Preparation of dianthraquinone-N,N'-dihydroazine and its chlorination products

A process for preparing dianthraquinone-N,N'-dihydroazine (I) ##STR1## and its chlorination products (Ia) ##STR2## where n is 1 or 2, by condensation of 1-aminoanthraquinone (II) in the presence of an alkaline condensing aid, an oxidizing agent and a cyclic urea derivative at from 80.degree. to 150.degree. C. and subsequent purification and/or chlorination comprises using N,N'-dimethylpropyleneurea as the urea derivative.

The present invention relates to an improved process for preparing 
dianthraquinone-N,N'-dihydroazine (I) 
##STR3## 
and its chlorination product (Ia) 
##STR4## 
where n is 1 or 2, by condensation of 1-aminoanthraquinone (II) in the 
presence of an alkaline condensing aid, an oxidizing agent and a cyclic 
urea derivative at from 80.degree. to 150.degree. C. and subsequent 
purification and/or chlorination. 
The anthraquinone derivatives (I) and (Ia) correspond to the important vat 
dyes C.I. Vat Blue 4 (C.I. 69800, customarily referred to as indanthrone), 
C.I. Vat Blue 14 (C.I. 69810, n=11), and C.I. Vat Blue 6 (C.I. 69825, n=2, 
3,3'-dichloroindanthrone). 
Indanthrone can be prepared by condensation not only of 
2-aminoanthraquinone but also of 1-aminoanthraquinone. 
In the traditional process of preparation, 2-aminoanthraquinone is heated 
in a sodium hydroxide/potassium hydroxide melt to 200.degree.-225.degree. 
C. in the presence of oxidizing agents such as sodium nitrate or sodium 
chlorate. However, this reaction gives rise to appreciable amounts of 
undesirable by-products such as alizarin, 2-amino-1-hydroxyanthraquinone 
and flavanthrone, which is why alternative methods starting from 
1-aminoanthraquinone have been proposed. 
In these later processes, 1-aminoanthraquinone is oxidized, preferably by 
air, in a phenoxide or hydroxide melt in the presence or absence of 
further auxiliaries such as dimethyl sulfoxide. DE-A-34 22 385 discloses a 
process wherein the condensation of 1-aminoanthraquinone takes place in 
the presence of 1,3-dimethylimidazolidin-2-one. 
However, even these processes are unsatisfactory because of likewise 
inadequate purity of the product and hence insufficient yields or because 
of the poor filtration properties of the product. 
The corresponding chloroindanthrones can, as will be known, be prepared by 
reacting indanthrone with chlorine in an inert, organic solvent such as 
nitrobenzene or in sulfuric acid in the presence of small amounts of 
manganese dioxide. Again, the indanthrone used must be sufficiently pure 
in order that a satisfactory chlorination product may be obtained. For 
this reason the condensation product is in general subjected to a 
reductive purification and a subsequent oxidation in air. 
It is an object of the present invention to make available indanthrone in 
high purities and good yields in an economical manner and hence also to 
make possible an advantageous production of chloroindanthrone. 
We have found that this object is achieved by a process for preparing 
dianthraquinone-N,N'-dihydroazine (I) 
##STR5## 
and its chlorination products (Ia) 
##STR6## 
where n is 1 or 2, by condensation of 1-aminoanthraquinone (II) in the 
presence of an alkaline condensing aid, an oxidizing agent and a cyclic 
urea derivative at from 80.degree. to 150.degree. C. and subsequent 
purification and/or chlorination, which comprises using 
N,N'-dimethylpropyleneurea as the urea derivative. 
N,N'-Dimethylpropyleneurea 
##STR7## 
is in general used in the process of the invention in amounts of from 0.05 
to 10 parts by weight, preferably from 0.1 to 5 parts by weight, 
particularly preferably from 1 to 3 parts by weight, per part by weight of 
1-aminoanthraquinone (II), if desired in the form of a mixture with an 
inert, organic solvent such as dimethyl sulfoxide, pyridine, toluene, 
xylene or nitrobenzene. 
The alkaline condensing aid used can be the bases customarily used for this 
purpose such as sodium hydroxide and in particular potassium hydroxide. 
They can be used in the form of a solid or preferably in the form of an 
aqueous solution, preferably of 50% strength by weight. The amount used is 
in general from 0.1 to 10 parts by weight, preferably 0.2 to 2.5 parts by 
weight, per part by weight of (II). 
Suitable oxidizing agents are air, oxygen, peroxidic salts such as 
perborates, nitrates and chlorates. Air and oxygen are particularly 
favorable. 
In some cases it can be of advantage to add to the reaction medium a 
wetting agent which does not react under the reaction conditions, for 
example a naphthalene or alkylnaphthalene-sulfonate or a sulfurated 
oleamide. 
1-Aminoanthraquinone (II) can be used as a powder, as a wet filter cake or 
as a suspension and this suspension may be admixed with all or some of the 
condensing aid. 
The reaction temperature in the process of the invention is in general from 
80.degree. to 150.degree. C. and depends on the amount of 
N,N'-dimethylpropyleneurea. 
The process is advantageously carried out by initially charging a mixture 
of 1-aminoanthraquinone (Ii) and N,N'-dimethylpropyleneurea, heating it to 
about 90.degree.-100.degree. C., and then adding the condensing aid while 
air is passed through the reaction mixture at a rate of about 200-300 
ml/min. After the addition has ended, the temperature is preferably raised 
to 120.degree.-130.degree. C., and some of the water distils off. 
The reaction takes in general from 4 to 12 h. Its end can be determined in 
a conventional manner using thin layer chromatography. 
The reaction mixture can be worked up for the indanthrone (I) in a 
conventional manner by precipitating with water and filtering off the 
precipitate. Here it is found that a product (I) prepared according to the 
invention gives appreciably reduced filtration times compared with a 
product obtained as described in DE-A-34 22 385. 
N,N'-Dimethylpropyleneurea can advantageously be recovered from the aqueous 
phase by distillation or solvent extraction and used for further 
reactions. 
Subsequently the product (I) is in general subjected to a customary 
purifying aftertreatment. To this end it is first suspended in water and 
reduced with a reducing agent such as sodium dithionite in the presence of 
a base such as sodium hydroxide to the leuco form. The sodium salt thereof 
can be filtered off again, washed with water and reoxidized with air to 
the indanthrone (I). 
If the chlorinated indanthrones (Ia) are to be prepared, it is likewise 
possible to employ one of the conventional chlorination techniques. A 
favorable option is the chlorination of indanthrone (I) in sulfuric acid, 
which in general is carried out as follows: 
The dry or as-filtered, still moist product (I) is dissolved in sulfuric 
acid to form a solution with a sulfuric acid concentration of about 92% by 
weight. Small amounts of manganese dioxide are added as catalyst, and 
chlorine is passed through the solution at about 50.degree.-55.degree. C. 
After the chlorination has ended, the reaction mixture is diluted with 
water to set the sulfuric acid concentration at about 83% by weight and 
then filtered. The filter residue is then completely dissolved in 98% 
strength by weight sulfuric acid and reduced, for example with aluminum 
powder, to form the desired chloroindanthrones (Ia). 
It is of advantage that the indanthrone (I) prepared according to the 
invention is directly obtained in a sufficiently pure form that in general 
a purifying aftertreatment can be dispensed with prior to chlorination. 
The process of the invention can thus be used to obtain not only 
indanthrone (I) but also its chlorine derivatives (Ia) in very good yields 
and high purities. The blue dyeings obtainable therewith are notable for 
purity of hue and brilliance. It is of particular advantage that 
indanthrone (I) is directly obtained in a readily filterable form and so 
can be isolated in an economical manner after short filtration times.

EXAMPLES 
Preparation of Indanthrone (I) and Chloroindanthrone (Ia) 
EXAMPLE 1 
A mixture of 150 g of 1-aminoanthraquinone (97.5% pure) and 230 g (220 ml) 
of N,N'-dimethylpropyleneurea was heated to 95.degree.-100.degree. C. Air 
was then passed through at a rate of 300 ml/min and at the same time 141 g 
of a 50% strength by weight sodium hydroxide solution were added dropwise 
over 3 h. The temperature was then raised to 125.degree.-130.degree. C. 
for 8 h and some of the water was distilled off. The end of the reaction 
was determined by thin layer chromatography (absence of 
1-aminoanthraquinone). 
The product (I) was precipitated by adding the reaction mixture to 800 ml 
of water, filtered off and washed. The filtration time was 2.5 h. 
For purification, the filter residue was stirred into a solution of 152 g 
of sodium hydroxide in 4,900 ml of water. 83 g of sodium dithionite were 
added at 60.degree. C. and the mixture was subsequently stirred for 20 
min. The precipitated sodium salt of the leucoindanthrone was then 
filtered off at 50.degree. C., washed and oxidized in air. 
The indanthrone (I) was obtained in a yield of 142 g, 98% of theory. 
COMATIVE EXAMPLE 1 
The condensation of 150 g of 1-aminoanthraquinone (97.5% pure) was carried 
out in 230 g (220 ml) of 1,3-dimethylimidazolidin-2-one as described in 
Example 1. 
The filtration to remove the product (I) took 60 h. 
The purification, which was also carried out in a similar manner, gave 137 
g of indanthrone (I), which corresponds to a yield of 95%. 
EXAMPLE 2 
To a solution of 80 g of indanthrone (I) of Example 1 in 800 g of 92% 
strength by weight sulfuric acid was added 4 g of manganese dioxide and 
then 64 g of chlorine were introduced at 50.degree.-55.degree. C. over 10 
h. The reaction mixture was introduced into 104 g of 75% strength by 
weight sulfuric acid, and 88 ml of water were added dropwise while the 
temperature was kept below 55.degree. C. 
After cooling down to room temperature, the precipitated chlorination 
product (Ia) was filtered off and washed with water. 
The filter residue was then dissolved in a mixture of 228 g of 96% strength 
by weight sulfuric acid and 320 g of oleum (24% by weight of SO.sub.3). 
After 2.4 g of aluminum powder had been added at 50.degree. C., the 
mixture was subsequently stirred for 1 h and then introduced into 2,000 ml 
of water. 
The resulting precipitate of product (I) was filtered off, washed neutral 
with water and dried. 
The yield obtained was 70 g of chloroindanthrone having a chlorine content 
of 6.9% by weight (n=1), corresponding to 81% of theory, based on (I). 
EXAMPLE 3 
102.6 g of 1-aminoanthraquinone (97.5% pure) were condensed in the presence 
of 200 g (190 ml) of N,N'-dimethylpropyleneurea as described in Example 1 
to form indanthrone (I). 
However, the as-obtained product (I) was not subjected to any purifying 
aftertreatment but directly chlorinated as described in Example 2. 
The yield obtained was 103 g of chloroindanthrone (Ia) having a chlorine 
content of 7.2% by weight (n=1), corresponding to 96% of theory, based on 
1 -aminoanthraquinone. 
EXAMPLE 4 
102.6 g of 1-aminoanthraquinone (97.5% pure) were condensed in the presence 
of 200 g (190 ml) of N,N'-dimethylpropyleneurea as described in Example 1 
to form indanthrone (I). 
The as-obtained product (I) was not further purified before being used in a 
chlorination. 
To this end the filter residue obtained was dissolved in 760 g of 91.5% 
strength by weight sulfuric acid. 155 g of chlorine were passed into this 
solution at 50.degree.-55.degree. C. over 21 h. Then 110 ml of water were 
added dropwise while the temperature was maintained below 55.degree. C. 
After cooling down to room temperature, the precipitated chlorination 
product (Ia) was filtered off and washed with 200 g of 80% strength by 
weight sulfuric acid. 
For purification, the filter residue was dissolved in 440 g of 98% strength 
by weight sulfuric acid. After addition of 2.2 g of aluminum powder at 
50.degree. C. the mixture was additionally stirred for 30 min until the 
exothermic reaction had ceased and then introduced into ml of water. 
The resulting precipitated product (Ia) was filtered off, washed neutral 
with water and dried. 
The yield obtained was 93 g of chloroindanthrone having a chlorine content 
of 13.6% by weight (n=2), corresponding to 81% of theory, based on 
1-aminoanthraquinone.