • Universal Indicator
    Universal indicator
    A Universal indicator is a pH indicator composed of a blend of several compounds that exhibits several smooth colour changes over a pH value range from 1-14 to indicate the acidity or basicity of solutions. Although there are a number of commercially available universal pH indicators, most are a...

  • pH indicator
    PH indicator
    A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...

    s
  • Methyl yellow
    Methyl yellow
    Methyl yellow, or C.I. 11020, is a chemical compound which may be used as a pH indicator.In aqueous solution at low pH, methyl yellow appears red...

  • Methyl orange
    Methyl orange
    Methyl orange is a pH indicator frequently used in titrations.It is often used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids...

  • Methyl violet
    Methyl violet
    Methyl violet is a family of organic compounds that are mainly used as dyes. Depending on the amount of attached methyl groups, the color of the dye can be altered. Its main use is as a purple dye for textiles and to give deep violet colors in paint and ink...


External links