NO742255L - - Google Patents

Description

Method for the production of

2,2,6,6-tetramethyl-4-oxopiperidine.

The preparation of 2,2,6,6-tetramethyl-4-oxopiperidine

is known. It consists in reacting 2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine with a Lewis acid, preferably zinc chloride or calcium chloride in the presence of water. This pyrimidine derivative, which can be used as a starting material, can be prepared from acetone and ammonia, but its isolation from the reaction medium and possible purification require complicated work.

Attempts have also already been made to combine both reaction steps, i.e. to realize the production of 2,2,6,6-tetramethyl-4-oxo-piperidine directly from acetone, without isolation of the pentamethyltetrahydropyrimidine. Corresponding attempts have so far resulted in no satisfactory yields, resulting in reaction mixtures whose separation is

difficult and difficult.

It has now surprisingly been found that, subject to certain process conditions, 2,2,6,6-tetramethyl-4-oxopiperidine can be produced directly from acetone in good yields and purity. The method consists of two process steps which can be carried out immediately one after the other so that it is above all suitable for large-scale production of tetramethylpiperidone. The method according to the invention is characterized by a) reacting acetone with ammonia in the presence of 0.2 to 12 mol%, referred to the acetone used, of an acid catalyst at 5 to 60°C and b) completing the reaction with or without the addition of further acetone by further heating, the total amount of acetone used in the reaction being in a molar ratio to the amount of ammonia used from equal to or greater than 1.6:1.

In the first step of the method, preferably at least 0.15 mol of ammonia is allowed to react with acetone, but for practical reasons it is more appropriate to saturate the reaction mixture with ammonia, therefore an excess of ammonia is preferred.

As a catalyst, either a Lewis acid can be used,

like for example. aluminum chloride, tin tetrachloride or preferably boron trifluoride or a boron trifluoride adduct; or one uses a proton acid or a salt of a proton acid with ammonia or a nitrogen-containing organic base, especially a primary, secondary or tertiary nitrogen base.

Examples for such protonic acids or for the acid components in salts used as acid catalysts are especially mineral acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, sulfuric acid and phosphoric acid, as well as sulphonic acids, such as aliphatic or aromatic sulphonic acids, e.g. methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid or naphthalenesulfonic acid, phosphonic acids or phosphinic acids, such as aliphatic or aromatic, e.g. methyl, benzyl or phenylphosphonic acid, or dimethyl, diethyl or phenylphosphinic acid and carboxylic acids such as monobasic, dibasic or tribasic aliphatic or aromatic carboxylic acids, e.g. saturated or unsaturated monobasic aliphatic carboxylic acids with 1-18 C atoms, such as formic acid, acetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, propionic acid, butyric acid, lauric acid, palmitic acid, stearic acid, acrylic acid, methacrylic acid and cinnamic acid, saturated and unsaturated dibasic aliphatic carboxylic acids such as oxalic acid, malonic acid, succinic acid, adipic acid, sebacic acid, tartaric acid, malic acid, fumaric acid and maleic acid, tribasic aliphatic carboxylic acids such as citric acid, monobasic aromatic carboxylic acids such as optionally substituted benzoic acids and naphthoic acids and dibasic aromatic carboxylic acids such as phthalic acid and terephthalic acid. Preferred are monobasic and dibasic, aliphatic or aromatic carboxylic acids and monobasic aromatic sulphonic acids, such as acetic acid, succinic acid, maleic acid, benzoic acid, o-iodobenzoic acid, m-methylbenzoic acid, p-tert-butylbenzoic acid, p-toluenesulphonic acid and cinnamic acid. As organic bases are suitable: aliphatic, alicyclic and aromatic, primary, secondary and tertiary amines, saturated and unsaturated nitrogen bases, urea, thiourea and basic ion exchange resins. Thus, aliphatic, primary amines are e.g. methylamine, ethylamine, n-butylamine, octylamine, dodecylamine and hexamethylenediamine, aliphatic secondary amines e.g. dimethylamine, diethylamine, di-n-propylamine and di-iso-butylamine, aliphatic tertiary amines e.g. triethylamine, alicyclic primary amines e.g. cyclohexylamine, aromatic primary amines e.g. aniline, toluidine, naphthylamine and benzidine, aromatic secondary amines e.g. N-methylaniline and diphenylamine, aromatic tertiary amines e.g. N,N-diethylaniline, saturated and unsaturated nitrogenous bases e.g. heterocyclic bases, e.g. pyrrolidine, piperidine, N-methyl-2-pyrrolidone, pyrazolidine, piperazine, pyridine, picoline, indoline, chinuclidine, morpholine, N-methylmorpholine, 1,4-diazabicyclo/-2 ,2 ,2_7-octane and triacetonamine, urea, thiourea and strong and weakly basic ion exchange resins. Acetonine as well as diacetonamine and triacetonamine are also preferred. Examples of preferred salts are: Cyclohexylamine formate, pyridine formate, pyridine^p-toluenesulfonate, di-n-butylamine acetate, di-n-butylamine benzoate, morpholine succinate, morpholine maleate, triethylamine acetate, triethylamine succinate, triethylamine maleate, aniline acetate, triacetonamine p-toluenesulfonate and acetonine hydrochloride.

Particular preference is given to ammonium chloride or boron trifluoride or a mixture of both compounds.

These catalysts are used in an amount from 0.2 to

12 moles, referred to the acetone used, preferably 2-5 moles are used.

As an additional co-catalyst, you can use: Potassium iodide, sodium iodide, lithium bromide, lithium iodide, lithium rhodanide, ammonium rhodanide, lithium cyanide, lithium nitrate, ammonium sulphide, bromine, iodine or a bromide, iodide, nitrate, methanesulfonate, benzenesulfonate or p-toluenesulfonate of ammonia, triethylamine, urea or thiourea, for example in amounts from 0.01 to 0.5 moles referred to acetone.

The reaction temperature in the first method step is 5 to 60°C, preferably 5 to 35, especially 5 to 25°C. It is advantageous in the first method step with the addition of a mono- or polyfunctional alcohol. Examples of suitable alcohols are methanol, butanol, cyclohexanol, benzyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monoethyl ether or 2-ethylhexanol. Lower monoalcohols such as methanol, ethanol and isopropanol are preferably used, of which methanol is particularly preferred.

The reaction time of this first method step, which takes place at a low temperature, is at least 1, preferably 3 hours.

A method variant is the following:

In connection with this first method section, a further amount of acetone and/or diacetone alcohol or mesityl oxide or phorone or diacetonamine or triacetonediamine is added to the reaction medium and the temperature is preferably increased to 40 to 65°C. In the usual case, acetone is added, namely an amount of at least 0.5, especially 1 part, preferably 2-4 parts per part of the initially used amount of acetone. As well as acetone, the acetone derivatives mentioned above can be used, preferably diacetone alcohol or its mixture with acetone. Furthermore, in this second method step, it may be advantageous to add additional catalyst to the reaction medium. This can take place together with the addition of acetone or acetone derivatives or also something later. As catalysts, the same substances as in the first process step are suitable, particularly suitable are boron trifluoride, ammonium chloride, concentrated sulfuric acid or hydrogen chloride.

The reaction time required for the second method step, which takes place at an elevated temperature, amounts to approx. 3 to 20 hours.

The following procedure is also advantageous for step b): 8-20 hours at 50~55°C or primarily 2-7 hours at 50-55°C and then a further 2-6 hours at reflux temperature, especially at approx. 56-60°C.

In both process steps, work can be done under pressure, e.g. at 1-30, especially 1-10, above all 1-3 atmospheres overpressure. In this case, temperatures above 60°C are possible.

The isolation of the tetramethylpiperidone can take place in a manner known per se, e.g. by addition of water and separation as hydrate or by addition of acid, such as hydrochloric acid, sulfuric acid or oxalic acid and separation as salt or by addition of an excess of lye, especially concentrated lye such as aqueous caustic soda or potassium lye and separation as an organic layer or especially by distillation, optionally after neutralization of the catalyst by addition of a base, such as sodium hydroxide, potassium hydroxide or sodium carbonate.

The acetone used in the first step of the method may contain to a certain extent water and/or condensation products of acetone, such as diacetone alcohol, mesityl oxide, phorone, diacetonamine and/or triacetonediamine. Such an addition can have a beneficial effect on the yield. A preferred condensation product of acetone is mesityl oxide and especially diacetone alcohol. Thereby, it is possible that during distillative processing at the end of the second step, distillate is formed to be used as raw material in the first step, which results in a high acetone turnover. Increases the water content of the reaction medium, e.g. in the case of such recycling too much, it pays to remove part of the water from the reaction mixture. This can, for example, take place by adding concentrated alkali to the reaction mixture at the end of the first step, e.g. caustic soda, and after a short period of stirring, the aqueous layer separates.

In the method according to the invention, an organic solvent can also be used. Organic solvents that are particularly suitable for the method according to the invention are e.g. hydrocarbons such as aromatics, e.g. benzene, toluene and xylene as well as aliphatics such as hexane, heptane and cyclohexane, as well as chlorohydrocarbons such as methylene chloride, trichloroethane, carbon tetrachloride, chloroform, ethylene chloride and chlorobenzene as well as ethers such as tetrahydrofuran, dioxane and diethyl ether as well as nitriles such as acetonitrile as well as aprotic polar solvents such as sulfolane, acetonitrile, nitromethane, dimethylformamide, dimethylacetamide, tetramethylurea, hexamethylphosphoric acid amide and dimethylsulfoxide as well as particularly preferred alcohols such as mono- or polyfunctional, unsubstituted or substituted aliphatic alcohols, e.g. lower alkanols such as methanol, ethanol, propanol, isopropanol and tert.-butanol, as well as cyclohexanol, benzyl alcohol, ethylene glycol monomethyl ether, glycol and propane-1,3-diol, above all a C-^-C^-alcohol, such as methanol, such as diacetone alcohol, phorone, diacetonamine, triacetonediamine and mesityl oxide. Mixtures of the above-mentioned solvents are also suitable.

The invention shall be explained with the help of some examples: Further advantageous designs of the method according to the invention appear from the appended claims.

Example 1.

A suspension consisting of 11 g of ammonium chloride and a mixture of 340 g of acetone and 64 g of methanol is saturated over 12 hours at 13 to 17°C with ammonia gas. The resulting colorless oil is then diluted with 350 g of acetone and kept for 15 to 20 hours with stirring at 50-55°C. The excess solvent is then removed by evaporation in a vacuum and the reddish residue is mixed with 36 g of water. The crystallization, which starts at 0 to 5°C, ends with 2 hours of stirring. 286 g of 2,2,6',6-tetramethyl-4-oxo-piperidine hydrate of melting point 55-60°C are obtained in the form of slightly yellow colored crystals.

The product is obtained as an oxalate salt with a decomposition point of 180°C, when the reaction mixture is neutralized with oxalic acid. Example 2.

Proceed as indicated in example 1, with the difference that in the second step 1.3 g of boron trifluoride, dissolved in ether, is added together with the addition of acetone. The isolation of 2,2,6,6-tetra-methyl-4- oxopiperidine proceeds as indicated in example 1.

Example 3»

Work is carried out as indicated in example 1, with the difference that instead of ammonium chloride, 1.3 g of bro trifluoride, dissolved in ether, is used. In the second method step, 11 g of ammonium chloride are then added together with the acetone to the reaction mixture.

Example 4-7.

A suspension consisting of 11 g of ammonium chloride, 340 g of acetone and 64 g of methanol is saturated over 4 hours at 13 to 17°C with ammonia gas. The resulting colorless oil is then diluted with 900 g of acetone and kept for 15 to 20 hours with stirring at 50-55°C.

■After the first 6 hours, 70 g of 97 l sulfuric acid is dripped into the solution over the course of 1-2 hours. At the end of the reaction time, the pH value of the reaction mixture is adjusted with 97% sulfuric acid over the course of 1-2 hours to the value 4.5 to 5. The formed suspension of the hydrosulphate of 2,2,6,6-tetramethyl-4- oxopiperidine is filtered at 5-10°C and washed with acetone. 655 g of the hydrosulphate salt is obtained, which corresponds to 381 g of 2,2,6,6-tetramethyl-4-oxopiperidine.

If you proceed as indicated above, but in the second step the amount of acetone and sulfuric acid specified in table 1 is used, then

you get the dividends stated in the third column of the table.

Example 8.

A suspension consisting of 11 g of ammonium chloride, 340 g of acetone and 64 g of methanol is saturated over 4 hours at 13 to 17°C with ammonia gas. The resulting colorless oil is then diluted with 900 g of acetone and kept for 15 to 20 hours with stirring at 50-55°C. After the first 6 hours, the pH of the solution is adjusted by introducing approx. 23 g of chlorine hydrogen gas to 8.5-8.6. At the end of the reaction time, the pH value of the reaction mixture is adjusted with hydrogen chloride over the course of 1-2 hours to the value 5 to 6. The formed suspension of hydrochloride of 2,2,6,6-tetramethyl-4-oxopiperidine is filtered at 0-5°C and washed with acetone. 400 g of the hydrochloride salt is obtained, which corresponds to 293 g of 2,2,6,6-tetramethyl-4-oxopiperidine.

After distilling off HgO and methanol and diluting the distillation residue with acetone, a further 95 g of hydrochloride, which corresponds to 70 g of 2,2,6,6-tetramethyl-4-oxo-piperidine, is isolated from the mother liquor.

Example 9.

In a mixture consisting of 126 g of acetone, 22.5 g of methanol

and 4.7 g of ammonium chloride, 40 g of ammonia gas is introduced during approx.

4 hours at 13-15°C. The reaction mixture is then stirred for 30 minutes at the same temperature. 220 g of diacetone alcohol and 110 g of acetone are then added to the reaction mixture, the whole is heated for 1 hour at 55°C and kept at this temperature for 12 hours. Processing of the mixture by fractional distillation yields 125 g of 2,2,6,6-tetramethyl-4-oxopiperidine. Example 10.

A suspension consisting of 11 g of ammonium chloride, 340 g of acetone and 64 g of methanol is saturated over 4 hours at 13 to* 17°C with ammonia gas. The resulting colorless oil is then diluted with 900 g of acetone and kept for 15 to 20 hours with stirring at 50-55°C.

According to the gas chromatogram, the resulting reaction mixture contains 378 g of 2,2,6,6-tetramethyl-4-oxopiperidine (triacetonamine)

which is isolated by distillation.

Example 11.

A suspension of 11 g of ammonium chloride, 340 g of acetone and

4 g of a 20% aqueous solution of ammonium sulphide is saturated within 4 hours at 13 to 17°C with ammonia gas. Then proceed as indicated in example 10.

At the end, the reaction mixture contains 450 g of triacetonamine.

Example 12.

A suspension of 11 g of ammonium chloride, 340 g of acetone and

1 g of potassium iodide is saturated within 4 hours, with ammonia gas. Then proceed as indicated in example 10. The reaction mixture contains 400 g of triacetonamine.

Example 13.

Proceed as in example 10, however, instead of 64 g of methanol, 64 g of dioxane is used.

The reaction mixture contains 314 g of triacetonamine. Example 14.

The procedure is the same as in example 10, however, instead of 64 g of methanol, 64 g of ethanol is used.

The reaction mixture contains 363 g of triacetonamine. Example 15.

Proceed as in example 10, however, instead of 64 g of methanol, 64 g of isopropanol is used.

The reaction mixture contains 350 g of triacetonamine. Example 16.

The same result as in example 15 is obtained when the methanol is replaced by 64 g of dimethylformamide.

Example 17.

Proceed as in example 10, however without methanol addition.

The reaction mixture contains 336 g of triacetonamine. Example 18.

A suspension consisting of 11 g of ammonium chloride, 340 g of acetone and 64 g of methanol is saturated over 4 hours at 13 to 17°C with ammonia gas.

The resulting colorless oil is then diluted with 1360 g of acetone and kept for 15-20 hours with stirring at 50-55°C.

The resulting reaction mixture contains 420 g of triacetonamine.

Example 19.

Proceed as in example 10, but stir

after dilution with 900 g of acetone first 6 hours at 50-55°C and then

3 hours under strong reflux (at 56-60°C).

The resulting reaction mixture contains 337 g of triacetonamine.

Example 20.

Proceed as in example 10, however, instead of 11 g of ammonium chloride, 5.5 g or 38 g ammonium chloride:

Claims (53)

1. Process for the production of 2,2,6,6-tetramethyl-4-oxopiperidine, characterized in that a) reacts acetone with ammonia in the presence of 0.2 - 12 moles, referred to used acetone, of an acid catalyst at 5 - 60°C, and b) completes the reaction with or without the addition of additional acetone by further heating, as the total amount of acetone used in the reaction to the amount of ammonia used is in a molar ratio equal to or greater than 1.6:1. 2. Method according to claim 1, characterized in that the acetone in process step a) is partially replaced with diacetone alcohol and/or mesityl oxide. 3. Process according to claim 1, characterized in that the acetone in method step b) is replaced in whole or in part with diacetone alcohol, mesityl oxide, phorone, diacetonamine or triacetonediamine. 4. Method according to claim 2, character sre:.' rtt in that the acetone is partially replaced by mesityl oxide. 5. Method according to claim 3, characterized in that the acetone is completely or partially replaced with diacetone alcohol. 6. Method according to claim 1, characterized in that the total amount of acetone used in the reaction to the amount of ammonia used is in a molar ratio of 2 - 6: 1. 7- Method according to claim 1, characterized in that in method step a) acetone and ammonia are used in a molar ratio of 0.8 - 1.1 : 1 and the remaining acetone is used in method step b). 8. Process according to claim 1, characterized in that the salt of a protonic acid with ammonia or a nitrogen-containing organic base is used as acid catalyst. 9. Method according to claim 8, characterized in that a mineral acid or an organic acid is used as the proton acid. 10. Method according to claim 9, characterized in that a sulphonic acid or a carboxylic acid is used as the organic acid. 11. Method according to claim 8, characterized in that the ammonium salt of a mineral acid is used as salt. 12. Method according to claim 8, characterized in that the ammonium salt of an organic acid is used as the ammonium salt. 13. Method according to claim 8, characterized in that a mineral acid salt of a nitrogen-containing organic base is used as salt. 14 . Method according to claim 8, characterized in that a salt of one is used as salt. nitrogenous organic base with an organic acid. 15- Method according to claim 8, characterized in that triacetonamine, triethylamine, hexametylenediamine, 1, 4-diazabicyclo/_~2,2,27-octane, urea or thiourea are used as nitrogenous organic base. 16. Method according to claim 8, characterized in that a salt of chloric, bromic or hydroiodic acid, of nitric acid, an organic sulphonic acid, cyanoacetic acid or of a haloacetic acid is used. 17- Method according to claim 8, characterized in that an ammonium salt of hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, benzenesulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, dichloro- or cyanoacetic acid is used. 18. Method according to claim 8, characterized in that a salt of hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, benzenesulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, dichloroacetic acid or cyanoacetic acid is used with triacetonamine, triethylamine, hexamethylenediamine, 1, 4-diazabicyclo/_~2 ,2j27octane, urea or thiourea. 19. Method according to claim 8, characterized in that ammonium chloride, ammonium bromide, ammonium iodide, ammonium formate, ammonium tosylate, urea nitrate, urea tosylate, hexamethylenediamine dihydrochloride or triacetonamine hydrochloride are used as salt. 20. Method according to claim 8, characterized in that hexamethylenediamine dihydrochloride is used. 21. Method according to claim 1, characterized in that one uses an acid, such as an acid catalyst. 22. Method according to claim 21, characterized in that a Lewis acid is used as acid. 23. Method according to claim 22, characterized in that boron trifluoride is used. 24. Method according to claim 21, characterized in that a protonic acid is used as acid. 25. Method according to claim 24, characterized in that a mineral acid or an organic acid is used as protonic acid. 26. Method according to claim 25, characterized in that sulfonic acid or a carboxylic acid is used as organic acid. 27. Process according to claim 24, characterized in that hydrochloric acid, formic acid, acetic acid, malonic acid, succinic acid, maleic acid, benzoic acid, cinnamic acid, benzenesulfonic acid or p-toluenesulfonic acid are used as protonic acid. 28. Process according to claim 1, characterized in that, in addition to the acidic catalyst, 0.01 to 0.5 mol, referred to in process step a) used acetone of a different cocatalyst is added. 29. Process according to claim 28, characterized in that potassium iodide, sodium iodide, lithium bromide, lithium iodide, lithium rhodanide, ammonium rhodanide, lithium cyanide, lithium nitrate, ammonium sulfide, bromine, iodine or a bromide, iodide, nitrate, ethanesulfonate, benzenesulfonate or p-toluenesulfonate are added as cocatalysts of ammonia, triethylamine, urea or thiourea. 30.> ; Method according to claim 1, characterized in that in method step a) one works at a temperature of 5 - 35°C. 31. Method according to claim 1, characterized in that in method step a) you work at a temperature of 5 - 25°C. 32. Process according to claim 1, characterized in that the reaction is carried out in the presence of a mono- or polyfunctional alcohol or mixtures of such alcohols. 33. Method according to claim 32, characterized in that a lower monoalcohol is used as alcohol. 34. Method according to claim 33, characterized in that methanol, ethanol, ethylene glycol monomethyl ether or mixtures of these solvents are used. 35" Method according to claim 33, characterized in that methanol is used as alcohol. 36. Method according to claim 1, characterized in that one per mol of acetone at least uses 0.15 mol of ammonia. 37. Method according to claim 32, characterized in that one a) allows acetone to react with 0.15 mol of ammonia per moles of acetone starting material in methanol or ethanol in the presence of 0.2 to 7 moles, referred to starting acetone, 1. of an ammonium salt of an acid with a pK value below 5.0 or 2. of corresponding acid elene or 3. boron trifluoride or 4. boron trifluoride in mixture with ammonium salt according to 1. resp. with acid according to 2. at temperatures between 5 and 25°C for at least 3 hours and then b) adds at least half of it in process step a) used acetone and allows the reaction to proceed at temperatures between 40 and 65°C for at least 3 hours. 38. Method according to claim 37, characterized in that in method step a) ammonium chloride or brotrifluoride or a mixture of both is used as a catalyst. 39. Method according to claim 38, characterized in that one a) saturates acetone with ammonia gas and carries out the reaction in methanol in the presence of 2-5 moles, referred to the acetone used, of ammonium chloride at temperatures between 10 and 17°C for 3 to 5 hours. b) the reaction continues at temperatures between 50 and 55°C for 8 to 20 hours. 40 . Process according to claim 1, characterized in that in step a) a Lewis or protonic acid is used as acidic catalyst and working at 5-35°C and in step b) the reaction is completed by adding further acetone and/or diacetone alcohol, mesityl oxide, phorone, diacetonamine or triacetonediamine by increasing the temperature. 41. Method according to claim 40, characterized in that in process step b) an additional amount of a Lewis acid or a protonic acid is added. 42. Method according to claim 37, characterized in that in method step b) an additional amount of a Lewis acid or a protonic acid is added. 43. Method according to claim 42, characterized in that in method step b) boron trifluoride or ammonium chloride is added. 44. Method according to claim 42, characterized in that in method step b) concentrated sulfuric acid is added. 45. Method according to claim 42, characterized in that hydrogen chloride is added in method step b). 46. Method according to claim 40, characterized in that in method step b) at least 0.5 parts of acetone and/or diacetone alcohol or mesityl oxide are added per part of the acetone used in step a). 47. Method according to claim 46, characterized in that in method step b) 2-4 parts of acetone and/or diacetone alcohol or mesityl oxide per part of the acetone used in step a). 48. Method according to claim 47, characterized in that in method step b) 2-4 times the amount of acetone used in method step a) is added. 49. Method according to claim 37, characterized in that in method step b) in addition, at least double the amount of acetone used in method step a) and 0.05 to 1 mol calculated on the acetone used in method step a) of 97%- ig sulfuric acid and allow the reaction to proceed between temperatures of 40 and 65°C for 8 to 20 hours. 50. Method according to claim 49, characterized in that instead of sulfuric acid in method step b) hydrochloric acid is added. 51. Method according to claim 48, characterized in that in method step b) 2-4 times the amount of acetone used in method step a) and 5 - 12 moles, referred to the acetone used in step a) of concentrated sulfuric acid or hydrogen chloride are added and allow the reaction to proceed for 8-20 hours at 40 to 65°C. 52. Method according to claim 2, characterized in that the acetone used contains water and/or lower monoalcohols. 53. Method according to claim 1, characterized in that the reaction is carried out at above 5°C and under pressure.