Year: 1899

page_text: I, OLIVER IMRAY, of Birkbeck Bank Chambers, Southampton Buildings, in the
County of London, Chartered Patent Agent, do hereby declare the nature of this
invention (as communicated to me from abroad by The Farbwerke vormals: Meister
Lucius Brüning, of Hoechst a/Main, in the Empire of Germany, Chemical Manufac
turers) to be as follows:-
The alkylation of dialkyrhodamines was first described in the German Patent
No. 48731 as being effected by heating dialkylrhodamines with alkyl halides and
thus for instance from diethylrhodamine and ethyl chloride is obtained the dyestuff
known as "Rhodamine 6 G." The description of the alkylation in said patent,
according to which tetraalkylrhodamines are obtained by heating dialkylrhodamines
with an alkyl halide, that is to say, an N-alkylation, has since proved to be erroneous,
it having been shewn in the German Patents No. 71490 and No. 73573 that the
rhodamines may be transformed into esters when treated with alcohols and mineral
acids, the usual means for esterification applied to carboxylic acids; for, on alkylating
dialkylrhodamines with alkylhalogenides as described in the German Patent No. 48731,
not the higher alkylated rhodamines alkylated at N but those alkylated at the
carboxylic group are obtained. The German Patent No. 73880 claims a specially
advantageous method of alkylation with an alkyl halide.
The present invention is based on the observation, that the alkylester of alkyl-
sulphuric acid, for instance, the methylester of methylsulphuric acid (dimethyl-
sulphate), act similarly to alkyl halides, in an alkylating manner upon dialkylrhoda-
mine bases and that in this case, just as with alkylhalide, no N-alkylation takes place,
but a carboxyl alkylation or esterification. This result is surprising in as much as
the alkylesters of alkylsulphuric acids readily act N-alkylating, without diluent and
mostly in an explosive-like manner, upon aromatic primary, secondary or tertiary
bases and the formation of tri- or tetraalkylrhodamines was to be expected and not
that of dialkylrhodaminealkylesters, all the more so, as an esterifying action of the
alkylesters of alkylsulphuric acids upon amido-carboxylic acids or their salts has not
hitherto been known and was still less to be foreseen in the case of dialkylrhodamines
as these alkylsulphuricalkylesters do not act upon the free carboxylic acids contain-
ing no basic groups or only at a very high temperature, with partial decomposition,
and upon carboxylic acids with basic properties, such as anthranilic acid, essentially
in an N-alkylating and not esterifying manner,

page_text: The action of alkylsulphuric acid alkylesters upon dialkylrhodaminebase takes place
for instance according to the formula;
The reaction takes place only with rhodamine base, and not with rhodamine salts ;
it differs thus chiefly from that which serves as base in the German Patents
No. 71490 and No. 73573 (alcohol & sulphuric acid or alcohol & alkylsulphuric acid)
and which can be carried out only with rhodamine salts and not with a rhodamine
base.
The process is as follows:-The finely pulverized dry dialkylrhodamine base and
the alkylsulphuric alkylester, for instance, dimethylsulphate, in molecular propor-
tion or with an excess of the latter, are thoroughly mixed, preferably with an
addition of some dry sodium carbonate, the mixture is then allowed to stand for some
time at indoor-temperature or heated for some time.
This new method offers by means of this easily obtained dimethylsulphate an
advantage over the alkylhalide process, as it can be carried out without solvent at a
low temperature and without pressure.
EXAMPLE I.
A thorough mixture of 40 parts by weight of diethylrhodamine base, 5 parts by
weight of solid sodium carbonate and about 20 parts by weight of dimethylsulphate
is allowed to stand for about 48 hours at indoor-temperature. The mass on becom-
ing solid is pulverized and stirred into water containing some hydrochloric acid. On
addition of some common salt, the hydrochloride completely separated and filtered
is dissolved in water; to this solution is added some sodium acetate so as to separate

page_text: small quantities of possibly unchanged dialkylrhodainine base and the dyestuff is
precipitated with hydrochloric acid and common salt.
EXAMPLE 11.
40 parts by weight of diethylrhodamine base and 20 parts by weight of dimethyl-
sulphate are heated for some hours to about 60° C. and the product of reaction is
washed as in Example 1 or directly employed as dyestuff.
ABEL & IMRAY,
Agents for the Applicant,
COMPLETE SPECIFICATION.
Process for Alkylating Dialkylrhodamines.
I, OLIVER IMRAY, of Birkbeck Bank Chambers, Southampton Buildings, in the
County of London, Chartered Patent Agent, do hereby declare the nature of this
invention (as communicated to me from abroad by The Farbwerke vormals:
Meister Lucius and Brüning, of Hoechst a/Main, in the Empire of Germany,
Chemical Manufacturers), and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement:-
The alkylation of dialkylrhodamines was first described in the German Patent
No. 48731 as being effected by heating dialkylrhodamines with alkyl halides and
thus for instance from diethylrhodamine and ethyl chloride is obtained the dyestuff
known as "Rhodamine 6G." The description of the alkylation in said patent,
according to which tetraalkyl rhodamines are obtained by heating dialkylrhodamines
with an alkyl halide, that is to say, an N-alkylation, has since proved to be erroneous,
it having been shewn in the German Patents No. 71490 and No. 73573 that the
rhodamines may be transformed into esters when treated with alcohols and mineral
acids, the usual means for esterification applied to carboxylic acids; for, on alkylating
dialkylrhodamines with alkyl halides as described in the German Patent No. 48731,
not the higher alkylated rhodamines alkylated at N but those alkylated at the
carboxylic group are obtained. The German Patent No. 73880 claims a specially
advantageous method of alkylation with an alkyl halide.
The present invention is based on the observation, that the alkylester of
alkylsulphuric acid, for instance, the methylester of methylsulphuric acid
(dimethylsulphate), act similarly to alkyl halides, in an alkylating manner upon
dialkylrhodamine bases and that in this case, just as with alkyl-halide, no
N-alkylation takes place, but a carboxylic alkylation or esterification. This result is
surprising in as much as the alkylesters of alkylsulphuric acids readily act
N-alkylating, without diluent and mostly in an explosive-like manner, upon aromatic
primary, secondary or tertiary bases and the formation of tri- or tetra- alkylrho-
damines was to be expected and not that of dialkylrhodamine alkylesters. This is
the more so as an esterifying action of the alkylesters of alkylsulphuric acids upon
amido-carboxylic acids or other salts has not hitherto been known and was still less
to be foreseen in the case of dialkylrhodamines, since these alkylsulphuricalkylesters
do not act upon the free carboxylic acids containing no basic groups or so act only
at a very high temperature, with partial decomposition, and act upon carboxylic acids
with basic properties, such as anthranilic acid, essentially in an N-alkylating and not.
esterifying manner,

page_text: The action of alkylsulphuric acid alkylesters upon dialkylrhodaminehase takes
place for instance according to the equation;

page_text: separate small quantities of possibly unchanged dialkylrhodamine base and the
dyestuff is precipitated with hydrochloric acid and common salt.
EXAMPLE II.
40 parts by weight of diethylrhodamine base and 20 parts by weight of dime-
thylsulphate are heated for some hours to about 60° C, and the product of reaction
is washed as in Example I or directly employed as dyestuff.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed, I declare that what I
claim is :-
The herein described process for alkylating dialkylrhodamines by acting on
dialkylrhodamine base with an alkylester of an alkylsulphuric acid, with or without
addition of alkali.
ABEL & IMRAY,
Agents for the Applicant.