Process for preparing pure 1-nitroanthraquinone

Pure 1-nitroanthraquinone substantially free of dinitroanthraquinone is prepared by: PA1 1. Nitrating anthraquinone or a mixture which contains anthraquinone with at least 90% nitric acid at a temperature of at least 0.degree. C wherein the mole ratio of nitric acid to anthraquinone is less than 20 to 1; PA1 2. Stopping the reaction when the anthraquinone conversion is at least 50% by cooling the reaction mixture to a temperature of at most 20.degree. C and/or by adjusting the mole fraction of nitric acid in the reaction mixture to a value of at most 0.86; PA1 3. Precipitating 1-nitroanthraquinone by adjusting the mole fraction of nitric acid to a value of from 0.7 to 0.4 and/or by reducing the temperature to at most 20.degree. C; and PA1 4. Separating the precipitated 1-nitroanthraquinone and subjecting it to vacuum distillation.

BACKGROUND 
This invention relates to a process for preparing 1-nitroanthraquinone 
substantially free of dinitroanthraquinone. 
In the processes hitherto known for producing 1-nitroanthraquinone from 
anthraquinone and nitric acid, nitration and purification of the resulting 
1-nitroanthraquinone have proved very difficult. 
Either the products obtained are not pure enough for conversion into dye 
intermediate products or the yield of pure product is so low as to render 
the process uneconomical. Thus, for example German Offenlegungsschrift No. 
2,162,538 claims the nitration of anthraquinone in nitric acid with a mole 
ratio of at least 20, in particular from 24 to 50. (The term "mole ratio" 
is used herein to denote the ratio of nitric acid to anthraquinone or 
anthraquinone plus nitration products.) 
The reaction is stopped by the addition of considerable quantities of 
water, with the result that the product obtained is purified by the dilute 
nitric acid thereby formed. The substances which go into solution, apart 
from a small quantity of 1-nitroanthraquinone, are mainly 
2-nitroanthraquinone, anthraquinone and 1,6- and 1,7-dinitroanthraquinone. 
Approximately 92% pure 1-nitroanthraquinone has been obtained by this 
method in a maximum yield of 74.5%. (All percentages herein are by weight 
unless otherwise stated.) 
Since the dilute nitric acid formed must be worked up and in some cases 
regenerated, it is a serious economic disadvantage to have to stop the 
reaction with a large quantity of water. For this reason, German 
Offenlegungsschrift No. 2,227,340 claims so-called nitration inhibitors, 
such as nitrites, phosphates or phosphoric acid, which are intended to 
reduce the reaction velocity. The disadvantage of this method is that it 
introduces foreign substances into the reaction mixture so that a separate 
operation is required to work up the nitric acid. 
Another possibility for stopping the nitration of anthraquinone with excess 
nitric acid has been described in German Offenlegungsschrift No. 
2,220,377. 
To regulate (reduce) the reaction velocity, the process described uses 
nitric acid diluted only to such a degree that, at the end of the 
nitration reaction, the total nitric acid content of the mixture is still 
above the azeotropic limit (68% nitric acid). Whereas nitric acid which 
has a concentration of at least 93%, and preferably 97%, is used for 
nitration and a mole ratio of from 20 to 120 is employed, the nitric acid 
used to reduce the nitration velocity is preferably at a concentration of 
from 70 to 80%, so that when nitration is terminated the nitric acid 
content of the nitration mixture is preferably from 75 to 90%. 
The resulting reaction mixture is separated into nitration products and two 
nitric acid fractions. If desired, the crystallised nitration product may 
first be separated and the remaining nitric acid fractionated, or 
alternatively a highly concentrated nitric acid may first be removed from 
the reaction mixture and the remaining mixture may then be divided into 
nitration product and dilute acid. The concentrated nitric acid should 
then be used again for subsequent nitration reactions and the dilute 
nitric acid for regulating the reaction velocity. 
The relatively large quantities of dilute nitric acid obtained by this 
operation result in a purer 1-nitroanthraquinone obtained by nitration 
because the major portion of the reaction by-products and the unreacted 
anthraquinone (with the exception of 1,5- and 1,8-dinitroanthraquinone) 
are dissolved in the dilute nitric acid while the 1-nitroanthraquinone 
crystallises. The disadvantages of this process lie in the fact that 
complete or partial purification of this dilute acid is necessary if the 
acid is to be used again to stop the reaction and hence act as a purifying 
agent to obtain a reasonably pure 1-nitroanthraquinone. 
The quantities of nitric acid which have to be handled are enormous. If, 
for example, nitration is carried out with a mole ratio of about 38 to 
40:1 and the reaction is stopped with 74-78.5% nitric acid, then the mole 
ratio after stopping the reaction is 78 to 100:1 (the proportion by weight 
of the resulting 78 to 87% nitric acid to anthraquinone plus 
nitroanthraquinone derivatives being approximately 22 to 37:1 ). 
In spite of these enormous efforts, the 1-nitroanthraquinone obtained is at 
the most 91% pure and the yield is approximately 65%. The product still 
contains substantial quantities of anthraquinone, 1,5-dinitroanthraquinone 
and 1,8-dinitroanthraquinone and cannot be used directly for the 
production of dye intermediate products without further purification. 
Thus, for example, German Offenlegungsschrift No. 2,206,960 describes the 
treatment of partly purified products which contain dinitroanthraquinone 
with aqueous Na.sub.2 SO.sub.3 solution in the presence of sodium 
hydroxide solution. The 1-nitroanthraquinone obtained by this method also 
has a maximum purity of only 97% (the remainder consisting of 1,5- and 
1,8-dinitroanthraquinone). In addition to 2-nitroanthraquinone and part of 
the dinitroanthraquinones, about 5% of 1-nitroanthraquinone enter the 
aqueous filtrate in the form of intensively coloured water-soluble 
compounds, and, together with the inorganic sulphur compounds, they 
heavily contaminate the effluent water. 
Other methods for completely separating the by-products of nitration, e.g., 
washing with acid amides (German Offenlegungschrift No. 2,039,822) or 
treatment with saturated chlorinated hydrocarbons which contain nitric 
acid (German Offenlegungsschrift No. 2,142,100) result in 
1-nitroanthraquinone which is only 95-96% pure (with a total yield via 
nitration and purification of 42 to 43%). 
No process has hitherto been described by means of which a very pure 
1-nitroanthraquinone, almost free from dinitroanthraquinone, can be 
obtained in economical yields. 
It has now surprisingly been found that very pure 1-nitroanthraquinone, 
which is almost free from dinitroanthraquinone and which can be used 
directly for the preparation of dye intermediate products, can be prepared 
without producing large quantities of dilute nitric acid, with the result 
that the nitration process can be rendered much more economical and much 
time, energy and expenditure of apparatus can be saved. In this process, 
anthraquinone or a mixture which contains anthraquinone is nitrated in the 
presence of highly concentrated nitric acid, in particular in &gt;90% nitric 
acid, with a mole ratio of nitric acid to anthraquinone of &lt;20:1 and at a 
temperature of .gtoreq.0.degree. C, in particular .gtoreq.45.degree. C; 
and the reaction is stopped by cooling the reaction mixture to 
temperatures below 30.degree. C and/or by lowering the mole fraction of 
nitric acid e.g., by the addition of diluents such as water and/or by 
distilling off nitric acid; the 1-nitroanthraquinone is precipitated, 
either by further cooling of the reaction mixture and/or by further 
reducting of the mole fraction of nitric acid, e.g., by the addition of 
diluents such as water and/or dilute nitric acid, in particular &lt;90% 
nitric acid and/or by further removal of nitric acid by distillation; and 
the precipitate is isolated and freed from nitric acid, in particular by 
vacuum drying, and finally subjected to vacuum rectification. 
In the text which follows, the term "mole fraction" is used herein to 
denote the mole fraction of nitric acid in a given total mixture in 
accordance with the following equation: 
EQU .gamma..sub.HNO.sbsb.3 = n.sub.HNO.sbsb.3 /(n.sub.HNO.sbsb.3 + n.sub.N + 
n.sub.H.sbsb.2O) 
where 
n = number of moles, and 
N = nitroanthraquinone derivatives and anthraquinone. 
The process according to the invention is characterised in that 
anthraquinone or a mixture which contains anthraquinone is nitrated with 
at least 90%, and in particular 95-100%, nitric acid at temperatures of at 
least 0.degree. C, in particular .gtoreq.45.degree. C, preferably 
55.degree.-75.degree. C, and with a mole ratio of nitric acid to 
anthraquinone of &lt;20:1, in particular 6:1 to 15:1; the reaction is stopped 
when the anthraquinone conversion is .gtoreq.50%, in particular 80 to 
100%, by cooling the reaction mixture to temperatures .ltoreq.30.degree. C 
and/or by adjusting the mole fraction of nitric acid to a value 
.ltoreq.0.86, for example by the addition of water and/or removal of 
nitric acid by distillation; 1-nitroanthraquinone is thereafter 
precipitated by adjusting the mole fraction of nitric acid to a value of 
from 0.7 to 0.4 by distilling off nitric acid and/or by diluting with 
water and/or by adding dilute nitric acid, and/or the 1-nitroanthraquinone 
is precipitated by lowering the temperature to .ltoreq.20.degree. C; and 
the precipitated 1-nitroanthraquinone is separated off and subjected to 
vacuum distillation, optionally in the presence of solvents which are 
stable under the conditions of distillation, which are inert towards 
nitroanthraquinone and which boil at temperatures between 100.degree. and 
350.degree. C. 
By mixtures which contain anthraquinone are meant mixtures which, in 
addition to anthraquinone, contain nitroderivatives of anthraquinone such 
as 1-nitroanthraquinone, 2-nitroanthraquinone and di-nitroanthraquinone. 
The relative proportion of anthraquinone to nitro-compounds of 
anthraquinone in such mixtures is not critical for the process according 
to the invention, but mixtures containing at least 50% by weight of 
anthraquinone are normally used. 
The process of nitration according to the invention can be carried out in 
conventional reaction apparatus such as flow tubes, tank cascades or 
separate tanks, either continuously or discontinuously. In order to obtain 
maximum possible yields of 1-nitroanthraquinone in continuous processes, 
the flow, if flow tubes are used, should be a distinct plug flow and 
Reynolds numbers should be .gtoreq.2300; if cascades or tanks are used, an 
ideal spectrum of residence times in the apparatus should be achieved. The 
reaction is preferably carried out adiabatically or partly adiabatically 
but may, of course, also be carried out isothermally. 
When nitration is carried out with mole ratios of nitric acid to 
anthraquinone of from 6:1 to 19:1, for example using 99% nitric acid, mole 
fractions of .gamma..sub.HNO.sbsb.3 = 0.69 to 0.87 become established. The 
point at which the reaction is stopped depends on the mole fraction of 
nitric acid in the mixture and of course also on the temperature. The 
reaction mixture must be adjusted to lower mole fractions at higher 
temperatures than at low temperatures. 
If, for example, nitration is carried out with a mole ratio of 19:1, 15:1, 
10:1 or 6:1, the reaction may be stopped by cooling to temperatures of 
.ltoreq.-5.degree. C, .ltoreq.5.degree. C, .ltoreq.15.degree. C or 
.ltoreq.30.degree. C respectively. The corresponding mole fractions are 
.gamma..sub.HNO.sbsb.3 = 0.871; 0.847; 0.793 or 0.694. The appropriate 
mole fractions may, of course, also obtained by stopping the reaction by 
rapidly distilling off concentrated nitric acid. At higher temperatures, 
the reaction mixture, must, of course, be adjusted to lower mole 
fractions. Thus, for example, at 65.degree. C (45.degree. C, 25.degree. C) 
and mole ratios of 18:1, 10:1 and 5:1, the appropriate acid concentrations 
are about 86% (90; 93), 91.5% (93.5; 95.5) and 95.5% (96.5; 97.5) and the 
appropriate mole fractions are 0.615 (0.692; 0.758); 0.702 (0.744; 0.791) 
and 0.733 (0.754; 0.775). These values can easily be obtained if water is 
added to the reaction mixture to stop the reaction. 
In the same way as the stopping of the reactions, the purification by 
crystallisation is also dependent upon the temperature and the mole 
fraction of nitric acid in the nitration mixture. Since nitric acid has a 
relatively high vapour pressure at elevated temperature, it would appear 
more suitable to filter off the crystallisate at room temperature or 
temperatures of up to 30.degree. C. The quantities and concentrations of 
nitric acid required for purification depend upon which impurities are to 
be separated and in what quantities. If, for example, 10% by weight (5% by 
weight) of anthraquinone is to be removed from the nitroanthraquinone 
mixture, then the acid concentrations may be adjusted, for example, to 
about 93% (82%), 84% (78%), 80% (76%) or 76% (72%) and the mole fractions 
accordingly to .gamma..sub.HNO.sbsb.3 = 0.69 (0.53), 0.58 (0.49), 0.52 
(0.47) or 0.46 (0.42). 
The same applies, of course, to the separation of 2-nitroanthraquinone from 
nitroanthraquinone mixtures. If, for example, about 8% by weight of 
2-nitroanthraquinone and less than 3% by weight of anthraquinone are to be 
separated, then the mole fractions must be adjusted to 
.gamma..sub.HNO.sbsb.3 = 0.51; 0.49; 0.47 or 0.42 if the acid 
concentrations are about 80%, 78%, 76% or 72%. In order to keep the loss 
of 1-nitroanthraquinone by separation as small as possible, the mole 
fractions should be large (small), i.e., the mole ratios small (large), 
when the acid concentrations are high (low). 
The larger the quantity of appropriately diluted nitric acid, the smaller 
is the loss of 1-nitroanthraquinone by separation, but large quantities of 
dilute nitric acid are uneconomical because the nitric acid must then be 
distilled and in some cases reconcentrated. It has now been found that 
1-nitroanthraquinone sufficiently pure for the next stage of the process 
is obtained by using 90-72% nitric acid for the process of crystallisation 
and the purification associated with it, and by adjusting the mole 
fractions accordingly to values between .gamma..sub.HNO.sbsb.3 = 0.70 and 
.gamma..sub.HNO.sbsb.3 = 0.42. 
The following possible combinations can be employed for stopping the 
reaction and for subsequent purification in the process according to the 
invention. 
If the reaction is stopped by the addition of a small quantity of water 
and/or by distilling off nitric acid and/or by cooling the reaction 
mixture, the required mole fraction for precipitation of 
1-nitroanthraquinone can be adjusted by adding water and/or dilute nitric 
acid and/or by distilling off nitric acid. 
If a mole ratio of nitration products and unreacted anthraquinone to nitric 
acid of .ltoreq.12:1 is obtained by distilling off nitric acid, or if 
nitration is carried out with these mole ratios, then 1-nitroanthraquinone 
precipitated at temperatures of up to 15.degree. C can be separated from 
the by-products in the filtrate. These by-products can be precipitated 
almost completely from the filtrate if the mole fraction is adjusted to a 
value of .ltoreq.0.4, e.g., by dilution with water or by partial or 
complete removal of nitric acid by distillation. This precipitated mixture 
of by-products which is removed in the usual manner contains almost all 
the 2-nitroanthraquinone. This can be isolated in a relatively pure form 
by carrying out the aforesaid precipitation as a fractional precipitation. 
Nitric acid free from organic products can be returned to the process, for 
example after reconcentrating it, or as a diluent. 
1-Nitroanthraquinone precipitated from nitric acid is obtained in a 
crystalline form and can be filtered off relatively easily (e.g. by means 
of a rotary, plane or pressure filter). The filter cake, after having been 
briefly washed with dilute nitric acid, may be washed until neutral with 
water in the usual manner and dried, or it may be directly freed from 
nitric acid in a vacuum (e.g., using a flow drier or roller drier). The 
dried 1-nitroanthraquinone is then subjected to vacuum distillation, in 
particular rectification. 
The temperatures and pressures given below indicate the conditions at the 
head of the distillation apparatus. 
Distillation may be carried out at a temperature of 200.degree.-400.degree. 
C and 0.5 to 100 Torr, preferably 235-330.degree. C and 1.5 to 50 Torr, in 
particular at 245.degree.-315.degree. C and 2.5 to 35 Torr. It has been 
found particularly suitable to carry out the distillation at temperatures 
of between 265.degree. and 300.degree. C and under a vacuum of 5 to 20 
Torr. The whole process may be carried out continuously or 
discontinuously. 
According to one particular variation, the already partly purified product 
and a solvent which boils at a temperature of 100.degree. to 350.degree. 
C, which is stable under the distillation conditions and which is inert 
towards the product, for example high boiling hydrocarbons or silicone 
oils, are distilled off together under the conditions indicated above, and 
in particular at 200.degree. to 350.degree. C and 0.5 to 100 Torr. 
1-Nitroanthraquinone which crystallises from the condensate is then 
removed by conventional methods. 
The process according to the invention may, for example, be carried out 
according to the following variations: 
Variation 1 
Nitration is stopped by transferring the whole reaction mixture to an 
evaporator, e.g., a thin layer contact evaporator or a falling film 
evaporator, and distilling off the required proportion of nitric acid, 
preferably rapidly. The mixture is then transferred from the sump to a 
crystallising apparatus in which 1-nitroanthraquinone is precipitated, by 
cooling the mixture to temperatures of up to 15.degree. C and/or by adding 
water or dilute nitric acid, and the precipitate is then separated in a 
separating device. The by-products dissolved in the filtrate can be 
precipitated by diluting the filtrate with water or by distilling off 
nitric acid. The nitric acid freed from organic products can be separated 
into a high-percentage nitric acid and a low-percentage nitric acid by 
means of a separating column. The high-percentage acid may be returned to 
the nitration process and the low-percentage acid may be used for the 
crystallisation step. 
The precipitated 1-nitroanthraquinone is freed from nitric acid, in 
particular by direct vacuum drying, and subjected to high vacuum 
rectification. 
Variation 2 
Nitration is stopped in a cooling apparatus by cooling to the appropriate 
temperatures of up to 25.degree. C, depending on the mole ratios. 
1-Nitroanthraquinone is then precipitated by diluting the reaction mixture 
with water and/or dilute nitric acid and/or by cooling the reaction 
mixture to 15.degree. C or lower, and it is then separated in a separating 
device. Further purification of the 1-nitroanthraquinone and working up of 
the filtrate are carried out as in Variation 1. 
Variation 3 
Nitration is stopped by adding a little water to the reaction mixture in a 
mixing vessel. The reaction mixture is then adjusted to a mole fraction of 
.ltoreq.0.7 by the addition of dilute nitric acid or further quantities of 
water and/or by distilling off the appropriate quantities of nitric acid. 
The precipitated 1-nitroanthraquinone is separated. Further purification 
of the 1 -nitroanthraquinone and working up of the filtrate are carried 
out as described in Variation 1. Combinations of these variations are, of 
course, also possible. 
The advantages of the process according to the invention lie in the fact 
that nitration can be stopped with small mole ratios (.ltoreq.19:1) by a 
relatively slight alteration of the conditions (e.g., temperature or mole 
fraction of nitric acid). 
The quantities of nitric acid required for crystallisation and the 
associated purification are also small so that the cost of redistillation 
and, if indicated, regeneration of nitric acid are not a substantial 
burden on the process. Moreover, the process provides high yields of pure 
1-nitroanthraquinone which is practically free from dinitroanthraquinone 
and can be used directly for the production of dyes. Another advantage of 
this process is that all the by-products of nitration can be isolated, if 
necessary by additional operations, and worked up. Thus, for example, the 
sump product of high vacuum rectification, which substantially contains 
only 1-nitroanthraquinone and 1,5- and 1,8-dinitroanthraquinone, can be 
renitrated, e.g., in concentrated nitric acid, to give a mixture of 1,5- 
and 1,8-dinitroanthraquinone from which 1,5- and 1,8-dinitroanthraquinone 
can be isolated in a practically pure form by measures similar to those 
described for the isolation of 1-nitroanthraquinone (fractional 
precipitation from nitric acid). 
In the following examples, the term "mole ratio" always refers to the ratio 
of nitric acid to anthraquinone or anthraquinone plus nitration products. 
Unless otherwise indicated, the crystallised product is separated at room 
temperature. The yield is always based on the quantity of anthraquinone 
put into the process. Degrees are given in .degree.C. All the batchwise 
processes described here can, of course, also be carried out continuously, 
and vice versa.

EXAMPLE 1 
A mixture of 2.08 kg of anthraquinone and 9.545 kg of 99% nitric acid per 
hour (mole ratio 15:1) cooled to 0.degree. is continuously reacted in a 
flow tube reactor at a temperature of 55.degree. and with a residence time 
of 10 minutes. To stop the reaction, the reaction mixture is transferred 
to an evaporator (e.g. thin layer, circulating or falling film evaporator) 
immediately on leaving the reactor. In this evaporator, 4.725 kg per hour 
of 99% nitric acid are distilled off under vacuum (acid concentration 
about 94.7%, .gamma..sub.HNO.sbsb.3 = 0.740). The nitric acid distilled 
off is used again for nitration while the sump product is transferred to a 
crystallisation vessel into which 5.986 kg per hour of 70% nitric acid are 
introduced (crystallisation acid 80%, .gamma..sub.HNO.sbsb.3 = 0.519). The 
crystallised product is separated by means of a centrifuge (e.g., also by 
means of a rotary, plane or pressure filter). It is then briefly washed 
with 75% nitric acid, freed from nitric acid under vacuum, melted, and 
subjected to vacuum rectification at 10 Torr and a head temperature of 
281.degree. C. The yield of 99.2% pure product is 1.683 kg per hour (66% 
of the theoretical amount). Organic constituents still dissolved in the 
mother liquor are precipitated by distilling off nitric acid and are 
separated. The nitric acid is separated by distillation into 99% nitric 
acid and 70% nitric acid. The 99% acid may be used for nitration, while 
the 70% acid may be used for crystallisation or may be reconcentrated. 
EXAMPLE 2 
208 g of anthraquinone and 509 g of 99% nitric acid (more ratio 8:1) are 
heated to 60.degree. C for 1 hour with stirring. The reaction mixture is 
then rapidly cooled to 0.degree. C, and 1584 g of 73% nitric acid are 
added (crystallisation acid 78%, .gamma..sub.HNO.sbsb.3 = 0.493). The 
crystallised product is filtered off, washed with a little 76% nitric 
acid, freed from nitric acid under vacuum and fractionally distilled at 15 
Torr and a head temperature of 292.degree.. 157 g of 98.5% 
1-nitroanthraquinone are obtained (61.2% of theoretical amount). 
EXAMPLE 3 
208 g of anthraquinone are introduced into 955 g of 99% nitric acid at 
0.degree. with stirring (mole ratio 15:1). The temperature of the reaction 
mixture rises to 55.degree. in about 6 minutes. This temperature is 
maintained by cooling until the total reaction time is 10 minutes. 316 g 
of 99% nitric acid (.gamma..sub.HNO.sbsb.3 = 0.791) are then distilled off 
very rapidly at this temperature under vacuum. 100 ml of water are then 
slowly added to the sump product (crystallisation acid 82%, 
.gamma..sub.HNO.sbsb.3 = 0.532). The precipitated product is 
suction-filtered, washed with a little 75% nitric acid and then with 
water, dried and subjected to fractional vacuum distillation at 10 Torr 
and a head temperature of 281.degree.. 172.1 g of 98.7% pure 
1-nitroanthraquinone (67.1% of the theoretical amount) are obtained as 
distillate. 
EXAMPLE 4 
208 g of anthraquinone are introduced into 1208 g of 99% nitric acid at 
0.degree. with stirring (mole ratio 19:1). After a reaction time of 110 
minutes at 0.degree., the temperature is rapidly reduced to -20.degree. to 
stop the reaction. 1797 g of 63.8% nitric acid (crystallisation acid 77%, 
.gamma..sub.HNO.sbsb.3 = 0.483) are then slowly added for crystallisation. 
When the crystallised product has been filtered, it is washed with a 
little 70% nitric acid, freed from nitric acid and subjected to vacuum 
rectification at 5 Torr and a head temperature of 262.degree.. 176.3 g of 
99% 1-nitroanthraquinone are obtained (69% of the theoretical amount). 
EXAMPLE 5 
A mixture of 208 g of anthraquinone and 382 g of 99% nitric acid (mole 
ratio 6:1) is heated to 75.degree. C for 10 hours with stirring and then 
slowly cooled to -10.degree. (.gamma..sub.HNO.sbsb.3 = 0.695). The 
precipitated product is filtered off, washed with a little 75% nitric 
acid, freed from nitric acid adhering to it by evaporation under vacuum, 
and fractionally distilled at 6 Torr and 267.degree. head temperature. 
151.5 g of 98.5% pure 1-nitroanthraquinone are obtained (59% of the 
theoretical amount). 
EXAMPLE 6 
208 g of anthraquinone are introduced with stirring into 99% nitric acid 
which is at a temperature of 45.degree. (955 g, mole ratio 15:1). The 
isothermal reaction is then stopped after 9 minutes by rapid addition of 
100 ml of water. Crystallisation is then brought about by slowly adding a 
further 105 ml of water (crystallisation acid 79%, .gamma..sub.HNO.sbsb.3 
= 0.500). The crystallisate is separated, washed with a little 75% nitric 
acid, freed from nitric acid adhering to it under a vacuum and 
fractionally distilled under a vacuum (5 Torr, head temperature 
265.degree.). 160.4 g of 99.4% pure 1-nitroanthraquinone are obtained (63% 
of the theoretical amount). 
EXAMPLE 7 
A mixture of 2.08 kg of anthraquinone and 9.545 kg of 99% nitric acid per 
hour (mole ratio 15:1) is cooled to 0.degree. and continuously reacted in 
a flow tube reactor with a residence time of 13 minutes and a final 
temperature of 55.degree.. The solution leaving the reactor is 
continuously cooled to -10.degree. to stop the reaction and introduced 
into a crystallising apparatus together with 19.33 kg per hour of 66.2% 
nitric acid (crystallisation acid 76%, .gamma..sub.HNO.sbsb.3 = 0.469). 
The precipitated product is continuously suction-filtered, washed with a 
little 76% nitric acid, freed from nitric acid adhering to it and 
subjected to continuous vacuum rectification (10 Torr, head temperature 
281.degree.). 1.740 kg of 98.9% pure 1-nitroanthraquinone are obtained per 
hour (68% of the theoretical amount). 
EXAMPLE 8 
208 g of anthraquinone are introduced into 764 g of 99% nitric acid (mole 
ratio 12:1) at room temperature with stirring. The reaction is then left 
to proceed adiabatically until the temperature reaches 45.degree.. The 
reaction is then continued isothermally at 45.degree. until the total 
reaction time is 17 minutes. The reaction is stopped by distilling off 330 
g of 99% nitric acid. 128.0 g of 50% nitric acid (crystallisation acid 
83.4%, .gamma..sub.HNO.sbsb.3 = 0.542) are slowly added to the sump 
product (acid concentration approximately 94.4%, .gamma..sub.HNO.sbsb.3 = 
0.725). The product which precipitates under these conditions is 
suction-filtered, washed with a little dilute nitric acid, freed from 
nitric acid by washing with water, dried and subjected to vacuum 
rectification at 8 Torr with a head temperature of 275.degree.. 162.3 g of 
98.2% pure 1-nitroanthraquinone are obtained as a distillate (63% of the 
theoretical amount). 
EXAMPLE 9 
208 g of anthraquinone are introduced into 1145 g of 99% nitric acid (mole 
ratio 18:1) at 25.degree. with cooling and the reaction mixture is stirred 
for 25 minutes. The reaction is then stopped by rapidly distilling off 693 
g of 99% nitric acid and the product is precipitated by slowly cooling the 
reaction mixture to 0.degree.. After washing with dilute nitric acid, the 
product is freed from nitric acid and distilled together with 800 g of 
paraffin oil at 30 Torr with a head temperature of between 250.degree. and 
300.degree.. 1-Nitroanthraquinone which precipitates from the condensate 
is filtered off and freed from paraffin oil by washing with petroleum 
ether. 163 g of 98.9% pure 1-nitroanthraquinone are obtained (63.5% of the 
theoretical amount). 
EXAMPLE 10 
208 g of anthraquinone in 969 g of 97.5% nitric acid (mole ratio 15:1) are 
heated to 35.degree. for 2 hours with stirring. The reaction is stopped by 
the addition of 103 ml of water. After removal of 265 g of 99% nitric acid 
by distillation (crystallisation acid 81%, .gamma..sub.HNO.sbsb.3 = 
0.520), the precipitated product is freed from nitric acid and dried and 
distilled at 30 Torr with head temperatures of 250.degree. to 300.degree., 
together with about 800 g of silicone oil. The yield of 99.2% 
1-nitroanthraquinone is 153 g (60% of the theoretical amount). 
EXAMPLE 11 
208 g of anthraquinone are introduced into 955 g of 99% nitric acid (mole 
ratio 15:1) with stirring at room temperature without cooling. When a 
temperature of 55.degree. is reached, the reaction is continued 
isothermally until the total reaction time is about 9 minutes. The 
reaction is then stopped by rapid removal of 376 g of 99% nitric acid by 
distillation (95.5% nitric acid, .gamma..sub.HNO.sbsb.3 = 0.779). 
Crystallisation is then started by slowly adding 1147 g of 70% nitric acid 
(crystallisation acid 78.1%, .gamma..sub.HNO.sbsb.3 = 0.492). The 
precipitated product is filtered off, briefly washed with dilute nitric 
acid, freed from nitric acid adhering to it by evaporation under vacuum 
and then fractionally distilled at 7 Torr with a head temperature of 
275.degree. C. 169.5 g of 98.5% pure 1-nitroanthraquinone (66% of the 
theoretical amount) are obtained.