Leucomalachite green

Leucomalachite Green [129-73-7] M 330,5, m 92-93°, pK 6.90 (several pK s). Crystd from 95% EtOH (lOmL/g), then from benzene/EtOH, and finally from pet ether. 

The oxidation off by Ce(lV) sulphate proceeds in two stages, i.e. an extremely rapid step k2 = 3.3 x 10 l.mole. sec at 18 followed by a much slower reaction This behaviour is also found in the oxidation of leucomalachite green (p. 406) and is attributed to two forms of Ce(IV) in slow equilibrium. 

Olafsson [427] has described a semiautomated determination of manganese in seawater using leucomalachite green. The autoanalyser had a 620 nm interference filter and 50 minute flow cells. Findings indicated initial poor precision was related to pFl, temperature, and time variations. With strict controls on sample acidity and reaction conditions, the semiautomated method had high precision, at least as good as that achieved by preconcentration and atomic absorption procedures, and provided precise, rapid, shipboard information... 

Fig. 3.20. HPLC-vis chromatograms, (a) Mixed standard 10 pg/kg equivalent (b) blank trout muscle extract, and (c) trout muscle spiked at /rg/kg. Peak heights in mV. Detection wavelength 618 nm. Peak identification MG = malachite green CV = crystal violet LMG = leucomalachit green LCV = leucocrystal violet. Reprinted with permission from J. A. Tarbin et al. [101].

Fig. 3.23. Structures of malachite green (MG), leucomalachite green (LMG) and demethylated derivatives. Reprinted with permission from S. J. Culp et al. [103].

As already mentioned, tertiary amines can not form similar addition products. With stabilized amines such as leuco crystal violet, leucomalachite green and similar dyes neutral and stable charge-transfer complexes were formed [94]. 

Tetramethylbenzidine and or/f o-tolidine are the most sensitive tests (capable of detecting blood in dilutions of 1 10 " and 1 10, respectively), while phenolphthalein and leucomalachite green are less sensitive but more selective. 

Fessard, V. Godard, X. Huet, S. Mourot, A. Poul, J. M. Mutagenicity of malachite green and leucomalachite green in in vitro tests. J. Appl. Toxicol. 1999,19,421 30. 

---