Crystal violet

Structural formula
General
Surname	Crystal violet
other names	{4- [4,4′-bis (dimethylaminophenyl) benzhydrylidene] cyclohexa-2,5-dien-1-ylidene} dimethylammonium chloride ( IUPAC ) CI Basic Violet 3 CI 42555 Hexamethyl- p- rosaniline chloride Hexamethyl- p -rosanilinium chloride Gentian violet Methyl violet 10B Methylrosanilium Methylrosanilium chloride Methylrosaniline blue pyoctanine
Molecular formula	C 25 H 30 ClN 3
Brief description	green, odorless solid
External identifiers / databases
CAS number 548-62-9 (chloride) 7438-46-2 (cation) EC number 208-953-6 ECHA InfoCard 100.008.140 PubChem 11057 ChemSpider 10588 DrugBank DBSALT000604 Wikidata Q420705
properties
Molar mass	407.99 g mol −1
Physical state	firmly
density	1.19 g cm −3 (20 ° C)
Melting point	189-194 ° C
solubility	little in water (10 g l −1 at 20 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 302-318-351-410 P: 273-280-305 + 351 + 338
Authorization procedure under REACH	particularly worrying : carcinogenic ( CMR )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Crystal violet (after the botanical name of the gentian and gentian violet is called) a violet cationic triphenylmethane .

Manufacturing

Crystal violet is obtained by condensation of Michler's ketone (4,4'-bis-dimethylamino-benzophenone) with N , N- dimethylaniline in the presence of phosphoryl chloride . There is an electrophilic substitution on the N , N -dimethylaniline in the para position by the carbon of the carbonyl group of Michler's ketone. Phosphoryl chloride serves as an electron pair acceptor for the oxygen of the carbonyl group of the ketone. The carbon atom is thus positively charged and thus able to attack the aromatic electrophilically. Water is then eliminated from the resulting carbinol base.

Very pure crystal violet needles recrystallized from water with a gold-greenish, metallic sheen.

properties

Crystal violet is usually in the form of fine, metallic gold shiny needles. It dissolves in water and other polar solvents with an intense purple color and dyes natural fibers a bright purple, but is relatively easy to wash out. It forms a charge transfer complex with iodine .

If sodium hydroxide solution is added to a very dilute crystal violet solution , the solution slowly becomes discolored. A hydroxide ion is attached to the carbenium ion formed in a mesomeric boundary form in the center of the molecule . This reaction can be investigated kinetically with a photometer (see photometry ). If there is a large difference in concentration (concentration of crystal violet much smaller than the concentration of sodium hydroxide solution), a pseudo-first order reaction takes place (see Kinetics (Chemistry) ).

use

Crystal violet is used as the dye in ink ribbons , as crystal violet lactone in carbonless papers or copying pins , and especially in the microscopic staining technique as the main component of the Gram stain , with the aid of which bacteria can be divided into two classes. It is also used in the plaque assay and occasionally in the sample buffer for agarose gel electrophoresis of DNA if a gel extraction follows.

Crystal violet is used as a pH indicator when determining the anhydrous content of weak bases. If a solution of crystal violet is slightly acidified, the color changes from violet to green because the auxochrome of the third nucleus loses its electron-donating ability and thus its color relevance by adding a proton. A stronger acidification leads to a yellow compound in which another auxochrome is deactivated by protonation.

For a long time, until other effective antimycotics were discovered, crystal violet was used medically to treat skin fungal diseases ( mycoses ), particularly athlete's foot , and oral thrush . To do this, it is brushed on as a pyoctanine solution (0.5–2%). In the western world today it is almost only used in naturopathy because of the coloring of the skin . In pediatric dermatology , it is still used in herds of atopic eczema when it is triggered by gram-positive bacteria or dermatophytes. According to WHO recommendations , crystal violet was classified as an essential drug until 2011.

It is used intravenously for the treatment of secondary pulmonary mycoses. The fungistatic effect of crystal violet is, depending on the type of mycosis, 10 to 100 times stronger than that of the widely used clotrimazole . It is surpassed by amphotericin B , which, however, is highly toxic in comparison. Therefore, crystal violet is often used in immunocompromised patients.

Crystal violet must not get into the eye, as it can cause serious damage there. Furthermore, overdosing should be avoided when used externally, since crystal violet, like the related and similarly used triphenylmethane dyes malachite green and brilliant green , has a cell-toxic effect on the skin.

In June 2019, the Canadian health authority Health Canada warned of a possible cancer risk from crystal violet and recommended that applications in veterinary medicine should also be stopped.

literature

• Gemeinhardt: Endomycoses. VEB Verlag der Wissenschaften, 1973.
• Braun, Guenther, Schubert: Dermatology - textbook for students. VEB Verlag für Volk und Gesundheit, 1986.

Web links

Commons : Crystal Violet  - collection of images, videos, and audio files

• Color characteristics of crystal violet

Individual evidence

1. ↑ ^{a b c d e f} Entry on crystal violet in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
2. ↑ Entry on [4- [4,4′-bis (dimethylamino) benzhydrylidene] cyclohexa-2,5-dien-1-ylidene] dimethylammonium chloride in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016 Manufacturers or distributors can expand the harmonized classification and labeling .
3. ↑ Entry in the SVHC list of the European Chemicals Agency , accessed on October 18, 2015.
4. ↑ Jansen / Ralle / Peper: reaction kinetics and chemical equilibrium. Aulis Verlag Cologne 1984, p. 49, p.206, ISBN 3-7614-0642-8 .
5. ↑ Hobein / Lutz: Microencapsulation. Practice series of chemistry Volume 49, Aulis Verlag Cologne 1989, page 43, ISBN 3-7614-1200-2 .
6. ↑ WHO Model Lists of Essential Medicines , March 2007, Section 13.2 (English: PDF; 379 kB)
7. ↑ Recall of Crystal Violet