Malachite green

This article describes the chemical dye, for the pigment color of the same name, see Malachite #As a pigment .

Structural formula
General
Surname	Malachite green
other names	4 - {[4- (Dimethylamino) phenyl] (phenyl) methylidene} -N, N-dimethylcyclohexa-2,5-diene-1-iminium chloride ( IUPAC ) 4,4'-bis (dimethylamino) tritylium chloride CI Basic Green 4 Diamond green Viktoriagrün B Viktoriagrün WB
Molecular formula	C 23 H 25 ClN 2 ( chloride ) C 46 H 50 N 4 · 2HC 2 O 4 · C 2 H 2 O 4 ( oxalate )
Brief description	deep green, shiny metallic crystals (chloride)
External identifiers / databases
CAS number 569-64-2 (chloride) 18015-76-4 (oxalate) 2437-29-8 (acid oxalate) 10309-95-2 (cation) EC number 209-322-8 ECHA InfoCard 100.008.476 PubChem 11294 ChemSpider 10820 DrugBank DB03895 Wikidata Q408815
properties
Molar mass	364.91 g mol −1 (chloride) 927.00 g mol −1 (oxalate)
solubility	Chloride: very good in water, ethanol , methanol and amyl alcohol
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 302-318-361d-410 P: 273-280-305 + 351 + 338-501
Toxicological data	80 mg kg −1 ( LD 50 ,  mouse ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Malachite green is a bright green cationic dye belonging to the triphenylmethane dyes . It was first synthesized in 1877 by the chemist Otto Fischer and independently of that, Oskar Doebner succeeded in 1878 .

Malachite green is not to be confused with malachite green , which is made from mineral malachite pigments and after which it is named.

Manufacturing

The colorless leuco base of malachite green is synthesized from N , N -dimethylaniline and benzaldehyde in the presence of zinc chloride or concentrated sulfuric acid. By oxidation with lead (IV) oxide or similar oxidizing agents in acid solution, the leuco base of malachite green over goes into the carbinol. Alternatively, Michler's ketone can be reacted with phenylmagnesium chloride in the laboratory . The carbinol base is formed after working up with aqueous ammonium chloride .

Production of malachite green. Oxidation of the leuco base [4,4'-bis (dimethylamino) triphenylmethane, top center] with lead (IV) oxide leads to the colorless carbinol base (top right). The subsequent action of hydrochloric acid produces the mesomeric-stabilized malachite green (below).

properties

Physical Properties

Malachite green has two absorption bands (approx. 420 nm and approx. 620 nm). The cation is very soluble in water. The undissociated substance precipitates as a pale green precipitate in a slightly basic environment. The leuco base is largely insoluble in water, but readily soluble in fat, which leads to an accumulation in the adipose tissue of treated animals and to a very slower excretion. The absorption coefficient at the absorption maximum at 622 nm in ethanol is 8.07 · 10 ⁴  L mol ⁻¹ cm ⁻¹ .

Chemical properties

Crystals of malachite green oxalate

Malachite green oxalate forms green, shiny metallic crystals that are easily soluble in water and ethanol. Malachite green is destroyed by chlorine . It can be used as a color indicator in chemistry. The color of the solution changes depending on the pH value:

Colors of malachite green
acidic form yellow	Transition zone 1 pH 0.2 to pH 1.8	typical color blue-green	Transition zone 2 pH 11.5 to pH 13.2	basic form colorless

use

General

In microscopy , malachite green is used to stain plant tissues infected with fungi, bacteria and as evidence of spore formation . Malachite green must not be used as a food coloring because it is classified as harmful. Occasionally colored papers and paper towels are colored with it. It is popular for coloring the " Easter nests ". Because of its low light fastness (light stability) it is no longer used in textile dyeing. If the two dimethyl amino groups are substituted by diethyl amino groups, the dye brilliant green is obtained , which is significantly more lightfast than malachite green.

Veterinary drugs

In many third countries (non-EU countries), because of its unsurpassed effectiveness, malachite green is an approved drug against fungi and parasites in fish, especially against ichthyophthiriosis . The substance is reduced again in the fish to the poorly water-soluble leuco base. As such, it forms long persistent residues bound to fat (half-life for trout and carp approx. 45 days). Therefore, malachite green is not listed in Appendices I to III of Regulation (EC) No. 2377/90 on the maximum permissible concentrations of substances permitted in food production. In the EU, this means a ban on its use in food-producing animals. Even treating trout spawn against fungal growth is prohibited. There must also be no traces of residues (neither malachite green nor the leuco base) in food. The previous German limit of 10 µg / kg was set to 0 µg / kg in compliance with the EU.

An almost equivalent substitute has not yet been found.

Residues in food

In food monitoring, malachite green is often found as a detectable drug residue in fish. In Germany, fish from aquaculture are regularly examined for residues from treatment with malachite green as part of the National Residue Control Plan. In 2003 the European Commission introduced a minimum performance limit (MRPL) for the determination of malachite green and leuco malachite green of 2 μg / kg, below which the cause of the exposure is to be determined, but the samples are no longer objected to. Fish caught in the wild can also be contaminated with malachite green, for example in the Moosach (Isar) .

literature

• Paul Karrer: Textbook of Organic Chemistry , 10th Edition. Georg Thieme, Stuttgart 1948. p. 645.
• Kurt Bauer, H. Dangschat, H.-O. Knöppler, J. Neudegger: Uptake and excretion of malachite green in rainbow trout . Archive f. Lebensmittelhygiene 39 (1988), pp. 97-102.

Web links

Commons : Malachite Green  - Collection of images, videos and audio files

Individual evidence

1. ↑ ^{a b} entry on malachite green. In: Römpp Online . Georg Thieme Verlag, accessed on May 29, 2014.
2. ↑ ^{a b} Entry on malachite green hydrochloride in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
3. ↑ Entry on [4- [α- [4- (dimethylamino) phenyl] benzylidene] 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 .
4. ↑ Data sheet Malachite Green chloride from Sigma-Aldrich , accessed on May 13, 2017 ( PDF ).
5. ^ Siegfried Hauptmann : Organic Chemistry , 2nd Edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, p. 757, ISBN 3-342-00280-8 .
6. ↑ Food: Fish from breeding facilities heavily contaminated with drugs in Spiegel Online from May 1, 2015. Retrieved May 1, 2015.
7. ↑ BVL - Das Bundesamt - Annual Report 2017 on the National Residue Control Plan (NRKP). Retrieved March 22, 2019 . 
8. ↑ DECISION OF THE COMMISSION of December 22, 2003 amending Decision 2002/657 / EC with regard to the establishment of minimum performance limits (MRPL) for certain residues in food of animal origin. In: Official Journal of the European Union. January 10, 2004, accessed March 22, 2019 . 
9. ↑ Carola Brand: Malachite green contaminated fish also in Isar near Moosburg. In: br.de . March 28, 2019, accessed September 23, 2019 .