Process for preparing N,N'-dialkyl-p-phenylenediamines

Abstract

The present invention relates to a novel process for preparing N,N'-dialkyl-p-phenylenediamines of formula (I) and to the use of N,N'-dicyclohexyl-p-phenylenediamine with a purity of more than 95.0% by weight as an antiaging agent in rubber mixtures, vulcanized rubber products and moldings obtainable therefrom, in particular tires.

Description

[Technical Field]

[0001] The present invention relates to a novel process for preparing N,N'-dialkyl-p-phenylenediamines of formula (I) and to the use of N,N'-dicyclohexyl-p-phenylenediamine with a purity of more than 95.0% by weight as an ageing stabilizer in rubber mixtures, vulcanizates and moldings obtainable therefrom, in particular tires. [Background technology]

[0002] N,N'-Dicyclohexyl-p-phenylenediamine has excellent suitability for protecting vulcanizates based on natural or synthetic rubber against the aging processes caused by the action of oxygen and ozone: it migrates to the surface of the vulcanizate, where it protects the rubber from the aforementioned effects.

[0003] Patent Document 1 describes a process for preparing N,N'-di-sec-alkyl-p-phenylenediamine. p-Nitroaniline or p-phenylenediamine is reacted with an aliphatic C3-C6 alkyl group in the presence of CuO, Cr2O3, and BaO. 12 It reacts with ketones.

[0004] Patent Document 2 describes a process for preparing N,N'-dialkyl-p-phenylenediamines. The catalyst selected is a mixture of three components: M1 (Ni, Co, or Fe), M2 (Re, Pd, and / or Ru), and M3 (Li, Ma, K, Rb, Ca, Mg, Sr, or Ba).

[0005] A drawback of these two aforementioned processes is that several catalysts are used, some of which are expensive and of environmental concern.

[0006] Patent Document 3 describes a process for preparing N,N'-di-sec-butyl-p-phenylenediamine, which proceeds by reductive alkylation of p-nitroaniline and a ketone in the presence of a platinum catalyst and activated carbon. In this process, p-nitroaniline and a ketone (butanone in this case) are added, followed by the addition of activated carbon and filtration to remove any impurities that may be present. The catalyst is added only after the activated carbon is removed by filtration. A conversion rate of 98.7% is described, but the final purity of the reaction product is not disclosed. It also applies that the described process requires the use of activated carbon to purify the starting materials. However, the use of activated carbon has several drawbacks, namely, the activated carbon must be removed from the reaction mixture in a further reaction step, which requires additional complexity and time. Furthermore, activated carbon may, for example, leave impurities in the reaction mixture or may clog pipelines and filters. Handling activated carbon powder is also problematic because the dust formed increases the level of complexity required to improve safety measures.

[0007] Patent Document 4 describes a process for preparing N,N'-dialkyl-p-phenylenediamines and further N,N'-dicyclohexyl-p-phenylenediamine, which proceeds by the reaction of p-nitroaniline and a ketone under hydrogen pressure and in the presence of a hydrogenation catalyst. It is stated that p-nitroaniline has low solubility in organic solvents, and that the use of an excess of a low-molecular-weight ketone (including cyclohexanone) as an alkylating agent results in the substitution of two amine hydrogen atoms of an aromatic amine. Various ethers are used as solvents. The purity of the reaction product is stated to be 93-97%. However, mono- and tri-alkylated by-products are obtained in a total amount of 3-7%, and in individual cases at least 1% each. These by-products are highly undesirable because they hinder the migration of N,N'-dialkyl-p-phenylenediamine, preferably N,N'-dicyclohexyl-p-phenylenediamine, to the surface of the vulcanizate, thereby limiting its effectiveness in the case of N,N'-dicyclohexyl-p-phenylenediamine. For example, the monoalkylated by-product is a free amine group that forms hydrogen bonds with other molecules, while the trialkylated by-product is sterically very bulky and bulky, two factors that hinder the migration described above. Furthermore, the catalyst used in this process is platinum applied to aluminum. The disadvantage is that the production of aluminum is often expensive and environmentally harmful. Furthermore, the hydrogenation time is relatively long, ranging from 4 to 5.2 hours. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Chinese Patent Application Publication No. 1370768A [Patent Document 2] Chinese Patent Application Publication No. 1947837A [Patent Document 3] Chinese Patent Application Publication No. 105061214A [Patent Document 4] U.S. Patent No. 4,140,718A

[0009] Therefore, there is a need for a process for preparing N,N'-dialkyl-p-phenylenediamines, preferably N,N'-dicycloalkyl-p-phenylenediamines, more preferably N,N'-dicyclohexyl-p-phenylenediamine, that overcomes the aforementioned shortcomings of the prior art. Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention was to provide a process for preparing N,N'-dialkyl-p-phenylenediamines, preferably N,N'-dicycloalkyl-p-phenylenediamines, more preferably N,N'-dicyclohexyl-p-phenylenediamines, which overcomes the drawbacks of the prior art and makes it possible to prepare N,N'-dialkyl-p-phenylenediamines, preferably N,N'-dicycloalkyl-p-phenylenediamines, more preferably N,N'-dicyclohexyl-p-phenylenediamines, in high purity and with only small amounts of mono- and trialkylated by-products (preferably N-alkyl-p-phenylenediamines and N,N,N'-trialkyl-p-phenylenediamines in the context of the present invention). [Means for solving the problem]

[0011] The purity of the reaction product thus obtained is confirmed in the context of the present invention preferably by gas chromatography according to ASTM-D 4937. This corresponds to the purity in % by weight.

[0012] In the context of the present invention, high purity exists when the reaction product prepared by the process of the present invention has a purity of greater than 95.0 wt.%, preferably greater than 96.0 wt.%, and most preferably greater than 97.0 wt.%, as determined by gas chromatography.

[0013] In the context of the present invention, small amounts of mono- and tri-alkylated by-products (preferably N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine) refer to a total of less than 3.0% by weight, preferably less than 2.5% by weight, more preferably less than 1.5% by weight, and most preferably less than 1.0% by weight of the two by-products. A small amount of N-alkyl-p-phenylenediamine is present when the latter is present in the reaction product to an extent of less than 1.0% by weight, preferably less than 0.5% by weight, and more preferably less than 0.3% by weight. A small amount of N,N,N'-trialkyl-p-phenylenediamine is present when the latter is present in the reaction product to an extent of less than 3% by weight, preferably less than 1.5% by weight, and more preferably less than 1.0% by weight.

[0014] It has surprisingly been found that the reaction of a compound of formula (II) with at least one ketone of formula (III) and a solvent of formula (IVa), (IVb) or (IVc) or mixtures thereof in the presence of a hydrogenation catalyst and hydrogen affords the corresponding N,N'-dialkyl-p-phenylenediamine of formula (I) in high purity, while only small amounts of mono- and tri-alkylated by-products are obtained.

[0015] process Thus, the present invention provides a compound of formula (I) [ka] A process for preparing N,N'-dialkyl-p-phenylenediamines of formula (II) [ka] wherein R1 and R2 are the same or different and are selected from the group consisting of -NH2 and -NO2. and compounds of formula (III) [ka] is converted in the presence of a hydrogenation catalyst and hydrogen, Z in formulas (I) and (III) are the same, and a) an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Z, and which is preferably a C4-C6 alkylene, more preferably a C5 alkylene, preferably a linear alkylene chain; or b) two alkyl groups, preferably linear alkyl groups, each bonded to a carbon atom adjacent to Z and forming an alkyl chain, preferably a linear alkyl chain, with said carbon atom, and together having the empirical formula C n H 2n+2 (wherein n is preferably 4 to 6, more preferably n is 5), The reaction is represented by formula (IVa) [ka] , formula (IVb) [ka] or formula (IVc) [ka] or a mixture thereof, Y in formulae (IVa), (IVb) and (IVc) are the same or different, preferably the same, and a) an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Y, and which is preferably a C4-C6 alkylene, more preferably a C5 alkylene, preferably a linear alkylene chain; or b) two alkyl groups, preferably linear alkyl groups, or one alkyl group and one hydrogen atom, each bonded to a carbon atom adjacent to Y and forming an alkyl chain, preferably a linear alkyl chain, with said carbon atom, and which together have the empirical formula C n H 2n+2(wherein n is preferably 4 to 6, more preferably n is 5) and represents two alkyl groups, preferably linear alkyl groups, or one alkyl group and one hydrogen atom. DETAILED DESCRIPTION OF THE INVENTION

[0016] The term "alkylene" in the above definitions of Y and Z preferably refers to C n H 2n Represents.

[0017] In the process of the present invention, Y in formulas (IVa), (IVb) and (IVc) and Z in formulas (I) and (III) can be the same or different. It is preferred that Y and Z in formulas (I), (III), (IVa), (IVb) and (IVc) are the same.

[0018] In a preferred embodiment of the process of the present invention, Z and Y in formulae (I), (III) and (IVa) are the same.

[0019] In a further preferred embodiment of the process of the present invention, Z and Y in formulae (I), (III) and (IVb) are the same.

[0020] In a further preferred embodiment of the process of the present invention, Z and Y in formulae (I), (III) and (IVc) are the same.

[0021] In a further embodiment of the invention, Z in formulae (I) and (III) is the same and different from Y in formulae (IVb) and (IVc).

[0022] The process of the present invention is a process for preparing N,N'-dialkyl-p-phenylenediamines of formula (I).

[0023] Z in formula (I) may represent two alkyl groups, preferably linear alkyl groups, each bonded to a carbon atom adjacent to Z and forming an alkyl chain, preferably a linear alkyl chain, together with the carbon atom, and the two alkyl groups of Z together represent the empirical formula C n H 2n+2 (wherein n is preferably 4 to 6, and more preferably n is 5).

[0024] Thus, the process of the present invention can be a process for preparing N,N'-alkyl-p-phenylenediamine, preferably N,N'-pentyl-, N,N'-hexyl-, N,N'-heptyl-p-phenylenediamine, more preferably N,N'-hexyl-p-phenylenediamine.

[0025] In a preferred embodiment of the process of the present invention, Z in formula (I) is an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Z, and the alkylene chain of Z is preferably a C4-C6 alkylene, more preferably a C5 alkylene.

[0026] Thus, preferably, the process of the present invention is a process for preparing N,N'-cycloalkyl-p-phenylenediamines.

[0027] More preferably, Z in formula (I) is a straight-chain alkylene chain that forms a cyclic ring together with the carbon atom adjacent to Z, and the straight-chain alkylene chain is preferably C4 to C6-alkylene, most preferably C5-alkylene.

[0028] Thus, more preferably, the process of the present invention is a process for preparing N,N'-cyclopentyl-p-phenylenediamine, N,N'-cyclohexyl-p-phenylenediamine and N,N'-cycloheptyl-p-phenylenediamine, most preferably N,N'-cyclohexyl-p-phenylenediamine.

[0029] The process of the present invention uses a compound of formula (II) wherein R1 and R2 are the same or different and are selected from the group consisting of -NH2 and -NO2.

[0030] Preferably, R1 and R2 are the same and -NH2, or different and are -NH2 and -NO2, more preferably different and are -NH2 and -NO2. Thus, more preferably, the compound of formula (II) is para-nitroaniline.

[0031] Any desired ketone of formula (III) can be used.

[0032] Y in the at least one ketone of formula (III) may represent two alkyl groups, preferably linear alkyl groups, each bonded to a carbon atom adjacent to Z and forming an alkyl chain, preferably a linear alkyl chain, together with the carbon atom, and the two alkyl groups of Z together represent the empirical formula C n H 2n+2 (wherein n is preferably 4 to 6, and more preferably n is 5).

[0033] Thus, the at least one ketone of formula (III) used may be a ketone selected from the group of pentanone, hexanone and heptanone, preferably a ketone selected from pentan-2-one, pentan-3-one, hexane-2-one, hexane-3-one, heptan-2-one, heptan-3-one and heptan-4-one.

[0034] In accordance with the above preferences for Y in formula (III), the at least one ketone of formula (III) used in step a) is preferably a cyclic ketone, more preferably a ketone selected from cyclopentanone, cyclohexanone and cycloheptanone.

[0035] Therefore, the ketone of formula (III) is most preferably cyclohexanone.

[0036] In the process of the present invention, it is preferred to use a ketone of formula (III).

[0037] It is possible to use any desired solvent of formula (IVa), (IVb) or (IVc) or mixtures thereof.

[0038] Y in the solvent of formula (IVa), (IVb) or (IVc) may represent two alkyl groups, preferably linear alkyl groups, or one alkyl group and one hydrogen atom, each bonded to a carbon atom adjacent to Y and forming an alkyl chain, preferably a linear alkyl chain, together with the carbon atom, and the two alkyl groups or one alkyl group and one hydrogen atom together represent the empirical formula C n H 2n+2 (wherein n is preferably 4 to 6, and more preferably n is 5).

[0039] Thus, the solvent of formula (IVa), (IVb) or (IVc) or mixtures thereof used is preferably one solvent selected from the group of pentanol, hexanol and heptanol or mixtures thereof, more preferably hexanol.

[0040] Preferably, Y in formula (IVa), (IVb) or (IVc) is an alkylene chain, preferably a linear alkylene chain, that forms a cyclic ring together with the carbon atom adjacent to Y, and the alkylene chain of Y is preferably a C4-C6 alkylene, more preferably a C5 alkylene.

[0041] In accordance with the preferences given above for Y in formula (IVa), the solvent of formula (IVa) used is preferably selected from cyclopentanol, cyclohexanol and cycloheptanol or mixtures thereof.

[0042] Most preferably, the solvent of formula (IVa) is cyclohexanol.

[0043] In accordance with the preferences given above for Y in formula (IVb), the solvent of formula (IVb) used is preferably selected from cyclopentane, cyclohexane and cycloheptane or mixtures thereof.

[0044] Most preferably, the solvent of formula (IVb) is cyclohexane.

[0045] In accordance with the preferences given above for Y in formula (IVc), the solvent of formula (IVc) used is preferably selected from methylcyclopentane, methylcyclohexane and methylcycloheptane or mixtures thereof.

[0046] Most preferably, the solvent of formula (IVc) is methylcyclohexane.

[0047] The solvent of formula (IV) is preferably a solvent of formula (IVb) or (IVc) or a mixture thereof, more preferably selected from cyclohexane and methylcyclohexane.

[0048] Most preferably, the solvent of formula (IV) is methylcyclohexane.

[0049] Preferably, ethers selected from the group consisting of glycol monoethers, glycol diethers and cyclic diethers are present in the process of the present invention in a molar ratio to the compound of formula (II) of less than 0.2:1.0, more preferably less than 0.05:1, even more preferably less than 0.01:1.0. Most preferably, ethers selected from the group consisting of glycol monoethers, glycol diethers and cyclic diethers are absent in the process of the present invention.

[0050] Thus, the above details and preferences for Z in formulae (I) and (III) and Y in formulae (IVa), (IVb) and (IVc) are applicable not only to the reaction in the process of the present invention but also to the optional subsequent work-up steps.

[0051] The hydrogenation catalyst used in the process of the present invention can be a standard catalyst for hydrogenation known from the prior art.

[0052] The hydrogenation catalyst preferably contains a metal selected from the group consisting of platinum, palladium and nickel, more preferably platinum.

[0053] The hydrogenation catalyst may be pre-impregnated on a solid support material such as, for example, carbon, aluminum, barium sulfate or calcium carbonate. Preferably, the hydrogenation catalyst is a carbon-impregnated catalyst.

[0054] The hydrogenation catalyst is more preferably platinum on carbon (Pt / C).

[0055] The hydrogenation catalyst may contain any amount of platinum, and preferably contains 1 to 10 wt % platinum, more preferably 1.5 to 5 wt % platinum, even more preferably 2 to 4 wt % platinum, even more preferably 2.5 to 3.5 wt % platinum, and most preferably 3 wt % platinum.

[0056] The use of a hydrogenation catalyst in the form of platinum impregnated on carbon also solves the further problem of providing a more environmentally friendly process compared to that disclosed in U.S. Pat. No. 4,140,718 A, which uses platinum impregnated on aluminum as the hydrogenation catalyst.

[0057] The hydrogenation catalyst may or may not contain water, and more preferably, the catalyst contains 30 to 70% by weight of water, even more preferably 50 to 70% by weight, and most preferably 60 to 65% by weight.

[0058] The hydrogenation catalyst may be dehydrated before use in the process of the present invention. Dehydration may be carried out by various known methods, such as azeotropic distillation. Dehydration is preferably carried out by azeotropic distillation. For this purpose, various solvents and solvent mixtures may be used.

[0059] The components used for the reaction in the process of the present invention may be used in various ratios relative to each other.

[0060] The ketone of formula (III) is preferably used in a molar ratio of 1.2:1.0 to 5.0:1.0, more preferably 1.5:1.0 to 3.0:1.0, and even more preferably 1.8:1.0 to 2.5:1.0 to the compound of formula (II).

[0061] The solvent of component (IV) is used in a molar ratio relative to the compound of formula (II) of preferably 1.5:1.0 to 10.0:1.0, more preferably 2.0:1.0 to 8.0:1.0, and even more preferably 3.0:1.0 to 5.0:1.0.

[0062] The hydrogenation catalyst is used in a weight ratio relative to the compound of formula (II) of preferably 1.0:100.0 to 6.0:100.0, more preferably 2.0:100.0 to 6.0:100.0, and even more preferably 2.0:1.0 to 4.0:100.0.

[0063] The components used for the reaction may be purified in advance or used without purification before the reaction. It is preferred that the components used for the reaction are used without prior purification. More preferably, the components used for the reaction are used with a purity of 90% or more, even more preferably 95% or more, even more preferably 98% or more, and most preferably 99% or more.

[0064] The components used for the reaction can be added to the reaction in any order.

[0065] It is preferred that the compounds of formulae (II), (III) and (IV) are charged first.

[0066] The components used in the process of the present invention are preferably placed in a protective gas atmosphere, such as an argon or nitrogen atmosphere, preferably a nitrogen atmosphere, prior to being reacted.

[0067] The reaction is preferably carried out at a temperature of 100 to 170°C, more preferably 90 to 150°C, even more preferably 95 to 140°C, and most preferably 125 to 135°C.

[0068] The reaction is preferably carried out at a hydrogen pressure of from 5 to 30 bar, more preferably from 10 to 20 bar, even more preferably from 13 to 17 bar.

[0069] The reaction is preferably carried out until no further absorption of hydrogen is observed. The absorption of hydrogen is preferably detected by monitoring the pressure change using a pressure gauge. The detection is more preferably carried out at intervals of less than 60 minutes, even more preferably less than 45 minutes, and most preferably less than 35 minutes.

[0070] The reaction time is preferably 50 to 400 minutes, more preferably 80 to 300 minutes, even more preferably 100 to 270 minutes, and most preferably 100 to 200 minutes.

[0071] Upon completion of the reaction, the reaction mixture may be stirred for a period of time preferably between 10 and 200 minutes, more preferably between 15 and 100 minutes, and even more preferably between 25 and 70 minutes.

[0072] In a preferred embodiment of the process of the present invention, the process is for preparing N,N'-dicycloalkyl-p-phenylenediamines of formula (I), wherein Y and Z in formulas (I), (III) and (IVa), (IVb) and (IVc) are the same and are linear alkyl chains, preferably C5-alkylene.

[0073] In the latter preferred embodiment, the solvent of formula (IV) is more preferably selected from solvents of formula (IVa) and (IVb).

[0074] This particularly preferred embodiment solves the further problem of providing a more efficient process compared to the process disclosed in US Pat. No. 4,140,718 A, which requires a hydrogenation time of 4 to 5.2 hours.

[0075] Preferably, the process of the present invention is a process for preparing N,N'-dialkyl-p-phenylenediamine of formula (I) having a purity of more than 95.0% by weight, more preferably 96.0% by weight or more, and most preferably more than 97.0% by weight, preferably as confirmed by gas chromatography according to ASTM-D 4937.

[0076] In the context of this application, the expression "preparation of N,N'-dialkyl-p-phenylenediamine of formula (I) with a purity of more than 95.0% by weight" is equivalent to "preparation of a composition comprising N,N'-dialkyl-p-phenylenediamine of formula (I) in a concentration of more than 95.0% by weight". The same applies to similar wording in this application and also in the "Use" section.

[0077] Preferably, the process of the present invention is a process for preparing N,N'-dialkyl-p-phenylenediamines of formula (I) containing less than 3.0% by weight, preferably less than 2.5% by weight, more preferably less than 1.5% by weight, and most preferably less than 1.0% by weight of the compounds N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine, preferably as determined by gas chromatography according to ASTM-D 4937.

[0078] Finishing process After reaction, the reaction mixture thus obtained can be worked up in a variety of ways known to those skilled in the art.

[0079] In a preferred embodiment of the process of the present invention, the reaction is followed by removal of the hydrogenation catalyst from the reaction mixture obtained after the reaction.

[0080] The removal can be carried out by various methods known to those skilled in the art, such as filtration, preferably filtration through a frit or a pressure suction funnel or removal by vacuum, preferably by filtration of the reaction mixture obtained after the reaction, more preferably by filtration of the hot reaction mixture.

[0081] After removing the hydrogenation catalyst from the reaction mixture, the solvent of the reaction mixture obtained after removing the hydrogenation catalyst can be removed by various methods known to those skilled in the art.

[0082] The removal is preferably carried out by distilling the reaction mixture obtained after removing the hydrogenation catalyst. The distillation temperature depends on the boiling point of the solvent used. The distillation is preferably carried out under reduced pressure.

[0083] The solvent mixture recovered after removal of the solvent can be used in another hydrogenation.

[0084] In a particularly preferred embodiment, following the reaction in the process of the present invention, the hydrogenation catalyst is removed from the reaction mixture obtained after the reaction, and the solvent is removed from the reaction mixture obtained after removing the hydrogenation catalyst. Preferably, the measurement of the purity of the N,N'-dialkyl-p-phenylenediamine of formula (I) and the measurement of the ratio of N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine, as confirmed by gas chromatography in accordance with ASTM-D 4937, are carried out after the hydrogenation catalyst and solvent have been removed.

[0085] After removal of the solvent from the reaction mixture, the distillation residue so obtained can be worked up in various ways known to those skilled in the art.

[0086] The distillation residue thus obtained is preferably cooled to crystallize out the N,N'-dialkyl-p-phenylenediamine of formula (I).

[0087] More preferably, the hot distillation residue so obtained is poured onto a crystallization sheet.

[0088] Optionally, the N,N'-dialkyl-p-phenylenediamine of formula (I) thus obtained can then be dried.

[0089] Drying can be carried out in a variety of ways known to those skilled in the art. Drying is preferably carried out under reduced pressure, more preferably at a pressure of less than 10 kPa, even more preferably at a pressure of less than 5 kPa.

[0090] use The present invention further provides the use of N,N'-dicyclohexyl-p-phenylenediamine having a purity of more than 95.0% by weight, preferably 96.0% by weight or more, most preferably more than 97.0% by weight, as an ageing stabilizer in rubber mixtures, vulcanizates and moldings obtainable therefrom, in particular tires, the purity preferably being confirmed by gas chromatography in accordance with ASTM-D 4937.

[0091] Even more preferably, N,N'-dicyclohexyl-p-phenylenediamine contains less than 3.0% by weight, preferably less than 2.5% by weight, more preferably less than 1.5% by weight, and most preferably less than 1.0% by weight of the compounds N-cyclohexyl-p-phenylenediamine and N,N,N'-tricyclohexyl-p-phenylenediamine.

[0092] More preferably, the N,N'-dicyclohexyl-p-phenylenediamine contains less than 0.5% by weight, even more preferably less than 0.3% by weight of the compound N-cyclohexyl-p-phenylenediamine.

[0093] N,N'-dicyclohexyl-p-phenylenediamine more preferably contains less than 3% by weight, even more preferably less than 1.5% by weight, and most preferably less than 1.0% by weight of the compound N,N,N'-tricyclohexyl-p-phenylenediamine.

[0094] The preferred ranges stated here apply equally to the use in rubber mixtures, vulcanizates and moldings, especially tires.

[0095] The descriptions and preferred ranges cited in connection with the present invention are equally applicable whether they are disclosed in the plural or in the singular.

[0096] The present invention will now be illustrated by the following examples, but is not limited thereto. [Example]

[0097] Process for preparing N,N'-dicyclohexyl-p-phenylenediamine

[0098] [Table 1]

[0099] [Table 2]

[0100] Preparation of N,N'-dicyclohexyl-p-phenylenediamine using the raw material amounts and reaction parameters listed in Table 2 for Examples 1-3 For each of Examples 1 to 3, the following procedure was carried out.

[0101] reaction First, p-nitroaniline of Example 1, 2 or 3, cyclohexanone, catalyst and each solvent were charged into a 3 L alloy autoclave (large paddle stirrer, 600 rpm) at room temperature.

[0102] The autoclave was closed and purged with nitrogen. A hydrogen pressure of 5 bar was applied at room temperature, and the autoclave was then heated to the respective temperatures of Examples 1, 2, and 3. Once the temperature was reached, the pressure was increased to 15 bar H2 pressure, and hydrogenation was carried out until zero absorption (H2 absorption of less than 1 bar within 30 minutes). Stirring was then continued at the same temperature and pressure for another 30 or 60 minutes. The autoclave was allowed to cool to 75°C, depressurized, and the reaction solution was removed.

[0103] Finishing process After the reaction, the reaction solution obtained was filtered while hot using a pressure suction funnel to remove the catalyst.

[0104] The catalyst so recovered can be used in another hydrogenation.

[0105] The reaction solution was stripped of low boiling compounds at 120°C / 50 mbar. The distillate was in two phases. The organic phase consisted mainly of solvent (>99%) and could be used in another hydrogenation.

[0106] The distillation residue thus obtained was a melt which was poured hot onto a crystallization sheet, and after cooling, the crystallized solid was crushed, pulverized and decanted.

[0107] [Table 3]

[0108] result As can be seen from Table 3, N,N'-dicyclohexyl-p-phenylenediamine was prepared with high purity, up to 97.73 wt %, in Examples 1, 2, and 3. The undesired by-products N-cyclohexyl-p-phenylenediamine and N,N,N'-tricyclohexyl-p-phenylenediamine were obtained in very small amounts, totaling less than 3 wt % in each example, even 1.5 wt % in Examples 1 and 2, and even less than 1 wt % in Example 2. The monoalkylation by-product N-cyclohexyl-p-phenylenediamine was less than 0.3 wt % in all of Examples 1, 2, and 3, and the trialkylation by-product was even less than 1 wt % in Example 2.

Claims

1. Formula (I) 【Chemistry 1】 A process for preparing N,N'-dialkyl-p-phenylenediamines of formula (II): 【Chemistry 2】 (wherein R1 and R2 are the same or different, and —NH ２ and -NO ２ selected from the group consisting of and compounds of formula (III) 【Transformation 3】 is converted in the presence of a hydrogenation catalyst and hydrogen, Z in the formulas (I) and (III) is the same, and a) an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Z, preferably C ４ ~C ６ - alkylene, more preferably C ５ an alkylene chain which is alkylene, preferably a linear alkylene chain, or b) two alkyl groups, preferably linear alkyl groups, each bonded to a carbon atom adjacent to Z and forming an alkyl chain, preferably a linear alkyl chain, with said carbon atom, and together having the empirical formula C ｎ H ２ｎ＋２ wherein preferably n=4 to 6, more preferably n=5, represents two alkyl groups, preferably linear alkyl groups, forming The reaction is represented by formula (IVa): 【Chemistry 4】 , formula (IVb) 【Transformation 5】 or formula (IVc) 【Transformation 6】 or a mixture thereof, Y in the formulae (IVa), (IVb) and (IVc) are the same or different, preferably the same, and a) an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Y, and preferably C ４ ~C ６ - alkylene, more preferably C ５ an alkylene chain which is alkylene, preferably a linear alkylene chain, or b) two alkyl groups, preferably linear alkyl groups, each bonded to a carbon atom adjacent to Y and forming an alkyl chain, preferably a linear alkyl chain, with said carbon atom, or one alkyl group and one hydrogen atom, which together have the empirical formula C ｎ H ２ｎ＋２ wherein preferably n=4 to 6, more preferably n=5, and represents two alkyl groups, preferably linear alkyl groups, or one alkyl group and one hydrogen atom forming

2. Z in the formulas (I) and (III) is an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Z, and the alkylene chain of Z is preferably C ４ ~C ６ - alkylene, more preferably C ５ 2. The process of claim 1, wherein the alkylene is -alkylene.

3. In the formula (IVa), (IVb) or (IVc), Y is the same and is an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring together with the carbon atom adjacent to Y. The alkylene chain of Y is preferably C ４ ~C ６ - alkylene, more preferably C ５ 3. The process according to claim 1 or 2, characterized in that:

4. 4. The process according to any one of claims 1 to 3, characterized in that the hydrogenation catalyst contains 1 to 10 wt.% platinum, preferably 1.5 to 5 wt.% platinum, more preferably 2 to 4 wt.% platinum, even more preferably 2.5 to 3.5 wt.% platinum, most preferably 3 wt.% platinum.

5. 5. The process according to any one of claims 1 to 4, characterized in that the solvent of formula (IV) is selected from the solvents of formula (IVb) and (IVc) or mixtures thereof, more preferably selected from cyclohexane and methylcyclohexane.

6. 6. The process according to any one of claims 1 to 5, characterized in that the reaction is carried out at a hydrogen pressure of from 5 to 30 bar, preferably from 10 to 20 bar, more preferably from 13 to 17 bar.

7. 7. The process according to any one of claims 1 to 6, characterized in that the reaction is carried out at a temperature of from 100 to 170°C, preferably from 90 to 150°C, more preferably from 95 to 140°C, even more preferably from 125 to 135°C.

8. 8. The process according to any one of claims 1 to 7, characterized in that the reaction time is between 50 and 400 minutes, preferably between 80 and 300 minutes, more preferably between 100 and 270 minutes, even more preferably between 100 and 200 minutes.

9. 9. The process according to any one of claims 1 to 8, characterized in that it is a process for preparing said N,N'-dialkyl-p-phenylenediamine of formula (I) in a purity of more than 95.0% by weight, preferably 96.0% by weight or more, more preferably more than 97.0% by weight, preferably as determined by gas chromatography according to ASTM-D 4937.

10. 10. Process according to any one of claims 1 to 9, characterized in that it is a process for preparing N,N'-dialkyl-p-phenylenediamines of formula (I) comprising less than 3.0% by weight, preferably less than 2.5% by weight, more preferably less than 1.5% by weight, most preferably less than 1.0% by weight of the compounds N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine, preferably as determined by gas chromatography according to ASTM-D 4937.

11. 11. The process according to any one of claims 1 to 10, characterized in that the at least one ketone of formula (III) is used in a molar ratio relative to the compound of formula (II) of 1.2:1.0 to 5.0:1.0, preferably 1.5:1.0 to 3.0:1.0, more preferably 1.8:1.0 to 2.5:1.

0.

12. The process for preparing N,N'-dicycloalkyl-p-phenylenediamine of formula (I), wherein Y and Z in formulas (I), (III) and (IVa), (IVb) and (IVc) are the same and preferably C ５ 12. The process according to claim 1, wherein the alkyl group is a linear alkyl chain that is -alkylene.

13. 1. Use of N,N'-dicyclohexyl-p-phenylenediamine having a purity of more than 95.0% by weight, preferably 96.0% by weight or more, most preferably more than 97.0% by weight, as an ageing stabilizer in rubber mixtures, vulcanizates and moldings obtainable therefrom, in particular tires, wherein said purity has preferably been confirmed by gas chromatography in accordance with ASTM-D 4937.

14. 14. Use according to claim 13, characterized in that the N,N'-dicyclohexyl-p-phenylenediamine contains less than 3.0% by weight, preferably less than 2.5% by weight, more preferably less than 1.5% by weight, most preferably less than 1.0% by weight of the compounds N-cyclohexyl-p-phenylenediamine and N,N,N'-tricyclohexyl-p-phenylenediamine, the purity preferably being confirmed by gas chromatography according to ASTM-D 4937.

15. 15. The process according to claim 9 or 10 or the use according to claim 13 or 14, characterized in that the purity of the N,N'-dialkyl-p-phenylenediamine of formula (I), after removal of the hydrogenation catalyst and the solvent, preferably checked by gas chromatography according to ASTM-D 4937, is determined according to claim 9 or 13, and the ratio of N-alkyl-p-phenylenediamine to N,N,N'-trialkyl-p-phenylenediamine is determined according to claim 10 or 14.

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