of toluene is attached to the funnel, and a new charge of 150 g.
of crude methyl red is placed in the paper. When extraction
is complete it is found that a certain amount of black amorphous
insoluble matter remains on the filter; this is discarded.
The crystals of methyl red are filtered off and washed with a
little toluene. The weight of pure material is 755-805 g.
The mother liquors are concentrated to one-fourth of their volume,
and the crystals which separate on cooling are recrystallized
from fresh toluene. The recovered toluene can, of course,
be employed again. The total yield of pure methyl red is 790--840 g.
It melts at 181-182'0.

The watery mother liquors from the crude methyl red are rendered
alkaline with sodium hydroxide and distilled until no more
dimethylaniline passes over. In this way 250 to 400 g.
of moist dimethylaniline are recovered.


2. Notes

The amount of hydrochloric acid indicated must not be reduced;
otherwise, diazoamino compounds are formed.

It is essential to keep the temperature low while unreacted diazobenzoic
acid remains in solution, in order to avoid decomposition.
If this precaution is not taken, the yields are considerably diminished,
through the formation of tarry by-products.

The use of a capillary tube for the addition of sodium nitrite
prevents loss of nitrous acid by local reaction at the surface