The Manufacture of New Dyes of the Rhodamine Series and Intermediate Products and Leuco-compounds related thereto.
Year: 1894

page_text: Date of Application, 20th Aug., 1894
Complete Specification Left, 13th May, 1895-Accepted, 15th June, 1895
PROVISIONAL SPECIFICATION.
The Manufacture of New Dyes of the Rhodamine Series and
Intermediate Products and Leuco-compounds related thereto.
I, JAMES YATE JOHNSON of 47 Lincoln's Inn Fields in the County of
London Gentleman do hereby declare the nature of this invention (which has
been communicated to me from abroad by The Badische Anilin and Soda Fabrik
of Ludwigshafen on Rhine in the Empire of Germany) to be as follows:-
If chloral hydrate and a dialkyl-meta-amidophenol be caused to react upon one
another, energetic chemical action ensues which is very liable to result in the
formation of a complex and valueless mixture of blue, violet and red colouring
matters and leuco compounds thereof difficult to isolate and purify. Under some
conditions pitch-like bodies which are similarly valueless are obtained. My foreign
correspondents have discovered that if the conditions be suitably chosen and
regulated a series of four reactions take place one after the other which constitute
a new and valuable process resulting finally in the formation of red rhodamine dyes
in uniform condition unmixed with other products.
The following are the reactions or stages of the process :-
(1.) Equi-molecular proportions of the dialkyl-meta-amidophenol chosen and of
chloral hydrate combine with one another on admixture without the application of
beat. One molecular proportion is split off. The product is, in each case, a
colourless base which is insoluble in water, slightly soluble in benzene but readily
soluble in alcohol, acetone and chloroform, and easily obtainable as crystals from
these solvents.
(2.) One molecular proportion of the intermediate product so obtained is heated
under suitable conditions as hereinafter set forth with one molecular proportion of
a dialkyl-meta-amido-phenol. A. dialkyl-meta-amido-phenol the same as that taken
in the first stage or a different one may be used. In the first case symmetrical
rhodamines are eventually obtained, but if a different dialkyl-meta-amido phenol
be used then asymmetrical rhodamines result of a new class not practically obtain-
able prior to this invention. If it be desired to produce symmetrical rhodamine
the first two stages of the reaction can readily be effected together (see Example 1
hereinafter given). The product of this phase of the process is in each case, a
leuco base or a salt thereof, which readily oxidizes to a blue colouring matter.
(3.) The leuco-bases are oxidized to new blue or greenish blue colouring matters.
This oxidation will take place if the free base be exposed to the action of the
air, especially if the atmosphere be rendered ammoniacal. But the blue colouring
matters are preferably obtained by treating solutions of their salts with an oxidizing
agent such for example as ferric chloride, chromic acid, peroxides, iodine and
the like.
(4.) If an aqueous solution of one of the blue-colouring-matters be left to itself
it changes slowly in the cold but rapidly on heating, into the desired red rhodamine
dyes. This and the preceding stage can, if desired be united into one by effecting
the oxydation at a suitably elevated temperature.

page_text: The following examples will serve to further illustrate the nature of the invention,
but I do not limit myself to the precise details therein given. The parts are by
weight.
EXAMPLE 1. PRODUCTION OF A SYMMETRICALLY CONSTITUTED RED
RHODAMINE DYE.
Grind together about one part of powdered chloral hydrate and three parts of
powdered diethyl-meta-amido-phenol. The mixture shortly assumes a slight blue
violet colour, cakes together and tends to become liquid. Finally it solidifies to a
nearly colourless mass. Allow this to stand for about an hour. The first stage is
now ended and this mass consists of the new intermediate product hereinbefore
described with the excess of unchanged diethyl-meta-amido phenol. Without any
isolation of these bodies reduce to powder, aud spread the material out in a thin
layer on plates or dishes and heat in a drying-chamber or similar apparatus raising
the temperature very slowly during about twelve hours from forty to finally seventy
degrees Centigrade. During this heating the mixture melts together usually
assuming a bluish-violet colour, but finally solidifies and at the surface acquires a
blue or greenish blue colour. This product of the second stage, which is brittle
aud glassy, contains the new leuco-base of the blue colouring matter.
product to a fine powder and suspend it in fifty times its weight of water.
leuco-base separates out as white flocks which soon assume a bluish colour.
Dissolve this by carefully adding dilute acid. Thoroughly stir the solution and
run in a dilute solution of ferric chloride (containing say about five per cent. Fe,Cl).
The mixture becomes intensely green-blue. The third stage of the process-that
is the oxidation of the leuco base-is complete when no further formation of colour
takes place on the addition of a further quantity of ferric chloride. To determine
this point take test portions of the mixture from time to time and precipitate the
dye with common salt then add a drop of ferric chloride, it will then be easy to
see if further formation of colour occurs or if the operation is ended.
Reduce this
The
During this third stage of the operation it is desirable to protect the blue
colouring matter from the further action of the oxidising agent and also to prevent
its premature conversion into the red dye. For this purpose add a precipitant such
for example as common salt to the solution so as to precipitate the colour from the
solution as it is formed. It separates out in the form of a semi-liquid tarry mass
with a coppery lustre. Separate from the mother liquor by decanting.
If a nitrate be used as precipitant, and added to the solution at the beginning,
then the blue colouring-matter can be obtained in the form of green crystals with
a metallic lustre. It dyes tannin mordanted cotton in the cold giving blue shades
which soon turn reddish.
To convert this blue colouring matter into the desired symmetrical rhodamine
dissolve it completely in water, preferably as hydrochlorate and allow the solution
to stand for about twelve hours or until the change to red is complete. To ascertain
this add sodium acetate to a test portion and extract with ether. If no blue dve
can be extracted the change is complete. Precipitate the dye from its solution by
adding dilute nitric acid till the colour of the solution has changed from red to
bluish-violet. Green shining crystals separate out.
If it be desired to covert the blue dye in its less soluble form of nitrate into the
red dye, mix it with say one hundred times the weight of boiling water and continue
boiling till the desired change is complete, concentrate the solution and allow
to cool, some of the red dye will crystallize out, a further quantity can be obtained
by adding dilute nitric acid as herein before described.
The new red rhodamine dissolves in water and in alcohol and gives beautiful
bluish red solutions possessing a yellow fluorescence. It dyes wool giving bright
bluish-red shades resembling rhodamine. On cotton mordanted with tannin it
dyes violet-red.

page_text: EXAMPLE 2: THE MANUFACTURE OF AN UNSYMMETRICAL RHODAMINE
FROM DIMETHYL- AND DI-ETHYL-META-AMIDOPHENOL.
This dye is prepared either from the condensation product from chloral-hydrate
and dimethyl-meta-amidophenolby further treatment with diethyl-meta-amidophenol
or the condensation product from chloral-hydrate and diethyl-meta-amido-phenol
is further treated with dimethyl-meta-amidophenol. Thus for instance mix
together molecular proportions of chloral hydraté and dimethyl-meta-amidophenol;
grinding these bodies together. The mixture first liquefies and then becomes solid.
The reaction is usually ended in about half an hour: The grind in one molecular
proportion of diethyl-meta-amidophenol and continue the treatment as described' in
the foregoing Example 1 so as to produce the leuco-base, the blue colouring matter
and finally the red-rhodamine.
The condensations with chloral hydrate herein before described can also be
efferted by the use of chloral itself; chloral 'alcoholates or similar derivatives
of chloral:
In all the reactions the conditions" described can be varied to a certain extent,
thus in the first stage benzene, toluene, amyl alcohol and the like may be used as
diluents, or solvents, for the reagents, and also in the second stage the reaction can
be moderated by the suitable use of solvents or the addition of indifferent bodies,
such as common Salt, 'sodium sulphate; or acetate, or bodies which absorb hydro-
chloric acid, such as chalk; magnesia, zincoxide, and the like; or of mixtures of the
above named substances.
COMPLETE SPECIFICATION.
The Manufacture of New Dyes of the Rhodamine Series and
Intermediate Products and Leuco-compounds related thereto.
1.JAMES YATE JOHNSON of 47 Lincoln's Inn Fields, in the "County of
Middlesex Gentleman, do hereby declares the nature of this invention (which has
been-communicated to me from abfond-by The Badische Anilin-and Soda Fabrik
of Ludwigshafen-on-Rhine in the Empite of Germany) and in what manner the
same is to be performed to be particularly described and ascertained' in'anď bý the
following statement!
If 'chloral hydrate and a dialkyl-meta-amidophenol be caused to react upon one
another, energetic chemical action ensues which is very liable to result in the
formation of a complex and valueless mixture of blue, violet and red colouring
matters; and leuco-compounds thereof difficult to isolate and purify. My foreign
correspondents 'have discovered that if the conditions be suitably chosen and
regulated the reaction will proceed in four consecutive stages which jointly
constitute a new and valuable synthetical process available for the manufacture of
new red ŕbodamine dyes'in fimiform condition unmixed with other products.
The following are the reactions upon which the four consecutive stages of the
process are based
(1) Dialkyl-meta-amidophenol and chloral hydrate combine with one another
without tlle application of heat in equi-molecular proportions' and under elimination
of one molecular proportion of water. The condensation product is in this case a
colourless base which is insoluble in water, slightly soluble in benzene, but readily
soluble in alcohol, acetone, or chloroform and easily obtainable in a crystallized
condition from these solvents:

page_text: (2) One molecular proportion of the condensation product thus obtained, if
beated under suitable conditions as hereinafter set forth combines with another
molecular proportion of dialkyl-meta-amidophenol. The principal product of this
second stage of the process is a leuco-base or a salt thereof, which will readily
oxidize to a blue colouring matter capable of subsequent transformation into the
desired red rhodamine-dye. A dialkyl-meta-amidophenol of the same kind as that
employed in the first stage or a different one may be used. In the first case new
symmetrical rhodamines are eventually obtained, but if a different dialkyl-meta-
amidophenol be used then asymmetrical rhodamines result of. a new class not
practically obtainable prior to this invention. If it be desired to produce
symmetrical rhodamine the first two stages of the process can readily be joined
together (see Example 1 hereinafter given).
(3) In the third stage of the process the before, named leuco-compounds_are
oxidized to their corresponding blue or greenish-blue colouring-matters. This
oxidation will take place if the free leuco bases be exposed to the action of the air,
especially if the atmosphere be rendered ammoniacal. But the blue colouring-
matters are preferably obtained by treating solutions of the leuco-compounds in
their saline state with an oxidizing agent such for example as ferric chloride,
chromic acid, peroxides, iodine and the like.
(4) In aqueous solution the blue colouring-matter changes slowly in the cold,
but rapidly on heating, into the desired red rhodamine dye. This and the
preceding stage of the process can, if desired be united into one: by effecting the
oxydation of the leuco-compounds at a suitable elevated temperature, but the best
results are obtained by submitting the blue colouring matters of the third stage in
their pure and separated condition to their subsequent transformation into red
rhodamines by the above mentioned action of water.
The following examples will serve to further illustrate the nature of the
invention, and the manner in which it can be carried into practical effect, but I do
not limit myself to the precise details therein given. The parts are by weight.
EXAMPLE 1. PRODUCTION OF A SYMMETRICALLY CONSTITUTED RED
RHODAMINE DYE.
Grind together about one part of powdered chloral hydrate and, three parts of
powdered diethyl-meta-amido-phenol. The mixture shortly assumes a slight blue-
violet colour, cakes together and tends to become liquid. Finally it solidifies to a
Dearly colourless mass. Allow this mass to stand for about an hour. The first
stage of the process is now ended resulting in the production of the new
intermediate condensation-product, hereinbefore described, in admixture with the
excess of unchanged diethyl-meta-amido-phenol. Without separating these bodies
reduce the said product to powder and spread the material out in a thin layer on
plates or dishes or other suitable surfaces and heat in a drying chamber or similar
apparatus, raising the temperature very slowly during about twelve hours from
forty to finally seventy degrees Centigrade. During this heating the mixture
melts together usually assuming a blueish-violet colour, but gradually solidities
and, at the surface, acquires a blue or greenish blue colour. This product of the
second stage of the process is brittle and glassy, and contains, as the principal
constituent, the leuco-base of a blue colouring-matter. Reduce this product to a
fine powder and suspend it in fifty times its weight of water. The leuco-base
separates out as white flocks which soon assume a bluish colour. Dissolve
this by carefully adding dilute acid. Thoroughly stir the solution and
run in a dilute solution of ferric chloride (containing say about five per
cent. Fe,Cl). The mixture becomes intensely green-blue:-The third stage of
the process (that is the oxydation of the leuco-base) is complète when, on the
addition of a further quantity of ferric chloride no further formation of colour
takes place. To determine this point, take test portions of the mixture, from time.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
:―
1. The manufacture of new red dyes of the rhodamine series by means of the
process in four consecutive stages as hereinbefore set forth.
2. The manufacture of a colourless basic condensation product by combining
equi-molecular proportions of a dialkyl-meta-amido-phenol and chloral hydrate (or
chloral or its alcoholic compounds) substantially as hereinbefore described.
3. The manufacture of a hasic leuco-product by heating one molecular
proportion of a colourless basic condensation-product, such as can be obtained as
hereinbefore set forth and claimed in the second claiming clause, with one
molecular proportion of a dialkyl-meta-amido-phenol substantially as hereinbefore
described.
4. The manufacture of new blue or greenish-blue colouring-matters by exposing
a leuco-product, such as can be obtained as hereinbefore described and claimed in
the third claiming clause, to an oxidizing treatment substantially as hereinbefore
described.
5. The conversion of blue or greenish-blue colouring-matters, such as can be
obtained as herein before described and claimed in the fourth claiming clause, into
the red rhodamine-dyes by the action of water as hereinbefore described.
6. The manufacture of the new rhodamine-dyes, and of the intermediate
products, and colouring-matters by the combination of two, or more, of the
processes herein claimed in the second, third, fourth and fifth claiming clauses into
one continued operation.
7. The manufacture of the new rhodamine-dyes and of the intermediate
colouring-matters and products in the manners herein before described in the
examples.
8. As new products the rhodamine-dyes and the intermediate colouring-matters
and condensation products such as can be obtained substantially in the manners
herein before described and claimed.
Dated the 13th dor of Ma. 1905
JOHNSONS & WILLCOX,
Agents.