Process for the preparation of low-salt, liquid dyestuff preparations

Process for the preparation of low-salt liquid dyestuff preparations, characterized in that they are obtained by: PA1 a) diazotization of an aromatic amine, PA1 b) 2-fold coupling of the diazo component obtained according to a) to I-acid-urea, in the presence of an inorganic base and in the absence of an organic base, PA1 c) desalination and, if appropriate, concentration by means of a pressure permeation of the reaction mixture obtained according to b), so that an inorganic salt content of less than 1% by weight is achieved.

The invention relates to a process for the preparation of low-salt, liquid 
dyestuff preparations of dyestuffs based on I-acid-urea, and to the use of 
liquid dyestuff preparations prepared in this way for dyeing and printing 
substrates containing hydroxyl and/or amide groups, in particular paper. 
It is already known from DE-A-30 02 062 that dyestuffs based on I acid-urea 
can be used for dyeing paper. However, only those dyestuffs which are 
prepared by the route of simultaneous coupling (diazotizing coupling) or 
those on which azo coupling is carried out in the presence of 
diethanolamine are employed in the form of their liquid dyestuff 
preparations. The dyestuffs prepared in this way, however, are obtained in 
a low yield (Example 2, 83% of theory; Example 3, 93% of theory). 
Furthermore, they have a low storage stability in the form of their liquid 
preparations (cf. Example 3). The dyestuffs thus prepared moreover contain 
substantial amounts of by-products, which remain in the preparation and 
impair the quality of the dyestuff in respect of its brilliance. In 
contrast, dyestuffs based on I-acid-urea which are prepared by another 
route are used exclusively in the form of their solid preparations (see 
Example 1). 
The dyestuffs based on I-acid-urea which are known from DE-A-21 03 756 are 
likewise employed for dyeing paper both in the form of their solid 
preparations and in the form of their liquid preparations. The dyestuff 
preparations comprise salts which can be dissociated in water, the liquid 
dyestuff preparations additionally comprising 0.5 to 5 parts by weight of 
an acid amide, preferably urea, per part of dyestuff. 
The liquid dyestuff preparations of dyestuffs with I-acid-urea as the 
coupling component which are known from DE-A 29 02 034 are always prepared 
from the solid dyestuff preparations, have a pH of greater than 12 and 
comprise hydrotropic agents. 
Such dyestuffs are also known from U.S. Pat. No. 1,509,442, but are 
employed for dyeing exclusively in the form of their salt-containing solid 
preparation. 
A process has now been found for the preparation of low-salt storage-stable 
liquid dyestuff preparations, which is characterized in that the dyestuff 
preparation is obtained by: 
a) diazotization of an aromatic amine, 
b) 2-fold coupling of the diazo component obtained according to a) to 
I-acid-urea, in the presence of an inorganic base and in the absence of an 
organic base, 
c) desalination and, if appropriate, concentration by means of a pressure 
permeation of the reaction mixture obtained according to b), so that an 
inorganic salt content of less than 1% by weight, based on the liquid 
dyestuff preparation, is achieved. 
Particularly preferred aromatic amines which are used for the diazotization 
of the process according to the invention are those containing sulpho 
groups or carboxyl groups. In particular, these are aminobenzenes 
containing sulpho groups or aminonaphthalenes, which are optionally 
further substituted. Preferably, these amines carry 1 to 4, preferably 1 
or 2, SO.sub.3 H groups. Examples of further substituents which may be 
mentioned are C.sub.1 -C.sub.4 -alkyl, in particular methyl, ethyl and 
n-propyl, C.sub.1 -C.sub.4 -alkoxy, such as methoxy, ethoxy or propoxy, 
halogen, such as Cl or fluorine, optionally substituted azobenzene or 
substituted or unsubstituted amino groups. 
Particularly preferred aromatic amines which may be mentioned are those of 
the following formulae (1)-(6). 
##STR1## 
The diazotization is in general carried out by the general processes (cf.: 
Houben-Weyl: Methoden der anorganischen Chemie [Methods of Inorganic 
Chemistry] Volume X/3, year 1965, edition 4, pages 7-112 and Volume Elba, 
part 2, year 1990, edition 4, pages 1060-1068). The diazotization is 
preferably carried out by the indirect method, an aqueous solution of a 
nitrite salt being added to an initial mixture of an arylamine, preferably 
a sulphonated or carboxylated arylamine, or an alkali metal salt thereof 
and excess acid at 0.degree. C. to 40.degree. C., preferably at 10 to 
25.degree. C. The diazotization by the direct method is furthermore 
preferred, an aqueous mixture of an arylamine, preferably a sulphonated or 
carboxylated arylamine, or an alkali metal salt thereof and an inorganic 
nitrite salt preferably being added to an aqueous initial portion of 
excess inorganic acid at a temperature of 0 to 40.degree.C., preferably 10 
to 25.degree. C. 
Preferred diazotizing agents which may be mentioned are NaNO.sub.2, 
LiNO.sub.2 or nitrosylsulphuric acid. NaNO.sub.2 is particularly 
preferred. 
The solution or suspension obtained after the diazotization is in general 
employed for coupling to I-acid-urea as described below. The two fold 
coupling to I-acid-urea is preferably carried out by a procedure in which 
the ratio of diazo component to coupling component is 2:1 to 2.5:1. 
I-acid-urea has the general formula 
##STR2## 
The coupling is in general carried out under known conditions, such as are 
known, for example, from DE-A 21 03 756, DE-A-2 103 757 and U.S. Pat. No. 
2,746,955. 
The coupling is preferably carried out by adding the diazo component to the 
coupling component, the pH of the coupling in general being kept at 5-10, 
preferably at 6-8.5, with the addition of an inorganic base. 
Possible particularly preferred bases are alkali metal hydroxides, 
carbonates or bicarbonates or acetates. Sodium or lithium is preferred as 
the alkali metal. 
The reaction mixture obtained when the coupling has ended is then 
preferably subjected to pressure permeation at a temperature of 
15-55.degree. C. An ultrafiltration membrane having a cut-off level of 
1000-1500 Dalton is employed here in particular. Preferred ultrafiltration 
membranes are those of polysulphones. The pressure permeation is 
preferably carried out under 10-50 bar, in particular 20-40 bar. The 
pressure permeation is carried out down to a salt content of less than 1%, 
the salt content preferably being determined as the chloride content. 
During the pressure permeation, the mixture is subjected to diafiltration 
and, if appropriate, the diafiltration preceding or following a possible 
concentration. 
The liquid dyestuff preparations prepared according to the invention 
preferably comprise no hydrotropic agents. Hydrotropic agents are to be 
understood as meaning solubility-improving additives. The following may be 
mentioned as examples of hydrotropic agents: low molecular weight amides, 
lactones, alcohols, glycols or polyols, low molecular weight ethers or 
oxyalkylation products and nitriles or esters. Hydrotropic agents are 
understood as meaning, in particular: methanol, ethanol, propanol, 
ethylene glycol, propylene glycol, diethylene glycol, thiodiethylene 
glycol and dipropylene glycol as well as triethylene glycol; butanediol; 
and .beta.-hydroxypropionitrile, pentamethylene glycol, ethylene glycol 
monoethyl and -propyl ether, ethylene diglycol monoethyl ether, 
triethylene glycol monobutyl ether, butyl polyglycol, formamide, 
dimethylformamide, pyrrolidone, N-methylpyrrolidone, glycol acetate, 
butyrolactone, urea and .epsilon.-caprolactam. They particularly 
preferably comprise, as essential constituents, only the dyestuff in the 
form of its alkali metal (or ammonium) salts and water. The dyestuff is 
preferably present as an alkali metal salt, in particular Na, Li or K 
salt, in particular the Na salt. The dyestuff preparations can also 
additionally comprise additives, such as, for example, diethanolamine. The 
liquid dyestuff preparation preferably has a pH of 6 to 8, which is 
established with alkali if necessary. The liquid dyestuff preparation 
obtained by the process according to the invention preferably comprises 
the dyestuff in an amount of 5 to 20% by weight, preferably 8 to 13% by 
weight, in the form of its alkali metal salt. Even at high dyestuff 
concentrations, no hydrotropic agents are necessary to obtain 
storage-stable preparations. The dyestuff preparations obtained by the 
process according to the invention are distinguished by a particularly 
high purity and a very good storage stability. 
Low-salt aqueous dyestuff preparations obtained by the process according to 
the invention which have an inorganic salt content of less than 1% by 
weight and a content of hydrotropic agents of less than 10% by weight, in 
particular less than 5% by weight, in each case based on the total amount 
of the preparation, and comprise a dyestuff which, in the form of its free 
acid, corresponds to the formula (II) 
##STR3## 
are also preferred. 
The aqueous dyestuff preparation comprising the dyestuff of the formula 
(II) preferably comprises no hydrotropic agents. The dyestuff of the 
formula (II) is preferably in the form of its alkali metal salt. 
The invention furthermore relates to low-salt aqueous dyestuff preparations 
with an inorganic salt content of less than 1% by weight and a content of 
hydrotropic agents of less than 10% by weight, in particular less than 5% 
by weight, in each case based on the total amount of the preparation, 
comprising a dyestuff which, in the form of its free acid, corresponds to 
the formula (II). 
The invention furthermore relates to low-salt aqueous dyestuff preparations 
with an inorganic salt content of less than 1% by weight, based on the 
total amount of the preparation, comprising at least one dyestuff which, 
in the form of a free acid, corresponds to the formula (I) 
##STR4## 
wherein A denotes a radical of the formula 
##STR5## 
Particularly preferred aqueous dyestuff preparations according to the 
invention comprise a dyestuff of the formula (I) wherein 
A denotes a radical of the formula 
##STR6## 
The liquid dyestuff preparation according to the invention comprising at 
least one dyestuff of the formula (I) preferably comprises no hydrotropic 
agents. It can likewise be prepared by the process according to the 
invention. The dyestuff is preferably present in the form of its alkali 
metal salt. 
The statements made for the preparations prepared according to the 
invention furthermore apply to the dyestuff preparations according to the 
invention comprising a dyestuff of the formula (I). 
The invention furthermore relates to a process for dyeing or printing 
substrates containing hydroxyl and/or amide groups using the liquid 
dyestuff preparations prepared by the process according to the invention 
or using the liquid dyestuff preparation according to the invention 
comprising the dyestuff of the formula (I). Substrates containing hydroxyl 
and/or amide groups are to be understood as meaning, in particular, paper, 
cotton and viscose, as well as leather. 
The liquid dyestuff preparations can be used by all the processes customary 
for substantive dyestuffs in the paper and textile industry, in particular 
in pulp and surface dyeing of paper for sized or non-sized grades, 
starting from bleached or unbleached cellulose of varying origin, such as 
softwood or hardwood sulphite and/or sulphate cellulose. They can also be 
used in dyeing yarn and piece goods of cotton, viscose and linen by the 
exhaust process from a long liquor or in the continuous process.

EXAMPLES 
Example 1 
Process for the preparation of the dyestuff of the formula (II) 
##STR7## 
0.91 mol of 2-sulpho-4-[(1-sulphophenyl)azo]aniline (di-yellow acid) was 
introduced into 1.4 l of softened water, and 1.2 mol of hydrochloric acid 
were added. 210 ml of sodium nitrite solution (300 g/l) were added at 
10-20.degree. C. in the course of about 30 minutes. The suspension of 
diazotized di-yellow acid thus obtained was subsequently stirred under an 
excess of nitrite at 20.degree. C. for 1 hour. Excess nitrite was then 
destroyed by addition of about 0.05 mol of amidosulphonic acid. 
A suspension of 0.43 mol of N,N'-bis[1-hydroxy-3-sulpho-6-naphthyl]urea 
(I-acid-urea) in 500 ml of softened water was added to this suspension. 
The entire mixture was added to an initial mixture of 0.10 mol of disodium 
hydrogen phosphate, 330 g of a naphthalenesulphonic acid/formaldehyde 
condensate and 800 ml of softened water at 30.degree. C. in the course of 
1 hour, the pH being kept at 7.5 by addition of about 800 ml of sodium 
carbonate solution (200 g/l). 
0.09 mol of di-yellow acid was diazotized analogously to the first 
diazotization (volume=about 700 ml) and then added to the coupling mixture 
at 30.degree. C., the pH being kept at 8.5 by addition of about 200 ml of 
sodium hydroxide solution (400 g/l). Yield 84% of theory, based on 
I-acid-urea. 
For the pressure permeation, the dyestuff thus obtained was first 
concentrated to a total volume of about 4.5 l over a polysulphone membrane 
(MWCO 1,000-1,500) at 25.degree. C. under 40 bar and then subjected to 
diafiltration with about 7 l of deionized water. 4,510 g of a 
storage-stable dyestuff solution (Cl.sup.- =0.08%) with a pH of 8.5 were 
obtained. When the dyestuff solution was used for pulp dyeing of paper, 
brilliant dyeings were obtained. 
Example 2 
Process for the preparation of a dyestuff of the formula (I) 
##STR8## 
1.0 mol of 4-amino-5-methoxy-2-methylbenzenesulphonic acid (cresidicinic 
acid) was dissolved in 1.4 l of softened water with 1.4 mol of sodium 
hydroxide. 240 ml of sodium nitrite solution (300 g/l) were added to this 
solution. The entire mixture was added to an initial mixture of 280 ml of 
softened water, 2.5 mol of hydrochloric acid and 6 mmol of sodium nitrite 
solution in the course of 30 minutes. The suspension of diazotized 
cresidic acid thus obtained was subsequently stirred under an excess of 
nitrite at room temperature for 1 hour. Excess nitrite was then destroyed 
by addition of about 0.05 mol of amidosulphonic acid. 
For the coupling, this suspension was added to a suspension of 0.5 mol of 
N,N'-bis[1-hydroxy-3-sulpho-6-naphthyl]urea (I-acid-urea) in 1.1 l of 
softened water at room temperature, the pH being kept at 6.0 by addition 
of a total of about 350 ml of sodium carbonate solution (200 g/l). Yield 
97% of theory, based on the I-acid-urea. 
For the pressure permeation, the dyestuff solution thus obtained was 
subjected to diafiltration with about 8 l of deionized water over a 
polysulphone membrane having a molecular weight cut-off level (MWCO level) 
of 1000-1500 Dalton at 50.degree. C. under 30 bar, and was then 
concentrated to a total volume of about 4 l. 4,100 g of a storage-stable 
dyestuff solution (Cl.sup.- =0.2%) with a pH of 7.0 were obtained. When 
this dyestuff solution was used for pulp dyeing of paper, brilliant 
dyeings were obtained.