3-Hydroxy-2-cyclobuten-1-on salts, their preparation and use.

The invention relates to new 3-hydroxy-2-cyclobuten-1-one salts according to formula I and to processes for their preparation and their use, in particular for the production of squaric acid.

The new 3-hydroxy-2-cyclobuten-1-one salts according to general formula I are valuable, stable substances. On the one hand, they are equivalents for the 1,3-cyclobutanedione, which decomposes at room temperature, or is of synthetic interest, on the other hand, they are intermediate products of a new synthesis of squaric acid.

Square acid is an interesting intermediate for the production of pharmaceuticals, dyes (Angew. Chem., 20, 1966, p.931) and herbicides (CH-PS 609 837).

Various processes for the production of square acid are known from the literature.

Several start with hexachloro-1,3-butadiene, which is cyclized to a chlorinated cyclobutene derivative using sodium ethanolate. These intermediates are hydrolyzed to sulfuric acid or other acids to square acid (Roedig, A. and Bernemann P., Liebigs Ann. Chem. 1956, 600, p. 1; Maahs, G., Liebigs Ann. Chem. 1965, 686, p. 55; Angew. Chemie, 1963, 75, p.982; Uehara, A. and Tsuchiya, R., Sci. Rep. Kanazawa Univ. 1980, 25, p.83; Fan, R. et al., Chemical Abstracts 1987, 106, 103798c). Morpholine is also used instead of sodium ethanolate (Maahs, G. and Hegenberg P., Angew. Chemie 1966, 78, p.927; Schmidt, AH and Ried., W., Synthesis 1978, p.869, Gadek, TR et al. 1976, U.S. Patent 4,104,308; Paine, AJ, Tetrahedron Letters, 1984, 25, p.135). The cyclization can also take place purely thermally (Müller, W. 1976, DE-PS 26 18 557; Schröder, M. and Schäfer, W. 1976, DE-PS 26 23 836; Maahs, G. and Rombusch, D. 1978, DE-PS 28 24 558; Rombusch, K. and Maahs, G. 1983 DE-OS 33 14 431).

Disadvantages of all of these processes are either modest yields or high expenditure (for example distillation with an extreme reflux ratio) and the special safety measures which are required when handling the carcinogenic starting material hexachloro-1,3-butadiene.

According to another process (Bellus, D. et al., Helv. Chim. Acta 61, 1978, p.1784), squamous acid is obtained from the fungal metabolite moniliformin by bromination and hydrolysis in 70% yield. However, moniliformin occurs only in small quantities in nature, and the known syntheses for this are complex and give only modest yields.

Another process, the electrochemical reductive tetramerization of carbon monoxide to square acid, requires a great deal of equipment and results in a product mixture from which square acid is difficult to obtain in pure form. (Silvestri, G. et al., Gazz. Chim. It. 1972, 102, p. 818; DE-OS 22 35 882; US Pat. No. 4,461,681, US Pat. No. 4,523,980, Fabre PL et al., Bull. Soc. Chim. Fr. 1988, p.933)

The object of the present invention was to propose a new synthesis of squaric acid which, from easily accessible starting materials, gives squaric acid in good yield and purity with a modest outlay.

The object of the present invention was achieved by finding new intermediates which can be prepared from an easily accessible starting material and from which square acid can be prepared without great effort.

The intermediates according to the invention have the general formula<chemistry id="chem0001" num="0001"><img file="EP0444563B1_D0001.tif" /></chemistry> wherein R is either an ammonium group of the general formula<chemistry id="chem0002" num="0002"><img file="EP0444563B1_D0002.tif" /></chemistry> in which R₁, R₂ and R₃ are the same or different and represent a hydrogen atom, a C₁-C₄ lower alkyl or a cycloalkyl group, or R represents an alkali metal atom. The preferred radicals R₁, R₂ and R₃ of the ammonium group are a hydrogen atom, a C₁ - C₄ lower alkyl or a cyclohexyl group, in particular a hydrogen atom, a methyl or ethyl group or a cyclohexyl group. When R represents an alkali metal atom, the alkali metals sodium and potassium are preferred.

The preferred compounds of general formula I are: 3-hydroxy-2-cyclobuten-1-one diethylammonium salt 3-hydroxy-2-cyclobuten-1-one-cyclohexylammonium salt 3-hydroxy-2-cyclobuten-1-one-cyclohexyldimethylammonium salt 3-Hydroxy-2-cyclobuten-1-one dicyclohexylammonium salt 3-hydroxy-2-cyclobuten-1-one-dicyclohexylmethylammonium salt 3-hydroxy-2-cyclobuten-1-one ammonium salt 3-Hydroxy-2-cyclobuten-1-one sodium salt 3-hydroxy-2-cyclobuten-1-one potassium salt

The starting material used for the process of the invention is 3-acetoxy-2-cyclobuten-1-one, which is referred to below as triketen, optionally a distillation residue from diketene production with a triketen content of expediently 5 to 60% by weight, or 1,3-cyclobutanedione. These starting materials mentioned are reacted with a base to give the end product according to formula I. Either an amine of the general formula is expediently used as the base<chemistry id="chem0003" num="0003"><img file="EP0444563B1_D0003.tif" /></chemistry> in which R₁, R₂ and R₃ have the meaning given, or an alkali metal alcoholate or alkali metal hydroxide is used. Cyclohexyldimethylamine, dicyclohexylamine, diethylamine, cyclohexyldimethylamine, dicyclohexylmethylamine or ammonia are preferably used as amines of the general formula III.

The reaction of triketene as starting material is expediently carried out with 0.5 to 4 moles of an amine of the general formula III, based on 1 mole of triketene.

The reaction of 1,3-cyclobutanedione as the starting material is advantageously carried out with 0.5 to 4 moles of an amine of the general formula III, preferably with 0.5 to 1.5 moles, based on 1 mole of 1,3-cyclobutanedione.

The reaction is usually carried out at a temperature of from -40 to 50 ° C., preferably from 10 to 25 ° C. After a reaction time of 15 minutes to 5 hours, the end product according to formula I can be obtained by customary working up, for example by filtration.

Low-boiling aliphatic alcohols, C₁-C₄-carboxylic acids, C₁-C₄-carboxylic esters, low-boiling ethers and ketones, nitriles and aromatic hydrocarbons can be used as solvents. Representatives of these solvent groups are, for example, acetone, toluene, diethyl ether, diisopropyl ether, t-butyl methyl ether and dichloromethane, ethanol, acetonitrile, acetic acid and ethyl acetate; preferably ethyl acetate, ethanol or acetonitrile is used.

The 3-hydroxy-2-cyclobuten-1-one salts according to formula I can also by reacting the starting materials with 0.8 to 2.5 moles of an alkali metal alcoholate or an alkali metal hydroxide, such as with sodium or potassium hydroxide, sodium or potassium ethanolate , Sodium or potassium methoxide, based on 1 mole of starting material, preferably with 0.8 to 1.2 moles of sodium hydroxide, potassium hydroxide, sodium methoxide or sodium ethanolate.

The reaction is expediently carried out, like the reaction of the starting material with the amine according to formula III, at a temperature of from -40 to 50 ° C., preferably from 10 to 25 ° C. After a reaction time of 15 minutes to 5 hours, the end product according to formula I can be obtained by customary working up, for example filtration.

As the solvent, the same ones as those described above can be used.

The new 3-hydroxy-2-cyclobuten-1-one salts can also be prepared in two stages by converting triketene to 1,3-cyclobutanedione by acid hydrolysis in a first stage and then converting this intermediate into the 3-Hydroxy-2-cyclobuten-1-one salt, as already described, transferred. Sulfuric acid, hydrochloric acid, formic acid, trifluoroacetic acid can be used as the acid, preferably an excess of aqueous formic acid is used. The hydrolysis is usually carried out at a temperature of 0 to 30 ° C, preferably 15 to 30 ° C. After a reaction time of generally 15 minutes to 24 hours, the 1,3-cyclobutanedione can be worked up in the usual manner, advantageously by extraction and recrystallization.

The new 3-hydroxy-2-cyclobuten-1-one salts according to formula I are suitable for the production of squaric acid, with squaric acid being isolated in good yield and purity, or they can be used again for the production of 1,3-cyclobutanedione.

To produce square acid, the 3-hydroxy-2-cyclobuten-1-one salts according to formula I are halogenated in a first stage and then hydrolyzed to square acid in a second stage.

The first stage, the halogenation of 3-hydroxy-2-cyclobuten-1-one salt, is advantageously carried out with 2 to 4 moles of bromine, chlorine or sulfuryl chloride based on 1 mole of starting material, preferably with 2.5 to 3.5 moles of bromine , carried out. The halogenation can also be carried out first with 0.25 to 1 mol of bromine and then with 2.0 to 3.0 mols of chlorine or sulfuryl chloride, based on 1 mol of starting material.

The halogenation is usually carried out at a temperature from -40 to + 40 ° C, preferably from -25 to 25 ° C. After a reaction time of appropriately 30 minutes to 4 hours, the halogenated cyclobutenone can be isolated in good yield or hydrolyzed directly to the squaric acid. C₁ - C₄ carboxylic acids, C₁ - C₄ carboxylic acid ethyl esters, carboxylic acid anhydrides and chlorinated hydrocarbons can be used as solvents. Representatives of these solvent groups are, for example, acetic acid, ethyl acetate, acetic anhydride, carbon tetrachloride, methylene chloride, chloroform, preferably acetic acid, ethyl acetate or methylene chloride.

The second stage, hydrolysis to square acid, can be carried out with mineral acids such as sulfuric acid, hydrochloric acid, hydrobromic acid, phosphoric acid, with sulfonic acids such as aqueous methanesulfonic acid, with water or with carboxylic acids such as aqueous formic acid and aqueous trifluoroacetic acid. Mineral acids, such as, for example, concentrated sulfuric acid or hydrochloric acid, carboxylic acids, such as, for example, aqueous formic acid, sulfonic acids, such as, for example, aqueous methanesulfonic acid, are preferably used in excess. The hydrolysis is expediently carried out at a temperature of 50 to 150 ° C., preferably at a temperature of 90 to 100 ° C. The hydrolysis to square acid with water is carried out under reflux. After a reaction time of 2 to 48 hours, square acid is obtained in good yield.

example 1

Production of 1,3-cyclobutanedione from triketen

4.1 g of triketen (33 mmol) were dissolved in 10 g of sulfuric acid and 30 g of ice. After 15 minutes, the mixture was extracted with methylene chloride (2 times 25 ml each), then dried over calcium chloride, then filtered and concentrated. 2.1 g of the concentrated, solid material were slurried in diethyl ether (10 ml), then the mixture was filtered and then recrystallized in acetonitrile (13 ml). After recrystallization, 1.57 g of 1,3-cyclobutanedione (18.7 mmol), corresponding to a yield of 57%, based on the triketen used, was obtained.

Example 2

Preparation of 3-hydroxy-2-cyclobuten-1-one-diethylammonium salt

<ul id="ul0001" list-style="none"><li>a) 2.1 g of 1,3-cyclobutanedione (23.0 mmol) were suspended in 40 g of ethyl acetate. A solution of 1.84 g of diethylamine (25.0 mmol) in 10 g of ethyl acetate was added dropwise to this suspension at 20 ° C. in the course of 15 minutes. After stirring for 1 hour at room temperature, the suspension was filtered off and then dried. 3.05 g of the title product were obtained with a purity (according to HPLC) of 93.7%, corresponding to a yield of 79.2%, based on cyclobutanedione. M.p .: 93 ° C - 94 ° C</li><li>b) To a solution of 3.25 g of 3-acetoxy-2-cyclobutenon-1-one (triketen, content, 97%; 25.0 mmol) in 40 g of ethyl acetate, was at 20 ° C within 18 min a solution of 3.67 g of diethylamine (99.5%; 50.0 mmol) in 10 g of ethyl acetate was added dropwise. The reaction mixture was stirred for a further 1 hour at room temperature, then filtered off and dried under vacuum. 3.75 g of the title product were obtained with a purity of 94.1% (according to HPLC), corresponding to a yield of 89.8%, based on 3-acetoxy-2-cyclobuten-1-one. M.p .: 94 ° C - 96 ° C<dl id="dl0001"><dt>1 H-NMR: (CDCl₃, 300 MHz) δ in ppm</dt><dd>1.38 t, J = 9 Hz, 3H 3.01 q, J = 9 Hz, 2H 2.90 s, 2H 4.35 s, 1H 9.5 b, 2H</dd></dl></li></ul>

Example 3

Preparation of 3-hydroxy-2-cyclobuten-1-one-cyclohexyldimethylammonium salt

<ul id="ul0002" list-style="none"><li>a) A solution of 3.21 g of N, N- was added to a suspension of 2.1 g of 1,3-cyclobutanedione (91.9%; 23.0 mmol) in 40 g of ethyl acetate at 20 ° C. in 15 minutes. Dimethylcyclohexylamine (99%; 25.0 mmol) in 10 g ethyl acetate was added dropwise. After stirring at room temperature for 1 hour, the suspension was filtered off and dried under vacuum. 4.27 g of the title product were obtained with a purity of 94.8% (according to HPLC), corresponding to a yield of 83.3%, based on cyclobutanedione. Mp: 88 ° C - 90 ° C<dl id="dl0002"><dt>1 H-NMR: (CDCl₃, 300 MHz) in δ ppm</dt><dd>1.10 - 1.49, m, 5H 1.65 - 1.80, vol, 1H 1.88 - 2.01, vol, 2H 2.04 - 2.13, bd, 2H 2.78 - 2.91, m, 1H 2.66, b, 6H 13.2, b, 1H</dd></dl></li><li>b) 3.24 g of 3-acetoxy-2-cyclobuten-1-one (triketen, 25.0 mmol) were dissolved in 1.90 g of absolute ethanol (41.3 mmol) and 40 g of ethyl acetate. 6.45 g of cyclohexyldimethylamine (99%; 50.0 mmol), dissolved in 10 g of ethyl acetate, were added dropwise to this solution at 20 ° C. in the course of 20 minutes. After stirring at room temperature for 2 hours, the suspension was filtered off and dried under vacuum. 4.09 g of the title product with a content of 94.5% (according to HPLC), corresponding to a yield of 73.2%, based on 3-acetoxy-2-cyclobuten-1-one (triketen), were obtained. M.p .: 91.5 ° C - 92.4 ° C</li></ul>

Example 4

Preparation of 3-hydroxy-2-cyclobuten-1-one-dicyclohexylmethylammonium salt

<ul id="ul0003" list-style="none"><li>a) A solution of 4.99 g of dicyclohexylmethylamine (25.0 mmol) in 10 g of ethyl acetate was added dropwise to a suspension of 2.11 g of 1,3-cyclobutanedione (23.0 mmol) at 20 ° C. and the mixture was stirred for 1 hour . After stirring for a further 30 minutes at 5 ° C., the suspension was filtered off and dried under vacuum. 5.53 g of the title product were obtained with a purity of 94.7% (according to HPLC), corresponding to a yield of 81.4%, based on cyclobutanedione. M.p .: 91.4 ° C - 92.6 ° C</li><li>b) 3.24 g of 3-acetoxy-2-cyclobuten-1-one (triketen, 97.5%; 25.0 mmol) were dissolved in 1.9 g of ethanol (41.3 mmol) and 40 g of ethyl acetate. 9.83 g of dicyclohexylmethylamine (98.9%; 50.0 mmol), dissolved in 10 g of ethyl acetate, were added dropwise to this solution at 20 ° C. in 15 minutes and the mixture was stirred at room temperature for 1 hour. After stirring for a further hour at 5 ° C., the suspension was filtered off and dried under vacuum. 3.21 g of the title product with a content of 94.5% (according to HPLC), corresponding to a yield of 43.5%, based on 3-acetoxy-2-cyclobuten-1-one, were obtained. M.p .: 91.4 ° C - 92.4 ° C<dl id="dl0003"><dt>1 H-NMR: (CDCl₃, 300 MHz) δ in ppm</dt><dd>1.09 - 1.42, m, 6H 1.42 - 1.66, vol, 4H 1.67 - 1.78, vol, 2H 1.88 - 2.03, vol, 4H 2.04 - 2.16, vol, 4H 2.64, s, 3H 2.93, b, 2H 3.13, m, 2H 4.33, b, 1H</dd></dl></li></ul>

Example 5

Preparation of 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt

<ul id="ul0004" list-style="none"><li>a) A solution of 7.1 g of dicyclohexylamine () was added to a suspension of 3.0 g of 1,3-cyclobutanedione (97%; 34.6 mmol) in ethyl acetate (52.2 ml) at 20 ° C in 15 minutes. 98%; 38.3 mmol) in 15 ml of ethyl acetate. After stirring at room temperature for 1 hour, the suspension was washed 4 times with ethyl acetate and dried under vacuum. 9.4 g of the title product were obtained with a content of 94.7% (according to HPLC), corresponding to a yield of 96.7%, based on cyclobutanedione. M.p .: 188 ° C - 188.7 ° C</li><li>b) 1000 g of distillation residue from the diketene production, containing 22.0% of 3-acetoxy-2-cyclobuten-1-one (1.74 mol), were dissolved in 1078 ml of ethyl acetate (970 g). 707.4 g of dicyclohexylamine (98%; 3.81 mol) were added dropwise to this black solution at 10 ° C. in the course of 60 minutes. After stirring for 90 minutes at + 10 ° C., the suspension was filtered off, slurried 3 times with ethyl acetate and dried under vacuum. 518 g of the title product with a content of 65.5% (HPLC), corresponding to a yield of 73.4%, based on 3-acetoxy-2-cyclobutenon-1-one, were obtained. M.p .: 169.7 ° C - 172.4 ° C<dl id="dl0004"><dt>Cleaning:</dt><dd>259 g 3-Hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt (crude; 65.5%; 0.64 mol) were suspended in 207.2 g glacial acetic acid and 310.8 g ethyl acetate and stirred for 2 hours at room temperature. The product was washed 3 times with ethyl acetate and dried under vacuum. 176 g of the title product with a content of 90.2% (according to HPLC) were obtained, corresponding to a yield of 93.6%.</dd></dl> M.p .: 188 ° C - 190 ° C<dl id="dl0005"><dt>1 H-NMR: (CD₃OD, 300MHz) δ in ppm</dt><dd>1.13 - 1.49, m, 10H 1.66 - 1.80, vol, 2H 1.80 - 1.97, vol 4H 2.81, s, 2H 4.29, s, 1H 3.09 - 3.27, m, 2H</dd></dl></li></ul>

Example 6

Preparation of 3-hydroxy-2-cyclobuten-1-one ammonium salt

<ul id="ul0005" list-style="none"><li>a) A solution of 0.425 g of ammonia gas (25 mol) in 25 was added to a solution of 2.16 g of 1,3-cyclobutanedione (97%; 25.0 mmol) in 25 g of acetonitrile at 20 ° C. within 10 minutes g of acetonitrile were added dropwise. After stirring for 30 min at room temperature, the suspension was filtered off, washed with acetonitrile (10 ml) and dried under vacuum. 1.48 g of the title product were obtained with a content of 78% (according to HPLC), corresponding to a yield of 47.0%, based on cyclobutanedione. M.p .: 94 ° C -96 ° C</li><li>b) In a solution of 6.5 g of 3-acetoxy-2-cyclobuten-1-one (triketen; 97%; 50.0 mmol) in 58.5 g of acetonitrile, at 2 ° C. in 30 min. 3, 1 g of ammonia gas (182.3 mmol) was introduced. The reaction mixture was stirred for a further 30 minutes at 2 ° C., then filtered off, then washed with acetonitrile (20 ml) and dried under vacuum. 4.88 g of the title product with a content (according to HPLC) of 94%, corresponding to a yield of 90.7%, based on 3-acetoxy-2-cyclobuten-1-one, were obtained. Mp 109 ° C - 110 ° C<dl id="dl0006"><dt>1 H-NMR: (d₆-DMSO) δ in ppm</dt><dd>2.49, s, 2H 3.91, s, 1H 7.25, b, 4H</dd></dl></li></ul>

Example 7

Preparation of 3-hydroxy-2-cyclobuten-1-one sodium salt

<ul id="ul0006" list-style="none"><li>a) To a solution of 1.74 g of 1,3-cyclobutanedione (97%; 20.0 mmol) in 20 g of acetonitrile, a solution of sodium ethanolate containing 0.506 g of sodium (22 mmol) was added at 20 ° C. in 20 minutes. in 15 g of absolute ethanol, added dropwise. The reaction mixture was stirred for a further 15 minutes at room temperature, then filtered off and dried under vacuum. 1.58 g of the title product were obtained with a purity of 92.6% (according to HPLC), corresponding to a yield of 69.0%, based on cyclobutanedione. MP:&gt; 280 ° C<dl id="dl0007"><dt>1 H-NMR: (d₆-DMSO) δ in ppm</dt><dd>2.49, s, 2H 3.92, s, 1H</dd></dl></li><li>b) A solution was added to a solution of 3.23 g of 3-acetoxy-2-cyclobuten-1-one (triketen, 97.5%; 25.0 mmol) in 20 g of acetonitrile at 20 ° C. within 15 minutes of 1.099 g sodium hydroxide (27 mmol) in absolute ethanol (10 g) was added dropwise. After stirring for about 2 hours, the suspension was filtered off at room temperature, washed with acetonitrile (5 ml) and dried under vacuum. 2.38 g of the title product were obtained with a content of 87.2% (according to HPLC), corresponding to a yield of 89.8%, based on 3-acetoxy-2-cyclobuten-1-one.</li><li>c) To a solution of 28.4 g of distillation residue from the diketene production with a content of 44.4% 3-acetoxy - 2-cyclobuten-1-one (triketene; 98 mmol) in 250 g of ethyl acetate was in A solution of 4.6 g of sodium hydroxide (115 mmol) in 75 g of absolute ethanol was added dropwise at 45 ° C. for 45 minutes. The suspension was filtered. The residue was dried under vacuum.</li><li>17.1 g of the title product with a content of 46.7% (according to HPLC) corresponding to a yield of 75.3%, based on 3-acetoxy-2-cyclobuten-1-one, were obtained.</li></ul>

Example 8

Preparation of 3-hydroxy-2-cyclobuten-1-one potassium salt

A solution of 1.8 g of potassium hydroxide was added to a solution of 3.23 g of 3-acetoxy-2-cyclobuten-1-one (triketen, 97.5%; 25 mmol) in acetonitrile (20 g) at room temperature within 10 minutes (27.5 mmol) in absolute ethanol (40 g) was added dropwise. After stirring for 30 minutes, the suspension was filtered off at room temperature, washed with acetonitrile (5 ml) and dried under vacuum. 1.99 g of the title product were obtained with a content of 81.5% (according to HPLC), corresponding to a yield of 53.1%, based on 3-acetoxy-2-cyclobuten-1-one. Mp&gt; 260 ° C

Example 9

Manufacture of square acid

<ul id="ul0007" list-style="none"><li>a) 3.66 g (50 mmol) of 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt were suspended in methylene chloride (100 ml) and cooled to -20 ° C. Then 10.63 g (150 mmol) of chlorine gas was introduced. After a reaction time of 30 minutes, the mixture was warmed to room temperature with stirring, methylene chloride was distilled off on a rotary evaporator, and ethyl acetate (100 ml) was added. The precipitate was filtered off and the mother liquor was concentrated on a Rotavapor. The residue so obtained (11.63 g) was stirred with concentrated sulfuric acid (25 ml) at 100 ° C. for 15 hours. After cooling in an ice bath, the precipitate was filtered off, then washed 3 times with acetone (20 ml) and dried for 15 hours at 50 ° C. and 50 mbar. 1.22 g of gray powder containing 88% of squaric acid, corresponding to a yield of 19%, based on 3-hydroxy-2-cyclobuten-1-one-cyclohexylammonium salt, were obtained.</li><li>b) 73.2 g (1 mol) of 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt were suspended in ethyl acetate (1.5 l) and then cooled to 0 ° C. 474.5 g of bromine (3 mol) in ethyl acetate (500 ml) was added with stirring. The precipitate was filtered off after 30 minutes and washed twice with ethyl acetate (250 ml). Mother liquor and washing solutions were combined and concentrated. There remained 442.75 g of residue. 415.25 g of this residue were then added to water (34 g) and sulfuric acid (500 ml). After stirring at room temperature for 12 hours, the precipitate was filtered off and washed twice with acetone (100 ml). 111.47 g of white title product with a squaric acid content of 94.6%, corresponding to a yield of 92.45%, based on the 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt used, were obtained.</li><li>c) 3.66 g (50 mmol) of 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt were suspended in ethyl acetate (100 ml). Then 20.25 g of sulfuryl chloride (150 mmol) were added dropwise at room temperature with stirring. After a reaction time of 1 hour, the mixture was slurried with ethyl acetate (50 ml), then filtered, and the filtrate was concentrated on a rotavapor. There remained 11.7 g of a semi-liquid residue. 11.7 g of this material was added to concentrated sulfuric acid (25 ml) and water (1.7 g). After a reaction time of 2 hours, the residue was filtered off and washed 4 times with acetone (5 ml). 1.3 g of the title product were obtained with a square acid content of 92.29%, corresponding to a yield of 23.14% based on the 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt used.</li><li>d) 3.66 g (50 mmol) of 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt were suspended in ethyl acetate (100 ml). After adding 3.95 g of bromine (25 mmol) in 20 minutes, 16.87 g of sulfuryl chloride (125 mmol) were added dropwise in 30 minutes with stirring. After a total reaction time of 105 minutes, the precipitate was washed twice with ethyl acetate (50 ml). Mother liquor and washing solutions were combined and concentrated. The residue (11.32 g) was added to concentrated sulfuric acid (25 ml) and water (1.7 g) at 100 ° C. After a reaction time of 2 hours, the residue was filtered off and washed 4 times with acetone (5 ml). 5.26 g of white title product with a square acid content of 92.7%, corresponding to a yield of 85.4%, based on the 3-hydroxy-2-cyclobuten-1-one-dicyclohexylammonium salt used, were obtained.</li></ul>

Example 10:

Production of 1,3-cyclobutanedione starting from 1,3-cyclobutanedione-dicyclohexylammonium salt

146.0 g (0.5 mol) of 1,3-cyclobutanedione dicyclohexylammonium salt with a content of 90.9% (according to HPLC) were suspended in acetonitrile (1400 ml) and cooled to 10 ° C. 21.0 g of HCl gas (0.573 mol) were introduced into this light brown suspension within 20 minutes. The reaction mixture was then stirred at + 10 ° C. for a further 30 minutes and then filtered. The amine hydrochloride was then washed with acetonitrile (100 ml). The mixture was then concentrated in vacuo to 220 g, then cooled in an ice bath for 30 minutes, filtered, washed twice with ether (100 ml) and dried at room temperature for 10 minutes at 20 mbar. 32.07 g of the title product with a content of 89.8% (according to HPLC), corresponding to a yield of 68.5%, based on cyclobutanedione dicyclohexylamine salt, were isolated. Mp: 103 -105 ° C (dec.)<dl id="dl0008"><dt>1 H-NMR (d₆-DMSO) δ in ppm</dt><dd>3.06, s, 2H 4.75, s, 1H 9.5 - 12.5, b, 1H</dd></dl>