GB2047681A - Preparation of 2,2,6,6- tetramethyl-4-oxopiperidine - Google Patents

Abstract

A process for preparing 2,2,6,6- tetramethyl-4-oxopiperidine by the catalysed reaction of an acetone compound and an ammonia donor compound, comprises bringing together in the liquid phase at least one acetone compound and at least one dissimilar ammonia donor compound in the presence of a catalytically effective amount of a hydrazine hydrohalide of the general formula R1R2N-NR3R4.nHX, in which R1, R2, R3 and R4, which can be the same or different, are C1-18 alkyl radicals, C4-20 cycloalkyl radicals, C6-18 aryl radicals, C7 to 21 alkaryl radicals, C7-21 aralykyl radicals or hydrogen atoms; X is a bromine, chlorine or iodine atoms and n is 1 or 2, and recovering 2,2,6,6- tetramethyl-4-oxopiperidine from the reaction mixture.

Description

SPECIFICATION Process for the preparation of triacetonamine The present invention is concerned with a new process for the preparation of 2,2,6,6-tetramethyl-4oxopiperidine, which is a known compound sometimes referred to as triacetonamine.

Triacetonamine is a key intermediate in the preparation of certain 4-substituted 2,2,6,6-tetramethylpiperidine derivatives which are excellent for protecting synthetic resin compositions against the deleterious influence of heat and light. For an outline of howtriacetonamine is used as an intermediate in the preparation of effective stabilisers, reference is made to U.S. Patent Specification No.4,124,564.

Triacetonamine has been known at least since the work of W. Heinz (Annalen der Chemie, 203, 336/1880).

Heinz converted acetone to phorone (2,6-dimethylhepta-2,5-dien-4-one) in about 30% yield and reacted this with ammonia to give triacetonamine in 70% yield. H.K. Hall (J.A.C.S., 79, 5447/1957) has described the reaction of acetone with ammonia in the presence of calcium chloride for 7 days which gave an about 20% yield of triacetonamine after careful fractional distillation to separate the desired product from a different basic nitrogen compound having a similar boiling point. R.B. Bradbury (J.C.S., 1947, 1394-99) has described reactions of acetone and ammonia, alone and with a number of different catalysts, which did not give any triacetonamine.Bradbury's product, obtained in 17% yield without catalyst and in 35% to 90% yield depending on the choice of catalyst, was 2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine hydrate which was split to diacetonamine

oxalate by the action of alcoholic oxalic acid.

U.S. Patent Specification No.3,513,170 discloses the conversion of Bradbury's pyrimidine (acetonine) to triacetonamine by the action of a Lewis acid in the presence of water. The Lewis acids used include zinc chloride, calcium chloride and picric acid. The same U.S. Patent Specification also discloses the reaction of diacetone alcohol or acetone with acetonine and/or ammonia to give triacetonamine, as well as the reaction of triacetonamine with diacetone alcohol and calcium chloride under similar conditions to give a higher condensation product,1,9-diaza-2,2,8,8,10,10-hexa methyl-4-oxospiro-(5,5)-u ndecane, having an empirical formula C15H28N20.

U.S. Patent Specification No.3,943,139 discloses the preparation of triacetonamine by heating phorone with aqueous ammonia and basic catalysts, such as lithium, sodium, calcium or barium hydroxide, in an autoclave under pressure.

U.S. Patent Specification No. 3,953,459 discloses the preparation of triacetonamine from acetonine with acetone or diacetone alcohol either in the presence or in the absence of water and an acidic catalyst, such as boron trifluoride, in a controlied amount of 0.2 to 12 mole %, referred to the acetonin.

U.S. Patent Specification No.3,959,295 discloses the preparation of triacetonamine from ammonia and acetone or an acidic self-condensation product of acetone in the presence of acidic catalysts in two stages carried out at two different temperatures, such as about 15 C. in the first stage and 50 - 55"C. in the second stage, the amount of acetone used being at least 1.6 moles per mole of ammonia.

U.S. Patent Specification No. 3,959,298 discloses the preparation of triacetonamine from acetonine and water in the presence of at least 0.125 mole acid catalyst per mole of acetonin. The catalysts used include an acetonin salt, an ammonium salt, an amine salt, a mineral acid and an organic acid.

U.S. Patent Specification No.3,960,875 discloses the preparation of triacetonamine by heating acetonin with acetone or diacetone alcohol in an alcohol solvent without the use of a catalyst.

U.S. Patent Specification No. 3,963,730 discloses the preparation of triacetonamine by heating acetonin with acetone under anhydrous conditions, using an ammonium or amine salt catalyst, such as ammonium chloride, ammonium formate, acetonin hydrochloride, pyridine hydrochloride, a hydrochloric acid-treated carboxylic acid type ion exchange resin, acetonin acetate or urea nitrate.

Consideration of the prior art as a whole leaves a confused and contradictory impression, with no clear indication of the nature of the key process variables or directions towards a practically workable process.

According to the present invention, 2,2,6,6-tetramethyl-4-oxopiperidine (hereinafter referred to as triacetonamine) is prepared by a catalytic process from an acetone compound and an ammonia donor compound, which comprises bringing together in the liquid phase at least one acetone compound and at least one dissimilar ammonia donor compound in the presence of a catalytically effective amount of a hydrazine hydrohalide of the general formula R1R2N-NR3R4 nHX, in which R1, R2, R3 and R4,which can be the same or different, are alkyl radicals containing up to 18 carbon atoms, cycloalkyl radicals containing 4 to 20 carbon atoms, aryl radicals containing 6 to 18 carbon atoms, alkaryl radicals containing 7 to 21 carbon atoms, aralkyl radicals containing 7 to 21 carbon atoms or hydrogen atoms;X is a bromine, chlorine or iodine atom and n is 1 or 2, and recovering triacetonamine from the reaction mixture.

The amount of catalytically effective hydrazine hydrohalide required is moderate. As little as 0.01% by weight, referred to the acetone compound, is effective, a preferred range of concentrations being from 0.05% to 10% by weight, referred to the acetone compound. Larger amounts can be used but tend to be wasteful and uneconomic.

A rs rnhar rzf fiinrtinn rnll f tinn S n-CatalVsts together with the hydrazine hydrohalide catalyst, inter-acting beneficially to enable better results to be obtained than with either ingredient alone.

The acetone compound used as starting material for the preparation of triacetonamine by the process of the present invention can be acetone, a condensation product of acetone with itself, such as diacetone alcohol, mesityl oxide or phorone, or a condensation product of acetone with ammonia, such as diacetonamine, triacetonediamine or 2,2,4,4,6-pentamethyl-1 ,2,5,6-tetrahydropyrimidine (hereinafter referred to as acetonin). The ammonia donor compound used as starting material can be ammonia or a condensation product of acetone with ammonia, such as diacetonamine, triacetonediamine or acetonin, provided that the acetone compound and the ammonia donor compound are not identical. A plurality of acetone compounds can be used in combination in the process of the present invention, as can a plurality of ammonia donor compounds.Some combinations of starting materials which can be used according to the present invention to prepared triacetonamine in the presence of a hydrazine hydro-halide catalyst include acetone with ammonia, diacetone alcohol with ammonia, acetonine with ammonia, acetone with diacetonamine, acetone with acetonine, mesityl oxide with acetonine, diacetone alcohol with triacetonediamine, acetone with ammonia and acetonin, mesityl oxide and phorone with ammonia and diacetone alcohol and mesityl oxide with ammonia and diacetonamine.

In the general formula of the hydrazine hydrohalide catalyst, the alkyl radicals R1, R2, R3 and R4 can be, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec.-butyl, t.-butyl, amyl, isoamyl, 2-ethyl-butyl, h-hexyl, 4-methy-2-pentyl, heptyl, octyl, iso-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, nonyl, decyl, isodecyl, undecyl, lauryl, myristyl, cetyl or stearyl. Aryl radicals R1, R2, R3 and R4 can be for example, phenyl, naphthyl, anthracenyl, phenanthryl, biphenylyl and terphenylyl.Cycloalkyl radicals R1, R2, R3 and R4 can be, for example, cyclobutyl, cyclopentyl, dimethyl-cyclobutyl, methylcyclopentyl, cyclohexyl, 3-methyl-cyclohexyl, 3,3,5-trimethylcyclohexyl, 4-t.-butylcyclo-hexyl, norbornyl, dihydrocyclopentadienyl, dihydroabietyl and dehydroabietyl.Alkaryl radicals R1, R2, R3 and R4 can be, for example otolyl, m-tolyl, m-tolyl,p-tolyl, 2,3-xylyl, 2,5-xylyl,3,5-xylyl,4-t-butylphenyl,2-t-butyl-5-methylphenyl, octylphenyl, nonylphenyl, dodecyl-o-tolyl, pentadecylphenyl, dimethylnaphthyl and diamylnaphthyl. Aralkyl radicals R1, R2, R3 and R4 can be, for example, benzyl, 1 -phenylethyl, 7-phenylheptyl and p-dodecylbenzyl.lnert substituents can also be present in the R1, R2, R3 and R4 radicals, such as alkoxyl, nitro and halogen, as, for example, in 4-nitrophenyl, 3,4-dichlorophenyl and 6,7-dimethoxynaphthyl radicals.

Examples of the hydrazine hydrohalide catalysts of the above-given general formula include mono and di salts of hydrogen bromide, chloride and iodide of hydrazine, N-methylhydrazine, N,N-dimethylhydrazine, N,N'-dimethylhydrazine, N-propylhydrazine, N-isopropyl-hydrazine, N,N-dipropylhydrazine, N,N' dipropylhydrazine, N-butylhydrazine, N,N-dibutylhydrazine, N-methyl-N-butyl-hydrazine, N cyclohexylhydrazine, N-phenylhydrazine, N-N-diphenylhydrazine, N,N'-diphenylhydrazine, N,N,N'triphenylhydrazine, N-benzylhydrazine, N-phenyl-N-benzyl hydrazine, N-methyl-N-p-nitrophenylhydrazine and N-naphthylhydrazine.

Co-catalysts which can be used with the hydrazine hydrohalide catalyst include bromine and iodine; lithium, sodium and potassium bromide; lithium, sodium and potassium iodide; ammonium bromide and iodide; lithium and ammonium thiocyanate; ammonium sulphate, lithium nitrite, ammonium chloride, lithium cyanate; urea and thiorea hydrobromide, hydroiodide, nitrite, methane-sulphonate, benzenesulphonate and p-toluenesulphonate; maleic acid hydrazide, 2,2'-thiodiethanol, triethanol-amine, dicyandiamide and barium hydroxide, and synthetic absorbents, such as magnesium silicate hydrate, aluminium silicate hydrate, activated carbon and diatomateous earth.

Furthermore, Lewis acids known as catalysts for the preparation of triacetonamine can be used with the hydrazine hydrohalide catalysts for greater effectiveness than is obtainable with either catalyst type alone.

When a co-catalyst is used together with the hydrazine hydrohalide catalyst, the amount of co-catalyst is usually from 0.01 to 10% by weight and preferably from 0.1 to 5% by weight, referred to the acetone compound.

The relative proportions of acetone compound and ammonia donor compound used in the preparation of triacetonamine by the process of the present invention can be varied over a wide range. If desired, ammonia can be used in excess, for example by saturating the reaction mixture with ammonia gas at normal or superatmospheric pressure or by charging liquid ammonia. With liquid ammonia donor compounds, such as acetonin or diacetonamine, the molar ratio of acetone ro ammonia donor compound can be from 0.1 to 1 to more than 1 1 and preferably 1 1 to 10 : excess acetone functioning as a solvent.

The reactants, catalysts, co-catalyst when used, solvent and the like can be charged all at once or in several portions as the reaction proceeds.

The process of the present invention is carried out in the liquid phase at any temperature and pressure at which the reaction mixture is liquid. Preferably, the reaction temperature is from 0 C. to the boiling point of the reaction mixture, the range of 30 to 60"C. being particularly preferred. Such a temperature is easily established by beginning the reaction at ambient temperature when acetone is used as the acetone compound starting material and heating the reaction mixture to the reflux temperature of boiling acetone.

For a particularly rapid operation, the reaction temperature can be adjusted to 70 to 110 C. by the use of higher boiling starting materials (e.g. diacetone alcohol, phorone or acetonin), as well as by working at a superatmospheric pressure of up to 30 atmospheres and preferably of 1 to 5 atmospheres.

The reaction time is usually from about 3 to about 20 hours and is in inverse relationship to the reaction temperature.

The use of a solvent in the preparation of triacetonamine by the process of the present invention is not critical but a solvent can be employed, if desired. Solvents which can be used include, for example, aliphatic hydrocarbons, such as pentane and hexane; cyclohydrocarbons, such as cyclohexane: aromatic hydrocarbons, such as benzene, toluene and xylene; chlorinated hydrocarbons, such as methylene chloride, 1,1,1-trichloroethane and carbon tetrachloride; nitriles, such as acetonitrile; neutral polar solvents, such as sulpholane, nitromethane, dimethylformamide, dimethyl-acetamide, tetramethylurea, hexamethylphosphoric acid triamide and dimethylsulphoxide; alcohols, such as methanol, ethanol, ispropanol, butanol, tert.-butanol,2-ethylhexanol, cyclohexanol, benzyl, alcohol, ethylene glycol, propylene glycol, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; ketones, such as acetone, methylethylketone, diethylketone, methyl-n-propylketone, di-n-propylketone, diisopropyl-ketone, di-n-butylketone, acety lacetone, hexane-2,5-dione, cyclohexanone, diacetone alcohol and mesityl oxide; and ethers, such as tetrahydrofuran, dioxan and diethyl ether.

In the preparation of triacetonamine according to the process of the present invention, the presence or absence of water is not critical. It is not necessary to add any water nor to take steps to exclude it. Some water is formed as a by-product of the reaction between acetone and ammonia; such water can be removed as it forms or it can be allowed to accumulate and become part of the solvent system. At the end of the reaction, the lowest boiling components of the mixture are unreacted acetone, water and solvent, if used; these can be stripped off and used in subsequent preparations without separation from one another.

Triacetonamine can be recovered from the reaction mixture by conventional techniques, for example by precipitation as the hydrate by adding water or by precipitation of a hydrohalide, sulphate or oxalate salt by adding the appropriate acid or by distillation, preferably afteradding an excess of a strong alkali, such as a concentrated aqueous potassium or sodium hydroxide solution.

The following Examples are given for the purpose of illustrating the present invention: Example 1 A flask equipped with a Dim rots condenser and a gas inlet tube was charged with 180 g. acetone, 9 g.

methanol and 1.8 g. N.N'-dimethylhydrazine dihydro-chloride and ammonia gas was passed in for 5 hours at 40 to 45"C, while stirring. Passing in of ammonia gas was then discontinued and the reaction mixture kept 15 hours at the same temperature, the colourless, clear liquid turning to light red via yellow. The reaction mixture was stripped in vacua, a light red residue being obtained. 93.0 g. Triacetonamine were obtained by vacuum distillation (yield 58%, referred to acetone used).

This Example demonstrates the preparation and recovering in high yield of triacetonamine by a process of the present invention.

Example 2 Ammonia gas was introduced into a mixture of 50 g. acetone and 1.8 g. hydrazine monohydrochloride for 4 hours at 40 to 450C. 130 g. acetone were then added and the reaction allowed to continue for 15 hours at 40 to 450C. The reaction mixture was worked up as in Example 1 to give 105.8 g. triacetonamine (yield: 66%).

This Example demonstrates the preparation and recovery in high yield of triacetonamine by a process according to the present invention.

Example 3 Ammonia gas was introduced into a mixture of 350 g. acetone, 8.5 g. water and 17.5 g. N-phenyl-hydrazine monohydrochloride for 5 hours at 30 to 35"C. After discontinuing the gas supply, the reaction mixture was heated to 50 to 55"C. and left to react for 12 hours. After solvent removal in vacuo, the light-red residue obtained was mixed with acetone and hydrogen chloride introduced until the pH was 7. The precipitated crystals were filtered off and washed with water to give 211.9 g. triacetoamine hydrochloride.

This Example demonstrates the preparation and recovery in high yield of triacetonamine in the form of the hydrochloride salt by a process according to the present invention.

Examples 4 to 9 Ammonia gas was introduced into a mixture of 270 g. acetone, 13.5 g. methanol and 2.7 g. of each of the catalysts mentioned below for 4 hours at 45 to 500C. After discontinuing the gas introduction, the reaction mixture was kept 15 hours at the same temperature to complete the reaction. The reaction solution was then analysed by gas chromatography, the following results being obtained. For controls, zinc chloride and ammonium chloride were used as examples of Lewis acids.

No. Catalyst Yield of triacetonamine (9.) Control 1 Zinc chloride 52.9 2 Ammonium chloride 81.8 3 None None Example 4 N-methylhydrazine mono- 144.3 hydrochloride 5 N-naphthylhydrazine 134.7 dihydrochloride 6 N,N,N' -triphenylhydrazine 129.9 hydrochloride 7 Hydrazine hydrobromide 125.1 8 N,N-dibutylhydrazine 120.3 hydrobromide 9 N-isopropylhydrazine 120.4 hydrobromide The results of these Examples demonstrate the importance of using a catalyst and the superior catalytic effectiveness of hydrazine hydrohalide catalysts in the preparation oftriacetonamine by the process of the present invention, compared with previously used catalysts.

Example 10 Ammonia gas was introduced into a mixture of 180 g. acetone, 9 g. dimethylformamide and 5.5. g.

hydrazine dihydrochloride for 1 hour while maintaining the temperature at 40 to 45 C.

After discontinuing the gas supply, the reaction mixture was reacted for 2 hours at the same temperature, whereafter ammonia gas was again introduced for 1 hour. This process was repeated four times. After the last introduction, the reaction was continued for 10 hours at the same temperature to give 115.8 g.

triacetonamine, which was recovered as in Example 1.

This Example demonstrates the preparation and recovery in high yield of triacetonamine by a process according to the present invention in which the catalyst is a hydrazine dihydrohalide and in which a solvent is used.

Examples ii to 16 Ammonia gas was introduced into mixtures of 255 g. acetone, 13 g. benzene, 0.8 g. hydrazine dihydrochloride and 1.3 g. of each co-catalyst mentioned below for 6 hours, while maintaining the temperature at 15 to 20"C.

The gas introduction was discontinued and the temperature raised to 50 to 55"C. and maintained for 18 hours.

The reaction solution obtained was analysed by gas chromatography in the same way as in Example 4.

Example Co-catalyst Yield of No. triacetonamine (g.) 11 None 138.6 12 Potassium iodide 159.0 13 Ammonium sulphide 152.2 14 Thiodiethanol 150.0 15 Lithium bromide 154.5 16 Maleic acid hydrazide 161.3 The results of these example, taken together with the results of Examples 4 to 9 and Controls 1 and 2 above, show the unexpected enhanced effectiveness of hydrazine hydrohalide - cocatalyst combinations in inrrPnsinn thr 'jipid nf trincetonsmine obtainable bv a nrocess accordina to the present invention.

Example 17 An autoclave was charged with 180 g. acetone and 1.8 g. N-butylhydrazine monohydrochloride. The head space gas was replaced completely with ammonia gas and the mixture reacted for 2 hours at 90"C., while stirring.

The autoclave was returned to normal pressure an the reaction continued for 12 hours at the reflux temperature of the unreacted acetone.

According to gas chromatographic analysis, the reaction solution contained 101.0 g. triacetonamine.

This Example demonstrates the preparation in high yield of triacetonamine by a process of the present invention carried out at superatmospheric pressure and at a temperature higher than the normal boiling point of acetone.

Examples 18to20 The process was carried out as in Example 1 except that the N-benzylhydrazine hydrobromide was used as catalyst. The yield of triacetonamine was determined by gas chromatography.

Example Amount of catalyst Yield of No. (g.) triacetonamine (g.) 18 0.45 83.4 19 1.8 89.8 20 3.6 91.4 These Examples demonstrate preparation in high yield oftriacetonamine by a process according to the present invention in which the concentration of the hydrazine hydrohalide catalyst used is varied over an eightfold range.

Examples 21 to 24 To examine the combined effects of the hydrazine hydrohalide catalyst with a known catalyst for production of triacetonamine, 1.8 g. N-methyl-N-nitrophenyl hydrazine hydrochloride, 50 g. acetone, 9 g.

dioxan and 1.8 g. prior art catalyst were treated with ammonia gas for 4 hours, while cooling to 10 to 1 5"C.

The gas supply was discontinued, 130 g. acetone were added and the reaction was continued at 50 - 550C. for 20 hours. The solution was then analysed to determine the yield of triacetonamine.

Example Second catalyst Yield. of No. triacetonamine (g.) 21 None 85.0 22 Ammonium chloride 99.4 23 Zinc chloride 93.0 24 Boron trifluoride 96.2 diethyl ether solution The results of these Examples, taken together with the results of Examples 4 to 9 and Controls 1 and 2 above, show the unexpected and beneficial effect of using a known catalyst as second catalyst, together with hydrazine hydrohalide, in increasing the yield of triacetonamine.

Example 25 83 g. Acetone, 15 g. isopropanol and 3 g. N-cyclo-hexylhydrazine hydroiodide were maintained at 45 to 50"C. while adding dropwise 217 g. of acetone and introducing ammonia gas for 3 hours. After discontinuing the gas supply, the reaction was continued for 12 hours at the same temperature to give 144.3 g.

triacetonamine.

The results of this Example demonstrate the effectiveness of a cycloaliphatic hydrazine hydrohalide catalyst in the preparation of triacetonamine by a process according to the present invention in high yield.

Example 26 Ammonia gas was introduced into a mixture of 50 g. acetone, 130 g. diacetone alcohol and 3 g.

N-phenyl-N-benzyl hydrazine hydrochloride for 8 hours at ambienttemperature. During the initial period, the temperature rose to about 50"C. due to the exothermic reaction.

After discontinuing the gas supply, the reaction mixture was reacted for 18 hours at the reflux temperature of acetone, 88.2 g. triacetonamine being obtained.

The results of this Example demonstrate the effectiveness of an aromatic hydrazine hydrohalide catalyst in the preparation of triacetonamine in high yield by a process according to the present invention, in which diacetone alcohol is used as the acetone compound starting material.

Example 27 Ammonia gas was introduced into a mixture of 680 g. acetone, 130 g. ethanol and 24 g. hydrazine dihydrochloride for 5 hours, while maintaining the temperature at 40 to 45"C.

After discontinuing the gas supply, 1800 g. acetone and 12 g. hydrazine dihydrochloride were added and the reaction continued for 15 hours at the same temperature.

According to gas chromatographic analysis, the reaction solution obtained contained 1546.4 g.

triacetonamine.

The results of this Example demonstrate the preparation in high yield of triacetonamine by a process according to the present invention.

Examples 28-31 Ammonia gas was introduced into a mixture of 165 g. acetone, 6g. N-(3-methylphenyl)-hydrazine monohydrochloride and co-catalyst as shown below for 5 hours, while maintaining the temperature at 20 to 25"C.

After discontinuing the gas supply, 430 g. acetone and 8.9 g. N-(3-methylphenyl)-hydrazine monohydroch chloride were introduced and the reaction mixture was reacted at 50 to 55"C. for the first 5 hours and then continued for 12 hours at the reflux temperature of acetone. The yield of triacetonamine was determined by gas chromatographic analysis.

Example Co-catalyst Yield of No. triacetonamine (g.) 28 Barium hydroxide octahydrate 8.9 9. 333.9 29 Triethanolamine 29.8g. 344.5 30 Diatomaceous earth 21.4 g. 318.0 31 iodine 16.7g. 339.2 The results of these Examples demonstrate the preparation in high yield of triacetonamine by a process in which a hydrazine hydrohalide catalyst and co-catalyst are used according to the present invention.

Example 32 A flask with attached condenser was charged with 80 g. acetonine, 80 g. acetone, 16 g. methanol and 1.6 g.

N-phenylhydrazine monohydrochloride and the mixture reacted at 50 to 550C. for 18 hours, while stirring.

The reaction solution was stripped under reduced pressure to give a light red residue. This residue was distilled in vacuo to give 60.4 g. triacetonamine. White crystals were obtained by recrystallisation from petroleum ether having a melting point of 34 - 36"C. The nature of the product was confirmed by the IR spectrum and gas chromatography.

Example 33 A mixture of 104 g. acetonine, 156 g. acetone and 1.0 g. N-(4-methylphenyl)-hydrazine hydrochloride was reacted at the reflux temperaure of acetone for 15 hours. 70.1 g. of the desired product were obtained in the same way as in Example 32.

The results of Examples 32 and 33 demonstrate the preparation in high yield of triacetonamine by a process in which a hydrazine hydrohalide is used as catalyst with acetone and acetonine as the ammonia donor compound according to the present invention.

Example 34 A mixture of 95 g. acetonin hydrate, 165 g. acetone, 0.17 g. N,N'-dibutylhydrazine hydrochloride and 2.5 g.

maleic acid hydrazide was reacted at 50 to 55"C. for 20 hours. 616 g..Triacetonamine was obtained in the same manner as in Example 32.

The results of this Example demonstrate the preparation in high yield of triacetonamine by a process including the use of a hydrazine hydrohalide catalyst and maleic hydrazide co-catalyst with acetone and acetonine as the ammonia donor compound starting material.

Example 35 A mixture of 83 g. acetonine, 167 g. acetone, 17 g. water and 4.2 g. N,N'-dimethylhydrazine dihydrochloride was reacted at 50 to 55"C. for 15 hours and then stripped under reduced pressure, followed by the addition of acetone to the light-red residue obtained and adjustment of the pH to 7 with hydrogen chloride gas. The precipitated crystals were filtered off, washed with acetone and dried to give 72.2 g.

triacetonamine hydrochloride.

The results of this Example demonstrate the preparation in high yield of triacetonamine, recovered in the form of its hydrochloride salt, by a process using a hydrazine hydrohalide catalyst, acetone and acetonine as the ammonia donor compound starting material in accordance with the present invention.

Example 36 Example 32 was repeated except that 80 g. diacetone alcohol were used instead of acetone, 58.8 g. ofthe desired product being obtained.

The results of this Example demonstrate the preparation in high yield of triacetonamine by a process according to the present invention in which diacetone alcohol and acetonine are used as the acetone compound and ammonia donor compound starting materials, respectively.

Examples 37- 41 A mixture of 110 g. acetonin, 330 g. acetone, 10 g. benzene and 3.3 g. of each catalyst listed below was reacted at the reflux temperatures of acetone for 15 hours. The reaction solutions were analysed by gas chromatography, triacetonamine produced being shown below: Example Catalyst Yield of No. triacetonamine (g.) Control 4 None 5.3 5 Ammonium chloride 51.6 Example 37 N-methyl-N-butylhydrazine 78.6 hydrochloride 38 N-butylhydrazine dihydro- 85.2 chloride 39 N,N'-dimethylhydrazine 83.0 dihydrochloride 40 Hydrazine hydrobromide 77.5 41 N-isopropylhydrazine hydro 73.1 bromide The results of these Examples demonstrate the preparation in high yield of triacetonamine by the process of the present invention in which various hydrazine hydrohalide catalysts are used.

Example 42 A mixture of 70 g. acetonin, 40 g. dioxan, 0.4 g. N-(3-methylphenyl)-hydrazine hydrochloride and 4 g.

activated carbon was stirred at 40 to 45"C. and treated dropwise with 140 g. acetone for 3 hours.

The reaction mixture was then warmed to 50 to 55"C. and further reacted for 12 hours. The solution obtained was analysed by gas chromatography and confirmed to contain triacetonamine.

The results of this Example demonstrate the successful use of a hydrazine hydrohalide catalyst and activated carbon co-catalyst in the process of the present invention.

Examples 43 to 49 In order to examine the effect of co-catalysts, a mixture of 100 g. acetonin, 150 g. acetone, 0.4 g.

N-naphthylhydrazine hydrochloride and 5 g. of the co-catalysts shown below was reacted at 50 ta 55"C. for 17 hours. The following results were obtained, according to the gas chromatographic analysis.

Example Co-catalysts Yield of No. triacetonamine (g.) 43 None - 68.4 44 Barium oxide 80.5 45 Lithium nitrite 77.5 46 Thiodiethanol 78.5 47 Dicyandiamide 80.4 48 Triethanolamine 83.6 49 Ammonium iodide 82.9 The results of these Examples confirm the successful use of a hydrazine hydrohalide catalyst, together with each of several co-catalysts, in the preparation of triacetonamine by the process according to the present invention.

Example 50 A mixture of 480 g. acetonin, 520 g. acetone, 240 g. isopropanol and 5 g. N,N,N'-triphenylhydrazine hydrochloride was reacted at 45 to 50"C, for 3 hours.

300 g. Acetone were then added and the reaction continued at the same temperature for 3 hours. This process was repeated twice and, after the last addition of acetone, the reaction was continued for 6 hours at the same temperature. The reaction solution obtained was analysed and found to contain 352.7 g.

triacetonamine.

The results of this Example demonstrate the successful use of a triarylhydrazine hydrohalide catalyst and an organic solvent in the preparation of triacetonamine by a process according to the present invention.

Examples 51 to 54 In order to examine the combination effect of hydrazine hydrohalide catalyst with a Lewis acid, a mixture of 90 g. acetonin, 180 g. acetone, 0.5 g. N-benzylhydrazine hydrobromide and less than 0.5 g. of one of the Lewis acids mentioned below was reacted at the reflux temperature of acetone for 13 hours.

The following results were obtained by gas chromatographic analysis of the reaction mixture for triacetonamine present therein: Example Lewis acids Yield of No. triacetonamine (g.) 51 None 58.9 52 Zinc chloride 70.7 53 Ammonium chloride 81.4 54 Calcium chloride 73.4 The results of these Examples show the unexpected benefit of using a Lewis acid as a second catalyst, together with a hydrazine hydrohalide in the preparation of triacetonamine by the process according to the present invention.

Example 55 An autoclave was charged wih 120 g. acetonin, 120 g. acetone, 25 g. dimethylformamide and 1.2 g.

hydrazine dihydrochloride and reacted at 85"C. for 5 hours. After return to normal pressure, the reaction solution was analysed by gas chromatography and found to contain 99.1 g. triacetonamine.

The results of this Example demonstrate the successful use of a hydrazine hydrohalide catalyst in the preparation of tracetonamine from acetone and acetonin as ammonia donor compound at a temperature above the normal boiling of acetone and at a pressure above atmospheric to maintain the liquid phase.

Example 56 80 g. Acetonin, 580 g. acetone, 24 g. water and 1.9 g. N-phenylhydrazine hydrochloride were reacted at 50 55 C. for 3 hours. 50 g. Acetonin and 1.3 g. catalyst were then added to the reaction solution and reacted for 3 hours. This procedure was repeated twice and after the last addition of acetonin and catalyst, the reaction was continued for 10 hours at the same temperature to give 185.2 g. triacetonamine after stripping and vacuum distillation.

The results of this Example demonstrate the successful use of a semi-continuous technique forthe preparation of triacetonamine from acetone, acetonin as the ammonia donor compound and a hydrazine hydrohalide catalyst according to the present invention.

Claims (17)

1. A process for preparing 2,2,6,6-tetramethyl-4-oxopiperidine by the catalysed reaction of an acetone compound and an ammonia donor compound, comprising bringing together in the liquid phase at least one acetone compound and at least one dissimilar ammonia donor compound in the presence of a catalytically effective amount of a hydrazine hydrohalide of the general formula RrR2N-NR3R4.nHX, in which Fl1, R2, R3 and R4, which can be the same or different, are alkyl radicals containing up to 18 carbon atoms, cycloalkyl radicals containing 4 to 20 carbon atoms, aryl radicals containing 6 to 18 carbon atoms, alkaryl radicals containing 7 to 21 carbon atoms, aralkyl radicals containing 7 to 21 carbon atoms or hydrogen atoms;; Xis a bromine, chlorine or iodine atom and n is 1 or 2, and recovering 2,2,6,6-tetramethyl-4-oxopiperidine from the reaction mixture.

2. A process according to claim 1, wherein the acetone compound is acetone or diacetone alcohol.

3. A process according to claim 1 or 2, wherein the ammonia donor compound is ammonia or acetonine.

4. A process according to any of the preceding claims, wherein the amount of hydrazine hydrohalide used is at least 0.01%, referred to the acetone compound.

5. A process according to claim 4, wherein the amount of hydrazine hydrohalide used is from 0.05 to 10% by weight, referred to the acetone compound.

6. A process according to any of the preceding claims, wherein R1, R2, R3 and R4 are all hydrogen atoms.

7. A process according to any of the preceding claims, wherein the hydrazine hydrohalide contains at least one alkyl radical.

8. A process according to any of the preceding claims, wherein the hydrazine hydrohalide contains at least one aryl radical.

9. A process according to any of the preceding claims, wherein the hydrazine hydrohalide contains at least one cycloalkyl radical.

10. A process according to any of the preceding claims, wherein the hydrazine hydrohalide contains at least one aralkyl radical.

11. A process according to any of the preceding claims, wherein a co-catalyst is also present.

12. A process according to claim 11, wherein the co-catalyst is bromine or iodine; a chloride, bromide or iodide of lithium, sodium, potassium or ammonium; lithium or ammonium sulphates orthiocyanate; a urea or thiourea hydrobromide, hydroiodide, nitrite, methane-sulphonate, benzenesulphonate or toluenesul phonate; maleic hydrazide, hydrazide, thiodiethanol, 2,2'2"-nitrilotriethanol; barium oxide or hydroxide; a synthetic absorbent; or a Lewis acid.

13. A process according to claim 11 or 12, wherein the co-catalyst is used in an amount of from 0.01 to 10% by weight, referred to the acetone compound.

14. A process according to claim 13, wherein the co-catalyst is used in an amount of from 0.1 to 5% by weight, referred to the acetone compound.

15. Process according to any of the preceding claims, wherein the reaction is carried out in a solvent.

16. Process according to claim 1 for preparing 2,2,6,6-tetramethyl-4-oxopiperidine, substantially as hereinbefore described and exemplified.

17. 2,2,6,6-Tetramethyl-4-oxopiperidine, whenever prepared by the process according to any of claims 1 to 16.