Methyl violet

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Methyl violet 2B
IUPAC name	Methyl violet 2B
Identifiers
CAS number	8004-87-3 Y
SMILES	[Cl-].CN(C)c1ccc(cc1)C(=C2C=CC(=[NH2+]) C=C2)c3ccc(cc3)N(C)C
Properties
Molecular formula	C24H28N3Cl
Molar mass	393.958 g/mol (6B)
Melting point	137 °C (279 °F)
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Methyl violet is the name given to a group of similar chemicals used as pH indicators and 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.

Methyl violet should not be confused with methyl blue or methylene blue, two other stains.

Compounds and Uses

The term methyl violet encompasses three main molecules, each with different uses. They are all soluble in water, ethanol, diethylene glycol and dipropylene glycol. Specifically, methyl violet 2B is 2.93% solution in water and 15.21% soluble in ethanol, due to the hydrophobicity of the aromatic rings.

Methyl Violet 2B

Methyl Violet 6B

Methyl Violet 10B

Methyl Violet 2B

Methyl violet 2B is the tetramethyl homolog. In pure crystals it is lustrous and blue-green in color; melting at 137°C (279°F). It is used as a pH indicator in chemistry, with a range between 0 and 1.6. The protonated form (found in acidic conditions) is yellow, turning blue-violet above pH levels of 1.6. It can be supplied as crystals, which are dissolved in the solution being tested, or as pH paper^{[citation needed]}.

Methyl Violet 6B

Methyl violet 6B contains five methyl groups. It is a darker blue than 2B.

Methyl Violet 10B

Methyl violet 10B has six methyl groups. It is known in medicine as Gentian violet (or crystal violet) and is the active ingredient in a Gram stain, used to identify bacteria. Gentian violet destroys cells and can be used as a disinfectant^{[citation needed]}. It is poisonous to some or most animals, including dogs and cats, and should never be used as a wash for animals' skin.

10B also inhibits the growth of many Gram positive bacteria, except streptococci. When used in conjunction with nalidixic acid (which destroys gram-negative bacteria), it can be used to isolate the streptococci bacteria for the diagnosis of an infection.

Methyl violet also binds to DNA. This means it can be used in cell viability assays in biochemistry. However, this binding to DNA will cause replication errors in living tissue, possibly leading to mutations and cancer.

Degradation

Methyl violet is a mutagen and mitotic poison, therefore concerns exist regarding the ecological impact of the release of methyl violet into the environment. Methyl violet has been used in vast quantities for textile and paper dyeing, and 15% of such dyes produced worldwide are released to environment in wastewater. Numerous methods have been developed to treat methyl violet pollution. The three most prominent are chemical bleaching, biodegradation, and photodegradation.

Chemical bleaching

Chemical bleaching is achieved by oxidation or reduction. Oxidation either destroys the dye completely or causes a change in the bonding of the chromophore^{[citation needed]}. Two examples of dye oxidants are sodium hypochlorite (NaClO, common bleach) and hydrogen peroxide. NaClO produces hypochlorous acid (HClO), hypochlorite ions (ClO^-) and chlorine, which are all in equilibrium:

NaOCl + H₂O Na⁺ + OH⁻ + H⁺ + OCl⁻

When any one of these compounds come in contact with the amine groups of the dye, they hydrolyze and degrade them. Methyl violet has three amine groups, and when one or more of these groups are hydrolyzed the molecule must rearrange itself to form a more stable compound. This breaks the chromophore bonds, meaning the molecule no longer absorbs light.

Hydrogen peroxide breaks the dye's bonds by forming radical species in the presence of light. These oxidize the dye by adding oxygen atoms on to the nitrogen in the amine group.

The reduction of methyl violet mostly occurs in microorganisms but it can be attained chemically using sodium dithionite and sodium hydrosulfide^{[citation needed]}.

Biodegradation

Biodegradation is the most interesting and most investigated method of dye degradation. This method is suitable because biodegradation could occur in large sewage plants with specialized microorganisms- which is highly cost effective. Certain animals and plants can degrade this dye, as well as microorganisms^{[citation needed]}, but the microorganisms are the most practical solution.

Two microorganisms that have been studied in depth are the White Rot Fungus and the bacterium Nocardia Corallina. In particular, the White Rot Fungus degraded a 12.3 µM methyl violet solution to 35% of the initial concentration in 6 hours. In 12 hours only 1% remained and after 72 hours the dye was deemed to be completely degraded^{[citation needed]}.

Nocardia Carollina's growth was inhibited by the toxic dye at the start of an incubation, but was able to degrade dyes with a concentration of under 5 µmol cm⁻³. The bacteria were completely inhibited with concentrations higher than 7 µmol cm^{−3[citation needed]}.

Photo degradation

Light alone is not enough to cause major degradation of methyl violet^{[citation needed]}. However, with the addition of large band-gap semiconductors, TiO₂ or ZnO, the photodecomposition speeds up.

The mechanism behind the TiO₂ catalysis is that it causes the production of oxygen free radicals, which break up the dye molecule. The rate of degradation can be increased by adding oxidizers or radical-forming molecules such as hydrogen peroxide, or Ag⁺ ions.

Other methods

Many others methods have been developed to treat the contamination of dyes in a solution such as:

Electrochemical Degradation

This is accomplished by running DC current through the dye solution to break the dye apart. This works well with dyes that are molecularly simple, but is ineffective against very complex dyes. This methods work very well when it is used to decomposed methyl violet. This method can be further improved by the addition of a redox mediator such as Co^+2/+3 .

Ion Exchange Membrane

In this method a membrane is used to separate the cation of the dye from the solution. The experimental results indicates that the addition of an organic solvent containing ions (1M NaCl and 60% CH₃OH) increases the separation of the cation from solution to 100%.

Laser Degradation

It was found that Kr⁻² excited with a 530 nm laser allowed for electron transfer from the triplets state to the Cationic dye methyl violet. The addition of this electron to the cation forces the molecule to rearrange.

Absorption

Absorbance of the dye from solution has been observed using solid Porous material such as: Pumice powder Porous silicon additive Porous glass Activated charcoal Micro tubes Ceramics

Many methods are available for dye removal from waste water but most are expensive, impractical or they just allow for the polluted dye to leave from one source to the next. In current removal techniques many of the procedure listed are used in combination to degrade the dye in the waste water.

See also

• Potassium ferrocyanide
• Potassium ferricyanide
• Methylene blue
• Methyl blue
• Egyptian Blue
• Han Purple
• Gentian violet
• Fluorescein

References

• [*Kristallviolett – ein pH-Indikator (in German)
• Mechanism of action of sodium hypochlorite [1]
• Hydrogen Peroxide[ [2]
• XP-Chloro Degradation Malachite green US Patent 2755202)
• Senthilkumaar S., and Porkodi.(2005). Heterogeneous Photocatalytic Decomposition of Crystal Violet in UV-illuminated Sol Gel
• Derived Nanocrystalline TiO2 Suspension. Journal of Colloid and Interface Science. 288(1):184-189.
• Bumpus J.A. and Brook B. J.(1988). Biodegradation of Crystal Violet by the White Rot Fungus Phanerochaete chrysosporium. Applied and Environmental Microbiology.54(5):1143-1150.
• Pizzolato T. M. et al.(2002). Colour Removal with NaClO of Dye Wastewater From Agate-processing plant in Rio Grande do Sul, Brazil. International journal of Mineral Processing.65 (1-4):203-211.
• Bhasikuttan C.A. et al.(2008).Photo ionization of Crystal Violet in Aqueous Solution. Photochemistry and Photobiology.62(2):245-250.
• Yatome C. et al.(1993).Degradation of Crystal Violet by Nocardia corallina. Applied Microbiology and Biotechnology.38-565-569.
• Bhasikuttan A.C. et al.(1995). Oxidation of Chrystal Violet and Malachite green in aqueous solutions- a kinetic spectrophotometric study. Journal of Photochemistry and photobiology A:Chemistry. 90(2-3):177-182.
• Sahoo, A.K.G. and Pal, A.(2005. Photocalalytic Degradation of Cystal violet(C.I. Violet) on Dilver Ion Doped TiO₂. Dyes and Pigments. 66(3):189-196.
• Saroman , M. A. et al.(2004). Electrochemical Decolonization of Structurally Different Dyes. Chemosphere. 57(3):233-239.
• Wu, J. et al. (2008). Removal of Catonic Dye Methyl Violet 2B From Water by Cation Exchange Membrances. Journal of Membrance Science.309(1-2):239-245.