306 
its peculiarities is that when heated it is converted into violet 
methyl-rosaniline, with loss of methyl-chloride. 
A new method of producing rosaniline violet was proposed 
by Lauth, and patented by MM. Porrier and Chappat, in June, 
1866. The process consisted in taking aniline, in which hydro- 
gen had been replaced by an alcohol radical, and oxidising this 
instead of first preparing rosaniline, and then replacing the 
hydrogen in the colouring matter by the radical. The product 
proposed for this purpose was methyl-aniline. 
Owing to the improved method of methylating aniline, which, 
I believe, was first proposed by Messrs, Gerard and Delaire 
(Bull. Chem. Soc. [2] vii. 360), this process has become a very 
important one, and large quantities of dimethyl-aniline are now 
used, the oxidation being effected by copper salts. The product, 
according to the reseaches of Otto Fischer, consists chiefly of 
pentamethylpararosaniline. 
The most important advance in the production of green 
colouring matters of the triphenyl-methane series was the 
discovery of the benzaldehyde, Victoria or malachite green. 
In 1877, Otto Fischer, whilst investigating the condensation 
products of tertiary aromatic bases (Ber. xz, 1625), obtained 
by the action of benzaldehyde on dimethyl-aniline in presence 
of chloride of zinc, a colourless base of the formula C,,;H,,N,, 
the salts of which, when exposed to the air, rapidly oxidised to 
a fair blue-green dyestuff, which, he thought, would prove to be 
of complicated constitution. A little later (Ber. xi,, 950) he 
_ showed that by oxidising this colourless base with some of the 
ordinary oxidising agents, this green could be more easily produced, 
and that it stood to the colourless compound in the same way as 
rosaniline does to leucaniline. Emil and Otto Fischer after- 
wards say (Ber. xii. 796) that the first experiments for the 
production of this green were made by the Badische Aniline 
und Soda Fabrik, in March, 1878. About this time Oscar 
Doebner (Zev. xi. 950) found that a green colouring matter was 
produced by heating benzaldehyde with benzyl trichloride and 
zinc chloride. This product has been found to be identical with 
that of Fischer’s. This green colouring matter is now largely 
made from benzaldehyde, as this process is found to be the best. 
A similar compound is also~ prepared from diethyl-aniline, and 
is known as brilliant green. It is a beautifully crystalline body. 
It is rather curious that this produces shades of colour some- 
what yellower than the green fram dimethyl-aniline, whereas, 
being of a higher molecular weight, we should have expected 
it to be blue. 
The principal difficulty which had to be contended with in 
the production of these colouring matters was the need of a 
supply of benzaldehyde The usual method of obtaining it 
from bitter almonds, which was the only one in use, was quite 
out of the question, so that other sources had to be looked for. 
The Badisches Aniline und Soda Fabrik, however, successfully 
overcame this difficulty. At first they experimented with the 
process of Lauth and Grimaux, which consists in the oxidation 
of benzyl-chloride, with an aqueous solution of lead nitrate ; 
but the product made by this process was too dear. But they 
found that the decomposition of benzylidene-dichloride, by 
means of water, as observed by Cahours (Aum. Chem. Suppl. 
2306) and Limprecht (Azz. Chem. 139, 316) gave them a means 
of producing this compound successfully, the reaction being as 
follows :— 
C,H;CHCl,+ OH,=C,H;.CHO+ 2HCl. 
This process, which they have successfully employed since 
March, 1878, consists in the preparation of benzylidenedichloride 
from pure toluene, and in the subsequent treatment of this 
chlorinated body with milk of lime, at 100° C. 
I have stated that the group of colouring matters under con- 
sideration are called triphenylmethane derivatives, and to show 
how this has been proved to be the case, I must now refer very 
briefly to some of the theoretical work which has led to this 
knowledge. The most important of this refers to rosaniline. I 
have already drawn attention to the work of Hofmann, which 
gave us the first knowledge of the composition of this colouring 
matter, and the further information that it contained hydrogen, 
which could be displaced by phenyl and alcohol radicals ; but as 
to the matter of constitution, I think the experiments of Caro 
and Wanklyn were the first, as they showed the relation which 
existed between rosaniline and aurine, or rosolic acid, and, in 
fact, produced rosolic acid from rosaniline; but it is to the 
beautiful researches of Emil and Otto Fischer that we are in- 
debted for a clear knowledge of the constitution of this class of 
colouring matter. 
NA TGR 
[Fly 30, 1885 
But to clear the ground before proceeding further, I must re- 
mind you that ordinary commercial rosaniline, or magenta, pre- 
pared from aniline and toluidines, is a mixture of colouring 
matters. This was first known by Mr. Nicholson, who found 
that for the production of the finest blues it was necessary to 
purify the base and separate one of these before phenylating ; 
but it is only of later years that the difference between these 
bodies has been carefully studied and explained. The base 
examined by Hofmann contained C,,, and is the chief constituent 
of commercial rosaniline. The other contains Cy9, and is now 
called pararosaniline, because it is produced from aniline and 
paratoluidine. Similarly, in commercial aurine, two compounds 
are found, one containing C.9, now called rosolic acid, and one 
containing C,9, now called aurine ; and these latter can be pro- 
duced from the corresponding rosanilines ; and Dale and Schor- 
lemmer have also shown that aurine can be also converted into 
pararosaniline, by the action of ammonia (¥. Chem. Soc., 
XXxil, 121). 
Emil and Otto Fischer, however, by submitting the leuco 
compound of commercial rosaniline to the diazo reaction, ob- 
tained the hydrocarbon C,,H,,, and from rosaniline prepared 
from paratoluidine and aniline, the hydrocarbon Cy Hj,. 
And this latter hydrocarbon was found to be identical with 
Kekule’s triphenylinethane— 
C,H.“ \H 
: Shaphenyimethane: 
On nitrating this hydrocarbon they obtained a trinitro deriy- 
ative, which, when reduced, gave the tri-amido body, 
NH,C,H C,H,NH, 
6 ek 4 
NH,C,H, H 
Leucaniline, 
which is paraleucaniline, and by carefully heating its hydro- 
chloride to 150-160", it was converted into pararosaniline. 
Also they found that by oxidising trinitrotriphenylmethane 
they obtained trinitrotriphenylcarbinol, and this when reduced 
gaye pararosaniline direct. 
From these results the constitution of the base is evidently — 
NH,C,H, C,H,NH, 
De 
NH,C,Hy OH 
Pararosaniline. 
The salts— the hydrochloride, for example—being 
NHCeHa / CsH,NH.HCl1 
Cc 
NH,C,H,7 
Pararosanilinehydrochloride. 
Similar results were obtained from the hydrocarbon from 
rosaniline ; it is tolyldiphenylmethane :-— 
CoHy(CHs)\ 64 CoHs 
Ne 
C,H; 
The rosolic acid and aurine corresponding to the rosanilines 
are constituted in an analogous manner :— 
HOCH 7 CgH,O HO CoH / CgHsO 
we | and CH, 1G: | 
HOC,Hy, HOC,Hy 
Aurin. Rosolic Acid. 
From these results we see the beautiful relationships of the 
yarious colouring matters of this series to each other, and by it 
obtain information which is of practical value, as well as theo- 
retical, From the following formulz of a few of these products. 
their relationships are seen :— 
H H 
Marsh gas yeC 
H H 
CoHs. Jos 
Triphenylmethane Pic 
6<46 
NH,C,H C,H,NH, 
6 NGS 
NH,C,H,” “HL es 
NH,Cyl C,H,NH, 
6 Nef 4 2 
NH,C,H,” OH 
Leucopararosaniline 
Pararosaniline 
