Bindschedlers green

Because of the great instability of the quinonoid salts it is necessary to work rapidly, using greatly diluted and cool solutions. 

The p-quinonediimines are the parent substances of the indamine dyes and of the tricyclic quinonoid salts of the phenazine, phenthiazine, and phenoxazine groups which are related to them. (Detailed information on this subject is to be found in special works, e.g. of Nietzki-Mayer and of Bucherer.) 

The new p-phenylenediamine derivative so formed is further dehydrogenated to a quinonoid indamine dye  

Preparation of Bindschedler s Green.1—Dimethyl-p-phenylene-diamine (7 g.) and dimethylaniline (6 g.) are dissolved in a mixture of 40 c.c. of concentrated hydrochloric acid and 40 c.c. of water. Into the solution, which is kept cool in ice and is stirred mechanically or 

are placed in a distilling flask, along with 20 c.c. of 2 N-hydrochloric acid, and distilled with steam through a water-cooled condenser. Characteristic yellow needles of quinone soon pass over. 

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Methylene blue from Bindschedler green-thiosulfonic acid. 312... 

Fig. 5. Stmctural interrelationships among diaryl and triaryl carbonium dyes. Pyronine = xanthene (61), R = CH3 is Bindschedler s Green.

Ferricyanide has been employed as an electron acceptor for lactate in place of NAD Alternatively, diaphorase can be used in conjunction with ferricyanide Bindschedler s Green ferricenium or dichlorophenylindophenol to catalyze the oxidation of NADH while providing a more easily monitored species than NADH itself. 

Bindschedler s Green (6.204) can be made by condensing p-nitroso-N,N-dimethylaniline with N,N- dimethyl aniline. A similar condensation with 2-naphthol gives Meldola s Blue (6.209 Cl Basic Blue 6), the first oxazine dye, discovered in 1879. The symmetrical Cl Basic Blue 3 (6.210) is of more commercial significance. It is synthesised by nitrosation of N,N-diethybrn-anisidine followed by condensation with N,N-diethybm-aminophenol, and is used for dyeing acrylic fibres. This dye is now classified by ETAD as toxic [73]. 

If the oxidation which leads to the formation of Bindschedler s green takes place in the presence of hydrogen sulphide the process is varied by the entrance of sulphur. In principle, however, the mechanism is the same as before. The following formulae show that an addition of H—8H and a subsequent intramolecular addition of a mercaptan group are stages in the reaction ... 

Experiments—Pass hydrogen sulphide slowly into the most concentrated aqueous solution of Bindschedler s green obtainable, until after some time the colour has changed to yellowish-red. Now add dilute hydrochloric acid and the solution of 0-3 g. of sodium dichromate. Precipitate the methylene blue formed by adding zinc chloride solution. 

Other types of basic dyes proposed for spectrophotometric determination of elements include the antipyrine dyes (Chrompyrazoles) [76,77], azo dyes [78], and the indamine dye Bindschedler s Green (formula 30.1). 

Test kits based on immobilized Bindschedler s green and N,N-diethyl-p-phenylenediamine were proposed for the rapid determination of active chlorine in water [3]. 

Methylene blue is formed from dimethyl-p-phenylenediamine, with an indammonium salt (Bindschedler s green) as an intermediate this condenses with hydrogen sulphide giving the thiazine dye (Fig. 5-1). Iron(//f) chloride is the usual oxidant for the condensation and cyclization reactions, but iron(//7) sulphate or oxalate may be used instead. The colour intensity of the dye is pH dependent. According to Cline (1969) the optimum pH is 0.35. 

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