The insoluble dark impurity present in small amounts is filtered off,
and the filtrate is transferred to a 10-l. crock and chilled
with stirring. It is then mixed with a mush of 2.5 kg.
of ice and 750 cc. of concentrated hydrochloric acid. The crock
is cooled externally with ice, and the contents stirred continuously.
When the temperature reaches about 3'0, a filtered solution of 360 g.
of sodium nitrite in 700 cc. of water is dropped in slowly,
through a long capillary tube reaching below the surface
of the liquid, until a faint but permanent reaction to starch
potassium iodide paper is obtained; the temperature is kept
between 3'0 and 5'0. This operation requires all but about 30 cc.
of the nitrite solution and occupies one and a half to two hours.
To the solution of the diazonium salt are now added 848 g.
of dimethylaniline; this may be done rapidly, as the temperature
does not rise appreciably. Stirring is continued for one hour,
the temperature being kept at 5'0 Five hundred cc. of a filtered
solution of 680 g. of crystallized sodium acetate diluted to 1200 cc.
are then added, and the stirring continued for four hours.
If a foamy solid rises to the surface during this time and refuses
to become incorporated by the stirrer, a few drops of ethyl acetate may
be added to reduce the foam. The mixture is allowed to stand overnight
in an ice bath which is well insulated by several thicknesses of burlap;
the temperature must be kept below 7'0 to get a good yield of product.
The remainder of the sodium acetate solution is then added
with stirring, and after the mixture has been stirred for an
additional period of one to three hours, the temperature is allowed
to rise slowly to 20-25'0 in the course of twenty-four hours.
Just enough sodium hydroxide solution is then added, with stirring,
to cause the mixture to have a distinct odor of dimethylaniline
(about 240 cc. of a 40 per cent solution are generally required),