Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

BINDSCHBDLBK'S GKEBN 321
disappear again on further reduction. The dye is also reformed by
adding 5 c.c. of the original solution of the diamine salt.
Because of the great instability of the quinonoid salts it is necessary
to work rapidly, using greatly diluted and cool solutions.
The y-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.)
Let us consider the process of indamine formation, taking our quinonediimine
base as the starting point. In accordance with a general
addition reaction which is characteristic of all quinonediimines and also
plays a part in the formation of aniline black from aniline (cf. p. 312),
the dimethylquinonediimonium salt is capable of combining with great
ease with one molecule of aniline or dimethylaniline :
>N(CH3)2
>N(CH3)2.
The new y-phenylenediamine derivative so formed is further dehydrogenated
to a quinonoid indamine dye :
the constitution of which is in complete accord with Willstatter's theory.
This dye, known as " Bindschedler's green ", is of no practical importance
since, like all indamines, it is easily hydrolysed, especially by acids :
Preparation of Bindschedler's Green. 1 —Dimethyl-^-phenylenediamine
(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
1 Ber., 1883, 16, 464, 868 ; 1915, 48, 1087.