Preparation of tetrachloro-3-iminoisoindolin-1-one

Tetrachloro-3-iminosisoindolin-1-one (I) or its alkali metal salt (Ia) is prepared by reacting tetrachloro-ortho-phthalodinitrile with lithium hydroxide, sodium hydroxide and/or potassium hydroxide in substantially anhydrous tert-butanol and, if desired, liberating (I) from (Ia) by means of a dilute acid.

The present invention relates to a process for the preparation of 
tetrachloro-3-iminoisoindolin-1-one (I) or its alkali metal salt (Ia) by 
reacting tetrachloro-orthophthalodinitrile with an alkali metal hydroxide 
in an organic solvent and, if desired, liberating (I) from (Ia) by means 
of a dilute acid. 
German published application DAS No. 2,250,852 describes the preparation of 
tetrachloro-3-iminoisoindolin-1-one (I) by partial hydrolysis and 
cyclization of tetrachloro-ortho-phthalodinitrile (II) in the presence of 
alkali metals, a 1:1 mixture of water and an organic solvent 
advantageously being used as the solvent, and alcohols such as methanol, 
ethanol and isopropanol being employed as organic solvents. Tertiary 
alcohols are not mentioned. The resulting yields of pure compounds are 
about 80%, based on (II). Substantially lower yields are obtained if the 
water content of the solvent mixture is reduced (Comparative Example 1 
with 67% and Example 7) and in particular if the reaction is carried out 
in anhydrous alcohols. For example, the reaction of (II) with sodium 
hydroxide or potassium hydroxide in anhydrous ethanol or methanol 
according to Examples 14 and 15 gives yields of only 43.5 and 51% of the 
sodium and potassium salt, respectively, of (I). 
A process which gives improved yield and purity is described in German 
published application DAS No. 2,850,782. In this process, the 
halo-ortho-phthalodinitrile is reacted simultaneously with ammonia and 
hydrogen peroxide in a mixture of water and an organic solvent. In this 
reaction, large amounts of oxygen are liberated in a short time, and the 
process is therefore not acceptable industrially. For example, a violent 
explosion during the hydrolysis of o-tolunitrile with H.sub.2 O.sub.2 is 
reported in Organ. Synthesis Vol. II, 586 (1943). 
J. Org. Chem. 41 (1976), 3769 describes the conversion of simple 
mononitriles, including benzonitrile, to the corresponding carboxamides by 
hydrolysis with sodium hydroxide or potassium hydroxide in anhydrous 
methanol or tert-butanol. The yield of benzamide is about 90%. 
Mononitriles cannot be compared with the dinitriles to be used here since 
no cyclization takes place. 
It is an object of the present invention to provide a technically simple 
and safe process which gives tetrachloro-3-iminoisoindolin-1-one (I) or 
its alkali metal salt (Ia) in high yields and good purity. 
We have found that this object is achieved, and that 
tetrachloro-3-iminoisoindolin-1-one (I) 
##STR1## 
or its alkali metal salt (Ia) can particularly advantageously be prepared 
by reacting tetrachloro-ortho-phthalodinitrile (II) 
##STR2## 
with an alkali metal hydroxide in an organic solvent and, if desired, 
liberating (I) from (Ia) by means of a dilute acid, if the reaction is 
carried out using lithium hydroxide, sodium hydroxide or potassium 
hydroxide in substantially anhydrous liquid tert-butanol. 
The reaction according to the invention is described by the following 
equation: 
##STR3## 
The dinitrile (II) used as a starting material can readily be prepared from 
ortho-phthalodinitrile in a known manner, for example by the chlorination 
processes described in German patent Nos. 1,643,744 and 1,932,421, these 
processes giving (II) in purities of from 92 to 99%. 
In view of German published application DAS No. 2,250,852, it is surprising 
that the hydrolysis of (II) in anhydrous or substantially anhydrous 
tert-butanol leads to a substantial increase in yield from about 80 to 
more than 90% compared with the reaction in an aqueous organic medium, and 
that the hydrolysis in tert-butanol takes place in a substantially more 
advantageous manner than in other anhydrous alcohols, such as ethanol or 
methanol. 
The water content of the tert-butanol used in the novel process is 
advantageously less than 5, preferably less than 1, % by weight. As the 
water content increases, the yields decrease. 
The amount of tert-butanol is not critical. The solvent is advantageously 
used in an amount such that the reaction mixture remains stirrable before, 
during and after the reaction. The weight of tert-butanol used is 
preferably from 5 to 15, in particular from 6 to 10, times the weight of 
(II). 
Suitable alkali metal hydroxides are lithium hydroxide, sodium hydroxide 
and potassium hydroxide and mixtures of these. The amount of alkali metal 
hydroxide can be varied within wide limits, but not less than 1 mole per 
mole of (II) should be used in order to achieve high yields. As a rule, 
from 1 to 5, in particular from 1.1 to 2.5, preferably from 1.2 to 2.0, 
moles of alkali metal hydroxide are used per mole of 
tetrachloro-ortho-phthalodinitrile (II). The hydroxide may advantageously 
be added in a finely powdered form to the reaction mixture. 
The reaction is advantageously carried out under atmospheric pressure in 
liquid tert-butanol. The reaction temperatures are therefore restricted by 
the melting point and boiling point of the solvent. The reaction is 
advantageously carried out at from 26.degree. to 80.degree. C., in 
particular from 40.degree. to 70.degree. C., preferably from 45.degree. to 
55.degree. C. At above 40.degree. C., the reaction is as a rule complete 
after from 1 to 2 hours. 
The alkali metal salt of (I), which salt is present in the reaction mixture 
after the reaction, can be isolated in a known manner, for example by 
filtration. If conversion to tetrachloro-3-iminoisoindolin-1-one is 
desired, either the crude reaction mixture can be acidified or, 
advantageously, the salt can first be isolated and then reacted with an 
acid. (I) is liberated from the salt by a known method, for example by 
reaction with a dilute mineral acid or an organic water-soluble acid, such 
as acetic acid.

The process is advantageously carried out as follows: the dinitrile (II) is 
added to the substantially anhydrous tert-butanol, and the finely divided 
alkali metal hydroxide is then added to the stirred mixture. After the 
reaction in the abovementioned temperature range, the reaction mixture is 
advantageously cooled to about 25.degree. C. and filtered. The solid 
alkali metal salt can then be converted to the free 
tetrachloro-3-iminoisoindolin-1-one by, for example, introducing the salt 
into dilute acid. 
By using substantially anhydrous tert-butanol as a solvent, the filtrate 
can advantageously be re-used several times, preferably from 1 to 5 times, 
as a reaction medium, without purification being necessary. Recycling of 
the tert-butanol makes the procedure particularly economical. 
In the novel process, pure tetrachloro-3-iminoisoindolin-1-one (I) can be 
obtained in yields of from 95 to 98%, based on the starting material (II). 
The content of (I) is determined by titration with perchloric acid. The 
purity of the product, which is generally about 95%, is determined by HPLC 
(reversed phase high pressure liquid chromatography; Rosil 5 .mu.m, 
external standard). 
(I) is used as an intermediate for the preparation of pigments having good 
lightfastness and good heat stability. 
EXAMPLE 1 
400 g of liquid tert-butanol and 53 g (0.2 mole) of 
tetrachloro-ortho-phthalodinitrile were initially taken in a flask. 17 g 
(0.3 mole) of finely powdered KOH were added, after which the reaction 
mixture was stirred for 2 hours at 48.degree.-52.degree. C. and then 
cooled to 20.degree. C., and the solid was filtered off over a suction 
filter. 
The filtrate collected (about 330 g) was supplemented with fresh 
tert-butanol and re-used as a reaction medium. 
The filtration residue was suspended in 400 ml of water, the mixture was 
brought to pH .congruent.6 by adding dilute acetic acid, and the solid was 
filtered off under suction, washed with water and dried under reduced 
pressure. 
Yield: 54 g (95%) of tetrachloro-3-iminoisoindolin-1-one. 
Purity according to HPLC =97.5%. 
EXAMPLE 2 
The process of Example 1 was repeated, except that finely divided sodium 
hydroxide was used instead of potassium hydroxide. 
Yield: 52 g (92%) of tetrachloro-3-iminoisoindolin-1-one. 
Purity according to HPLC=95%. 
EXAMPLE 3 
(a) The procedure described in Example 1 was followed. The tert-butanol 
filtrate (330 g) obtained after isolation of the reaction product was made 
up to 400 g by adding pure tert-butanol and used for a further reaction as 
described in Example 1. 
Yield: 56 g (98%) of tetrachloro-3-iminoisoindolin-1-one. 
Purity according to HPLC=95%. 
(b) The tert-butanol filtrate obtained after isolation of the reaction 
product under (a) was made up to 400 g and used for a further reaction as 
described in Example 1. 
Yield: 55 g (96.7%) of tetrachloro-3-iminoisoindolin-1-one. 
Purity according to HPLC=93%. 
(c) The tert-butanol filtrate obtained after isolation of the reaction 
product under (b) was made up to 400 g and used for a further reaction as 
described in Example 1. 
Yield: 54 g (95%) of tetrachloro-3-iminoisoindolin-1-one. 
Purity according to HPLC=92%. 
COMATIVE EXAMPLE 1 
According to German published application DAS No. 2,850,782 
5 parts of sodium hydroxide are dissolved in 12.5 parts of water, and 75 
parts of ethanol are added to the thoroughly stirred solution. 20 parts of 
3,4,5,6-tetrachlorophthalodinitrile are added to the solution, after which 
stirring is continued for 5 hours at from 70.degree. to 78.degree. C. and 
the reaction mixture is then cooled to 15.degree. C. and filtered under 
suction. The resulting cake is washed with water and then added to 100 
parts of a 5% strength aqueous acetic acid. The mixture is stirred and 
filtered under suction, after which the cake obtained is washed thoroughly 
with water and dried under reduced pressure to give 7.16 parts of a solid, 
which is identified as 3-imino-4,5,6,7-tetrachloroisoindolin-1-one. The 
purity according to HPLC is 94.0% and the yield is 67%. 
COMATIVE EXAMPLE 2 
The procedure described in Example 1 is followed, except that a solvent 
mixture consisting of water and tert-butanol is used instead of 
tert-butanol. As shown in the table below, the yield decreases with 
increasing water content. 
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tert-butanol H.sub.2 O 
Yield 
Example [g] [g] [%] 
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1 400 0 95 
2a 396 4 94 
2b 380 20 91 
2c 280 120 80 
2d 160 240 63 
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