Meldola blue

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Structural formula
Structural formula of Meldola Blau
General
Surname Meldola blue
other names
  • N , N -dimethyl-9 H -benzo [a] phenoxazin-9-iminium chloride ( IUPAC )
  • 9- (Dimethylamino) benzo [a] phenoxazin-7-ium chloride
  • CI Basic Blue 6
  • CI 51175
  • BASIC BLUE 6 ( INCI )
Molecular formula
  • C 18 H 15 ClN 2 O (as chloride)
  • C 18 H 15 ClN 2 O · ½ ZnCl 2 (as hemi-double salt with zinc chloride)
Brief description

dark green to black crystal powder

External identifiers / databases
CAS number
  • 966-62-1 (as chloride)
  • 7057-57-0 (as double salt with ZnCl 2 )
EC number 213-524-1
ECHA InfoCard 100.012.295
PubChem 101929
ChemSpider 92090
Wikidata Q27275599
properties
Molar mass
  • 310.78 g mol −1 (as chloride)
  • 378.92 g mol −1 (as hemi double salt with ZnCl2)
Physical state

firmly

Melting point

280 ° C with decomposition

solubility

soluble in water and in ethanol

safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Meldola Blue is a blue phenoxazine - dye whose synthesis and properties for the first time in 1879 by Raphael Meldola described.

The basic (cationic) 1,4-oxazine derivative is in the form of a chloride salt; in most cases, however, the better crystallizing hemi - zinc chloride compound (compare, for example, brilliant cresyl blue ) is isolated.

Occurrence and representation

According to the original procedure , the N , N -dimethyl-4- nitrosoaniline formed in the nitrosation of N , N -dimethylaniline is isolated as the hydrochloride and then added to a solution of 2-naphthol in glacial acetic acid at 110.degree .

Synthesis of Meldola Blau

When it cools down, "magnificent, long, bronze-colored needles with a copper sheen" form.

An industrial process avoids the isolation of the toxic nitroso compound and describes the addition of a suspension of the intermediate stage in an aqueous-alcoholic medium to an ethanolic β-naphthol solution at 70 ° C, which contains anhydrous zinc chloride. When it cools down, the double salt of Meldola Blau precipitates with zinc chloride.

properties

As a double salt with zinc chloride, Meldola blue is a dark green to black crystalline solid that dissolves in water in blue-violet and in ethanol in dark blue color with an absorption maximum λ max at 650 nm (in 50% aqueous ethanol). In polar solvents, such as. For example, pyridine , ethylene glycol and cellosolve , Meldola blue is also readily soluble.

Applications

Meldola blue was initially thought to be a useful blue textile dye; However, because of its low absorption by wool and silk fibers, it could not hold its own against the much more light-stable indigo . Its technical applications are limited to the coloring of paper and leather.

Meldola blue has gained greater importance as a redox-active dye in biology. The color change from blue to the colorless leuco form during electron acceptance ( reduction ) can be used to determine reducing coenzymes , such as B. NADH or NADPH and the corresponding dehydrogenases in aqueous solutions, but also on carriers (paper strips) or in biosensors .

Redox reactions at Meldola Blau

Individual evidence

  1. ↑ Entry on BASIC BLUE 6 in the CosIng database of the EU Commission, accessed on February 6, 2020.
  2. ↑ a b Meldola's blue. (PDF; 186 kB) Carbosynth Ltd., March 22, 2019, accessed on February 5, 2020 (English).
  3. ↑ a b c R. Meldola: Effect of nitrosodimethylaniline on phenols which do not contain the methyl group . In: Ber. German Chem. Ges. Volume 12 , no. 2 , 1879, p. 2065-2066 , doi : 10.1002 / cber.187901202221 .
  4. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  5. ^ R. Meldola: V. On a new class of coloring matters from the phenols . In: J. Chem. Soc. tape 39 , 1881, p. 37-40 , doi : 10.1039 / CT8813900037 .
  6. ↑ Patent US3665601 : Process for the manufacture of basic oxazine dyestuffs. Applied on February 13, 1969 , published on April 11, 1972 , applicant: Farbwerke Hoechst AG, inventor: N. Ottawa, G. Schäfer. ‌
  7. ^ A b Edward Gurr: Synthetic Dyes in Biology, Medicine and Chemistry . Academic Press, London, UK 1971, ISBN 978-0-12-309650-0 , pp. 74-75 .
  8. ↑ M. Hope Roberts, RW Horobin: Biomedical applications and chemical nature of three dyes first Synthesized by Raphael Meldola: isamine blue, Meloda's blue and naphthol green B . In: Biotechnic & Histochemistry . tape 8 , no. 4 , 2012, p. 295-299 , doi : 10.3109 / 10520295.2011.639722 .
  9. ↑ P. Kugler, K.-H. Wrobel: Meldola Blue: A new electron carrier for the histochemical demonstration of dehydrogenases . In: Histochemistry . tape 59 , no. 2 , 1978, p. 97-109 , doi : 10.1007 / bf00518505 .
  10. ↑ Patent DE1959410 : Indicator for determining the reduced pyridine coenzymes . Registered on November 26, 1969 , published on June 16, 1971 , applicant: Boehringer Mannheim GmbH, inventors: HU Bergmeyer, E. Haid, M. Nelboeck-Hochstetter, G. Weimann. ‌