Process for the production of sulphoalkyl quaternary salts

Sulphoalkyl and sulphoalkenyl quaternary salts of heterocyclic nitrogen compounds are prepared by reacting heterocyclic compounds containing a tertiary ring nitrogen atom at an elevated temperature with an O-sulphoalkyl or O-sulphoalkenylisourea compound.

The present invention relates to a process for the production of 
sulphoalkyl quaternary salts of tertiary amines, especially of 
heterocyclic bases containing nitrogen. 
These kinds of quaternary salts, which contain positively charged groups 
and negatively charged groups inter-connected by covalent bonds, are also 
known as betaines. They play an important part in a number of commercial 
processes. In these processes the betaines are either used directly as 
such, e.g. in electro plating, or are used as intermediates and further 
reacted. When sulphoalkyl betaines are used as intermediates, it is often 
advantageous not to isolate them after they have been prepared, but to 
carry out the further reaction as a stage subsequent to the process of 
their production. As intermediates, the sulphoalkyl betaines play an 
important role, for example, in the synthesis of the polymethine dyes 
which are used as spectral sensitising dyes for materials which are 
sensitive to light, especially for photographic silver halide emulsions. 
The present invention therefore further relates to the conversion of 
heterocyclic bases via the sulphoalkyl quaternary salts into polymethine 
dyes. 
Processes for the production of sulphoalkyl quaternary salts of tertiary 
amines have been known for a long time. The tertiary base is reacted with 
a sulphoalkylating agent, usually at a raised temperature. The following 
are examples of sulphoalkylating agents: 
Haloalkane sulphonic acids, e.g. 2-bromoethanesulphonic acid as described 
in U.S. Pat. No. 2,503,776; sodium iodoethanesulphonate as described in 
Belgian Pat. No. 669,308; sodium iodobutane sulphonate as described in 
U.S. Pat. No. 2,912,329 or 3-chloro-2-hydroxypropane sulphonic acid as 
described in German Auslegeschrift No. 1,177,482. Disadvantages of these 
sulphoalkylating agents are the high reaction temperatures which are 
necessary and the excess of a tertiary base which is necessary in the use 
of the free sulphonic acids, for absorbing the hydrogen halide which is 
produced in the reaction. Known sulphoalkylating agents also include 
sultones: propane sultone, butane sultone and isopentane sultone are 
described in German Pat. No. 929,080; propene sultone is described in 
German Auslegescrift No. 1,447,579 and 2-chloropropane sultone is 
described in GB Pat. No. 1,090,626. A disadvantage of the sultones is 
partly their great carcinogenic potential, which makes their use a safety 
hazard for the people who work with them. This is discussed by H. Druckrey 
et al. Naturwiss. 55, (1968) 449 and Z. Krebsforschung 75, (1970) 69. 
Another process for the production of sulphoalkyl quaternary salts from 
heterocyclic bases is described in Research Disclosure No. 16 374 
(November 1977). According to this process, hydroxy alkane sulphonic acid 
and hydroxy alkene sulphonic acid are used for sulphoalkyl quaternisation. 
This process also requires comparatively high temperatures presumably 
because in the reaction water is released and has to be removed from the 
reaction medium. Because of the particular reaction conditions (high 
temperatures, acidic medium, the sulphoalkyl quaternary salts from certain 
particularly sensitive nitrogen bases (e.g. oxazole bases and thiadiazole 
bases) and also from bases containing acid-sensitive groups, for example 
alkoxy groups and nitrile groups, can be obtained by this process only 
with difficulty in the required high yield. Moreover, under these 
conditions, 2-methylthiothiadiazole bases tend to a displacement on 
quaternisation which has the effect that the sulphoalkyl radical replaces 
the methyl group in the 2-position and gives rise to difficulties during 
the subsequent condensation reaction to form the cyanine dye. 
For these reasons, the object of the present invention was to provide a 
process for the production of sulphoalkyl quaternary salts, which does not 
have the disadvantages mentioned above. 
A process has now been found for the production of sulphoalkyl quaternary 
salts and sulphoalkenyl quaternary salts of tertiary amines and more 
preferably of heterocyclic bases containing at least one nitrogen atom, in 
which the teriary amine is reacted with an O-sulphoalkyl isourea compound 
or an O-sulphoalkenyl isourea compound. The reaction generally takes place 
at elevated temperature, e.g. at a temperature of between 80.degree. and 
200.degree. C., preferably at a temperature of between 110.degree. and 
160.degree. C. 
In general the reaction takes place very smoothly within the last named 
temperature range. However, it can also be carried out outside this 
temperature range depending to a certain extent on the nature of the 
solvent used. 
Suitably tertiary amines include in principle all quaternisable derivatives 
of ammonia (NH.sub.3), in which each of the three hydrogen atoms is 
substituted, e.g. by a carbon atom of an alkyl or aryl radical or by a 
carbon atom or a heteroatom of a heterocyclic ring, in which case, it is 
preferred that the nitrogen atom of the tertiary amine forms part of the 
heterocyclic ring. Particularly preferred heterocyclic bases include those 
of the general formula I 
##STR1## 
in which Z represents the members required to complete a heterocyclic 
group comprising at least one 5- or 6-membered heterocyclic ring: the 
heterocyclic group may have benzene, naphthalene or further heterocyclic 
rings condensed to the 5- or 6-membered heterocyclic ring mentioned above 
and the heterocyclic group may carry further substituents such as alkyl, 
aralkyl or aryl groups, alkoxycarbonyl groups, acyl groups, cyano groups, 
halogen atoms, alkoxy groups, alkylthio groups, mercapto groups and sulpho 
groups. Suitable heterocyclic rings are those which are known from the 
cyanine dyes, for example: 
Pyrroline (e.g. 4,4-dimethyl-pyrroline); oxazoline (e.g. 
4,4-dimethyloxazoline); thiazoline (e.g. 5-methylthiazoline); 
selenazoline; indoline (e.g. 3,3-dimethylindoline, 
3,3-dimethyl-5-methoxyindoline and 3,3-dimethyl-5-diethylamino-indoline); 
benzimidazole (e.g. 1-ethyl-5-trifluormethylbenzimidazole, 
1-methyl-5-chlorobenzimidazole, 1-ethyl-5,6-dichlorobenzimidazole, 
1-ethyl-5-cyanobenzimidazole, 1-methyl-5-carbethoxybenzimidazole, 
1-ethyl-5-acetylbenzimidazole, 1-methyl-benzimidazole-5-sulphonic acid 
pyrrolidide, 1-ethyl-benzimidazole-5-sulphonic acid dimethylamide, 
1-ethyl-5-phenylthiobenzimidazole, 1-methyl-5-methylthiobenzimidazole and 
1-methyl-5-chloro-6-methylthiobenzimidazole); oxazole (e.g. 
4-methyloxazole, 4,5-diphenyloxazole, 4-methyl-5-carbethoxyoxazole, 
benzoxazole, 5-chlorobenzoxazole, 5-phenylbenzoxazole, 
6-methoxybenzoxazole, 5-methyl-6-methoxybenzoxazole, 5-bromobenzoxazole, 
5-iodobenzoxazole, naphtho [2,1-d]oxazole, naptho [1,2-d]oxazole, 
naptho-[2,3-d]oxazole, 4,5,6,7-tetrahydrobenzoxazole, 
benzo-furo[2,3-f]benzoxazole; thiazole (e.g. 4-methyl-thiazole, 
4-phenylthiazole and 4-methyl-thiazole-5-acrylic acid ether ester, 
benzothiazole, 5-methylbenzothiazole, 6-methylbenzothiazole, 
5-chlorobenzothiazole, 5-methoxybenzothiazole, 6-methoxy-benzothiazole, 
5,6-dimethylbenzothiazole, 5,6-dimethoxy-benzothiazole, 
5-methyl-6-methoxybenzothiazole, 5-brombenzothiazole, 
5-phenylbenzothiazole, 6-methylthiobenzothiazole, 
6-dimethylaminobenzothiazole, 5-chloro-6-methoxybenzothiazole, 
5,6-methylendioxybenzothiazole, 6-.beta.-cyano ethoxybenzthiazole, 
5-carbomethoxybenzothiazole, 5-nitro-benzothiazole, 
5-phenylthiobenzothiazole, 5-thienyl-benzothiazole, 
6-hydroxybenzothiazole, 4,5,6,7-tetrahydrobenzothiazole, 
4-oxo-4,5,6,7-tetrahydrobenzothiazole, naphtho[2,1-d]thiazole, 
naphtho[1,2-d]thiazole, 4,5-dihydronaptho[1,2-d]thiazole, 
5-methoxynaphtho[1,2-d]thiazole and 
5,7,8-trimethoxynaphtho[1,2-d]thiazole; selenazole (e.g. benzoselenazole, 
5-methylbenzoselenazole, 5,6-dimethylbenzoselenazole, 
5-methoxybenzoselenazole, 5-methyl-6-methoxybenzoselenazole, 
5,6-dimethoxy-benzoselenazole, 5,6methylendioxybenzoselenazole, 
6-methyl-benzoselenazole and naphtho[1,2-d]selenazole); 1,3,4-oxadiazole 
(e.g. 5-methyl-1,3,4-oxadiazole and 5-phenyl-1,3,4 -oxadiazole); 
1,3,4-thiadiazole (e.g. 5-methyl-1,3,4-thiadiazole, 
2,5-bis-methylthio-1,3,4-thiadiazole, 5-benzylthio-1,3,4-thiadiazole, 
2-mercapto-5-methylthio-1,3,4-thiadiazole and 
5-carbethoxymethylthio-1,3,4-thiadiazole); pyridine (e.g. 2-methylpyridine 
and 4-methylpyridine); pyrimidine (e.g. 2-methyl-4-methylthiopyrimidine); 
quinoline (e.g. 6-methylquinoline, 6-methoxyquinoline, 8-chloroquinoline, 
6-fluoroquinoline, 5,6-benzoquinoline, 5,6-benzoquinoline and 
6,7-benzoquinoline) and imidazo[4,5-b] quinoxaline; 
n=0 or 1 
Y represents hydrogen; a halogen atom; a saturated or olefinically 
unsaturated aliphatic hydrocarbon group, preferably containing up to 6 
carbon atoms, which may be substituted, e.g. methyl, ethyl, allyl, 
cyanoalkyl, halo alkyl or alkoxyalkyl; an alkoxy group, e.g. 
carboxyalkoxy; an alkylthio group, e.g. carboxyalkylthio, sulphoalkylthio 
or carbalkoxyalkylthio, or a mercapto group. 
Y may for example represent a polymethine chain with 1, 3 or 5 methine 
groups, at the end of which there is an N-alkylated heterocyclic base 
mostly attached at the 2-position, as is known in the chemistry of cyanine 
dyes. Reference is made here to F. M. Hamer, "The Cyanine Dyes and Related 
Compounds," (1964), Interscience Publishers John Wiley and Sons. Compounds 
of Formula I, in which Y is defined as above are described as 
"dequaternised cyanine dyes." When such dequaternised cyanine dyes are 
reacted in the process of the present invention, the direct products of 
the process are suitable as sensitising dyes without further reaction. 
Suitable O-sulphoalkyl isourea compounds and O-sulphoalkenyl isourea 
compounds are in particular those of the general formula (II): 
##STR2## 
in which X represents a saturated or olefinically unsaturated bivalent 
aliphatic hydrocarbon radical preferably containing up to 7 carbon atoms 
which may be substituted. This hydrocarbon radical may be substituted, for 
example, by hydroxyl, halogen, alkoxy or cyano; 
R.sup.1, R.sup.2, R.sup.3 and R.sup.4 which may be the same or different, 
represent hydrogen, a saturated or unsaturated aliphatic hydrocarbon 
group, or a cycloalkyl group or any two of the substituents R.sup.1, 
R.sup.2, R.sup.3 and R.sup.4 may represent the atoms required to complete 
a 5- or 6-membered heterocyclic ring containing at least one nitrogen 
atom, or R.sup.1 and/or R.sup.3 may represent aryl if the other radical 
attached to the same nitrogen atom (R.sup.2, R.sup.4) is hydrogen. 
Examples of X are the following groups: 
##STR3## 
in which m represents an integer of from 1 to 3. 
Alkyl groups which contain up to 4 carbon atoms are the preferred examples 
of the groups R.sup.1, R.sup.2, R.sup.3 and R.sup.4, such as methyl, 
ethyl, n-propyl and iso-propyl; these radicals may be further substituted, 
e.g. with aryl. Other examples include cyclohexyl and phenyl. 
The reactions are generally carried out without the use of a solvent, but 
they can also be performed in the presence of a suitable solvent. Suitable 
solvents include all solvents which are inert in the reaction according to 
the invention, and which have a high dissolving power for the reaction 
components, for example phenol, m-cresol, dimethylformamide, 
N-methylpyrrolidone, toluene, m-xylene, chlorobenzene and anisole. 
The sulphobetaines of the tertiary amines produced according to the process 
of the invention, are preferably those of the following formula (III) 
##STR4## 
in which n, X, Y and Z have the meanings which have already been defined. 
The compounds have a wide range of uses. For example they are suitable as 
conducting salts in electroplating. Furthermore, when in the quaternary 
salts produced by the process according to the invention Y represents a 
suitable group, for example, as has already been mentioned, a methine 
chain with 1, 3 or 5 methine groups, on the end of which there is a 
N-alkylated heterocyclic base, the compound is a cyanine dye. Compounds of 
this kind are known and can be used without further processing in the 
spectral sensitisation of light sensitive silver halide emulsions. 
However, the compounds which are produced directly by the process 
according to the invention are also useful as intermediates for the 
synthesis of polymethine dyes. So, for example, the sulphoalkyl or 
sulphoalkenyl quaternary salts of heterocyclic bases which are produced by 
the process according to the invention are preferably not isolated, but 
after the quaternisation reaction is completed they are reacted without a 
further purification operation in a known way into polymethine dyes. In 
the monograph of F. M. Hamer, "The Cyanine Dyes and Related Compounds" 
which has already been mentioned, many cyanine dyes are described, which 
are derived from many different heterocyclic bases. Cyanine dyes with 
sulphoalkyl groups have proved to be particularly favourable for a number 
of reasons, especially because of their low residual dyeing. 
The isourea compounds used according to the invention can be produced by 
known processes or rather by processes analogous to known processes. Thus, 
O-sulphopropyl isourea, according to K. Furakawa et al [Kogyo Kagaku 
Zasshi 59, 1028 (1956)] can be obtained by the reaction of urea with 
propane sultone. The corresponding O-sulphopropyl-N,N'-diethyl isourea is 
obtained according to German Offenlegungsschrift No. 2,423,482 by the 
analogous conversion of N,N'-diethylurea. 
Instead of propane sultone, other sultones may be used e.g. n-butane 
sultone, isobutane sultone or propene sultone. Instead of urea or 
N,N'-diethylurea, other ureas, which are substituted from one to four 
times, can be sulphoalkylated at the oxygen atom. Ureas which are 
substituted four times, and in which two radicals consist of aryl groups, 
do not react any further. Another process for the production of isourea 
compounds according to the invention consists in the addition which is 
known per se of hydroxyl compounds to carbodiimide. Reference is made to 
Houben-Weyl, Methoden der Organischen Chemie VIII, S. 170; or E. Schmidt, 
F. Moosmuller, Liebigs Ann. 597, 235 (1955). As hydroxyl compounds, the 
corresponding hydroxy alkane or hydroxyalkene sulphonic acids are used 
here, for example 3-hydroxy-propane-1-sulphonic acid; 
4-hydroxybutane-1-sulphonic acid; 4-hydroxybutane-2-sulphonic acid or 
3-hydroxy-prop-1-en-1-sulphonic acid. 
The hydroxy alkane or hydroxy alkene sulphonic acids, and processes for 
their production are known. They can for example be produced by the 
reaction of a halo substituted alcohol with an alkali metal sulphite or by 
the addition of bisulphite or SO.sub.2 to a corresponding unsaturated 
alcohol or rather to a corresponding unsaturated aldehyde, followed by 
reduction. Thus, 3-hydroxy-1-propane sulphonic acid is produced from allyl 
alcohol by the addition of sodium bisulphite [J. H. Helberger, Liebigs 
Ann. Chem. 588, 71 (1974)]. 3-Hydroxy-2-methyl-1-propane sulphonic acid is 
produced by the addition of bisulphite to methacrolein, followed by 
reduction with H.sub.2 /Raney-Ni [C. W. Smith et al., J. Amer,chem.Soc. 
75, 748 (1953)]. Analogous to this, 4-hydroxy-2-butane sulphonic acid can 
also be produced from croton aldehyde [G. Haubner, Mh. Chemie 12, 541 
(1891)]. 4-hydroxy-1-butane sulphonic acid can be obtained by the reaction 
of 4-chloro-n-butanol with sulphite [J. H. Helberger, H. Lantermann, 
Liebigs Ann. Chem. 586, 161 (1954)]. 3-hydroxy-1-propene sulphonic acid 
can be obtained by the addition of bisulphite to propargyl alcohol as a 
mixture of the cis- and trans-isomers as described in German 
Auslegeschrift No. 1,146,870. 
The isourea compounds of the general formula (II), which are used in the 
production process of the present invention, can be thought at as internal 
isouronium salts, although in cases where at least one of the radicals 
R.sup.1 to R.sup.4 represents hydrogen, the compound can also be present 
in the tautomeric sulphonic acid form, the equilibrium being between the 
formulae: 
##STR5## 
Examples of the isourea compounds used according to the invention are given 
below: 
Compound 1: Anhydro-O-[3-sulphopropyl]-isouronium hydroxide, Mp. 
184.degree.-187.degree. C. 
Compound 2: Anhydro-O-[3-sulphopropyl]-N-methylisouronium hydroxide, Mp. 
138.degree.-144.degree. C. 
Compound 3: Anhydro-O-[3-sulphopropyl]-N,N'-dimethylisouronium hydroxide, 
Mp. 175.degree.-177.degree. C. 
Compound 4: Anhydro-O-[3-sulphopropyl]-N,N,N',N'-tetramethyl-isouronium 
hydroxide. 
Compound 5: Anhydro-O-[3-sulphopropyl]-N,N'-diethylisouronium hydroxide, 
Mp. 162.degree.-163.degree. C. 
Compound 6: Anhydro-O-[3-sulphopropyl]-N-phenyl-isouronium hydroxide, Mp. 
168.degree.-170.degree. C. 
Compound 7: Anhydro-O-[3-sulphopropyl]-N,N'-diphenylisouronium hydroxide, 
Mp. 244.degree.-248.degree. C. 
Compound 8: Anhydro-O-[3-sulphopropyl]-N,N'-ethyleneisouronium hydroxide, 
decomposes at 165.degree. C. 
Compound 9: Anhydro-O-[4-sulphobutyl]-isouronium hydroxide. 
Compound 10: Anhydro-O-[3-sulphobutyl]-N,N'-dimethylisouronium hydroxide, 
Mp. 155.degree.-156.degree. C. 
Compound 11: Anhydro-O-[3-sulphoprop-1-enyl]-N,N'-dimethyl-isouronium 
hydroxide. 
Compound 12: Anhydro-O-[3-sulphopropyl]-N,N'-dicyclohexyl-isouronium 
hydroxide. 
Compound 13: Anhydro-O-[3-sulphopropyl]-N,N'-diisopropyl-isouronium 
hydroxide. 
Compound 14: Anhydro-O-[3-sulphopropyl]-N-benzyl-N'-methyl-isouronium 
hydroxide. 
Compound 15: Anhydro-O-[3-sulphobutyl]-isouronium hydroxide, Mp. 
210.degree.-212.degree. C. 
The process according to the invention for the production of sulphoalkyl 
and sulphoalkenyl quaternary salts is explained in more detail in the 
following examples: 
The process according to the invention provides the desired sulphoalkyl or 
sulphoalkenyl quaternary salts in a controlled reaction, under mild 
conditions. Because the reaction temperatures are lower compared to other 
processes and because the quaternisation agents which are used according 
to the invention react in a practically neutral way, more sensitive bases, 
especially nitrogen bases which are sensitive to acid such as oxazole 
bases, thiadiazole bases, alkoxy substituted bases and cyano substituted 
bases, can be easily and controllably quaternised. The process is also 
suitable for the quaternisation of 2-methylthioazole bases, which 
quaternisation proceeds substantially in the absence of the 
requaternisation, which otherwise occurs very easily.

EXAMPLE 1 
Anhydro-2,5,6-trimethyl-3-[3-sulphopropyl]-benzothiazolium hydroxide, Mp. 
288.degree. C. 
(a) 1/100 mol of 2,5,6-trimethylbenzothiazole is mixed with 2 ml of 
m-cresol and after the addition of 1/100 mol of Compound 1, is heated for 
3 hours at 140.degree. C. The melt obtained is then ground finely with 
acetone and the crystalline product obtained is suction-filtered and 
recrystallised from ethanol. 
Yield: 53% of the theory. 
(b) Analogous to (a), 0.01 mol of the base is reacted with 0.01 mol of 
Compound 3. 
Yield: 73%. 
(c) Analoguous to (a) using Compound 8 instead of Compound 1, in the 
presence of dimethylsulphoxide. 
Yield: 50%. 
(d) Analogous to (a) using Compound 8 instead of Compound 1 and 2 g phenol 
instead of m-cresol, with heating for 2 hours at 140.degree. C. Propanol 
is used for working up the product. 
Yield: 80%. 
(e) Analogous to (a) using Compound 5 instead of Compound 1. 
Yield: 70%. 
EXAMPLE 2 
Anhydro-2,5-dimethyl-6-methoxy-3-[3-sulphopropyl]-benzoselenazolium 
hydroxide, Mp. 299.degree.-300.degree. C. 
0.01 mol of 2,5-dimethyl-6-methoxybenzoselenazole is mixed with 1.5 ml 
m-cresol and, after the addition of 0.01 mol of Compound 3, the mixture is 
heated at 135.degree. C. for 1 hour while being stirred. The melt is then 
ground finely with propanol and the crystallised quaternary salt is 
filtered by suction. 
Yield: 60%. 
EXAMPLE 3 
Anhydro-1-[3-sulphopropyl]-quinaldinium hydroxide (Mp. 284.degree. C.) is 
obtained by heating quinaldine and Compound 5 in an equivalent molar ratio 
for 1 hour at 125.degree. C. and working up with ethyl acetate, acetone 
and ethanol, the yield being 30%. In place of Compound 5, Compound 2 can 
also be used. 
EXAMPLE 4 
Anhydro-2-methyl-5-phenyl-3-[3-sulphopropyl]-benzoxazolium hydroxide, Mp. 
301.degree. C. 
(a) By heating 2 g of 2-methyl-5-phenylbenzoaxazole for 3 hours with 2 g of 
Compound 3 at 140.degree. C. and subsequently grinding it finely with 
isopropanol. 
Yield: 0.8 g. 
(b) By the introduction of 2.1 g 2-methyl-5-phenylbenzoxazole into a 
mixture of 2.4 g of Compound 5 and 1.5 ml m-cresol at 125.degree. C. over 
a period of 30 minutes, stirring for one hour at 125.degree. C. and 
working up with ether and ethanol. 
Yield: 1.7 g=51%. 
EXAMPLE 5 
Anhydro-1,2-dimethyl-5-pyrrolidinosulphonyl-3-[3-sulpho-propyl]-benzimidazo 
lium hydroxide (Mp. 339.degree. C.) is obtained by the reaction of 0.01 mol 
of 1,2-dimethyl-5-pyrrolidinosulphonylbenzimidazole with 0.01 mol of 
Compound 5 by heating to 125.degree. C. for 2 hours, and treating the 
reaction product with boiling methanol, with a 40% yield. 
If Compound 6 is used instead of Compound 5, a 50% yield is obtained. 
EXAMPLE 6 
Anhydro-2-methylthio-3-[3-sulphopropyl]-benzothiazolium hydroxide, Mp. 
243.degree.-246.degree. C. 
0.01 mol 2-methylthiobenzothiazole is heated with 0.01 mol of Compound 3 
with the addition of 1 ml m-cresol for 1.5 hours at 135.degree. C. After 
cooling, grinding finely with propanol and standing overnight the 
quaternary salt crystallises. 
Yield: 30%. 
EXAMPLE 7 
Anhydro-2,5-bis-methylthio-3-[3-sulphopropyl]-1,3,4-thiadiazolium 
hydroxide, Mp. 207.degree.-209.degree. C. 
(a) 0.01 mol of 2,5-bis-methylthio-1,3,4-thiadiazole is heated with 0.01 
mol of Compound 4 for 40 minutes at 100.degree. C. After cooling, it is 
worked up with a little propanol. 
Yield: 2.7 g=90%. 
(b) Analogous to (a) with Compound 3 instead of Compound 4, with the 
addition of 2 g of phenol and working up by washing with ether and 
crystallisation from propanol. 
Yield: 33%. 
EXAMPLE 8 
Anhydro-5-phenyl-5',6'-dimethyl-3-ethyl-3'-[3-sulfo-butyl]-oxathiacarbocyan 
ine hydroxide, Mp. 290.degree.-292.degree. C.: 1.8 g of 2,5,6-trimethyl 
benzothiazole is stirred with 2.3 g of Compound 10 with the addition of 
0.5 ml m-cresol for 1 hour at 125.degree. C. The quaternary salt produced 
is not isolated, but is taken up in 15 ml ethanol and after the addition 
of 3.4 g of 2-[2-phenyliminoethylidene]-3-ethyl-5-phenylbenzoxazoline, 1 
ml triethylamine and 0.3 g acetic anhydride, is converted into the dye by 
stirring for 1 hour at room temperature. Purification is carried out with 
ethanol. 
Yield: 2 g, maximum absorption: 531 nm (methanol).