Process for preparation of N, N-dialkyl-p-phenylenediamine

Abstract

The invention relates to a novel method for producing N, N '-dialkyl-p-phenylenediamine of formula (I) and to the use of N, N'-dicyclohexyl-p-phenylenediamine with a purity of greater than 95.0% by weight as an aging stabilizer in rubber mixtures, cured rubber products and molded bodies, in particular tyres, which can be obtained therefrom. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a novel process for the preparation of N,N'-dialkyl-p-phenylenediamines of the formula (I), and to the use of N,N'-dicyclohexyl-p-phenylenediamine having a purity of greater than 95.0% by weight as an anti-aging stabilizer in rubber mixtures, cured products and molded articles, in particular tires, obtainable therefrom. Background Art

[0002] N,N'-Dicyclohexyl-p-phenylenediamine is excellently suitable for protecting cured products based on natural rubber or synthetic rubber against the aging process caused by the action of oxygen and ozone. It migrates to the surface of the cured product, where it protects the rubber against the above-mentioned effects.

[0003] CN 1370768A describes a process for the preparation of N,N'-di-sec-alkyl-p-phenylenediamines. p-Nitroaniline or p-phenylenediamine is reacted with an aliphatic C3-C 12 ketone in the presence of CuO, Cr2O3 and BaO.

[0004] CN 1947837A describes a process for the preparation of N,N'-dialkyl-p-phenylenediamines. The selected catalyst 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] The disadvantages of the above two processes are the use of several catalysts, some of which are expensive and have environmental problems.

[0006] CN 105061214A describes a process for the preparation of N,N'-di-sec-butyl-p-phenylenediamine, which starts with the reductive alkylation of p-nitroaniline and a ketone in the presence of a platinum catalyst and activated carbon. In this process, after adding p-nitroaniline and the ketone (here methyl ethyl ketone), activated carbon is added to filter out possible impurities. The catalyst is added only after the activated carbon has been removed by filtration. A conversion rate of 98.7% is described, but the final purity of the product is not stated. In the said process, activated carbon is also required to clean the starting materials. However, the use of activated carbon has some disadvantages: the activated carbon must be removed from the reaction mixture in an additional reaction step, which requires additional complexity and additional reaction time. In addition, there is a risk that activated carbon will leave impurities in the reaction mixture and clog pipes and filters. The handling of activated carbon powder is also problematic because, due to increased safety measures, the dust formed causes an increased level of complexity.

[0007] US 4140718A describes a process for the preparation of N,N'-dialkyl-p-phenylenediamines and also N,N'-dicyclohexyl-p-phenylenediamine, which starts from the reaction of p-nitroaniline and a ketone in the presence of hydrogen and a hydrogenation catalyst. This shows that p-nitroaniline has poor solubility in organic solvents, and when using a ketone with a low molecular weight (which also includes cyclohexanone) as an excess alkylating agent, both amine hydrogen atoms of the aromatic amine are replaced. Various ethers are used as solvents. The purity of the product is expressed as 93% - 97%. However, the mono- and tri-alkylated by-products obtained total 3% - 7%, and in individual cases at least 1% each. These by-products are highly undesirable because they disrupt the migration of N,N'-dialkyl-p-phenylenediamine, preferably N,N'-dicyclohexyl-p-phenylenediamine, to the surface of the cured product, and thus limit the efficacy in the case of N,N'-dicyclohexyl-p-phenylenediamine. For example, the mono-alkylated by-product forms hydrogen bonds with other molecules due to its free amine group, and the steric requirements of the tri-alkylated by-product are very high and bulky - both factors hinder the above-mentioned migration. In addition, the catalyst used in this process is platinum applied to aluminum. Its disadvantage is that the production of aluminum is usually expensive and environmentally harmful. The hydrogenation time of 4 - 5.2 hours is also relatively long.

[0008] Accordingly, there is a need for a process for the preparation of N,N'-dialkyl-p-phenylenediamines, preferably N,N'-dicycloalkyl-p-phenylenediamines, more preferably N,N'-dicyclohexyl-p-phenylenediamine, which overcomes the above-mentioned disadvantages of the prior art. Summary of the Invention

[0009] The object of the present invention is to provide a process for the preparation of N,N'-dialkyl-p-phenylenediamines, preferably N,N'-dicycloalkyl-p-phenylenediamines, more preferably N,N'-dicyclohexyl-p-phenylenediamine, which overcomes the disadvantages of the prior art and enables the preparation of N,N'-dialkyl-p-phenylenediamines, preferably N,N'-dicycloalkyl-p-phenylenediamines, more preferably N,N'-dicyclohexyl-p-phenylenediamine, with high purity and with only a small amount of mono- and tri-alkylated by-products (in the context of the present invention, preferably N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine).

[0010] The purity of the resulting product is preferably determined by gas chromatography according to ASTM-D 4937 in the context of the present invention. This corresponds to the purity in % by weight.

[0011] In the case of determining the purity by gas chromatography, high purity exists in the context of the present invention when the product prepared by the process of the present invention has a purity greater than 95.0% by weight, preferably not less than 96.0% by weight, and most preferably greater than 97.0% by weight.

[0012] In the context of the present invention, a small amount of mono- and trialkylated by-products (in the context of the present invention, preferably N-alkyl-p-phenylenediamines and N,N,N′-trialkyl-p-phenylenediamines) means that the sum of these two by-products is 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. When the N-alkyl-p-phenylenediamine is present in the product in an amount of less than 1.0% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, a small amount of N-alkyl-p-phenylenediamine is present. When the N,N,N′-trialkyl-p-phenylenediamine is present in the product in an amount of less than 3% by weight, preferably less than 1.5% by weight, more preferably less than 1.0% by weight, a small amount of N,N,N′-trialkyl-p-phenylenediamine is present.

[0013] 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 a mixture thereof, in the presence of a hydrogenation catalyst and hydrogen leads to a corresponding N,N′-dialkyl-p-phenylenediamine of formula (I) in high purity, while obtaining only small amounts of mono- and trialkylated by-products.

[0014] Method

[0015] Accordingly, the present invention provides a process for preparing an N,N′-dialkyl-p-phenylenediamine of formula (I)

[0016]

[0017] wherein a compound of formula (II)

[0018]

[0019] wherein R1 and R2 are each the same or different and are selected from the group consisting of -NH2 and -NO2,

[0020] and at least one ketone of formula (III)

[0021]

[0022] are converted in the presence of a hydrogenation catalyst and hydrogen,

[0023] wherein Z in formulas (I) and (III) is the same, and

[0024] a) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the alkylene chain of Z is preferably C4-C6-alkylene, more preferably C5-alkylene,

[0025] or

[0026] b) represents two alkyl groups, preferably straight-chain alkyl groups, each bonded to a carbon atom adjacent to Z and together with that carbon atom forming an alkyl chain, preferably a straight-chain alkyl chain, and wherein the two alkyl groups of Z together form the empirical formula C n H 2n+2 , preferably wherein n = 4 - 6, more preferably wherein n = 5,

[0027] characterized in that the reaction is carried out in the presence of a solvent having formula (IVa)

[0028]

[0029] having formula (IVb)

[0030]

[0031] or having formula (IVc),

[0032]

[0033] or a mixture thereof,

[0034] wherein Y in formulas (IVa), (IVb) and (IVc) is the same or different, preferably the same, and

[0035] a) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Y, and wherein the alkylene chain of Y is preferably a C4 - C6 - alkylene, more preferably a C5 - alkylene,

[0036] or

[0037] b) represents two alkyl groups, preferably straight-chain alkyl groups, or one alkyl group and one hydrogen atom, each bonded to a carbon atom adjacent to Y and together with that carbon atom forming an alkyl chain, preferably a straight-chain alkyl chain, and wherein the two alkyl groups or the one alkyl group and the hydrogen atom together form the empirical formula C n H 2n+2 , preferably wherein n = 4 - 6, more preferably wherein n = 5.

[0038] The term "alkylene" in the above definitions of Y and Z preferably represents C n H 2n .

[0039] 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. Y and Z in formulas (I), (III), (IVa), (IVb) and (IVc) are preferably the same.

[0040] In a preferred embodiment of the method of the present invention, Z and Y in formulas (I), (III) and (IVa) are the same.

[0041] In a further preferred embodiment of the method of the present invention, Z and Y in formulas (I), (III) and (IVb) are the same.

[0042] In a further preferred embodiment of the method of the present invention, Z and Y in formulas (I), (III) and (IVc) are the same.

[0043] In a further embodiment of the present invention, Z in formulas (I) and (III) is the same and different from Y in formulas (IVb) and (IVc).

[0044] The method of the present invention is a method for preparing N,N'-dialkyl-p-phenylenediamine having formula (I).

[0045] Z in formula (I) may represent two alkyl groups, preferably straight-chain alkyl groups, each bonded to the carbon atom adjacent to Z and together with this carbon atom forming an alkyl chain, preferably a straight-chain alkyl chain, and wherein the two alkyl groups of Z together form the empirical formula C n H 2n+2 , preferably where n = 4 - 6, more preferably where n = 5.

[0046] Thus, the method of the present invention may be a method 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.

[0047] In a preferred embodiment of the method of the present invention, Z in formula (I) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the alkylene chain of Z is preferably C4-C6-alkylene, more preferably C5-alkylene.

[0048] Preferably, the method of the present invention is thus a method for preparing N,N'-cycloalkyl-p-phenylenediamine.

[0049] More preferably, Z in formula (I) is a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the straight-chain alkylene chain is preferably C4-C6-alkylene, most preferably C5-alkylene.

[0050] More preferably, the method of the present invention is thus a method 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.

[0051] In the method of the present invention, a compound of formula (II) is used, where R1 and R2 are each the same or different and are selected from the group consisting of -NH2 and -NO2.

[0052] Preferably, R1 and R2 are the same and are -NH2, or are different and are -NH2 and -NO2, and more preferably are different and are -NH2 and -NO2. More preferably, the compound of formula (II) is thus p-nitroaniline.

[0053] Any desired ketone of formula (III) can be used.

[0054] Y in at least one ketone of formula (III) can represent two alkyl groups, preferably straight-chain alkyl groups, each bonded to the carbon atom adjacent to Z and together with that carbon atom forming an alkyl chain, preferably a straight-chain alkyl chain, and where the two alkyl groups of Z together form the empirical formula C n H 2n+2 , preferably where n = 4 - 6, more preferably where n = 5.

[0055] Thus, at least one ketone of formula (III) used can be a ketone selected from the group consisting of pentanone, hexanone, and heptanone, preferably selected from pentan-2-one, pentan-3-one, hexan-2-one, hexan-3-one, heptan-2-one, heptan-3-one, and heptan-4-one.

[0056] According to the above preference for Y in formula (III), at least one ketone of formula (III) used in step a) is preferably a cyclic ketone, more preferably selected from cyclopentanone, cyclohexanone, and cycloheptanone.

[0057] Most preferably, the ketone of formula (III) is thus cyclohexanone.

[0058] It is preferred to use a ketone of formula (III) in the method of the present invention.

[0059] Any desired solvent of formula (IVa), (IVb), or (IVc) or a mixture thereof can be used.

[0060] Y in the solvent of formula (IVa), (IVb), or (IVc) can represent two alkyl groups, preferably straight-chain alkyl groups, or one alkyl group and one hydrogen atom, each bonded to the carbon atom adjacent to Y and together with that carbon atom forming an alkyl chain, preferably a straight-chain alkyl chain, and where the two alkyl groups or the one alkyl group and the hydrogen atom together form the empirical formula C n H 2n+2 , preferably where n = 4 - 6, more preferably where n = 5.

[0061] Accordingly, the solvent or mixture thereof having formula (IVa), (IVb) or (IVc) used may be a solvent preferably selected from the group consisting of pentanol, hexanol and heptanol, or a mixture thereof, more preferably hexanol.

[0062] Preferably, Y in formula (IVa), (IVb) or (IVc) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Y, and wherein the alkylene chain of Y is preferably a C4-C6-alkylene, more preferably a C5-alkylene.

[0063] According to the above preference for Y in formula (IVa), the solvent having formula (IVa) used is preferably selected from the group consisting of cyclopentanol, cyclohexanol and cycloheptanol, or a mixture thereof.

[0064] Most preferably, the solvent having formula (IVa) is cyclohexanol.

[0065] According to the above preference for Y in formula (IVb), the solvent having formula (IVb) used is preferably selected from the group consisting of cyclopentane, cyclohexane and cycloheptane, or a mixture thereof.

[0066] Most preferably, the solvent having formula (IVb) is cyclohexane.

[0067] According to the above preference for Y in formula (IVc), the solvent having formula (IVc) used is preferably selected from the group consisting of methylcyclopentane, methylcyclohexane and methylcycloheptane, or a mixture thereof.

[0068] Most preferably, the solvent having formula (IVc) is methylcyclohexane.

[0069] The solvent having formula (IV) is preferably a solvent having formula (IVb) or (IVc), or a mixture thereof, more preferably selected from cyclohexane and methylcyclohexane.

[0070] Most preferably, the solvent having formula (IV) is methylcyclohexane.

[0071] The ether preferably selected from the group consisting of monoethers of diols, diethers of diols and cyclic diethers preferably exists in the process of the present invention in a molar ratio of less than 0.2:1.0, more preferably less than 0.05:1, even more preferably less than 0.01:1.0 with the compound having formula (II). Most preferably, the ether preferably selected from the group consisting of monoethers of diols, diethers of diols and cyclic diethers does not exist in the process of the present invention.

[0072] Therefore, the above details and preferences for Z in formulas (I) and (III) and Y in formulas (IVa), (IVb) and (IVc) apply not only to the reaction in the process of the present invention, but also to the optional subsequent work-up.

[0073] The hydrogenation catalyst used in the method of the present invention can be a standard catalyst for hydrogenation known from the prior art.

[0074] The hydrogenation catalyst preferably contains a metal selected from the group consisting of platinum, palladium, and nickel, more preferably platinum.

[0075] The hydrogenation catalyst can be applied to a solid support material, such as carbon, aluminum, barium sulfate, or calcium carbonate. The hydrogenation catalyst is preferably a carbon-supported catalyst.

[0076] The hydrogenation catalyst is more preferably carbon-supported platinum (Pt / C).

[0077] The hydrogenation catalyst can contain any amount of platinum. The hydrogenation catalyst preferably contains 1% - 10% by weight of platinum, more preferably 1.5% - 5% by weight of platinum, even more preferably 2% - 4% by weight of platinum, even more preferably 2.5% - 3.5% by weight of platinum, and most preferably 3% by weight of platinum.

[0078] Compared with the method disclosed in US 4140718A, which uses aluminum-supported platinum as the hydrogenation catalyst, using a hydrogenation catalyst in the form of carbon-supported platinum solves the additional problem of providing a more environmentally friendly method.

[0079] The hydrogenation catalyst can contain or can not contain water. The catalyst preferably contains water, more preferably 30% - 70% by weight, even more preferably 50% - 70% by weight, and most preferably 60% - 65% by weight.

[0080] The hydrogenation catalyst can be dehydrated before being used in the method of the present invention. The dehydration can be carried out in various known ways, such as by azeotropic distillation. The dehydration is preferably carried out by azeotropic distillation. For this purpose, various solvents and solvent mixtures can be used.

[0081] The components for the reaction in the method of the present invention can be used in different ratios to each other.

[0082] Preferably, the ketone having the formula (III) is 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 with the compound having the formula (II).

[0083] Preferably, the solvent of component (IV) is used in a molar ratio of 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 with the compound having the formula (II).

[0084] Preferably, the hydrogenation catalyst is used in a weight ratio of 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 with the compound of formula (II).

[0085] The components used in the reaction can be used without prior purification or purified before the reaction. Preferably, the components used in the reaction are used without prior purification. More preferably, the components used in the reaction are used with a purity of ≥90%, even more preferably ≥95%, even more preferably ≥98%, and most preferably ≥99%.

[0086] The components used in the reaction can be added to the reaction in any order.

[0087] Preferably, an initial charge of the compounds of formula (II), (III), and (IV) is present.

[0088] The components used in the process of the present invention are preferably subjected to a protective gas atmosphere, such as an argon or nitrogen atmosphere, preferably a nitrogen atmosphere, before the reaction.

[0089] The reaction is preferably carried out at a temperature of 100 °C - 170 °C, more preferably 90 °C - 150 °C, even more preferably 95 °C - 140 °C, and most preferably 125 °C - 135 °C.

[0090] The reaction is preferably carried out under a hydrogen pressure of 5 - 30 bar, more preferably 10 - 20 bar, and even more preferably 13 - 17 bar.

[0091] The reaction is preferably carried out until no further absorption of hydrogen can be detected. The absorption of hydrogen is preferably detected by monitoring the pressure change using a manometer. The detection is more preferably carried out at intervals of less than 60 min, even more preferably less than 45 min, and most preferably less than 35 min.

[0092] The reaction time is preferably 50 min to 400 min, more preferably 80 min to 300 min, even more preferably 100 to 270 min, and most preferably 100 to 200 min.

[0093] After the reaction is completed, the reaction mixture can be continuously stirred. This continuous stirring is preferably carried out for 10 min to 200 min, more preferably 15 min to 100 min, and even more preferably 25 min to 70 min.

[0094] In a preferred embodiment of the process of the present invention, the process is a process for preparing N,N'-dicycloalkyl-p-phenylenediamine of formula (I), wherein Y and Z in formula (I), (III), and (IVa), (IVb), and (IVc) are the same and are straight-chain alkyl chains, which are preferably C5-alkylene.

[0095] More preferably, the solvent of formula (IV) in the latter preferred embodiment is selected from solvents of formulas (IVa) and (IVb).

[0096] Compared with the method disclosed in US 4140718A which requires a hydrogenation time of 4 - 5.2 hours, this particularly preferred embodiment solves the additional problem of providing a more efficient method.

[0097] The method of the present invention is preferably a method for preparing N,N'-dialkyl-p-phenylenediamine of formula (I), the purity of which is preferably greater than 95.0% by weight, more preferably not less than 96.0% by weight, and most preferably greater than 97.0% by weight as determined by gas chromatography according to ASTM-D 4937.

[0098] In the context of the present application, the expression "preparing N,N'-dialkyl-p-phenylenediamine of formula (I) with a purity greater than 95.0% by weight" is equivalent to "preparing a composition containing N,N'-dialkyl-p-phenylenediamine of formula (I) to an extent greater than 95.0% by weight". This equally applies to similar text paragraphs in the present application and also to the "use" section.

[0099] The method of the present invention is preferably a method for preparing N,N'-dialkyl-p-phenylenediamine of formula (I), which comprises a total of compounds of N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine in an amount preferably 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 as determined by gas chromatography according to ASTM-D 4937.

[0100] Post-treatment

[0101] After the reaction, the resulting reaction mixture can be post-treated in various ways known to those skilled in the art.

[0102] In a preferred embodiment of the method of the present invention, the reaction is followed by removal of the hydrogenation catalyst from the reaction mixture obtained after the reaction.

[0103] The removal can be carried out in various ways known to those skilled in the art, such as filtration, preferably via a fritted glass or pressure suction filter, or by suction. The removal is preferably carried out by filtering the reaction mixture obtained after the reaction, more preferably by filtering the hot reaction mixture.

[0104] After removing the hydrogenation catalyst from the reaction mixture, the solvent of the reaction mixture obtained after removing the hydrogenation catalyst can be removed in various ways known to those skilled in the art.

[0105] It is carried out by removing, preferably by distillation, 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.

[0106] The solvent mixture recovered after removing the solvent can be used for another hydrogenation.

[0107] In a particularly preferred embodiment, after 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. The determination of the purity of N,N′-dialkyl-p-phenylenediamine having the formula (I) (preferably determined by gas chromatography according to ASTM-D 4937) and the determination of the ratio of N-alkyl-p-phenylenediamine and N,N,N′-trialkyl-p-phenylenediamine are preferably carried out after removing the hydrogenation catalyst and the solvent.

[0108] After removing the solvent from the reaction mixture, the resulting distillation residue can be post-treated in various ways known to those skilled in the art.

[0109] The resulting distillation residue is preferably cooled, wherein N,N′-dialkyl-p-phenylenediamine having the formula (I) crystallizes.

[0110] More preferably, the resulting hot distillation residue is poured onto a crystallization plate.

[0111] Optionally, the resulting N,N′-dialkyl-p-phenylenediamine having the formula (I) can be dried thereafter.

[0112] The drying can be carried out in various ways known to those skilled in the art. The drying is preferably carried out under reduced pressure, more preferably under a pressure of less than 10 kPa, and even more preferably under a pressure of less than 5 kPa.

[0113] Use

[0114] The present invention further provides the use of N,N′-dicyclohexyl-p-phenylenediamine having a purity of greater than 95.0% by weight, preferably not less than 96.0% by weight, and most preferably greater than 97.0% by weight as an aging stabilizer in rubber mixtures, cured products, and molded articles (especially tires) obtainable therefrom, wherein the purity is preferably determined by gas chromatography according to ASTM-D 4937.

[0115] Further preferably, the N,N′-dicyclohexyl-p-phenylenediamine contains compounds N-cyclohexyl-p-phenylenediamine and N,N,N′-tricyclohexyl-p-phenylenediamine in a total amount 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.

[0116] More preferably, the N,N′-dicyclohexyl-p-phenylenediamine contains the compound N-cyclohexyl-p-phenylenediamine in an amount of less than 0.5% by weight, and even more preferably less than 0.3% by weight.

[0117] More preferably, the N,N′-dicyclohexyl-p-phenylenediamine contains the compound N,N,N′-tricyclohexyl-p-phenylenediamine in an amount of less than 3% by weight, even more preferably less than 1.5% by weight, and most preferably less than 1.0% by weight.

[0118] The preferred ranges cited apply analogously to the use in rubber mixtures, cured products, and molded articles, in particular tires.

[0119] The descriptions and preferred ranges cited in the context of the present invention are equally applicable, regardless of whether they are disclosed in the plural or the singular.

[0120] The present invention will be illustrated by the following examples, but is not limited thereto. Detailed Description

[0121] Example

[0122] Method for preparing N,N′-dicyclohexyl-p-phenylenediamine

[0123] Table 1: List of raw materials, abbreviations, and manufacturers

[0124]

[0125] Table 2: Initial amounts of raw materials and reaction parameters

[0126]

[0127]

[0128] Prepare N,N′-dicyclohexyl-p-using the amounts of raw materials and reaction parameters specified for Examples 1-3 in Table 2 p-Phenylenediamine

[0129] The following procedure was carried out for each of Examples 1-3.

[0130] Reaction

[0131] At room temperature, a 3 L alloy autoclave (large paddle stirrer, 600 rpm) was initially charged with p-nitroaniline, cyclohexanone, a catalyst, and the corresponding solvent for the respective Example 1, 2, or 3.

[0132] Close the autoclave and purge with nitrogen. At room temperature, establish a hydrogen pressure of 5 bar and then heat the autoclave to the respective temperatures of Examples 1, 2, and 3. After reaching the temperature, increase the pressure to 15 bar H2 and carry out the hydrogenation until the uptake is zero (<1 bar H2 uptake within 30 min). Thereafter, continue stirring for an additional 30 or 60 min at the same temperature and pressure. Cool the autoclave to 75 °C and relieve the pressure, and remove the reaction solution.

[0133] Post-treatment

[0134] The reaction solution obtained after the reaction is hot-filtered through a pressure suction filter to remove the catalyst.

[0135] The recovered catalyst can be used for another hydrogenation.

[0136] Remove the low-boiling substances from the reaction solution at 120 °C / 50 mbar. The distillate is biphasic. The organic phase consists mainly of the solvent (>99%) and can be used for another hydrogenation.

[0137] The bottoms obtained are a melt, which is poured hot onto crystallization plates. After cooling, the crystallized solid is broken, pulverized, and transferred.

[0138] Table 3: Purity of the products prepared according to Examples 1, 2, and 3* 1 , in [% by weight]

[0139] Example 1 Example 2 Example 3 N-Cyclohexyl-p-phenylenediamine 0.23 0.07 0.15 N,N'-Dicyclohexyl-p-phenylenediamine 96.45 97.73 96.00 N,N,N'-Tricyclohexyl-p-phenylenediamine 1.04 0.80 2.60

[0140] * 1 : Measured by gas chromatography according to ASTM-D 4937 after removal of the hydrogenation catalyst and the solvent

[0141] Result

[0142] As is evident from Table 3, N,N′-dicyclohexyl-p-phenylenediamine in Examples 1, 2, and 3 is prepared in high purity up to 97.73% by weight. Only small amounts of the unwanted by-products N-cyclohexyl-p-phenylenediamine and N,N,N′-tricyclohexyl-p-phenylenediamine are obtained, amounting to less than 3% by weight in total in each example, even below 1.5% by weight in Examples 1 and 2, and even below 1% by weight in Example 2. The monoalkylated by-product N-cyclohexyl-p-phenylenediamine is even present in all of Examples 1, 2, and 3 at less than 0.3% by weight, and the trialkylated by-product in Example 2 is even below 1% by weight.

Claims

1. A method for preparing an N,N'-dialkyl-p-phenylenediamine of formula (I) wherein a compound of formula (II) wherein R1 and R2 are each the same or different and are selected from the group consisting of -NH2 and -NO2, and at least one ketone of formula (III) is converted in the presence of a hydrogenation catalyst and hydrogen, wherein Z in formulas (I) and (III) is the same, and a) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the alkylene chain of Z is preferably C4-C6-alkylene, more preferably C5-alkylene, or b) represents two alkyl groups, preferably straight-chain alkyl groups, each of which is bonded to the carbon atom adjacent to Z and together with this carbon atom forms an alkyl chain, preferably a straight-chain alkyl chain, and wherein the two alkyl groups of Z together form the empirical formula C n H 2n+2 , preferably wherein n = 4-6, more preferably wherein n = 5, characterized in that The reaction is carried out in the presence of a solvent having formula (IVa) having formula (IVb) or having formula (IVc), or a mixture thereof, wherein Y in formulae (IVa), (IVb) and (IVc) is the same or different, preferably the same, and a) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Y, and wherein the alkylene chain of Y is preferably C4-C6-alkylene, more preferably C5-alkylene, or b) represents two alkyl groups, preferably straight-chain alkyl groups, or one alkyl group and one hydrogen atom, each of which is bonded to the carbon atom adjacent to Y and together with this carbon atom forms an alkyl chain, preferably a straight-chain alkyl chain, and wherein the two alkyl groups or the one alkyl group and the hydrogen atom together form the empirical formula C n H 2n+2 , preferably where n = 4 - 6, more preferably where n = 5.

2. The method according to claim 1, characterized in that, Z in formulae (I) and (III) is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the alkylene chain of Z is preferably C4-C6-alkylene, more preferably C5-alkylene.

3. The method according to any one of claims 1 and 2, characterized in that, Y in formulae (IVa), (IVb) and (IVc) is the same and is an alkylene chain, preferably a straight-chain alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Y, and wherein the alkylene chain of Y is preferably C4-C6-alkylene, more preferably C5-alkylene.

4. The method according to any one of claims 1-3, characterized in that, The hydrogenation catalyst contains 1% - 10% by weight of platinum, preferably 1.5% - 5% by weight of platinum, more preferably 2% - 4% by weight of platinum, even more preferably 2.5% - 3.5% by weight of platinum, and most preferably 3% by weight of platinum.

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

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

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

8. The method according to any one of claims 1-7, characterized in that The reaction time is 50 min to 400 min, preferably 80 min to 300 min, more preferably 100 to 270 min, even more preferably 100 to 200 min.

9. The method according to any one of claims 1-8, characterized in that The method is for preparing an N,N′-dialkyl-p-phenylenediamine having formula (I), and the purity of the N,N′-dialkyl-p-phenylenediamine of formula (I) is preferably greater than 95.0% by weight, preferably not less than 96.0% by weight, more preferably greater than 97.0% by weight, determined by gas chromatography according to ASTM-D 4937.

10. The method according to any one of claims 1-9, characterized in that The method is for preparing an N,N′-dialkyl-p-phenylenediamine having formula (I), and the N,N′-dialkyl-p-phenylenediamine of formula (I) contains preferably 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 in total of the compounds N-alkyl-p-phenylenediamine and N,N,N′-trialkyl-p-phenylenediamine, determined by gas chromatography according to ASTM-D4937.

11. The method according to any one of claims 1-10, characterized in that The at least one ketone having formula (III) is used in a molar ratio 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 with the compound having formula (II).

12. The method according to any one of claims 1-11, characterized in that The method is for preparing N,N′-dicycloalkyl-p-phenylenediamine of formula (I), wherein Y and Z in formula (I), (III) and (IVa), (IVb) and (IVc) are the same and are straight-chain alkyl chains, and the straight-chain alkyl chain is preferably C5-alkylene.

13. Use of N,N'-dicyclohexyl-p-phenylenediamine having a purity of greater than 95.0% by weight, preferably not less than 96.0% by weight, most preferably greater than 97.0% by weight as an aging stabilizer in rubber mixtures, cured products and molded articles, in particular tires, obtainable therefrom, wherein the purity is preferably determined by gas chromatography according to ASTM-D 4937.

14. The use according to claim 13, characterized in that N,N′-dicyclohexyl-p-phenylenediamine contains compounds N-cyclohexyl-p-phenylenediamine and N,N,N′-tricyclohexyl-p-phenylenediamine in a total amount 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, and the purity is preferably determined by gas chromatography according to ASTM-D 4937.

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

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