Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

328 TKIPHBNYLMBTHANB DYES
give colourless solutions. Leuco-malachite green is a weak base of the
aniline type. The dye is formed by oxidation of the base in acid solution
; as in the case of dimethyl-y-phenylenediamine (p. 319), two
hydrogen atoms are removed from y-positions
Cl
I /—\ /CeH5
C <
H ^ ^ H\C6H4.N(CH3)2
Cl
!6H4.N(CH3)2'
The formation of the acid dye benzaurin takes place in a quite
analogous manner. y-Tetramethyldiaminobenzophenone (Michler's
ketone), which is prepared technically from dimethylaniline and phosgene,
can, like benzaldehyde, be condensed with dimethylaniline in the
presence of phosphorus oxychloride. In this case, however, it is not a
methane derivative, a leuco-compound, which is obtained, but, as the
equation shows, the carbinol stage is at once reached. As will soon be
shown, however, this stage in acid solution is equivalent to the formation
of the dye.
[(H3C)2N.C6H4]2C:O +
—• [(CH3)2N.C6H4]2C(OH)_