Process for the preparation of 2,2,6,6-tetramethyl-piperidone-(4).

0001Various processes for the production of 2,2,6,6-tetramethylpiperidone- (4) (triacetonamine or also called 2,2,6,6-tetramethyl-4-oxopiperidine) are known. They usually consist in converting the precondensates of acetone, such as phoron and acetonin, to 2,2,6,6-tetramethylpiperidone- (4) in a further process step. However, some of these methods have the disadvantage that long reaction times result in only low yields and the by-products obtained in the aqueous lyes are ecological problems.

0002Some improvement has been achieved by reacting preformed phoron with aqueous ammonia at elevated temperature and pressure.

0003Furthermore, triacetonamine can be obtained by reacting 2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine (acetone) with acetone or its condensation products, such as diacetone alkchol, mesityl oxide or phoron, and water either in the heat or in the presence of protonic acids or their salts with ammonia or amines, or with basic ion exchangers or with Lewis acids, such as zinc chloride or calcium chloride, in the presence of water.

0004Triacetonamine can also be prepared from acetonine in the presence of at least 12.5 mole percent of an acidic catalyst under anhydrous conditions. All of these methods have the disadvantage that preliminary products must first be produced in a separate process.

0005In both cases, the pyrimidine derivative used as the starting material is likewise first prepared from acetone and ammonia and, after isolation and purification, is used to prepare 2,2,6,6-tetramethyl-4-oxopiperidine.

0006Methods are also known which start directly from acetone. When using acetone as the starting product, a two-stage and one-stage process is known. In the one-step process, acetone and ammonia are condensed in the presence of anhydrous calcium chloride. This process gives 2,2,6,6-tetramethylpiperidone- (4) in about 40 percent yield. In addition, large amounts of aqueous calcium chloride solution are produced during the condensation, the removal of which presents considerable difficulties because of the contamination with organic substances and because of the possibility of environmental pollution.

0007Surprisingly, a process for the preparation of 2,2,6,6-tetramethylpiperidone- (4) by reacting acetone and ammonia in the presence of solid, acidic catalysts and at elevated temperature has now been found which does not have the disadvantages described. This process is characterized in that acetone and ammonia are reacted in a molar ratio of 2-25: 1, preferably 3-12: 1, at temperatures in the range from 30-180 ° C, preferably 80-130 ° C, and as solid, acidic Catalysts are used both in use^pProducts as well as in the reaction mixture are practically insoluble. A condition for the suitability for this reaction is that the solid, acidic catalyst is insoluble in the reaction medium. Both inorganic and organic-based ones with active sulfonic acid residues or similarly active acid groups are suitable for the described reaction using solid, acidic catalysts. The chemical resistance of such fixed bed catalysts in aliphatic and also other solvents is extremely high, so that they are practically inconclusive in the reaction mixture.

0008Examples of suitable inorganic catalysts are, for example, acidic aluminum hydrosilicates of the bentonite and / or montmorillonite type and inorganic ion exchangers based on aluminum silicate of the zeolite, mordenite and / or erionite type, the acidity of which is sufficient to catalyze the reaction. Also suitable for this purpose are carrier materials, such as, for example, diatomaceous earth, which have first been treated with phosphoric acid and then have been subjected to a heat treatment between 700 and 1100 ° C. The preparation of such catalysts has been described in CA-PS 772 201. Further examples of solid, acidic catalysts are ion exchangers on an organic basis, especially those with a styrene-divinylbenzene copolymer as a matrix and with -S0₃^- as anchor groups. Products of this type are commercially available, for example, under the names "Amberlyst® 15", "Amherlite® 200" or "Leriratit® SP 12011. These types are particularly intended for use in non-aqueous solutions, especially since it has been established a long time ago that acidic exchangers can also be used for catalysis in non-aqueous solutions. The solid, acidic ion exchangers are expediently used in the ammonium or alkylammonium form, preference being given to those amines for the amine form which are formed as intermediate or end products in the reaction of acetone with ammonia.

0009Such catalysts are neither soluble in the starting products nor in the water-containing reaction mixture. As a result, they can be separated in batch operation by simple filtration and can be reused. Therefore the amount of catalyst used is not critical; 10-20% by volume based on the acetone used have proven to be favorable. However, the catalyst can also be arranged in a reactor as a fixed bed, which enables continuous operation.

0010Because of the low boiling point of the acetone, the reaction is expediently carried out under pressure, under the autogenous pressure of the system. The intrinsic pressure can also be increased by adding inert gases. Suitable inert gases are, for example, nitrogen, hydrogen and noble^Gase, like helium.

0011For batch operation there are reaction times between 0.2 - 6 hours, while LHSV values ​​(space / time exposure values) of 0.2 - 10 l A. acetone / 1 contact h are available for continuous operation.

0012In addition to acetone, its low molecular weight condensation products, in particular diacetone alcohol, mesityl oxide, and reaction products with ammonia, such as diacetonamine, acetone and triacetcinediamine, can also be used. If these products are by-products, they can be returned.

0013The new process has the advantage that acetone and ammonia can be converted directly and continuously under environmentally friendly conditions in one step. Another advantage is the possibility of recycling the resulting intermediates into the process, which enables higher yields of the end product, based on the acetone converted.

00142,2,6,6-Tetramethylpiperidone- (4 is a valuable starting product for the production of substances with stabilizer properties.

0015The process of the present invention is illustrated by the following examples:

Example 1:

00161.1 l of acetone and 200 ml of an acidic ion exchanger based on a styrene-divinylbenzene copolymer with sulfonic acid residues, which is commercially available under the name Lewatit® SP 120, were introduced into a 2 l stainless steel autoclave. It was purged with nitrogen; then 200 ml of liquid ammonia were added. The mixture was heated to 100 ° C. with vigorous stirring and held at this temperature for 4 hours. After cooling to room temperature, the pressure was released and the ion exchanger was filtered off. 960 g of reaction product were obtained. The gas chromatographic analysis showed the following composition:<tables id="tabl0001" num="0001"><img file="EP0004104A2_D0001.tif" /></tables>

0017If one takes into account that acetone, mesityl oxide and diacetonamine can be reused in the reaction, the conversion is 19.1%, but the triacetonamine yield ⁴9.7% based on sales.

Example 2:

0018According to Example 1, 1.1 l of acetone and 200 ml of ammonia were reacted. However, 200 ml of aluminumium hydrosilicate of the montmorillonite type, which is commercially available under the name K 10, were used as the catalyst, and the system pressure was raised to 125 bar with nitrogen after the reaction temperature had been reached. Gas chromatographic analysis of the reaction mixture showed the following composition:<tables id="tabl0002" num="0002"><img file="EP0004104A2_D0002.tif" /></tables>

0019This corresponded to a conversion of 14.0% and a triacetonamine yield of 39.3%.

Example 3:

0020According to Example 1, 1.1 l of acetone and 200 ml of ammonia were reacted. However, 200 ml of aluminum silicate of the mordenite type, commercially available under the name Zeolon 100, were used as the catalyst.

0021After four hours of reaction at 100 ° C. under autogenous pressure, the reaction mixture showed the following composition after analysis by gas chromatography:<tables id="tabl0003" num="0003"><img file="EP0004104A2_D0003.tif" /></tables>

0022With a conversion of 21.1%, this corresponded to a triacetamine yield of 35.1%.

Example 4:

0023According to Example 2, 1.1 l of acetone were reacted with 75 ml of liquid ammonia in the presence of 200 ml of aluminum hydrosilicate of the montmorillonite type at 80 ° C. under autogenous pressure. The following composition of the reaction mixture was determined by gas chromatographic analysis:<tables id="tabl0004" num="0004"><img file="EP0004104A2_D0004.tif" /></tables>

0024With a conversion of 22.4%, the triacetonamine yield was 69.6%.

Example 5:

0025A cylindrical reactor was filled with Lewatit® SP 120 in such a way that this catalyst material, separated by sieves, was arranged between two layers of Tonrashi rings. The bulk volume of the catalyst was 650 ml in the moist state, but shrank to 500 ml after treatment with acetone. The reactor was brought to a reaction temperature of 100 ° C. by means of electrical heating and then continuously charged with 1000 ml / h of acetone and 50 ml / h of ammonia by pumping the two reactants from templates into the lower part of the reactor in liquid form. The reaction product passed liquid from the upper reactor part into a separator and was continuously withdrawn from it; the system was run with inert gas (H₂) kept under a pressure of 70 bar.

0026According to GC analysis, the reaction product had the following composition:<tables id="tabl0005" num="0005"><img file="EP0004104A2_D0005.tif" /></tables>

0027This resulted in a conversion of 26.9%, which was calculated as in Example 1, and a 69.9% yield based on the conversion.

0028The trial was stopped after 86 days, although the sales and yield ratios had not been adversely affected.

Example 6:

0029The reaction components were pumped into the reactor under otherwise the same conditions as in Example 5 above, ie the trickle method was used. The results obtained do not differ from those listed in Example 5.

Examples 5a and 6a (processing of the process products):

0030The reaction products obtained according to Examples 5 and 6 were worked up by batchwise distillation. The first step was to work under normal pressure.

0031The first fraction was acetone. As the second fraction, mesityl oxide passed over as an azeotrope with the water of reaction, which was separated off using a phase separator. Pure mesityl oxide was obtained as the third fraction. The diacetonamine contained in the reaction mixture cleaved back into ammonia and mesityl oxide under the present conditions. The organic parts of these fractions were used again in the reaction. The distillation is then continued under vacuum. An N-containing intermediate fraction was obtained, which the pure triacetonamine fraction (bp₁₀ 78-82 ° C; n_D20 1.4630) followed; it corresponded to 16.3% of the product used in the distillation. The N-containing intermediate fraction and the distillation residue were discarded.

0032The percentages in the examples above are percentages by weight.