Procedure for the preparation of N,N''-dialkyl-p-phenylenediamine

Abstract

The present invention relates to a new process for preparing N,N'-dialkyl-p-phenylenediamine of formula (I) and to the use of N,N'-dicyclohexyl-p-phenylenediamine with a purity greater than 95.0% by weight as an anti-aging agent in rubber blends, vulcanized rubber products and molded bodies, in particular tires, which can be obtained from them.

Description

[0001] The present invention relates to a new method for the production of N,N' -Dialkyl- p- phenylenediamine of formula (I). Another disclosure is the use of the N,N' -Dicyclohexyl- p- Phenylenediamines in a purity of greater than 95.0 wt.% as an anti-aging agent in rubber compounds, vulcanizates and molded parts obtained therefrom, especially tires.

[0002] N,N' Dicyclohexyl p-phenylenediamine is ideally suited to protect vulcanizates based on natural or synthetic rubbers against aging processes caused by the effects of oxygen and ozone. It migrates to the surface of the vulcanizate and protects the rubber there from the aforementioned effects.

[0003] CN1370768A describes a process for the preparation of N,N'-di-sec-alkyl-p-phenylenediamine. p-Nitroaniline or p-phenylenediamine are reacted with aliphatic C3-C12 ketones in the presence of CuO, Cr2O3 and BaO.

[0004] CN1947837 A describes a process for the production of N,N' -Dialkyl- p -phenylenediamine. A mixture of three components is chosen as the catalyst: M1 (Ni, Co or Fe), M2 (Re, Pd and / or Ru) and M3 (Li, Ma, K, Rb, Ca, Mg, Sr or Ba).

[0005] A disadvantage of both of the aforementioned methods is that several catalysts are used, some of which are expensive and environmentally hazardous.

[0006] CN105061214A describes a process for the synthesis of N,N'-di-sec-butyl-p-phenylenediamine, starting with the reductive alkylation of p-nitroaniline and a ketone in the presence of a platinum catalyst and activated carbon. In this process, activated carbon is added after the addition of p-nitroaniline and the ketone (here, butanone) to filter out any impurities. The catalyst is added only after the activated carbon has been removed by filtration. A conversion rate of 98.7% is reported, but the final purity of the product is not specified. Furthermore, the described process requires the use of activated carbon to purify the starting materials. However, the use of activated carbon has several disadvantages: the activated carbon must be removed from the reaction mixture in a subsequent reaction step, which requires additional effort and reaction time.Furthermore, activated carbon poses the risk of leaving impurities in the reaction mixture and clogging pipes and filters, for example. Handling activated carbon powder is also problematic, as the resulting dust necessitates increased safety precautions.

[0007] US4140718A describes a process for manufacturing N,N' -Dialkyl- p -phenylenediamines as well as N,N'The reaction of dicyclohexyl p-phenylenediamine is described, starting with the reaction of p-nitroaniline and a ketone in the presence of hydrogen and a hydrogenation catalyst. It is described that p-nitroaniline is poorly soluble in organic solvents and that when low molecular weight ketones, including cyclohexanone, are used as alkylating agents, both amine hydrogen atoms of the aromatic amine are replaced when used in excess. Various ethers are used as solvents. The purities of the products are reported to be 93–97%. However, the mono- and trialkylated byproducts are obtained in total at a concentration of 3–7%, and individually at a concentration of at least 1%. These byproducts are highly undesirable because they inhibit the migration of the N,N' -Dialkyl- p -phenylenediamine, preferably of the N,N' -Dicyclohexyl- p -phenylenediamines, interfere with the surface of the vulcanizate and thus, in the case of N,N'Dicyclohexyl-p-phenylenediamine limits its effectiveness. The monoalkylated byproduct forms hydrogen bonds with other molecules due to its free amine group, and the trialkylated byproduct is sterically very demanding and bulky—both factors that hinder the migration described above. Furthermore, this process uses platinum grown on aluminum as a catalyst. A disadvantage of this is that aluminum production is often expensive and environmentally damaging. The hydrogenation time is also relatively long, at 4–5.2 hours.

[0008] Therefore, there was a need for a process for manufacturing N,N' -Dialkyl- p- phenylenediamine, preferably of N,N' -Dicycloalkyl- p -phenylenediamine, especially preferred of N,N' -Dicyclohexyl- p -phenylenediamine, which overcomes the aforementioned disadvantages of the prior art.

[0009] The object of the present invention was to provide a process for the production of N,N'-dialkyl-p-phenylenediamine, preferably from N,N' -Dicycloalkyl- p -phenylenediamine, especially preferred of N,N' -Dicyclohexyl- p -phenylenediamine, to provide a technology that overcomes the disadvantages of the prior art, and N,N' -Dialkyl- p -phenylenediamine, preferably N,N'-dicycloalkyl-p-phenylenediamine, particularly preferably N,N' -Dicyclohexyl- p -phenylenediamine, in high purity and with only small amounts of the mono- and trialkylated by-products (preferably within the scope of this invention) N -Alkyl- p -phenylenediamine as well as N,N,N' -Trialkyl- p- phenylenediamine).

[0010] The purity of the products obtained is preferably determined by gas chromatography according to ASTM-D 4937 within the scope of the present invention. It corresponds to a purity in wt.%.

[0011] High purity within the scope of the present invention is present if, in the case of determining the purity via gas chromatography, the product produced according to the inventive method has a purity of greater than 95.0 wt.%, preferably greater than or equal to 96.0 wt.%, and usually preferably greater than 97.0 wt.%.

[0012] A small amount of the mono- and trialkylated by-products (preferably within the scope of this invention) N -Alkyl- p -phenylenediamine as well as N,N,N' -Trialkyl- p -phenylenediamine) in the context of the present invention, the total amount of both by-products is less than 3.0 wt.%, preferably less than 2.5 wt.%, particularly preferably less than 1.5 wt.%, and most preferably less than 1.0 wt.%. A small amount N -Alkyl- p-Phenylenediamine is present when it is contained in the product at less than 1.0 wt%, preferably less than 0.5 wt%, and particularly preferably less than 0.3 wt%. A small amount N,N,N' -Trialkyl- p -phenylenediamine is present when it is contained in the product at less than 3 wt.%, preferably less than 1.5 wt.%, particularly preferably less than 1.0 wt.%.

[0013] Surprisingly, it was found that the reaction of a compound of formula (II) with at least one ketone of formula (III) and a solvent of formula (IVb) or (IVc), or mixtures thereof, in the presence of a hydrogenation catalyst and hydrogen, yields high purities of the corresponding N,N' -Dialkyl- p -phenylenediamines of formula (I) leads to the formation of only small amounts of mono- and trialkylated by-products. Proceedings

[0014] The subject matter of the present invention is therefore a method for producing N,N'- Dialkyl-p-phenylenediamine of formula (I) where a combination of formula (II) where R1 and R2 are either the same or different and are selected from the group consisting of -NH2 and -NO2, and at least one ketone of formula (III) in the presence of a hydrogenation catalyst and hydrogen, wherein Z is the same in formulas (I) and (III) and a) represents an alkylene chain, preferably a linear 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, particularly preferably C5 alkylene, or b) represents two alkyl groups, preferably linear alkyl groups, which are each bonded to the carbon atom adjacent to Z and together with this carbon atom form an alkyl chain, preferably a linear alkyl chain, and wherein the two alkyl groups of Z together form the molecular formula CnH2n+2, preferably with n=4-6, particularly preferably with n=5, characterized in that the reaction is carried out in the presence of a solvent of formula (IVb) or the formula (IVc) or mixtures thereof, wherein Y in formulas (IVb) and (IVc) is the same or different, preferably the same, and a) represents an alkylene chain, preferably a linear 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, particularly preferably C5 alkylene, or b) represents two alkyl groups, preferably linear alkyl groups, or an alkyl group and a 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 linear alkyl chain, and wherein the two alkyl groups or the one alkyl group and the hydrogen atom together form the molecular formula CnH2n+2, preferably with n=4-6, particularly preferably with n=5.

[0015] In the above definitions of Y and Z, the term "alkylene" preferably refers to C n H 2n .

[0016] In the method according to the invention, Y in formulas (IVb) and (IVc) and Z in formulas (I) and (III) can be the same or different. Preferably, Y and Z are the same in formulas (I), (III), (IVb) and (IVc).

[0017] In a preferred embodiment of the method according to the invention, Z and Y are the same in formulas (I) and (III).

[0018] In another preferred embodiment of the method according to the invention, Z and Y are the same in formulas (I), (III) and (IVb).

[0019] In another preferred embodiment of the method according to the invention, Z and Y are the same in formulas (I), (III) and (IVc).

[0020] In a further embodiment of the present invention, Z in formulas (I) and (III) is the same as and different from Y in formulas (IVb) and (IVc), respectively.

[0021] The method according to the invention is a method for producing N,N' -Dialkyl- p-phenylenediamine of formula (I).

[0022] Z in formula (I) can represent two alkyl groups, preferably linear 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 linear alkyl chain, wherein the two alkyl groups of Z together form the molecular formula C n H 2n+2, preferably with n=4-6, particularly preferably with n=5.

[0023] Accordingly, the process according to the invention can be a process for the production of N,N'-alkyl-p-phenylenediamine, preferably N,N'-pentyl-, N,N'-hexyl-, N,N'-heptyl-p-phenylenediamine, particularly preferably N,N'-pentyl-, N,N'-heptyl-p-phenylenediamine N,N' -Hexyl- p -phenylenediamine.

[0024] In a preferred embodiment of the process according to the invention, Z in formula (I) represents an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the alkylene chain of Z is preferably C 4 -C 6 -alkylene, particularly preferably C 5 -alkylene.

[0025] The method according to the invention is therefore preferably a method for producing N,N' -Cycloalkyl- p -phenylenediamine.

[0026] Particularly preferably, Z in formula (I) represents a linear alkylene chain which forms a cyclic ring with the carbon atom adjacent to Z, and wherein the linear alkylene chain is C 4 -C 6 -alkylene, most preferably C 5 -alkylene.

[0027] The inventive method is therefore particularly preferred as a method for producing N,N' -Cyclopentyl- p -phenylenediamine N,N' -Cyclohexyl- p -phenylenediamine and N,N' -Cycloheptyl- p -phenylenediamine, usually preferred by N,N' -Cyclohexyl- p- phenylenediamine.

[0028] In the method according to the invention, the compound of formula (II) is used, wherein R1 and R2 are either the same or different and are selected from the group consisting of -NH 2 and -NO 2 .

[0029] Preferably, R1 and R2 are the same and -NH2, or different and -NH2 and -NO2, particularly preferably different and -NH2 and -NO2. The compound of formula (II) is therefore para-nitroaniline, which is particularly preferred.

[0030] Any ketones of formula (III) can be used.

[0031] Y can represent two alkyl groups, preferably linear alkyl groups, in the at least one ketone of formula (III), each of which is connected to the carbon atom adjacent to Z and together with this carbon atom forms an alkyl chain, preferably a linear alkyl chain, wherein the two alkyl groups of Z together form the molecular formula C n H 2n+2, preferably with n=4-6, particularly preferably with n=5.

[0032] Accordingly, at least one ketone of formula (III) can be selected from the group 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.

[0033] According to the above preference for Y in formula (III), the at least one ketone of formula (III) used in step a) is preferably a cyclic ketone, particularly preferably selected from cyclopentanone, cyclohexanone and cycloheptanone.

[0034] The ketone of formula (III) is therefore usually preferred, namely cyclohexanone.

[0035] Preferably, a ketone of formula (III) is used in the process according to the invention.

[0036] Any solvents of formula (IVb) or (IVc) or mixtures thereof may be used.

[0037] Y can represent two alkyl groups, preferably linear alkyl groups, or one alkyl group and one hydrogen atom in the solvent of formula (IVb) or (IVc), each of which is bonded to the carbon atom adjacent to Y and together with this carbon atom forms an alkyl chain, preferably a linear alkyl chain, wherein the two alkyl groups or the one alkyl group and the hydrogen atom together form the molecular formula C n H 2n+2, preferably with n=4-6, particularly preferably with n=5.

[0038] Preferably, Y in formulas (IVb) or (IVc) represents an alkylene chain, preferably a linear 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, particularly preferably C5 alkylene.

[0039] According to the above preference for Y in formula (IVb), the solvent used in formula (IVb) is preferably selected from cyclopentane, cyclohexane and cycloheptane, or mixtures thereof.

[0040] The solvent of formula (IVb) cyclohexane is usually preferred.

[0041] According to the above preference for Y in formula (IVc), the solvent used in formula (IVc) is preferably selected from methylcyclopentane, methylcyclohexane and methylcycloheptane, or mixtures thereof.

[0042] The solvent of formula (IVc) methylcyclohexane is usually preferred.

[0043] The solvent of formula (IV) is a solvent of formula (IVb) or (IVc), or mixtures thereof, particularly preferably selected from cyclohexane and methylcyclohexane.

[0044] The solvent of formula (IV) methylcyclohexane is usually preferred.

[0045] Ethers, preferably selected from the group consisting of glycol monoethers, glycol diethers, and cyclic diethers, are preferably present in the process according to the invention in a molar ratio to the compound of formula (II) of less than 0.2 : 1.0, particularly preferably less than 0.05 : 1, and most preferably less than 0.01 : 1.0. Most preferably, no ethers, preferably selected from the group consisting of glycol monoethers, glycol diethers, and cyclic diethers, are present in the process according to the invention.

[0046] The aforementioned statements and preferences of Z in formulas (I) and (III) and Y in formulas (IVb) and (IVc) therefore apply not only to the implementation in the inventive process, but also to the optional subsequent work-up.

[0047] The hydrogenation catalyst used in the process according to the invention can be a catalyst known and commonly used for hydrogenation processes from the prior art.

[0048] Preferably, the hydrogenation catalyst contains a metal selected from the group consisting of platinum, palladium and nickel, particularly preferably platinum.

[0049] The hydrogenation catalyst can be mounted on a solid support material, for example carbon, aluminum, barium sulfate, or calcium carbonate. Preferably, the hydrogenation catalyst is a carbon-based catalyst.

[0050] Platinum on carbon (Pt / C) is particularly preferred as a hydrogenation catalyst.

[0051] The hydrogenation catalyst can contain any amount of platinum. Preferably, the hydrogenation catalyst contains 1–10 wt% platinum, particularly preferably 1.5–5 wt% platinum, very preferably 2–4 wt% platinum, very preferably 2.5–3.5 wt% platinum, and most preferably 3 wt% platinum.

[0052] The use of platinum as a hydrogenation catalyst on carbon solves the further problem of providing a more environmentally friendly process compared to the one disclosed in US4140718A, which uses platinum on aluminum as a hydrogenation catalyst.

[0053] The hydrogenation catalyst may or may not contain water. Preferably, the catalyst contains water, particularly preferably 30–70 wt.%, most preferably 50–70 wt.%, and most preferably 60–65 wt.%.

[0054] The hydrogenation catalyst can be dehydrated before use in the process according to the invention. Dehydration can be carried out in various known ways, for example by azeotropic distillation. Preferably, dehydration is carried out by azeotropic distillation. Various solvents and solvent mixtures can be used for this purpose.

[0055] The components used for implementation in the inventive method can be used in different ratios to each other.

[0056] The ketone of formula (III) is preferably used in the molar ratio 1.2 : 1.0 to 5.0 : 1.0, particularly preferably 1.5 : 1.0 to 3.0 : 1.0, most preferably 1.8 : 1.0 to 2.5 : 1.0, to the compound of formula (II).

[0057] Preferably, the solvent of component (IV) is added to the compound of formula (II) in a molar ratio of 1.5 : 1.0 to 10.0 : 1.0, particularly preferably 2.0 : 1.0 to 8.0 : 1.0, most preferably 3.0 : 1.0 to 5.0 : 1.0.

[0058] Preferably, the hydrogenation catalyst is added to the compound of formula (II) in a weight ratio of 1.0 : 100.0 to 6.0 : 100.0, particularly preferably 2.0 : 100.0 to 6.0 : 100.0, and most preferably 2.0 : 1.0 to 4.0 : 100.0.

[0059] The components used in the reaction can be used without prior cleaning or cleaned before the reaction. Preferably, the components used in the reaction are used without prior cleaning. Particularly preferably, the components used in the reaction are used in purities of ≥ 90%, very preferably ≥ 95%, very preferably ≥ 98%, and most preferably ≥ 99%.

[0060] The components used for implementation can be presented in any order.

[0061] Preferably, the combinations of formulas (II), (III) and (IV) are presented first.

[0062] Preferably, the components used in the process according to the invention are exposed to a protective gas atmosphere before implementation, such as an argon or nitrogen atmosphere, preferably a nitrogen atmosphere.

[0063] The reaction preferably takes place at a temperature of 100 - 170 °C, particularly preferably at 90 - 150 °C, most preferably at 95 - 140 °C, and most preferably at 125 - 135 °C.

[0064] The reaction preferably takes place at a hydrogen pressure of 5 - 30 bar, particularly preferably at 10 - 20 bar, and most preferably at 13 - 17 bar.

[0065] The reaction is preferably carried out until no further hydrogen uptake can be detected. Detection of hydrogen uptake is preferably performed by monitoring the pressure change on a manometer. Detection is particularly preferably performed at intervals of less than 60 minutes, most preferably at intervals of less than 45 minutes, and most preferably at intervals of less than 35 minutes.

[0066] The implementation time is preferably 50 min to 400 min, particularly preferably 80 min to 300 min, most preferably 100 min to 270 min, and most preferably 100 min to 200 min.

[0067] After the reaction has taken place, the reaction mixture can be stirred further. Preferably, such stirring is carried out for 10 to 200 minutes, particularly preferably for 15 to 100 minutes, and most preferably for 25 to 70 minutes.

[0068] In a preferred embodiment of the method according to the invention, the method is a method for producing N,N' -Dicycloalkyl- p -phenylenediamine of formula (I), wherein Y and Z are the same in formulas (I), (III), (IVb) and (IVc) and represent a linear alkylene chain, which is preferably C 5 alkylene.

[0069] Particularly preferred is the solvent of formula (IV) in the last-mentioned preferred embodiment a solvent of formula (IVb).

[0070] This particularly preferred embodiment solves the further problem of providing a more efficient process compared to the one disclosed in US4140718A, which requires hydrogenation times of 4 - 5.2 hours.

[0071] Preferably, the process according to the invention is a process for the preparation of N,N'-dialkyl-p-phenylenediamine of formula (I) in a purity of greater than 95.0 wt.%, particularly preferably greater than or equal to 96.0 wt.%, most preferably greater than 97.0 wt.%, preferably determined by gas chromatography according to ASTM-D 4937.

[0072] Within the scope of this application, the expression "production of" is used N,N' -Dialkyl- p- phenylenediamine of formula (I) in a purity greater than 95.0 wt.%", equivalent to "production of a composition containing N,N' -Dialkyl- p -phenylenediamine of formula (I) to greater than 95.0 wt%". The same applies to analogous passages in this application as well as in the section "Uses".

[0073] Preferably, the process according to the invention is a process for the preparation of N,N'-dialkyl-p-phenylenediamine of formula (I), which comprises the compounds N -Alkyl- p- phenylenediamine as well as N,N,N' -Trialkyl- p -phenylenediamine total less than 3.0 wt.%, preferably less than 2.5 wt.%, particularly preferably less than 1.5 wt.%, most preferably less than 1.0 wt.%, preferably determined by gas chromatography according to ASTM-D 4937. Processing

[0074] After the reaction, the resulting reaction mixture can be processed in various ways known to those skilled in the art.

[0075] In a preferred embodiment of the process according to the invention, the reaction is followed by the removal of the hydrogenation catalyst from the reaction mixture obtained after the reaction.

[0076] The removal can be carried out in various ways known to those skilled in the art, such as filtration, preferably via a frit or pressure filter, or suction. Preferably, the removal is carried out by filtration of the reaction mixture obtained after the reaction, particularly preferably by filtration of the hot reaction mixture.

[0077] After removal of the hydrogenation catalyst from the reaction mixture, the solvent obtained from the reaction mixture can be removed in various ways known to those skilled in the art.

[0078] Preferably, the removal is carried out by distillation of the reaction mixture obtained after removal of the hydrogenation catalyst. The distillation temperature depends on the boiling point of the solvent used. Distillation is preferably carried out at reduced pressure.

[0079] The solvent mixture recovered after the removal of the solvent can be used for further hydrogenation.

[0080] In a particularly preferred embodiment, the implementation of the process according to the invention is followed by the removal of the hydrogenation catalyst from the reaction mixture obtained after the reaction, as well as the removal of the solvent from the reaction mixture obtained after removal of the hydrogenation catalyst. The determination of the purity of the N,N' -Dialkyl- p -phenylenediamines of formula (I) and the determination of the proportions of N -Alkyl- p -phenylenediamine as well as N,N,N'- Trialkyl-p-phenylenediamine, preferably determined by gas chromatography according to ASTM-D 4937, is preferably obtained after removal of the hydrogenation catalyst and the solvent.

[0081] After removal of the solvent from the reaction mixture, the resulting distillation residue can be processed in various ways known to those skilled in the art.

[0082] Preferably, the resulting distillation residue is cooled, whereby the N,N' -Dialkyl- p- phenylenediamines of formula (I) crystallize out.

[0083] The hot distillation residue obtained is preferably placed on a crystallizing plate.

[0084] Optionally, the received N,N' -Dialkyl- p -phenylenediamine of formula (I) is subsequently dried.

[0085] Drying can be carried out in various ways known to those skilled in the art. Preferably, drying takes place under vacuum, particularly preferably at a pressure of less than 10 kPa, and most preferably at a pressure of less than 5 kPa. use

[0086] Another revelation is the use of N,N' -Dicyclohexyl-p-phenylenediamine in a purity greater than 95.0 wt.%, preferably greater than or equal to 96.0 wt.%, most preferably greater than 97.0 wt.%, as an anti-aging agent in rubber compounds, vulcanizates and molded parts obtained therefrom, in particular tires, wherein the purity is preferably determined by gas chromatography according to ASTM-D 4937.

[0087] In another revelation, the N,N' -Dicyclohexyl-p-phenylenediamine the compounds N -Cyclohexyl- p -phenylenediamine and N,N,N' -Tricyclohexyl- p- The total amount of phenylenediamine is less than 3.0 wt.%, preferably less than 2.5 wt.%, particularly preferably less than 1.5 wt.%, and most preferably less than 1.0 wt.%.

[0088] In another revelation, the N,N' -Dicyclohexyl-p-phenylenediamine the compound N -Cyclohexyl- p-phenylenediamine in less than 0.5 wt.%, most preferably in less than 0.3 wt.%.

[0089] In another revelation, the N,N' -Dicyclohexyl-p-phenylenediamine the compound N,N,N' -Tricyclohexyl- p -phenylenediamine in less than 3 wt.%, most preferably in less than 1.5 wt.%, most preferably in less than 1.0 wt.%.

[0090] The aforementioned preferred areas apply analogously to use in rubber compounds, vulcanizates and molded parts, especially tires.

[0091] Likewise, the descriptions and preferred areas mentioned within the scope of this invention apply regardless of whether they were disclosed in the plural or in the singular.

[0092] The invention will be explained using the following examples, without, however, limiting it to them. Examples Methods for the production of N,N' -Dicyclohexyl-p-phenylenediamine

[0093] Table 1: List of ingredients, abbreviations and manufacturers Trade name Explan Manufacturer / Distributor p-Nitroaniline Raw material, purity ≥ 99% Sigma-Aldrich Cyclohexanone Raw material, purity ≥ 99% Sigma-Aldrich Cyclohexanol Solvent, purity ≥ 99% Sigma-Aldrich Evonik Noblyst®< P2067 3% Pt / C Hydrogenation catalyst: Platinum / activated carbon (3 wt% platinum, 62.5 wt% H₂O) Evonik Industries Cyclohexane Solvent, purity ≥ 99% Sigma-Aldrich Methylcyclohexane Solvent, purity ≥ 99% Sigma-Aldrich Table 2: Amounts of raw materials used and reaction parameters Example 1 Example 2 Example 3 (not according to the invention) p-Nitroaniline 69 g (0.5 mol) 69 g (0.5 mol) 69 g (0.5 mol) Cyclohexanone 101 g (1.03 mol) 101 g (1.03 mol) 103 g (1.05 mol) catalyst 2 g 2 g 4 g Methylcyclohexane 188 g (1.91 mol) Cyclohexane 188 g (2.23 mol) Cyclohexanol 188 g (1.88 mol) Pressure [bar H 2 ] 15 15 15 Temperature [°C] 130 130 100 Intake in bar H2 135 130 146 Implementation time [min] 120 152 262 Stir [min] 60 60 30 Production of N,N' -Dicyclohexyl-p-phenylenediamine based on the quantities of the raw materials and reaction parameters of examples 1- given in Table 2. 3

[0094] The following procedure was carried out for examples 1-3. Implementation

[0095] p-nitroaniline, cyclohexanone, the catalyst and the respective solvent of example 1, 2 and 3 respectively were placed in a 3 L alloy autoclave (large blade stirrer, 600 rpm) at room temperature.

[0096] The autoclave was sealed and purged with nitrogen. A hydrogen pressure of 5 bar was set at room temperature, and the autoclave was then heated to the respective temperatures of Examples 1, 2, and 3. Upon reaching the target temperature, the pressure was increased to 15 bar H₂, and hydrogenation continued until zero uptake (<1 bar H₂ uptake in 30 min). The mixture was then stirred for 30 or 60 min at the corresponding temperature and pressure. Cooling was permitted to 75°C, the autoclave was depressurized, and the reaction solution was removed. Processing

[0097] The reaction solution obtained after the reaction was filtered hot through a pressure filter away from the catalyst.

[0098] The recovered catalyst can be used for further hydrogenation.

[0099] The reaction solution was purified of low-boiling components at 120°C / 50 mbar. The distillate was two-phase. The organic phase consisted mainly of the solvent (>99%) and can be used for re-hydrogenation.

[0100] A melt was obtained from the distillation sump, which was poured hot onto a crystallizing plate. After cooling, the crystallized solid was knocked off, crushed, and bottled. Table 3: Purity* 1< of the products produced according to examples 1, 2 and 3 in [wt%] Example 1 Example 2 Example 3 (not according to the invention) 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 * 1< : measured by gas chromatography according to ASTM-D 4937 after removal of the hydrogenation catalyst and the solvent Results

[0101] As can be seen from Table 3, N,N' -Dicyclohexyl-p-phenylenediamine was produced in examples 1, 2, and 3 in a high purity of up to 97.73 wt%. The undesired byproducts N -Cyclohexyl- p -phenylenediamine as well as N,N,N'-Tricyclohexyl p-phenylenediamine was obtained only in small amounts, totaling less than 3 wt% in each example, even less than 1.5 wt% in examples 1 and 2, and even less than 1 wt% in example 2. The monoalkylated byproduct N -Cyclohexyl- p- Phenylenediamine is present in all Examples 1, 2, and 3 in less than 0.3 wt%, and the trialkylated by-product in Example 2 is present in less than 1 wt%. Example 3 is not according to the invention.

Claims

1. Process for preparing N,N'-dialkyl-p-phenylenediamine of the formula (I) wherein a compound of the formula (II) where 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 the formula (III) are converted in the presence of a hydrogenation catalyst and hydrogen, where Z in the formulae (I) and (III) is the same and a) is an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Z, and where the alkylene chain of Z is preferably C4-C6-alkylene, more preferably C5-alkylene, or b) represents two alkyl radicals, preferably linear alkyl radicals, that are each bonded to the carbon atom adjacent to Z and together with that carbon atom form an alkyl chain, preferably a linear alkyl chain, and where the two alkyl radicals of Z together form the empirical formula CnH2n+2, preferably with n = 4-6, more preferably with n = 5, characterized in that the reaction is effected in the presence of a solvent of the formula (IVb) or of the formula (IVc) or mixtures thereof, where Y in the formulae (IVb) and (IVc) is the same or different, preferably the same, and a) is an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Y, and where the alkylene chain of Y is preferably C4-C6-alkylene, more preferably C5-alkylene, or b) represents two alkyl radicals, preferably linear alkyl radicals, or one alkyl radical and one hydrogen atom, that are each bonded to the carbon atom adjacent to Y and together with that carbon atom form an alkyl chain, preferably a linear alkyl chain, and where the two alkyl radicals or the one alkyl radical and the hydrogen atom together form the empirical formula CnH2n+2, preferably with n = 4-6, more preferably with n = 5.

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

3. Process according to either of Claims 1 and 2, characterized in that Y in the formulae (IVb) and (IVc) is the same and is an alkylene chain, preferably a linear alkylene chain, which forms a cyclic ring with the carbon atom adjacent to Y, and where the alkylene chain of Y is preferably C4-C6-alkylene, more preferably C5-alkylene.

4. Process according to any 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, most preferably 3% by weight of platinum.

5. Process according to any of Claims 1-4, characterized in that the solvent of the formula (IV) is selected from cyclohexane and methylcyclohexane.

6. Process according to any of Claims 1-5, characterized in that the reaction is effected at a hydrogen pressure of 5-30 bar, preferably of 10-20 bar, more preferably of 13-17 bar.

7. Process according to any of Claims 1-6, characterized in that the reaction is effected at a temperature of 100-170°C, preferably at 90-150°C, more preferably at 95-140°C, even more preferably at 125-135°C.

8. Process according to any 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. Process according to any of Claims 1-8, characterized in that the process is a process for preparing N,N'-dialkyl-p-phenylenediamine of the formula (I) in a purity of greater than 95.0% by weight, preferably not less than 96.0% by weight, more preferably greater than 97.0% by weight, preferably ascertained by gas chromatography to ASTM-D 4937.

10. Process according to any of Claims 1-9, characterized in that the process is a process for preparing N,N'-dialkyl-p-phenylenediamine of the formula (I) that includes the compounds N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine in a sum total of 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, preferably ascertained by gas chromatography to ASTM-D 4937.

11. Process according to any of Claims 1-10, characterized in that the at least one ketone of the 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, to the compound of the formula (II).

12. Process according to any of Claims 1-11, characterized in that the process is a process for preparing N,N'-dicycloalkyl-p-phenylenediamine of the formula (I), where Y and Z in the formulae (I), (III) and (IVb) and (IVc) are the same and are a linear alkyl chain which is preferably C5-alkylene.

13. Process according to either of Claims 9 and 10, characterized in that the purity of the N,N'-dialkyl-p-phenylenediamine of the formula (I) is determined according to Claim 9 and the proportions of N-alkyl-p-phenylenediamine and N,N,N'-trialkyl-p-phenylenediamine are determined according to Claim 10, preferably ascertained by gas chromatography to ASTM-D 4937, after removal of the hydrogenation catalyst and the solvent.

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