VIOLET CRYSTAL: CHARACTERISTICS, HOW IT IS OBTAINED AND USES - CHEMISTRY - 2024

The crystal violet is an organic, synthetic and alkaline triphenylmethane dye triamino-. Found as a dark green metallic luster powder. It receives several names, among which can be mentioned hexamethyl pararosaniline chloride or methyl violet, aniline violet, gentian violet, etc.

The name of the violet crystal dye was taken from its similarity to the color of the petals of violet and gentian flowers; its origin has nothing to do with the extracts of these flowers.

Source: By LHcheM, from Wikimedia Commons

The violet crystal is obtained by several routes, which include condensation, addition, chlorination reactions, among others. They all have N, N-dimethylaniline as their raw material.

It is used as a component in inks used for printing and in ballpoint pens. It is also used to dye leather, paper, detergents, fertilizers, among other products.

It was widely used as an antiseptic. It has antimitotic, antibacterial, antiparasitic, and antifungal properties. Its mechanism of action is bacteriostatic.

It is used in histology to stain tissue sections and in microbiology to color and classify bacteria according to their staining properties with the Gram stain.

characteristics

Source: Jynto via Wikipedia

The upper image shows the structure of the triaminetriphenylmethane molecule. The blue spheres correspond to the nitrogen atoms, and at the top, lies a nitrogen with a positive formal charge, which attracts the Cl ^- anion (green sphere).

The structure is flat in the three aromatic rings, due to sp ² hybridization of their carbon atoms. Note that, although the upper ring is aromatic, it does not contain the dotted lines inside. This means that the resonance of its double bonds is not favored.

The crystal violet molecule is conspicuously polar. Why? Because the three electronegative nitrogen atoms give up their pair of free electrons to the aromatic rings, and part of this electron density is attracted by the partially positively charged nitrogen atom (N ⁺). This polarity is evident in its high boiling point, much higher than that of water.

Molecular formula

C ₂₅ H ₃₀ ClN ₃

Formula weight

407.99 g / mol

Melting point

205 ºC

Boiling point

560.86 ºC

Density

1.19 g / cm ³ (20ºC)

Solubility

Soluble in water 50 g / L at 27ºC.

Crystal violet is insoluble in ether, it is soluble in water, chloroform and alcohol. When the violet crystal is dissolved in water, it will turn blue or purple.

Pka

9.4 at 25ºC

The color will vary with the acidity of the solution, at a pH greater than 1 the colorant is green, while at a pH lower than 1 the color is yellow. This variation in color reflects the different charge changes of the molecule.

Reactivity

It is sensitive to light, incompatible with acids and strong oxidizing agents, among other characteristics.

How is it obtained?

The violet crystal has been obtained by various routes. It was first prepared by Caro and Kern, two German chemists who reacted dimethylaniline with phosgene.

This reaction resulted in an intermediate product, 4,4'-bis (dimethylamino) benzophenone, also known as Michler's ketone. This ketone was then reacted with more dimethylaniline with phosphorous oxychloride and hydrochloric acid.

The mixed reagent of iodine with crystal violet chloride is known as gentian violet. Another way to prepare crystal violet is by the condensation reaction of dimethylamine and formaldehyde, resulting in a white colorant.

Depending on the pH, light or heat conditions, this white colorant can undergo reversible transformations that oscillate between two colors, passing through the colorless one.

Applications

Inks component

Gentian violet can be used in inks with which a wide variety of materials such as wood, leather, silk or paper are stained. It is used in paints, fertilizers, detergents, refrigerants.

It is used in printing inks, black and navy blue inks for ballpoint pens. Its use in hair dyes has also been described.

In cases of temporary skin marking

It is used to mark the skin, delimiting the area to be carried out for body surgeries. Likewise, it is used to mark the place on the skin where a piercing will be placed, and it is useful as a marker in allergy tests.

In the Gram stain

Source: Pixnio

Crystal violet is one of the components of the Gram staining method. This allows bacteria to be classified as Gram positive bacteria, or Gram negative bacteria. Some of them, however, are not colored with the Gram.

The use of crystal violet is based on its penetration through the thick cell wall of bacteria. Thus, its cellular structure retains the dye, staining the bacteria purple. This is the case with Gram positive bacteria.

Whereas if the bacteria have a thin cell wall, they are classified as Gram negative bacteria. Because of this, the dye cannot stay long enough inside them to dye them (the triamino-triphenylmethane molecule goes in and out easily).

Later, in the counterstaining process using this same Gram method, the bacteria are stained with fenicada fuscin, leaving them pink.

When bacteria do not have a cell wall, and do not present any type of staining, they are classified as bacteria that do not stain with the Gram.

As a treatment in some diseases

-The violet crystal was used very frequently as an antiseptic on wounds of the skin and mucosa (topical or external use), as well as in the treatment of various diseases, such as atopic dermatitis.

-Its usefulness in the treatment of hemorrhoids is described.

-It has antitumor properties.

-It has been used in neurodegenerative diseases, in multiple myeloma, and in breast cancer.

In treating infections

-The violet crystal has properties that help eliminate various kinds of microorganisms. Among them are fungi; that is, it is antifungal.

-It is used in the treatment of oral candidiasis, to eliminate athlete's foot, mycosis of the nails (onychomycosis), among other diseases, infections caused by fungi.

-It is used to treat some infections caused by bacteria, such as impetigo, which has been very useful especially for those who have an allergy to some antibiotics such as penicillin.

-It is also antiparasitic. It serves to eliminate helminth parasites (anthelminthic) and is effective against trypanosome protozoa.

-It is very useful for treating infections of the eyes and skin of animals such as cattle and even fish. It has been determined that the crystal violet dye has a predominance of bacteriostatic action.

In laboratories and biomedical research

-The violet crystal is used in laboratories as an acid-base indicator, varying its color from green at a pH of 0.5, to blue at a pH of 2. It can be used in the determinations of metallic ions such as zinc, cadmium, gold, mercury, among other ions.

-Crystal violet is a non-toxic alternative, used in place of the fluorescent dye ethidium bromide in electrophoretic DNA gel runs.

-The violet crystal and formalin are very useful to color and fix the cells obtained in culture media, facilitating the visibility of the cells.

References

1. Wikipedia. (2018). Crystal violet. Recovered from: en.wikipedia.org
2. Chemical Book. (2017). Crystal Violet. Recovered from: chemicalbook.com
3. PubChem. (2018). Gentian Violet. Recovered from: pubchem.ncbi.nlm.nih.gov
4. Monica Z. Bruckner. (2016, November 3). Gram Staining. Recovered from: serc.carleton.edu
5. DrugBank. (2018). Gentian Violet. Recovered from: drugbank.ca