Of the possible sulphonic acids of ortho toluidine the commercial
product of former days was the one in which the sulphonic acid group
was in the para position to the amino group, and meta to the methyl
group; thus this acid could find use in preparing the toluene meta
sulphonic acid if a method of replacing the amino group by hydrogen
could be found. This acid is not now on the market in America because
of its limited use in dyestuffs. It is mentioned in Schultz and Julius,
(“Farbestoff Tabellen”, 1894 Edition, Trans. by F. C. Green), Cain,
(“The Manufacture of Intermediate Products for Dyes”) and Nevile and
Winther, (Ber. d. chem. Ges. 13, 1940.), which latter give a method of
preparation which was used industrially,--the baking of ortho toluidine
sulphate. Their description is rather indefinite but after a few
preliminary trials a suitable method was found. I will describe all the
experiments attempted, and include the one finally adopted. The ortho
toluidine used was (“Practical.”) obtained from Eastman Kodak Co.
Experiment 1.
Ortho toluidine was suspended in water and conc. sulphuric acid added
with vigorous stirring until all the amine had dissolved. The solution
was heated to boiling until the sulphate had dissolved, and then cooled
and the crystals thus obtained filtered off and dried. This was then
powdered and ground with some powdered oxalic acid. These mixtures with
and without oxalic acid were then baked until a sample was completely
soluble in sodium hydroxide. The mass had become a deep grayish
purple. It dissolved in water to give a deep red solution. Nothing
satisfactory was obtained from any of these bakes, the formation of a
red dyestuff as mentioned by Nevile and Winther seeming to be formed in
a great quantity and very easily. Hence this method was discarded.
Experiment 2.
In this case an excess of sulphuric acid was used. After the oxalic
acid had all been decomposed or driven off the mass turned black and
became very pitchy. Nothing could be done with it so it was thrown away.
Experiment 3.
In this case an excess of ortho toluidine was used. The red dyestuff
was formed in great amount and very easily. The temperature was kept
below 195 to lose none of the toluidine which boiled at 199.
Experiment 4.
This method gave the best results and is the one employed in the
preparation of all the material used in the thesis. Equal weights of
ortho toluidine and sulphuric acid (100gms. of each were used; 100gms.
of ortho toluidine is 108cc., and 100gms. of sulphuric acid (s. g.
1.84) are 56cc.), were mixed and baked at 190-195 until a sample would
dissolve in ten per cent sodium hydroxide solution to give a clear
solution; this took one and a half hours. The mixture at first melts
in the solution of the sulphate and sulphuric acid formed by the heat
of combination; as heating is continued it gradually becomes solid and
finally very hard; it has become gray in color. When it is perfectly
dry a test is made to see if it dissolves in sodium hydroxide giving a
clear solution. If so, sulphonation is complete. By using an oven with
a glass door the reaction mixture can be watched and the completion of
the baking observed. However the test for complete solubility should
always be made. The addition of powdered oxalic acid to the reaction
mixture did not seem to be of advantage, because no visible reaction
commenced until this had been driven off or decomposed. It is usually
added in producing sulphonic acids by baking the sulphates of the
amines to increase the porosity of the mass and thus facilitate removal
of the product. However here the only effect seemed to be to retard
the reaction, as the product was the sane hard grayish mass as without
the acid, and it was just as difficult to dig it out. It took an hour
longer to complete the reaction with the addition of the oxalic acid.
The best results were obtained when the temperature of the oven was
kept at 193, although five degrees variation did not appreciably affect
the product. A lower temperature gives little or no action, while a
higher one drives off the ortho toluidine and also seems to favor the
formation of the red dyestuff.
As stated above, complete sulphonation is shown by the solubility of
the acid in ten per cent sodium hydroxide solution. If any unchanged
amine is present as sulphate the solution will become milky due to
liberation of the insoluble amine. On boiling a solution of the acid a
slight hydrolysis takes place so that the smell of ortho toluidine is
present, yet the solution is always perfectly clear.
The product or “bake” appears as a hard grayish mass, slightly porous.
It is dug out, pulverized, boiled up in a large evaporating dish,
containing water and a little (10cc.) hydrochloric acid, with animal
charcoal and filtered. The solution should be almost colorless. The
effect of the slight amount of hydrochloric acid was accidental; the
first solutions were always a deep red color due to some of the red
dyestuff seeming to be present, and the longer the solution was boiled
the redder it got. A little acid seems to prevent this entirely. The
solution is evaporated on a water bath until a scum has formed on the
surface when it is allowed to cool and crystallize. It crystallizes in
small almost white needles, which appear to fill the entire liquid;
this is deceptive as on filtering the bulk is considerably reduced.
They fall to a powder when they are dry. If they are colored red or
pink they are washed while still on the filter with water; alcohol does
not remove this color.
The acid as formed has no melting point, but chars and decomposes on
heating. A sample was tested for nitrogen and sulphur with very good
positive results. On fusion with caustic soda and acidification of the
product a positive reaction was obtained on the addition of bromine
water as is customary with phenols.
It was identified as identical with the acid of Nevile and Winther
(loc. cit.) by conversion thru the diazo compound into dinitro ortho
cresol, melting at 85.8 as described under the description of the diazo
compound.