Manufacture of Purpurine-sulpho Acid and Purpurine.
Year: 1895

page_text: Date of Application, 21st June, 1895
Complete Specification Left, 21st Mar., 1896-Accepted, 25th Apr., 1898
AND DRUNING, of Hoechst aДMain, in the Empire of Germany, Chemical
Manufacturers.]
Manufacture of Purpurine-sulpho Acid and Purpurine.
I, OLIVER IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Chartered Patent Agent, do hereby declare the nature of this
invention to be as follows:-
The property of alizarine of being converted into purpurine or derivatives of
purpurine under the oxidizing influence of nitric acid, has long been known. Thus
Strecker (Zeitschr. f. Chemie IV. 204) produced a nitro-oxyalizarine by reaction
of pure concentrated nitric acid upon alizarine, with previous formation of an
unstable intermediate product, which nitro-oxyalizarine proved to be nitro-
purpurine.
Early observations have also been made of the formation of small quantities of
purpurine in the nitration of alizarine, whether in a solution of sulphuric
acid 66° Bé., or in fuming sulphuric acid.
But in both cases the oxidation process takes place by no means smoothly.
Essentially different from alizarine is the behaviour in this respect of alizarine-
sulpho acid, obtained by sulphonation of alizarine with fuming sulphuric acid.
If this be dissolved in sulphuric acid and treated with nitric acid, with the
observance of certain precautions, it is converted smoothly into purpurine-sulpho
acid. It is of course not necessary to isolate the alizarine sulpho acid as such; the
colution of the alizarine sulpho acid in fuming sulphuric acid or concentrated
sulphuric acid obtained by the sulphonation of the alizarine is treated directly with
nitric acid.
The latter can be used either in the form of nitration acid or in the form of
nitrate salts suitable for the production of nitric acid.
The process for the production of purpurine sulpho acid is therefore of a very
simple nature; the following may serve as an example of the manufacture.
50 parts by weight of alizarine are sulphonated with 200 to 300 parts by weight of
fuming sulphuric acid of 10 to 20 p.c. anhydride at 120 to 150° C. until it is soluble
in water.
After dilution with some quantity of sulphuric acid 66° Bé. there are added
slowly to the sulphonation mass, under effective cooling, from 1 to 1 molecules of
nitric acid, either in the form of nitration acid or in the form of a nitrate salt,
taking care that the temperature does not rise much above 10° C.
After the introduction of the nitric acid, the reaction is allowed to take its
course at ordinary temperature, during about to 1 day, under effectual stirring,
and if necessary the mass is heated at the termination for a short time on the.
water bath.
For isolating the purpurine sulpho acid it can be separated as a potassium salt of
difficult solubility from the reaction liquid when diluted with water and boiled
either by salting with common salt or preferably by means of potassium chloride,
in the form of a potassium salt of difficult solubility.
The potassium salt of purpurine-sulpho acid forms small red crystals, which are

page_text: soluble with difficulty in cold water, more readily in hot water, with a reddish-
yellow colour. In dilute alkali the product is soluble with a pure red colour, and
it differs in this essentially from the alizarine sulpho acid which dissolves in alkali
with a blue-red colour.
An excess of alkali precipitates the purpurine sulpho-acid very readily as an
alkali salt, soluble with difficulty.
By heating with concentrated sulphuric acid or dilute mineral acids under
pressure, the purpurine-sulpho acid readily splits off the sulpho-group, and gives
pure purpurine.
In its application as a dye, the purpurine-sulpho acid differs essentially from the
alizarine sulpho acid. On alumina mordant, it dyes a fiery red, which has a much
bluer tinge than the dye obtained with alizarine sulpho acid.
Dated this 21st day of June 1895.
ABEL & IMRAY,
Agents for the Applicant.
Manufacture of Purpurine-sulpho Acid and Purpurine.
I, OLIVER IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Chartered Patent Agent, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
The property of alizarine of being converted into purpurine or derivatives of
purpurine under the oxidizing influence of nitric acid, has long been known.
Thus Strecker (Zeitschr. f. Chemie. IV 264) produced a nitro oxyalizarine by
reaction of pure concentrated nitric acid upon alizarine, with previous formation
of an unstable intermediate product which nitro-oxyalizarine proved to be nitro-
purpurine.
Early observations have also been made of the formation of small quantities
of purpurine in the nitration of alizarine, whether in a solution of sulphuric
acid 66° Bé. or in fuming sulphuric acid.
But in both cases the oxidation process takes place by no means smoothly.
Essentially different from alizarine is the behaviour in this respect of alizarine-
sulpho acid, obtained by sulphonation of alizarine with fuming sulphuric acid.
If this be dissolved in sulphuric acid and treated with nitric acid, with the
observance of certain precautions, it is converted smoothly into purpurine sulpho
acid. It is of course not necessary to isolate the alizarine sulpho acid as such; the
solution of the alizarine sulpho acid in fuming sulphuric acid or concentrated
sulphuric acid obtained by the sulphonation of the alizarine is treated directly with
nitric acid. The latter can be used either in the form of nitration acid or in the
form of nitrate salts suitable for the production of nitric acid.
The process for the production of purpurine sulpho acid is therefore of a very
simple nature; the following may serve as an example of the manufacture.
50 parts by weight of alizarine are sulphonated with 200 to 300 parts by weight of
fuming sulphuric acid of 10 to 20 p.c. anhydride at 120 to 150° C. until it is soluble
in water.
After dilution with some quantity of sulphuric acid 66° Bé. there are added
slowly to the sulphonation mass, under effective cooling from to molecules of
nitric acid, either in the form of nitration acid or in the form of a nitrate salt,
taking care that the temperature does not rise much above 10° C.
After the introduction of the nitric acid the reaction is allowed to take its course,
at ordinary temperature during about to 1 day, under effectual stirring, and

page_text: if necessary the mass is heated at the termination for a short time on the water
bath.
For isolating the purpurine sulpho acid it can be separated as a salt of difficult
solubility from the reaction liquid when diluted with water and boiled, either by
salting with common salt, or preferably by means of potassium chloride, in the
form of a potassium salt of difficult solubility.
The potassium salt of purpurine sulpho acid forms small red crystals, which are
soluble with difficulty in cold water, more readily in hot water, with a reddish
yellow colour. In dilute alkali the product is soluble with a pure red colour, and
it differs in this essentially from the alizarine sulpho acid which dissolves in alkali
with a blue red colour.
An excess of alkali precipitates the purpurine sulpho acid very readily as an
alkali salt, soluble with difficulty.
By heating with concentrated sulphuric acid or dilute mineral acids under
pressure, the purpurine sulpho acid readily splits off the sulpho group, and gives
pure purpurine.
In its application as a dye, the purpurine sulpho acid differs essentially from the
alizarine sulpho acid. On alumina mordant, it dyes a fiery red, which has a much
bluer tinge than the dye obtained with alizarine sulpho acid.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. Manufacture of purpurine sulpho acid by treating the solution of alizarine-
sulpho-acid in concentrated or weak fuming sulphuric acid with nitric acid or
suitable nitrates substantially as described.
2. The production of purpurine from the purpurine sulpho acid, referred to in
the preceding claim, by heating the same under pressure together with concentrated
sulphuric acid, or dilute mineral acids, substantially as described.
Dated this 21st day of March 1896.
ABEL & IMRAY,
Agents for the Applicant.