EP0809638A2

EP0809638A2 - Process for producing ammonium salts of 3-isopropyl-2,1,3-benzothiadiazine-4-on-2,2-dioxide

Info

Publication number: EP0809638A2
Application number: EP96902969A
Authority: EP
Inventors: Hans Rupert Merkle; Alfons Durein; Hanspeter Hansen; Karl-Friedrich Jäger
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1995-02-15
Filing date: 1996-02-01
Publication date: 1997-12-03
Also published as: NO309983B1; AR022849A1; IL116959A0; NO973758L; CA2211110C; ZA961171B; FI973339A; US5795983A; HUP9702423A3; HUP9702423A2; CN1175947A; SK284010B6; CZ292785B6; SK104797A3; NO973758D0; EP0866062A1; UA62910C2; HU221207B1; CZ296270B6; AU703200B2

Abstract

A process for producing salts of 3-isopropyl-2,1,3-benzothiadiazine-4-on-2,2-dioxide of general formula (I) (R1-R4 = H, lower alkyl, lower hydroxyalkyl) by reacting bentazone (IIa) in an organic solvent with an amine (IIIa), reacting bentazone (IIa) in an organic solvent virtually immiscible with water with an amine (IIIa) or an ammonium salt (IIIb) and taking salt (I) up in water or reacting bentazone (IIa) with an ammonium salt (IIIb) or sodium bentazone (IIb) with an ammonium salt (IIIc) in water.

Description

Process for the preparation of ammonium salts of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2,2-dioxide

description

The present invention relates to processes for the preparation of salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one-2, 2-dioxide of the general formula I.

in which the radicals R, R ² , R ³ and R ⁴ independently of one another represent hydrogen, lower alkyl or lower hydroxyalkyl.

Herbicidal benzothiadiazin-4-one-2,2-dioxide are known from DE-A 15 42 836, DE-A 21 64 459 and DE-A 22 17 722. There, ammonium salts are also mentioned as a form of use, the ammonium, methylammonium, trimethylammonium, ethylammonium, diethanolammonium and ethanol monium salts being particularly mentioned.

It is also generally known that the sodium, calcium and potassium salts of 3-isopropyl-2, 1,3-benzothiadiazin-4-one-2,2-dioxide (INN name: Bentazone) are very hygroscopic are. In the case of solid formulations of these salts, this leads to the product already clumping or even flowing away as a result of atmospheric moisture and as a result is no longer easy to dose.

When these salts are introduced into water-soluble film bags, the latter are also dehydrated by the interaction of the hygroscopic active substances with the films. As a result, the foils become brittle, i.e. their storage stability is no longer guaranteed.

In the synthesis of bentazone, the active substance is usually obtained in neutral form and generally dissolved in an organic solvent (cf. DE-A 27 10 382).

Most of the time, the active ingredient is subsequently converted into one of its salts, since these improve the bioavailability of bentazone. From US Pat. No. 5,266,553 it is known, for example, to formulate ammonium salts of bentazone as flowable, water-soluble solids. For this purpose, an aqueous mixture of the ammonium salt is first prepared in accordance with the general teaching of the patent. The solid formulation of the active ingredient is obtained from this by evaporating all the solvent and after-treating the product with a neutralizing base. However, the evaporation step when water is also used as the solvent requires a high expenditure of energy and the active substance is exposed to the elevated evaporation temperature for a very long time.

The present invention was therefore based on processes for the production of ammonium salts of bentazone, in which the disadvantages of the production process described above are avoided in whole or in part.

Accordingly, a process for the preparation of salts of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2,2-dioxide of the general formula I

in which the radicals R ¹ , R ² and R ³ independently of one another represent hydrogen, lower alkyl or lower hydroxyalkyl, which is characterized in that 3-isopropyl-2, 1,3-benzothiadiazine -4-on-2,2-dioxide (Ila)

in an organic solvent with an amine of the general formula purple

Ri - N - R ³ (purple). Furthermore, a process for the preparation of salts of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2, 2-dioxide of the general formula I

in which the radicals R ¹ , R ² , R ³ and R ⁴ independently of one another represent hydrogen, lower alkyl or lower hydroxyalkyl, which is characterized in that

a) 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2,2-dioxide (Ila)

in an organic solvent which is practically immiscible with water and, if desired, in the presence of water with an amine of the general formula purple

R ²

Ri - N - R ³ (purple)

or an ammonium salt of the general formula Ulb

wherein X is the anion of an acid of _pK a greater than 4 or the hydroxyl ion and n is equal to the number of negative charges of the anion X, are reacted and

b) the salt I takes up in water.

In addition, a process for the preparation of salts of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2,2-dioxide of the general formula I in which the radicals R ¹ , R ² , R ³ and R ⁴ independently of one another represent hydrogen, lower alkyl or lower hydroxyalkyl, which is characterized in that

a) 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2,2-dioxide (Ila)

H in water with an ammonium salt of the general formula Illb

wherein X is the anion of an acid with a _pK a greater than 4 or the hydroxyl ion and n is equal to the number of negative charges of the anion X, or

b) the sodium salt of bentazone (Ilb)

in water with an ammonium salt of the general formula IIIc

where Y is the anion of an acid and n is the number of negative charges of the anion Y.

Lower alkyl or lower hydroxyalkyl is understood to mean alkyl groups or hydroxyalkyl groups with up to 8, preferably with up to 6, carbon atoms, such as methyl, hydroxymethyl, ethyl, 2-hydroxyethyl, propyl, 3-hydroxypropyl and butyl.

The processes according to the invention are referred to below as processes A, B and C.

Procedure A

In process A, bentazone (Ila) is reacted with an amine purple in an organic solvent (see Scheme 1).

The amines purple are well known.

As a rule, the amine purple is used in an equimolar amount, based on bentazone (Ila). To complete the reaction, it may be advantageous to use the amine purple in excess. However, this excess generally does not need to exceed 10 mol%, based on Ila, in order to achieve complete conversion.

Suitable organic solvents are: aromatic hydrocarbons, preferably mono- to tri-methylated benzenes, especially toluene and the xylenes; Ketones, preferably with 3 to 9 carbon atoms, especially acetone; Esters, preferably of monocarboxylic acids with 1 to 5 carbon atoms with monoalkanols with 1 to 4 carbon atoms, especially ethyl acetate; Ethers, preferably with 4 to 8 carbon atoms, especially tetrahydrofuran; Haloalkanes, preferably mono- or dichloroalkanes with 2 to 4 C-atoms, especially 1, 2-dichloroethane, and also alkanols, preferably C 1 -C ₄ -alkanols, especially methanol or ethanol, and also mixtures cal of two or more of the aforementioned solvents.

The solvent used is particularly advantageously 1, 2-dichloroethane alone. Scheme 1

(Ha) (I)

R ^! -R ³ independently of one another H, lower alkyl or lower hydroxyalkyl α

Based on one mole of bentazone (Ila), 0.2 to 25 and especially 1 to 10 kg of solvent are normally used. The bentazone (Ila) can contain up to 2% by weight of water without this being detrimental to the process.

The process can be carried out at temperatures from 10 to 80 ° C. The temperature during the reaction has an influence above all on the solubility of the bentazone (Ila), which increases with the temperature.

Especially in those cases in which gaseous or low-boiling amines purple are involved, however, the temperature should not exceed 60 ° C. The reaction is preferably carried out at from 20 to 60 ° C., in particular from 25 to 50 ° C.

The reaction is generally carried out at a pressure of 0.5 to 10, preferably 1 to 3, bar and in particular at normal pressure (atmospheric pressure).

Devices which are usually suitable for such reactions are suitable as reactors.

The salt I precipitates at the reaction temperature and / or when the mixture cools and can be separated from the liquid phase in a manner known per se, above all by filtration. The yield of salt I is 95 to 100%.

Process A is particularly suitable for the production of the NH ₄ ⁺ salt of bentazone (I; R ^x -R ⁴ = H).

The preferred procedure is to introduce ammonia gas directly into the solution of bentazone (Ila) in the organic solvent or by removing the solution of

Bentazon (Ila) mixed with aqueous ammonia in the organic solvent.

Procedure B

In this process, bentazone (Ila) is reacted with an amine lilac or an ammonium salt Illb, if desired in the presence of water, in an organic solvent which is practically immiscible with water, and the salt I is taken up in water (see Scheme 2). Scheme 2

(I)

R ^ R ⁴ = independently of one another H, lower alkyl or lower hydroxyalkyl; X = anion of an acid of pK _s > 4 or the hydroxyl ion; n = number of negative charges of the anion X

The amines purple are well known. The same applies to the ammonium salts Illb (cf. Houben-Weyl, Methods of Organic Chemistry, 4th edition, Thieme Verlag, Stuttgart, volume 11/2, page 5 591 ff.).

As the anion X in the general formula IIIb, the carbonate ion and the hydrogencarbonate ion are preferred and the hydroxyl ion is particularly preferred. 0

As a rule, the amine purple or the ammonium salt Illb is used in an equimolar amount, based on bentazone (Ila). To complete the reaction, it may be advantageous to use an excess of the amine purple or the ammonium salt IIIb. However, this excess does not generally need to exceed 10 mol%, based on Ila, in order to achieve complete conversion.

Suitable organic solvents 0 which are practically immiscible with water are: alkanes, preferably having 5 to 8 carbon atoms, especially n-alkanes such as n-pentane and n-hexane and halogenated hydrocarbons, preferably haloalkanes such as mono- and dichloro- alkanes with 2 to 4 carbon atoms such as 1, 1-dichloroethane, 1,3-dichloropropane, 1,2-dichloropropane and in particular 1,2-dichloroethane. 5

Mixtures of two or more of these organic solvents which are practically immiscible with water are also suitable.

Particularly preferred as an organic solvent that is practically immiscible with water is 1,2-dichloroethane per se.

Based on one mole of bentazone (Ila), 1 to 4 and especially 1.5 to 3 kg of solvent are normally used.

5 The process can be carried out at temperatures from 20 to 80 ° C. The temperature during the reaction has an influence above all on the solubility of the bentazone (Ila), which increases with the temperature.

0 Especially in those cases where a gaseous or low-boiling amine purple is involved, the temperature should not exceed 60 ° C. The reaction of bentazone Ila with the amines purple or the ammonium salts Illb is preferably carried out at from 20 to 60 ° C., and in particular from 25 to 50 ° C. The reaction is generally carried out at a pressure of 0.5 to 10, preferably 1 to 3 bar and in particular at normal pressure (atmospheric pressure).

Devices which are usually suitable for such reactions are suitable as reactors.

The salt I formed is taken up in water, which can already be added during the reaction or only at the end of the reaction. If small amounts of the organic solution are removed by means of the water phase, these can be isolated in a manner known per se, for example by stripping or, if appropriate, by azeotropic distillation, for example in the case of 1,2-dichloroethane / water as the reaction medium, before the salt I is isolated - be removed at normal pressure or reduced pressure.

In order to completely absorb the salt, 1 to 5, preferably 2 to 4 and in particular 2.5 to 3.5 kg of water, based on 1 kg of salt I, are generally used. The salt I usually precipitates at the reaction temperature. The solution is usually cooled to complete the precipitation. The crystallization preferably takes place at 5 to 40 and in particular at 15 to 25 ° C.

A particular advantage of process B according to the invention is that in this way the organic solvent, after it has been separated from the water phase, can be used immediately for further reactions without it being partially or completely evaporated and / or by for the purpose of product isolation Distillation needs to be cleaned.

With process B, when the mother liquor is recycled, the salt I can generally be obtained with a yield of 98 to 100% and a purity of at least 98%.

Process B is particularly suitable for the production of the NH ₄ ⁺ salt of bentazone (I; R ⁱ -R ⁴ - H).

Procedure C

In process C, bentazone (Ila) is reacted in water with an ammonium salt Illb or the sodium salt of bentazone (Ilb) in water with an ammonium salt IIIc (see Scheme 3).

Scheme 3

(I)

(Ilb)

R1-R. = independently of one another H, lower alkyl, lower hydroxyalkyl;

Y = acid anion;

X = anion of an acid of pK _s > 4 or the hydroxyl ion; n = number of negative charges of the anion X or Y

Process C is particularly suitable for the production of the NH ₄ ^* salt of bentazone (I; R ^: -R ⁴ = hydrogen).

The ammonium salts Illb are generally known (cf. Houben-Weyl, Methods of Organic Chemistry, 4th edition, Thieme Verlag, Stuttgart, volume 11/2, page 591 ff.).

Anions Y in the general formula IIIc are: sulfate, hydrogen sulfate, phosphate, hydrogen phosphate or

Dihydrogen phosphate, preferably halide or acetate and in particular chloride, nitrate, formate, carbonate and hydrogen carbonate.

As acid anion Y in the general formula IIIc, or as the anion X of an acid of _pK a> 4 are preferably gencarbonation the carbonate ion and the hydro- and X for the hydroxyl ion is particularly preferred.

As a rule, the ammonium salt Illb is based on

Bentazon (Ila), and the ammonium salt IIIc, based on the sodium salt of bentazone (Ilb), used in an equimolar amount. To complete the reaction, it may be advantageous to use an excess of the ammonium salts. However, this excess does not generally have to exceed 10 mol%, based on Ila or Ilb, in order to achieve complete conversion.

Based on one mole of bentazone (Ila) or its sodium salt Ilb, 0.2 to 4 and especially 0.2 to 2 kg of water are normally used.

The sodium salt Na _n Y is usually more soluble in water than the salt I. If the latter remains partially dissolved, it can be separated by (fractional) crystallization. This method of operation is familiar to the person skilled in the art, so that further explanations for this are unnecessary.

To achieve a good yield in the crystallization, a molar ratio of water to salt I of 50 to 1 to 30 z 1 has proven particularly useful.

The process can be carried out at temperatures from 10 to 80 ° C. The temperature during the reaction has an influence above all on the solubility of the bentazone (Ila) and its sodium salt Ilb, which increases with the temperature. Preferably leading the reaction is carried out at temperatures from 20 to 70, and in particular from 40 to 60 ° C.

Devices which are usually suitable for such reactions are suitable as reactors.

With the method C, the salts I can generally be obtained with a yield of greater than 80% and a purity of at least 98 °. By recycling the mother liquor, a yield of more than 98% can be achieved.

The salt I prepared by one of the processes A to C can be isolated in a manner known per se. Where it already crystallizes out of the reaction mixture, this is done primarily by filtration. If the salt is obtained in dissolved form, the entire solution can be freed from the solvent by generally known methods, for example by evaporation, especially under reduced pressure.

The salt I obtainable by process B or C, which has been crystallized from an aqueous phase, generally already contains less than 10% by weight of water.

The salt I (of organic solvent or water) is generally dried at a temperature of 20 to 80, preferably 40 to 60 ° C. Drying can be done in conventional drying devices. The process is preferably carried out at reduced pressure or by heating product I in an air stream.

The mother liquors, which remain after separation of crystallized salt I, in some cases still contain up to 20% of the salt I in dissolved form. Where desired, this dissolved active ingredient can be isolated in a manner known per se, for example by concentrating the solution and recrystallization or by completely evaporating the mother liquor. The mother liquor can often also be returned to the process.

Granules from solutions of the salts I are obtained from the solutions obtained in the preparation or the crystallization mother liquors are preferably obtained by a fluidized bed process or by agglomeration on a powder of I, which ches was in turn produced by spray drying or vacuum drying.

The granules obtained in this way usually consist of 20 to 5 100% by weight of salt I. The grain size of these granules is generally from 200 μm to 3000 μm. The dust content of the granules is low. The dust content of a 30 g sample is less than 20 mg (CIPAC MT 171: "Dustiness of Granular Formulation") which ensures a high level of safety for the user. The bulk weight of such granules is generally 400-800 g / l.

The salts I show excellent storage behavior in water-soluble film bags. Such foil bags are known per se (EP-A 449 773, EP-A 493 553), so that further explanations for this are unnecessary.

The filled film bags usually contain 0.1 to 10 kg, preferably 0.5 to 5 kg, of active ingredient I. The thickness of the films 0 is 20 to 100 μm, preferably 30 to 60 μm. The water content in the polymeric films can be up to 20% by weight.

In addition to the salts I, the granules or the filled film bags obtained as described above can contain other conventional additives, e.g. Contain surfactants, fillers or other crop protection agents.

It was found that the salts I, and especially the NH ₄ ^* salt of bentazone, have a relatively low solubility in the respective reaction media compared to the starting materials Ila and Ilb. This effect is used in the process according to the invention to isolate the product I in a simple manner in solid form from the reaction mixture.

5 The ammonium salts and especially the NH ₄ ⁺ salt, on the other hand, dissolve much faster in water compared to the sodium salt that is mostly used, and this reduces the effort required for the preparation of aqueous active ingredient broths.

0

5 Examples

example 1

5 1.7-3 g of ammonia were gassed into a solution of 24 g of bentazone (Ila) in 2376 g of 1,2-dichloroethane with stirring at a temperature of 20-50 ° C., a suspension being formed. The solid was removed by filtration at 20 ° C. and solvent residues were removed under reduced pressure. 25.4 g of ammonium bentazone (mp. 180 ° C.) were obtained.

Example 2

In a solution of 24 g bentazone (Ila) in 16 g acetone 5 gaseous at 30-50 ° C with stirring 1.7 g ammonia. Ammonium bentazone precipitated out and was filtered off at room temperature. The crystals obtained were freed from the solvent at reduced pressure and 50 ° C. 19.5 g of ammonium bentazone were obtained. The mother liquor from the filtration was evaporated to dryness at reduced pressure and 50 ° C., and a further 6 g of ammonium benzon remained.

Example 3

5 4.8 g of ammonium carbonate were introduced into a suspension of 24 g of bentazone (Ila) and 300 g of water with stirring. The reaction mixture was stirred at 50 ° C. for 2 hours and freed from solid particles by filtration. After evaporation of the solution under reduced pressure, 25.5 g of ammonium bentazone remained.

Example 4

The procedure was as in Example 3, but 7.9 g of ammonium bicarbonate were used instead of the 35 ammonium carbonate. 25.5 g of ammonium bentazone were obtained.

Example 5

40 8 g of ammonium nitrate were introduced into a solution of 26.3 g of sodium bentazone in 21.7 g of water at 50 ° C. while stirring, and the reaction mixture was stirred for another hour. After cooling to 20 ° C., the precipitate was filtered off, washed twice with 5 ml of ice water and under reduced pressure and

45 50 ° C dried. 18.9 g of 99% purity ammonium bentazone were obtained. Example 6

The procedure was as described in Example 5, but 6.3 g of ammonium formate were used instead of the ammonium nitrate. The yield of ammonium bentazone was 21 g. The product was 98.4% pure.

Example 7

A solution of 24 g of bentazone (Ila) in 216 g of 1,2-dichloroethane was added with stirring at a temperature of 50-60 ° C with 34 g of ammonia water (5% solution of ammonia in water). After the addition had ended, the aqueous phase was separated off at 50-60 ° C. When the aqueous phase cooled, the ammonium bentazone precipitated out in crystalline form. The solid was separated off by filtration at 20 ° C. and freed from solvent residues at reduced pressure and a temperature of 50 ° C. 11.8 g of ammonium bentazone (mp. 180 ° C.) were obtained. The mother liquor was obtained by evaporation the water at reduced pressure and 50-60 ° C a further 13.7 g of ammonium bentazone.

Example 8

A solution of 24 g of bentazone (Ila) in 216 g of 1,2-dichloroethane was mixed with 22.5 g of a 20% aqueous solution of dimethylamine with stirring at a temperature of 30-50 ° C. After the addition had ended, the aqueous phase was separated off at 50-60 ° C. and evaporated to dryness under reduced pressure and 50-60 ° C. 28 g of dimethyla onium bentazone (mp. 145-147 ° C.; Reinhei> 99% according to HPLC analysis for bentazone and titration for dimethylammonium) were obtained.

Example 9

A mixture of 24 g bentazone (Ila), 4.8 g ammonium carbonate,

220 g of 1,2-dichloroethane and 300 g of water were stirred at 50-60 ° for 1 hour. The phases were then separated and the water was removed under reduced pressure and 50-60 ° C. 25.5 g of ammonium bentazone were obtained.

Example 10

According to Example 9, but using 7.9 g of ammonium hydrogen carbonate, 25.5 g of ammonium bentazone were obtained. Example 11

A 20% aqueous solution of ammonium bentazone was dried on a fluidized bed spray granulator at a drying air temperature of 120 ° C. The ammonium salt solution was injected and granulate particles formed by agglomeration and drying. The granules obtained contained 99.6% by weight of ammonium bentazone and had a residual water content of 0.4% by weight. The average grain size in the granulate was 0.3 mm (maximum diameter). The granules obtained were dust-free and quickly dissolved in water. It was also not hygroscopic, i.e. it remained flowable even after prolonged storage in moist air.

Example 12

A fluidized bed spray granulator was charged with 75 g of ammonium sulfate powder. Thereafter, 375 g of a 20% strength by weight aqueous solution of ammonium bentazone were injected into the granulator thus prepared at a drying air temperature of 120 ° C. Granulate particles were created by agglomeration and drying. The granulate obtained contained 50% by weight of ammonium bentazone and had a residual water content of 0.1-0.5% by weight. The average grain size in the granulate was 1-2 mm (maximum diameter). The granules obtained were dust-free and quickly dissolved in water. It was also not hygroscopic, i.e. it remained flowable even after prolonged storage in moist air.

Example 13

Physical behavior of the products

a) Investigation of the hygroscopicity of the salts

1 g of the sample was dried in vacuo at 50 ° C. for 48 hours. The dried samples were stored at 55% and 65% relative atmospheric humidity and 20 ° C. temperature and the weight gain of the samples was measured after reaching equilibrium. The flow properties of the samples and their appearance were also assessed. Substances critical with regard to hygroscopicity absorbed a lot of water from the air until they reached equilibrium. This led to the caking of the substances. The results are summarized in the following table. Type of rel. Ge properties after salt air weight storage moist increase [%] [%]

Sodium salt 55 12.6% clumped together, baked

Potassium salt 55 clumps 6.7%, baked

Potassium salt 55 12.0% clumped, baked

Ammonium salt 55 0.5% crystalline, flowable 65 0.5% capable crystalline, flowable b) Investigation of the behavior of the salts in the foil bag:

In each case 10 g of substance in the form of a granulate were sealed in foil bags. The filled foil bags (foil: Monosol 8030, manufacturer: Chris Craft Inc., USA) were then stored for 4 weeks at various temperatures in a water vapor-tight outer packaging. The stability of the films was expressed by the elasticity of the films when subjected to mechanical stress. When water was taken up from the film by the bentazone salt, the film became brittle. For example, the film Monosol 8030 in the presence of sodium bentazone in a closed container lost a large part of the residual moisture contained in the film. At room temperature, this decreased from an initial 14% to 6% in the equilibrium state. The result was embrittlement of the film and bursting of the bag under mechanical stress such as transport, bumping and loading. The results of model searches are summarized in the following table.

Type of salt T Properties of the foil bag

Sodium salt 20 brittle, brittle 30 brittle, brittle

Ammonium salt 20 elastic, stable 30 elastic, stable

Claims

Process for the preparation of salts of 3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide of the general

Formula I.

in which the radicals R ^' , R ² and R ³ independently of one another represent hydrogen, lower alkyl or lower hydroxyalkyl, characterized in that 3-isopropyl-2, 1, 3-benzothiaediazin-4-one-2 , 2-dioxide (Ila)

H in an organic solvent with an amine of the general formula purple

R ²

_R l _NR 3 (purple)

implements.

2. The method according to claim 1, characterized in that one uses an amine purple, in which the radicals R ¹ , R ² and R ^{3 are} hydrogen.

3. The method according to claim 1 or 2, characterized in that 1,2-dichloroethane is used as the organic solvent.

4. Process for the preparation of salts of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2,2-dioxide of the general formula I. in which the radicals R ¹ , R ² , R ³ and R ⁴ independently of one another stand for hydrogen, lower alkyl or lower hydroxyalkyl, characterized in that

a) 3-isopropyl-2, 1,3-benzothiadiazin-4-one-2,2-dioxide (Ila)

R ²

R ¹ NR ³ (purple)

or an ammonium salt of the general formula Illb

wherein X is the anion of an acid with a pKa value greater than 4 or the hydroxyl ion and n is equal to the number of negative charges of the anion X, and

b) the salt I takes up in water.

Process according to Claim 4, characterized in that 1,2-dichloroethane is used as the organic solvent.

6. The method according to claim 4 or 5, characterized in that one uses an amine purple or ammonium salt Illb, in which the radicals R ¹ to R ^{4 are} hydrogen. Process for the preparation of salts of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2, 2-dioxide of the general

Formula I.

in which the radicals R ¹ , R ² , R ³ and R ⁴ independently of one another stand for hydrogen, lower alkyl or lower hydroxyalkyl, characterized in that

a) 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2, 2-dioxide (Ila)

H in water with an ammonium salt of the general formula Illb

b) the sodium salt of 3-isopropyl-2, 1, 3-benzothiadiazin-4-one-2, 2-dioxide (Ilb)

in water with an ammonium salt of the general formula IIIc where Y is the anion of an acid and n is the number of negative charges of the anion Y.

8. The method according to claim 7, characterized in that the ammonium salt Illb contains the hydroxyl ion as anion X.

9. The method according to claim 7, characterized in that the ammonium salt IIIc contains as anion Y the carbonate or the hydrogen carbonate ion.