Nevile and Winther (loc. cit.), stated that they obtained a diazo
compound from their ortho toluidine sulphonic acid and described a few
properties, but gave no details of manipulation, so I made several
trials to determine the best acceptable method.
Experiment 1.
I suspended some ortho toluidine sulphonic acid in denatured alcohol,
and passed in a rapid current of nitrous fumes, generated by dropping
concentrated nitric acid into a saturated solution of sodium nitrite,
for fifteen minutes. The suspension became slightly warm, and rather
pasty at the end. I allowed it to stand a half hour, and at the end of
that time it had become very thick and pasty. I then filtered it off by
suction, washed with ether, and dried.
Experiment 2.
The procedure used was the same as above using ethyl alcohol in place
of denatured alcohol, but for some reason no diazotization appeared to
take place. The acid was filtered off and used again.
Experiment 3.
A saturated water solution of the acid was made by boiling some of
it up with water, cooling and filtering. No precipitate appeared on
passing in nitrous fumes.
Experiment 4.
Some of the acid was dissolved in sodium carbonate solution, sodium
nitrite solution added, and after cooling, concentrated hydrochloric
acid added drop by drop. Nitrous fumes were given off, but no
precipitate appeared.
Experiment 5.
This seems to be the best method and the one employed hereafter in the
preparation of all the material subsequently used. The solid ortho
toluidine sulphonic acid is suspended in concentrated hydrochloric
acid and vigorously stirred. The solution becomes warm and the
crystals change in appearance, probably due to the formation of the
hydrochloride. The mass is then cooled to 5°, and sodium nitrite
solution added slowly with stirring. Immediate reaction takes place,
and the mass becomes very pasty as in the first experiment. After
obtaining a reaction with starch iodide paper the mixture was allowed
to stand a half hour, then filtered by suction, washed with ether and
dried. In appearance it was identical with the diazo compound obtained
in experiment 1, and can be kept in the same way.
That it was a diazo compound was shown as follows: It was spotted on
a piece of filter paper with an alkaline solution of H acid--a red
coloration indicates the formation of a red azo dyestuff.
Some of the diazo compound was boiled with dilute nitric acid as
described by Nevile and Winther, and a yellowish precipitate of needles
obtained, which on recrystallization from denatured alcohol gave
light yellow needles of dinitro ortho cresol, (3-hydroxy 3,5-dinitro
toluene), melting at 83.5-84° uncorr. (Nevile and Winther gave 85°
for the pure substance.) This dinitro compound was obtained in nearly
quantitative yield indicating that the diazo compound was presumably
pure.