METHOD FOR STABILIZING AT LEAST MONOALKYL-SUBSTITUTED DIAMINOCYCLOHEXANES

Description

[0001] The present invention relates to a process for stabilizing at least monoalkyl-substituted diaminocyclohexanes, in which at least one reducing agent (R) and optionally water are added to a composition (ZE). The composition (ZE) contains at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water. By adding the at least one reducing agent (R) and optionally water to the composition (ZE), a composition (ZP) is obtained which contains at least 0.05 wt. % water, based on the total weight of the composition (ZP).The at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from one of the compounds according to the general formulas (I), (II) or (III), in which R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 and R 4 ' are independently selected from H and C 1 -C 4 -alkyl, wherein at least one radical R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 or R 4 ' is C 1 -C 4 -alkyl, and wherein first a distillation of the composition (ZE) is carried out with removal of higher-boiling by-products and to obtain a distilled composition (DZE) which contains the at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water, followed by the addition of the at least one reducing agent (R) and optionally water to the distilled composition (DZE) while maintaining the composition (ZP), wherein the composition (ZP) contains 0.05 to 3 wt.% water, based on the total weight of the composition (ZP).Further objects of the invention are the composition (ZP) and its use, for example, for the production of hardeners for epoxy resins.

[0002] Cycloaliphatic diamines such as alkyl-substituted diaminocyclohexanes generally exhibit better light, UV, and weather resistance than corresponding aromatic diamines, making them important starting materials for various products, such as coating materials. Many cycloaliphatic amines are typically colorless liquids in their pure form. However, they often tend to discolor over time due to impurities such as metals or metal compounds or impurities from byproducts of the manufacturing process. This tendency toward discoloration limits the application range of cycloaliphatic amines, which is why it is desirable to purify such materials accordingly and prevent or minimize discoloration for as long as possible.Since the formation of color-causing impurities varies in each amine manufacturing process and in each amine product, the decolorization and color stabilization of some amines is not automatically suitable for other amines.

[0003] The prior art therefore discloses, in some cases, very different approaches for decolorizing amines in the short term or improving their color stability in the long term: For example, US 3,922,306 discloses a process for decolorizing aliphatic amines in which an aliphatic amine and an alkali metal borohydride are heated to 50 to 70 °C for several hours and then separated. According to US 3,922,306, a corresponding decolorization could not be achieved using other reducing agents such as sodium sulfite, sodium dithionite, hydrazine, or phosphinic acid.

[0004] US Pat. No. 7,169,268 discloses a process for producing a color-stable tertiary amine by distilling a tertiary amine in the presence of ethylenediamine or an ethyleneamine derivative. The distilled tertiary amine discolors less rapidly than the corresponding untreated tertiary amine; however, the color stability studies in US Pat. No. 7,169,268 show that the amine's discoloration increases even after a short period of exposure to air. Longer-term color stability can be achieved by storing the tertiary amine in an inert gas atmosphere.

[0005] US 4,731,165 discloses a process for decolorizing triethylenetetraamine, according to which triethylenetetraamine is catalytically purified using a sulfonic acid-based ion exchange resin. The purification of the triethylenetetraamine with the ion exchange resin takes place under reduced pressure and elevated temperatures, and following the purification step, the ion exchange resin is separated from triethylenetetraamine by distillation. According to US 4,731,165, the process is also suitable for purifying other polyalkylenepolyamines, but contains no information regarding the long-term color stability of the amines.

[0006] US 5,362,914 describes a continuous process for reducing the discoloration of polyethylenepolyamines. This process involves hydrogenating polyethylenepolyamines in the presence of a cobalt-, copper-, and chromium-containing catalyst in a hydrogen atmosphere at elevated temperatures and pressure. The polyethylenepolyamines can be distilled before hydrogenation or used as a crude product, and hydrogenation is followed by a further distillation step. Although the process described in US 5,362,914 is suitable for decolorizing polyethylenepolyamines, the resulting polyethylenepolyamines also tend to discolor in air and, according to US 5,362,914, should be stored under a nitrogen atmosphere.

[0007] An alternative process for decolorizing polyethylenepolyamines is disclosed in US Pat. No. 4,609,436, in which polyethylenepolyamines are treated with a chlorinated hydrocarbon and stirred at elevated temperatures. Following treatment of the polyethylenepolyamines with the chlorinated hydrocarbon, a distillation follows, in which the polyethylenepolyamine is separated from the chlorinated hydrocarbon.

[0008] US Pat. No. 6,774,264 discloses a process for improving the color stability of N,N-dialkylalkanolamines by hydrogenating the corresponding amines in the presence of a palladium catalyst under anhydrous conditions. The hydrogenation in US Pat. No. 6,774,264 is carried out primarily to remove unsaturated by-products formed during the production of N,N-dialkylalkanolamines.

[0009] US Pat. No. 5,847,221 discloses a process for decolorizing alkanolamines or alkyleneamines, in which the corresponding amine is treated with a polymeric, solid acid catalyst in the presence of small amounts of water at elevated temperatures and pressure for several hours to remove or decompose metal catalyst residues from the respective production process of the amines and compounds with conjugated double bonds. Following the decolorization step, a distillation step can be carried out.

[0010] US Pat. No. 5,359,139 discloses a process for treating tertiary amines in which a tertiary amine is treated with ascorbic acid, which is then separated from the tertiary amine by distillation. In the tertiary amines treated in this way, discoloration of the tertiary amines under acidic conditions can be largely avoided.

[0011] While the above-mentioned methods describe possibilities for the immediate purification of various amines, compositions with long-term color-stable amines are usually accessible through the use of certain stabilizers.

[0012] For example, US Pat. No. 4,602,108 discloses the color stabilization of linear or branched aliphatic amines using suitable stabilizers such as nitrilotrismethylenephosphonic acid, 8-hydroxyquinoline, or ethylenediaminetetraacetic acid. The stabilizer is only slightly or poorly soluble in the aliphatic amine.

[0013] WO 2011 / 084865 discloses a composition containing an oxidation-sensitive amine and an oxidation inhibitor. The oxidation inhibitor can be a radical scavenger such as phenylimidazole or glutamine, or an antioxidant such as ascorbic acid. The use of the oxidation inhibitor is primarily intended to prevent the formation of formaldehyde and dimethylformamide, which are often formed during storage in air with the oxidation-sensitive amines described in WO 2011 / 084865.

[0014] In ""Color-Stabilized DYTEK® DCH-99 amine Adducts for Epoxy Curing, Invista, March 14, 2012" discloses the stabilization of 1,2-diaminocyclohexane, which contains a stabilizer system of sodium borohydride, water, benzyl alcohol, triethylamine, and an epoxy resin to reduce the discoloration of the amine during storage in air. Additional amounts of sodium borohydride and water increase color stability. The weight fraction of the stabilizer system is significantly greater than the weight fraction of the 1,2-diaminocyclohexane.

[0015] US Pat. No. 5,516,935 A discloses a process for producing diisocyanates in which an aliphatic or cycloaliphatic amine is reacted with phosgene and a solvent in the gas phase in a reactor and then purified. Cycloaliphatic diamines such as 2,3-, 2,4-, or 2,6-diamino-1-methylcyclohexanes can be used as cycloaliphatic amines.

[0016] In Michael Ash et al., "Industrial Chemical Thesaurus," June 1, 2009, pages 56 to 57, XP55448549, color-stabilized amine adducts stabilized by sodium borohydride (NaBH 4 ) in water are disclosed. The described amine adducts are obtained by reacting 1,2-diaminocyclohexane with an epoxy resin in the presence of a mixture of triethanolamine and benzyl alcohol as a reaction accelerator.

[0017] The object of the present invention is to provide a process for stabilizing at least monoalkyl-substituted diaminocyclohexanes.

[0018] This object is achieved by a process for stabilizing at least monoalkyl-substituted diaminocyclohexanes, comprising the addition of at least one reducing agent (R) and optionally water to a composition (ZE) which contains at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water, to obtain a composition (ZP), wherein the composition (ZP) comprises the at least one reducing agent (R), the at least one at least monoalkyl-substituted diaminocyclohexane (A) and additionally at least 0.05 wt.% water, based on the total weight of the composition (ZP), characterized in that the at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from one of the compounds according to the general formulas (I), (II) or (III) in which R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 and R 4 ' are independently selected from H and C 1 -C 4 alkyl, wherein at least one radical R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 or R 4 ' is C 1 -C 4 alkyl; characterized in that first a distillation of the composition (ZE) is carried out with separation of higher-boiling by-products and to obtain a distilled composition (DZE) which contains the at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water, whereupon the addition of the at least one reducing agent (R) and optionally water to the distilled composition (DZE) takes place to obtain the composition (ZP), wherein the composition (ZP) contains 0.05 to 3 wt.% water, based on the total weight of the composition (ZP).

[0019] It was surprisingly found that the discoloration of at least monoalkyl-substituted diaminocyclohexanes during storage in air can be significantly reduced if at least one reducing agent (R) and optionally water are added before storage.

[0020] Both under thermal stress and during prolonged storage of the stabilized at least monoalkyl-substituted diaminocyclohexanes in air, significantly less color deepening occurs than with unstabilized, at least monoalkyl-substituted diaminocyclohexanes.

[0021] Without being bound to any theory, the at least one reducing agent (R) can prevent the formation of condensation products of the at least monoalkyl-substituted diaminocyclohexanes or optionally other amines contained in the composition (ZE) as well as their color-providing secondary products, which can arise over time by storage of at least monoalkyl-substituted diaminocyclohexanes in air.

[0022] In addition, the process according to the invention does not require the removal of water, which may be present as a residue from the corresponding preparation processes in the at least monoalkyl-substituted diaminocyclohexanes, which makes complex separation processes for removing water from the at least monoalkyl-substituted diaminocyclohexanes unnecessary.

[0023] In the context of the present invention, the terms "(color) stability," "(color) stabilization," or "(color) stable" mean that the color number of an amine or an amine-containing composition remains unchanged at a low level over an extended period of time or increases comparatively slightly. The color number is determined by long-term storage tests, in which the color quality of a compound is determined by measuring the transmittance of the incident light. For this purpose, a solution of a certain concentration in a cuvette with a known path length is illuminated with a light beam of a defined wavelength. The percentage of transmitted light energy at a given wavelength results in a defined color number. The determination of the Hazen color number according to the APHA platinum-cobalt color scale is commonly used for weakly colored solutions. The determination of the Hazen color number according to the APHA platinum-cobalt color scale is generally carried out in accordance with DIN EN ISO 6271.

[0024] In the context of the present invention, the term "condensation product" encompasses all compounds that are formed in a reaction with elimination of water, ammonia, carbon dioxide, hydrogen halides or alcohols.

[0025] The present invention will be explained in detail below.

[0026] The present invention relates to a process for stabilizing at least monoalkyl-substituted diaminocyclohexanes.

[0027] In the process according to the invention, at least one reducing agent (R) is added to a composition (ZE) which contains at least one at least monoalkyl-substituted diaminocyclohexane as component (A).

[0028] The composition (ZE) is the mixture containing the at least one at least monoalkyl-substituted diaminocyclohexane (A). The at least one at least monoalkyl-substituted diaminocyclohexane (A) can be present in any desired amount in the composition (ZE). All of the following statements regarding the composition (ZE) therefore refer to the corresponding mixture before the addition of the at least one reducing agent (R).

[0029] The composition (ZE) preferably contains at least 69% by weight, preferably at least 90% by weight and particularly preferably at least 94% by weight of the at least one at least monoalkyl-substituted diaminocyclohexane (A), based on the total weight of the composition (ZE).

[0030] In a further embodiment, the composition (ZE) preferably contains at least 85% by weight, preferably at least 90% by weight and particularly preferably at least 95% by weight of the at least one at least monoalkyl-substituted diaminocyclohexane (A), based on the total weight of the composition (ZE).

[0031] In the context of the present invention, the at least one at least monoalkyl-substituted diaminocyclohexane (A) is understood to mean a compound which has a cyclohexane ring with two amino groups and with at least one or more alkyl substituents.

[0032] Alkyl-substituted diaminocyclohexanes are known in principle to the person skilled in the art and can be prepared by any process known to the person skilled in the art. Suitable processes for preparing alkyl-substituted diaminocyclohexanes include, for example, the metal-catalyzed hydrogenation of alkyl-substituted diaminobenzene derivatives, as disclosed, for example, in WO 2009 / 090179 and WO 2009 / 153123.

[0033] Preferably, the at least one at least monoalkyl-substituted diaminocyclohexane (A) is at least one at least monoalkyl-substituted 1,2-, 1,3- or 1,4-diaminocyclohexane, in particular at least one at least monoalkyl-substituted 1,3-diaminocyclohexane.

[0034] Preferably, the at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from one of the compounds according to the general formulas (I), (II) or (III) in which R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 and R 4 ' are independently selected from H and C 1 -C 4 alkyl, where at least one radical R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 or R 4 ' is C 1 -C 4 alkyl.

[0035] In the context of the present invention, the term C 1 -C 4 -alkyl, as used, for example, for the radical R 1< in the general formulas (I), (II), and (III), means that this substituent is an alkyl radical having 1 to 4 carbon atoms. The alkyl radical can be either linear or branched. Examples of alkyl radicals are methyl, ethyl, n-propyl, n-butyl, and their branched isomers.

[0036] Preferably, R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 and R 4 ' are independently selected from H or methyl.

[0037] Preferably, the at least one at least monoalkyl-substituted diaminocyclohexane (A) has the general formula (I), wherein R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 and R 4 ' are independently selected from H or C 1 -C 4 alkyl, wherein exactly one radical R 1 , R 1 ', R 2 , R 2 ', R 3 , R 3 ', R 4 or R 4 ' is C 1 -C 4 alkyl.

[0038] Particularly preferably, the at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from 1,3-diamino-4-methylcyclohexane or 1,3-diamino-2-methylcyclohexane.

[0039] The at least one at least monoalkyl-substituted diaminocyclohexane (A) can be exactly one at least monoalkyl-substituted diaminocyclohexane as well as mixtures of two or more different at least monoalkyl-substituted diaminocyclohexanes.

[0040] In a preferred embodiment, the at least one at least monoalkyl-substituted diaminocyclohexane (A) is a mixture of 1,3-diamino-4-methylcyclohexane and 1,3-diamino-2-methylcyclohexane. The weight proportions of 1,3-diamino-4-methylcyclohexane and 1,3-diamino-2-methylcyclohexane in this mixture can, in principle, be arbitrary. In this preferred embodiment, the at least one at least monoalkyl-substituted diaminocyclohexane (A) preferably contains 50 to 95 wt. % of 1,3-diamino-4-methylcyclohexane and 5 to 50 wt. % of 1,3-diamino-2-methylcyclohexane, based on the total weight of the at least one at least monoalkyl-substituted diaminocyclohexane (A).

[0041] In a further preferred embodiment, the at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from 1,3-diamino-2-methylcyclohexane or 1,3-diamino-4-methylcyclohexane.

[0042] Furthermore, the composition (ZE) may optionally contain water. In principle, the water may have been introduced into the composition (ZE) in any desired manner. The water may, for example, be a residue from the preparation process of the at least one at least monoalkyl-substituted diaminocyclohexane (A).

[0043] The composition (ZE) preferably has a water content of at least 0.05% by weight, preferably of at least 0.08% by weight and particularly preferably of at least 0.1% by weight, based on the total weight of the composition (ZE).

[0044] Furthermore, the composition (ZE) preferably has a water content of at most 1 wt.%, preferably of at most 0.8 wt.% and particularly preferably of at most 0.5 wt.%, based on the total weight of the composition (ZE).

[0045] In a preferred embodiment, the composition (ZE) has a water content of 0.05 to 1 wt.%, preferably of 0.08 to 0.8 wt.% and particularly preferably of 0.1 to 0.5 wt.%, based on the total weight of the composition (ZE).

[0046] The composition (ZE) may contain further compounds in addition to the at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water.

[0047] The further compounds are preferably residues from the respective production process of the corresponding at least one at least monoalkyl-substituted diaminocyclohexane (A). These residues include, for example, unsubstituted or at least monoalkyl-substituted aminocyclohexanes, impurities by metals and metal compounds from hydrogenation catalysts, higher-boiling by-products, or solvent residues such as, for example, isopropanol, isobutanol, tert-butanol, dimethoxyethane, dioxane, or tetrahydrofuran.

[0048] Higher-boiling by-products are those components that have a higher boiling point than the at least one at least monoalkyl-substituted diaminocyclohexane (A), with the boiling point of the higher-boiling by-products preferably being at least 2 °C, more preferably at least 4 °C, and most preferably at least 6 °C higher than the standard boiling point of the at least one at least monoalkyl-substituted diaminocyclohexane (A). For the purposes of the present invention, the term "standard boiling point" refers to the boiling point at atmospheric pressure of 1.013 bar.

[0049] If two or more at least monoalkyl-substituted diaminocyclohexanes (A) are present in the composition (ZE), the boiling point of each higher-boiling by-product is higher than the highest boiling point of the two or more at least monoalkyl-substituted diaminocyclohexanes (A).

[0050] The higher boiling by-products preferably have a molecular weight in the range of 100 to 500 g / mol, more preferably 120 to 370 g / mol and particularly preferably 150 to 300 g / mol.

[0051] The higher boiling by-products preferably contain at least one cyclohexane fragment (residue), more preferably two cyclohexane fragments (residues), or at least one cyclohexane fragment (residue) and at least one aromatic fragment (residue).

[0052] These include, for example, unsubstituted or at least monoalkyl-substituted aromatic amines and secondary amines which can be formed as condensation products of two or more molecules of the at least one at least monoalkyl-substituted diaminocyclohexane (A) with elimination of ammonia, such as, for example, N 1< -(3-amino-4-methylcyclohexyl)-4-methylcyclohexane-1,3-diamine and its isomers. Furthermore, the higher-boiling by-products also include condensation products of the at least one at least monoalkyl-substituted diaminocyclohexane (A) with other compounds present in the composition (ZE) which have amino groups, such as, for example, with unsubstituted or at least monoalkyl-substituted aromatic amines or optionally unsubstituted or at least monoalkyl-substituted monoaminocyclohexanes.

[0053] Furthermore, during storage of the at least one at least monoalkyl-substituted diaminocyclohexane (A) in air, higher-boiling by-products may form over time due to oxidation reactions, which may contribute to the discoloration of the at least one at least monoalkyl-substituted diaminocyclohexane (A) in the composition (ZE). These include, for example, imino compounds and olefinically unsaturated compounds, which may form by oxidation of the aforementioned condensation products.

[0054] Corresponding compounds include, for example, oxidized condensation products such as N-(3-imino-4-methylcyclohexyl)-4-methylcyclohex-1-en-1-amine and its isomers as well as oxidized condensation products of the at least one at least monoalkyl-substituted diaminocyclohexane (A) with other compounds contained in the composition (ZE) which have amino groups.

[0055] Preferably, the higher-boiling by-products are selected from unsubstituted or at least monoalkyl-substituted aromatic amines or secondary amines, imines and / or olefinically unsaturated compounds which are formed by condensation reactions and optionally oxidation reactions of the at least one at least monoalkyl-substituted diaminocyclohexane (A), optionally with further amines contained in the composition (ZE).

[0056] Particularly preferably, the higher-boiling by-products are selected from N 1< -(3-amino-4-methylcyclohexyl)-4-methylcyclohexane-1,3-diamine or N-(3-imino-4-methylcyclohexyl)-4-methylcyclohex-1-en-1-amine and their isomers.

[0057] In one embodiment, the composition contains (ZE) 95 to 99.999 wt.% of at least one at least monoalkyl-substituted diaminocyclohexane (A), 0.001 to 5 wt.% higher boiling compounds, based on the total weight of the composition (ZE), whereby the sum of all components in the composition (ZE) amounts to 100 wt.%.

[0058] In a further embodiment, the composition contains (ZE) 94 to 99.949 wt.% of at least one at least monoalkyl-substituted diaminocyclohexane (A), 0.05 to 1 wt.% Water, 0.001 to 5 wt.% higher boiling compounds, based on the total weight of the composition (ZE), whereby the sum of all components in the composition (ZE) amounts to 100 wt.%.

[0059] Preferably, the further compounds contained in the composition (ZE) are removed before the addition of the at least one reducing agent (R) takes place (see below).

[0060] In the process according to the invention, at least one reducing agent (R) is added to the composition (ZE) to obtain the composition (ZP).

[0061] The addition of the at least one reducing agent (R) can be carried out by any method known to the person skilled in the art and is preferably carried out with stirring.

[0062] The addition of the at least one reducing agent (R) can, in principle, take place at any desired temperature. The addition of the at least one reducing agent (R) preferably takes place at low temperatures, preferably in the range from 5 to 60 °C and particularly preferably in the range from 10 to 40 °C.

[0063] The duration of the addition of the at least one reducing agent (R) can, in principle, take place within very broad time spans. The duration of the addition of the at least one reducing agent (R) is preferably in the range of 10 minutes to 8 hours, more preferably in the range of 15 minutes to 5 hours, and most preferably in the range of 20 minutes to 3 hours. The person skilled in the art selects the duration of the addition of the at least one reducing agent (R) accordingly in order to obtain a homogeneous solution of the composition (ZP).

[0064] The composition (ZP) is the mixture comprising the at least one reducing agent (R), the at least one at least monoalkyl-substituted diaminocyclohexane (A), and additionally at least 0.05 wt.% water, based on the total weight of the composition (ZP). Consequently, all information regarding the composition (ZP) refers to the mixture after the addition of the at least one reducing agent (R) and, if appropriate, water.

[0065] The at least one reducing agent (R) can contain exactly one reducing agent or mixtures of two or more different reducing agents. The at least one reducing agent (R) preferably contains at least one component containing hydride ions.

[0066] Preferably, the at least one reducing agent (R) contains at least one boron or aluminum compound containing hydride ions. Such compounds are known in principle to the person skilled in the art.

[0067] Particularly preferably, the at least one reducing agent (R) is selected from lithium borohydride, sodium borohydride, potassium borohydride, sodium cyanoborohydride, lithium aluminum hydride, sodium aluminum hydride, or potassium aluminum hydride. Most preferably, the at least one reducing agent (R) is sodium borohydride.

[0068] In the composition (ZP), the at least one reducing agent (R) can in principle be present in all amounts customary for stabilizers and known to the person skilled in the art. The composition (ZP) preferably contains 0.005 to 0.2 wt.% of the at least one reducing agent (R), based on the total weight of the composition (ZP). Preferably, the composition (ZP) contains 0.007 to 0.15 wt.% and particularly preferably 0.01 to 0.1 wt.% of the at least one reducing agent (R), based on the total weight of the composition (ZP).

[0069] The at least one reducing agent (R) can be added as a solid, in a solution (L), or in a suspension (S). If the at least one reducing agent (R) is added in a solution (L) or in a suspension (S), the solution (L) or the suspension (S) can in principle contain any desired solvent. Preferably, the solution (L) or the suspension (S) contains water, amines, ethers, or alcohols as solvent; particularly preferably, the solution (L) or the suspension (S) contains water as solvent.

[0070] The at least one reducing agent (R) is preferably completely dissolved in the composition (ZP). This means that the composition (ZP) preferably contains no solid particles of the at least one reducing agent (R). Consequently, the at least one reducing agent (R) can preferably not be separated from the composition (ZP) by filtration.

[0071] Analogously, reaction products of the at least one reducing agent (R) with higher-boiling by-products optionally present in the composition (ZP) or with oxidizing agents such as oxygen, preferably atmospheric oxygen, are preferably completely dissolved in the composition (ZP). This means that the composition (ZP) preferably also contains no solid particles of the aforementioned reaction products of the at least one reducing agent (R). Consequently, the aforementioned reaction products of the at least one reducing agent (R) can preferably not be separated from the composition (ZP) by filtration.

[0072] In one embodiment, the at least one reducing agent (R) is added in a solution (L), wherein the solution (L) preferably contains at least one basic compound (B). In another embodiment, the at least one reducing agent (R) is added in a suspension (S), wherein the suspension (S) preferably contains at least one basic compound (B). All of the following preferences for the solution (L) apply accordingly to the suspension (S).

[0073] The solution (L) can contain exactly one basic compound (B) or mixtures of two or more different basic compounds (B).

[0074] The amount of the at least one basic compound (B) in the solution (L) is not critical for the process according to the invention. The solution (L) preferably contains 0.1 to 75 wt.% of the at least one basic compound (B), based on the total weight of the solution (L). The solution (L) preferably contains 5 to 70 wt.% and particularly preferably 10 to 65 wt.% of the at least one basic compound (B), based on the total weight of the solution (L).

[0075] The at least one basic compound (B) can, in principle, be any basic compound known to the person skilled in the art. Preferably, the at least one basic compound (B) is a basic alkali or alkaline earth metal compound. Particularly preferably, the at least one basic compound (B) is selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, or calcium carbonate. Very particularly preferably, the at least one basic compound (B) is selected from sodium hydroxide, potassium hydroxide, or sodium carbonate.

[0076] In a preferred embodiment, the mixture (G) contains the following components: a) 5 to 20 wt.% of the at least one reducing agent (R), b) 10 to 65 wt.% of the at least one basic compound (B), and c) 15 to 85 wt.% water, where the weight proportions of components a), b) and c) total 100 wt.%.

[0077] As already mentioned above, especially during storage of the at least one at least monoalkyl-substituted diaminocyclohexane (A) in air, higher-boiling by-products may form over time, which are involved in the discoloration of the at least one at least monoalkyl-substituted diaminocyclohexane (A).

[0078] According to the invention, therefore, a distillation of the composition (ZE) is first carried out with separation of higher-boiling by-products and to obtain a distilled composition (DZE) which contains the at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water, whereupon the addition of the at least one reducing agent (R) and optionally water to the distilled composition (DZE) takes place to obtain the composition (ZP), wherein the composition (ZP) comprises at least 0.05 wt.% water, based on the total weight of the composition (ZP).

[0079] For the sake of completeness, it is noted that in this embodiment, the addition of the at least one reducing agent (R) takes place to the distilled composition (DZE) and not to the composition (ZE).

[0080] Distillation can be carried out by any method known to the person skilled in the art and considered technically appropriate for the particular embodiment.

[0081] Distillation can be carried out, for example, on a rotary evaporator, a distillation column, by Kugelrohr distillation or short path distillation.

[0082] Distillation can also be carried out in several steps using one or a combination of different distillation techniques and can be carried out continuously or discontinuously.

[0083] Distillation can, in principle, be carried out in air or in the absence of oxygen. To avoid undesired oxidation reactions by the at least one at least monoalkyl-substituted diaminocyclohexane (A) or other compounds present in the composition (ZE) during distillation, distillation is preferably carried out in the absence of oxygen. "In the absence of oxygen" in the context of the present invention means that the volume fraction of oxygen in the distillation apparatus is less than 0.1 vol.%, preferably less than 0.1 vol.%, and particularly preferably less than 0.01 vol.%, based on the total volume of the distillation apparatus.

[0084] In principle, distillation can be carried out at any temperature. Distillation is preferably carried out at a temperature in the range of 70 to 180 °C, more preferably in the range of 80 to 170 °C, and particularly preferably in the range of 90 to 160 °C.

[0085] In principle, distillation can be carried out at any pressure. Distillation is preferably carried out at a pressure in the range of 0.1 to 500 mbar, more preferably in the range of 0.5 to 300 mbar, and particularly preferably in the range of 1 to 100 mbar.

[0086] In a preferred embodiment, the distillation is carried out at a temperature in the range from 70 to 180 °C, preferably in the range from 80 to 170 °C and particularly preferably in the range from 90 to 160 °C and at a pressure in the range from 0.1 to 500 mbar, preferably in the range from 0.5 to 300 mbar and particularly preferably in the range from 1 to 100 mbar.

[0087] The composition (ZP) obtained by the process according to the invention contains at least 0.05 wt.% water, based on the total weight of the composition (ZP).

[0088] The composition (ZP) contains 0.05 to 3 wt.%, preferably 0.10 to 2 wt.% and particularly preferably 0.15 to 1.5 wt.% of water, based on the total weight of the composition (ZP).

[0089] In principle, the water can have been added to the composition (ZP) in any way.

[0090] In one embodiment, at least a portion of the water contained in the composition (ZP) is already present in the composition (ZE), wherein the composition (ZE) preferably has a water content of 0.05 to 1 wt. %, preferably 0.08 to 0.8 wt. %, and particularly preferably 0.1 to 0.5 wt. %, based on the total weight of the composition (ZE). As already mentioned above, the water can, for example, be a residue from the preparation process of the at least one at least monoalkyl-substituted diaminocyclohexane (A).

[0091] If distillation is carried out before the addition of the at least one reducing agent (R), the water contained in the composition (ZE) is preferably not completely removed. If the composition (ZE) has a water content of 0.05 to 1 wt. %, preferably 0.08 to 0.8 wt. %, and particularly preferably 0.1 to 0.5 wt. %, based on the total weight of the composition (ZE), it is particularly preferred that no water be removed at all by distillation.

[0092] In the event that the composition (ZE) has a water content of more than 1 wt.%, based on the total weight of the composition (ZE), the distillation preferably separates off such an amount of water until the distilled composition (DZE) contains at most 1 wt.%, preferably at most 0.8 wt.% and particularly preferably 0.5 wt.% water, based on the total weight of the composition (DZE).

[0093] In a further embodiment, the process according to the invention additionally comprises the addition of water. The addition of water can be carried out by any method known to the person skilled in the art and is preferably carried out with stirring.

[0094] The addition of water can take place together with the at least one reducing agent (R) or before or after the addition of the at least one reducing agent (R).

[0095] The water that is added can in principle be any water, for example demineralized water or single or multiple distilled water.

[0096] If the at least one reducing agent (R) is added in a solution (L) containing water as solvent or in a suspension (S) containing water as solvent, the additional addition of water can in principle be omitted. However, water is preferably also added if the at least one reducing agent (R) was added in a solution (L) or in a suspension (S).

[0097] In a further embodiment, at least part of the water contained in the composition (ZP) is already contained in the composition (ZE) and the process according to the invention additionally comprises the addition of water.

[0098] The weight ratio of water to the at least one reducing agent (R) in the composition (ZP) is preferably at least 1:1, more preferably at least 2:1 and particularly preferably at least 4:1.

[0099] Furthermore, the weight ratio of water to the at least one reducing agent (R) in the composition (ZP) is preferably at most 100:1, preferably at most 50:1 and particularly preferably at most 30:1.

[0100] In a preferred embodiment, the weight ratio of water to the at least one reducing agent (R) in the composition (ZP) is preferably 100:1 to 1:1, preferably 50:1 to 2:1 and particularly preferably 30:1 to 4:1.

[0101] The water is preferably completely mixed in the composition (ZP). This means that the composition (ZP) preferably does not have separate water phases. Consequently, the water contained in the composition (ZP) preferably cannot be separated from the composition (ZP) by phase separation.

[0102] A further object of the present invention is the composition (ZP) which is prepared by the process according to the invention.

[0103] The composition (ZP) preferably contains the following components: 96.8 to 99.945 wt.% at least one at least monoalkyl-substituted diaminocyclohexane, 0.005 to 0.2 wt.% at least one reducing agent (R) and 0.05 to 3 wt.% Water.

[0104] The at least monoalkyl-substituted diaminocyclohexanes stabilized by the process according to the invention can be used as synthetic building blocks for the production of surfactants, pharmaceuticals and crop protection agents, stabilizers, light stabilizers, polymers, isocyanates, hardeners for epoxy resins, catalysts for polyurethanes, intermediates for the production of quaternary ammonium compounds, plasticizers, corrosion inhibitors, synthetic resins, ion exchangers, textile auxiliaries, dyes, vulcanization accelerators, emulsifiers and / or as starting substances for the production of ureas and polyureas.

[0105] A further subject matter of the present invention is thus also the use of the composition (ZP) for the production of surfactants, pharmaceuticals and crop protection agents, stabilizers, light stabilizers, polymers, isocyanates, hardeners for epoxy resins, catalysts for polyurethanes, intermediates for the production of quaternary ammonium compounds, plasticizers, corrosion inhibitors, synthetic resins, ion exchangers, textile auxiliaries, dyes, vulcanization accelerators, emulsifiers and / or as starting substances for the production of ureas and polyureas.

[0106] In particular, 1,3-diamino-2-methylcyclohexane and 1,3-diamino-4-methylcyclohexane can be used as monomer building blocks for polyamides, as hardeners for epoxy resins or as starting materials for the production of the corresponding isocyanates.

[0107] The following examples are intended to further illustrate the present invention, but do not limit the present invention thereto.

[0108] The Hazen color number according to APHA in the following examples is determined according to DIN EN ISO 6271 and is carried out using a Lange colorimeter (LICO 400). The Hazen color number is determined using Lange LZM 130 50 mm disposable plastic cuvettes. The measured samples each weigh 60 g. Example 1

[0109] Samples of an undistilled composition (ZE), which contains a mixture of 1,3-diamino-2-methylcyclohexane and 1,3-diamino-4-methylcyclohexane and 0.15 wt% water, are filled into 250 mL screw-capped vials, mixed with sodium borohydride and, if necessary, water to obtain a composition (ZP) and stored in an oven at 80°C (see experiments 1 and 2 in Table 1).

[0110] Likewise, 895 g of the composition (ZE) are distilled at 1 mbar and 104 °C (head temperature) through a distillation bridge. This yields 805 g of a distilled composition (DZE), which contains approximately 0.15 wt.% water. Samples of this distilled composition (DZE) are also filled into 250 mL screw-capped vials, mixed with sodium borohydride and, if necessary, water to obtain a composition (ZP), and stored in an oven at 80 °C (see experiments 3 to 9 in Table 1).

[0111] As a reference, an undistilled sample (V1) without sodium borohydride addition and a distilled sample (V2) without sodium borohydride addition are stored and measured. All samples are regularly opened, ventilated, and approximately 6 g are taken per measurement for color determination.

[0112] The corresponding experimental data are presented in Table 1. The columns show the Hazen color number at the times indicated in the top row. Table 1 Attempt NaBH 4 [wt.%] Water addition [wt%] 0h 24 h 48h 72h 96h 168 h 192 h 240h V1 - - 12 29 48 78 149 318 683 >1000 V2 - - 0 0 5 15 31 89 204 509 1 0,05 - 12 48 77 103 106 220 282 385 2 0,05 + 0,3 12 29 54 79 49 66 135 261 3 0,1 + 0,5 0 58 92 122 128 96 72 67 4 0,1 + 1,0 0 15 38 45 54 22 23 74 5 0,1 + 1,5 0 10 17 12 44 25 68 178 6 0,05 + 0,2 0 51 92 100 92 127 140 188 7 0,05 + 0,5 0 56 69 75 85 56 59 167 8 0,05 + 1,0 0 12 28 58 49 23 34 226 9 0,01 - 0 15 24 32 32 22 29 121

[0113] The experimental data presented in Table 1 show that the Hazen color number of the composition (ZP) can be kept significantly lower over the long term if at least one reducing agent (R) and, if appropriate, water are used (Experiments 1 to 9). If the composition (ZE) was first distilled and then at least one reducing agent (R) and, if appropriate, water were added (see Experiments 3 to 9), the Hazen color number is lower over a longer period than for undistilled stabilized compositions (ZP) (see Experiments 1 and 2). Example 2

[0114] Samples of an undistilled composition (ZE), which contains a mixture of 1,3-diamino-2-methylcyclohexane and 1,3-diamino-4-methylcyclohexane and 0.15 wt% water, are filled into 250 mL screw-capped vials, treated with sodium borohydride or Borol™< (12.5 wt% sodium borohydride in an aqueous, 14 molar solution of sodium hydroxide, available from Dow Chemicals) and, if necessary, water to obtain a composition (ZP) and stored in an oven at 80°C (see experiments 1 and 2 in Table 2).

[0115] Likewise, 860 g of the composition (ZE) were distilled at 1 mbar and 104 °C (head temperature) through a distillation bridge. This yielded 730 g of a distilled composition (DZE), which contained approximately 0.15 wt.% water. Samples of this distilled composition (DZE) were also filled into 250 mL screw-capped vials, mixed with sodium borohydride or borole and, if necessary, water to obtain a composition (ZP), and stored in an oven at 80 °C (see experiments 3 to 7 in Table 2).

[0116] As a reference, a distilled sample (test V3) without the addition of a reducing agent (R) is stored and measured. Since the undistilled composition (ZE) is identical to the undistilled composition (ZE) from Example 1, the reference measurement of the undistilled sample without the addition of a reducing agent (R) corresponds to Test V1 from Example 1. All samples are regularly opened, ventilated, and approximately 6 g are taken per measurement for color determination.

[0117] In experiments 1 to 5, Borol™< is used as the reducing agent (R), and in experiments 6 and 7, sodium borohydride is used as the reducing agent (R). The data on the weight fraction of at least one reducing agent (R) in Table 2 below always refer to the amount of sodium borohydride used. For example, if Borol™< is used as the reducing agent (R), the designation "0.02 wt.%" means that a specific amount of Borol™< is used until 0.02 wt.% sodium borohydride has been added using Borol™<.

[0118] The corresponding experimental data are shown in Table 2. The columns show the Hazen color number at the times indicated in the top row. Table 2 Attempt Reducing agent (R) [wt.%] Water addition [wt%] 0h 24 h 48h 72h 96h 168 h 192 h 240h V1 - - 12 29 48 78 149 318 683 >1000 V3 - - 0 1 3 12 30 102 251 538 1 0,02 - 0 71 116 155 208 368 487 653 2 0,04 - 0 105 97 97 130 412 360 501 3 0,01 - 0 8 14 15 12 24 33 152 4 0,02 - 0 10 17 22 16 20 35 218 5 0,04 - 0 32 63 72 83 67 83 185 6 0,02 + 0,1 0 19 38 39 52 34 41 115 7 0,04 +0,2 0 39 89 94 100 75 70 177

[0119] The experimental data presented in Table 2 show that the Hazen color number of the composition (ZP) can be kept significantly lower over the long term if at least one reducing agent (R) and, if appropriate, water are used (Experiments 1 to 7). If the composition (ZE) is first distilled and then at least one reducing agent (R) and, if appropriate, water are added (see Experiments 3 to 7), the Hazen color number is lower over a longer period than with undistilled stabilized compositions (ZP) (see Experiments 1 and 2). Example 3

[0120] 449 g of an undistilled composition (ZE), containing 99.76 wt.% of a mixture of 1,3-diamino-2-methylcyclohexane and 1,3-diamino-4-methylcyclohexane and 0.24 wt.% of other compounds, are distilled at 70 mbar and 136 °C (head temperature). 51 g of a first fraction are obtained and separated, followed by 343 g of a distilled composition (DZE). The distilled composition (DZE) contains no water.

[0121] Samples of this distilled composition (DZE) are filled into 250 mL screw-capped vials, mixed with a reducing agent (R) and stored in an oven at 80°C.

[0122] As a reference, a distilled sample (test V1) without the addition of a reducing agent (R) is stored and measured. All samples are regularly opened, ventilated, and approximately 6 g are taken per measurement for color determination.

[0123] In Experiment V2, Borol™< (12.5 wt.% sodium borohydride in an aqueous, 14 molar solution of sodium hydroxide, available from Dow Chemicals) is used as the reducing agent (R), and in Experiment V3, sodium borohydride is used as the reducing agent (R). The data on the weight proportions of the at least one reducing agent (R) in Table 3 below always refer to the amount of sodium borohydride used. If Borol™< is used as the reducing agent (R), the designation "0.1 wt.%," for example, means that a specific amount of Borol™< is used until 0.1 wt.% sodium borohydride has been added using Borol™<. When using Borol™<, the water content of the samples is always below 0.1 wt.%.

[0124] The corresponding experimental data are shown in Table 3. The columns show the Hazen color number at the times indicated in the top row. Table 3 Attempt Reducing agent (R) [wt.%] 0h 24 h 48h 72h 96h 168 h 192 h 240h V1 - 0 0 3 11 32 78 159 305 V2 0,1 0 3 9 45 104 253 402 791 V3 0,1 1 96 123 195 260 339 837 >1000

[0125] The experimental data presented in Table 3 show that for a long-term low Hazen color number, in addition to the at least one reducing agent (R), at least 0.05 wt.% water, based on the total weight of the composition (ZP), must be present in the composition (ZP). Example 4

[0126] Samples of an undistilled composition (ZE), which contains a mixture of 1,3-diamino-2-methylcyclohexane and 1,3-diamino-4-methylcyclohexane and 0.15 wt% water, are filled into 250 mL screw-capped vials, treated with sodium borohydride or a sodium borohydride stock solution to obtain a composition (ZP) and stored in an oven at 60°C (see experiments 1 and 2 in Table 4).

[0127] As a reference, an undistilled sample (V1) without sodium borohydride is stored and measured. All samples are regularly opened, ventilated, and approximately 6 g are taken per measurement for color determination.

[0128] The sodium borohydride stock solution is prepared as follows: 2 g of NaBH4 powder are placed in a 100 mL stirred flask equipped with a bubble counter under nitrogen, and then 18 g of the composition (ZE) are added. After one hour of stirring, the NaBH4 is almost completely dissolved, except for a few crystals. The supernatant solution is used as the NaBH4 stock solution.

[0129] The corresponding experimental data are shown in Table 4. The columns show the Hazen color number at the times indicated in the top row. Table 4 Attempt NaBH 4 [wt.%] Addition of stock solution [wt.%] 0h 24 h 48h 72h 144h 168 h 192 h 312 h 336 h 360 h 384 h 408 h V1 - - 21 27 36 47 89 106 128 233 277 326 386 454 1 0,01 - 21 41 36 35 48 57 67 107 122 141 171 183 2 - 0,01 21 38 32 32 51 60 70 111 129 147 172 198

[0130] The experimental data presented in Table 4 show that the Hazen color number of the composition (ZP) can be kept significantly lower in the long term when sodium borohydride or a sodium borohydride stock solution is used (Experiments 1 and 2).

Claims

1. A process for stabilizing at least monoalkyl-substituted diaminocyclohexanes comprising addition of at least one reductant (R) and optionally water to a composition (ZE) comprising at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water to obtain a composition (ZP), wherein the composition (ZP) comprises the at least one reductant (R), the at least one at least monoalkyl-substituted diaminocyclohexane (A) and additionally at least 0.05% by weight of water based on the total weight of the composition (ZP), wherein the at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from one of the compounds according to general formulae (I), (II) or (III) in which R1, R1', R2, R2', R3, R3', R4 and R4' are independently of one another selected from H and C1-C4-alkyl, wherein at least one radical R1, R1', R2, R2', R3, R3', R4 or R4' is C1-C4-alkyl. wherein said process comprises initially performing a distillation of the composition (ZE) to remove higher boiling byproducts and to obtain a distilled composition (DZE) comprising the at least one at least monoalkyl-substituted diaminocyclohexane (A) and optionally water followed by the addition of the at least one reductant (R) and optionally water to the distilled composition (DZE) to obtain the composition (ZP), wherein the composition (ZP) comprises 0.05 to 3% by weight of water based on the total weight of the composition (ZP).

2. The process according to claim 1, wherein the at least one at least monoalkyl-substituted diaminocyclohexane (A) is selected from 1,3-diamino-4-methylcyclohexane or 1,3-diamino-2-methylcyclohexane.

3. The process according to any of claims 1 to 2, wherein the composition (ZE) comprises at least 85% by weight, preferably at least 90% by weight and particularly preferably at least 95% by weight of the at least one at least monoalkyl-substituted diaminocyclohexane (A) based on the total weight of the composition (ZE).

4. The process according to any of claims 1 to 3, wherein the at least one reductant (R) is selected from lithium borohydride, sodium borohydride, potassium borohydride, sodium cyanoborohydride, lithium aluminum hydride, sodium aluminum hydride or potassium aluminum hydride; the at least one reductant (R) is preferably sodium borohydride.

5. The process according to any of claims 1 to 4, wherein the composition (ZP) comprises 0.005 to 0.2% by weight, preferably 0.007 to 0.15% by weight and particularly preferably 0.01 to 0.1% by weight of the at least one reductant (R) based on the total weight of the composition (ZP).

6. The process according to any of claims 1 to 5, wherein the at least one reductant (R) is added in the form of a solid, in a solution (L) or in a suspension (S) .

7. The process according to claim 6, wherein the mixture (G) comprises at least one basic compound (B) selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate or calcium carbonate.

8. The process according to claim 6 or 7, wherein the solution (L) comprises the following components: a) 5% to 20% by weight of the at least one reductant (R) , b) 10% to 65% by weight of the at least one basic compound (B) and c) 15% to 85% by weight of water, wherein the weight fractions of the components a), b) and c) altogether sum to 100% by weight.

9. The process according to claims 1 to 8, wherein i) the distillation is effected at a temperature in the range from 70°C to 180°C, preferably in the range from 80°C to 170°C and particularly preferably in the range from 90°C to 160°C, and / or ii) the distillation is effected at a pressure in the range from 0.1 to 500 mbar, preferably in the range from 0.5 to 300 mbar and particularly preferably in the range from 1 to 100 mbar.

10. The process according to any of claims 1 to 9, wherein i) at least a portion of the water present in the composition (ZP) is already present in the composition (ZE), wherein the composition (ZE) comprises a water content of 0.05% to 1% by weight, preferably of 0.08% to 0.8% by weight and particularly preferably of 0.1% to 0.5% by weight based on the total weight of the composition (ZE), and / or ii) the process additionally comprises the addition of water, and / or iii) at least a portion of the water present in the composition (ZP) is added together with the at least one reductant (R).

11. The process according to any of claims 1 to 10, wherein the composition (ZP) comprises 0.10% to 2% by weight and preferably 0.15% to 1.5% by weight of water based on the total weight of the composition (ZP).

12. The process according to any of claims 1 to 11, wherein the weight ratio of water to the at least one reductant (R) in the composition (ZP) is 100:1 to 1:1, preferably 50:1 to 2:1 and particularly preferably 30:1 to 4:1.

13. A composition (ZP) produced by the process according to any of claims 1 to 12.

14. The use of the composition (ZP) according to claim 13 for the production of surfactants, pharmaceutical and plant protection products, stabilizers, light stabilizers, polymers, isocyanates, hardeners for epoxy resins, catalysts for polyurethanes, intermediates for producing quaternary ammonium compounds, plasticizers, corrosion inhibitors, synthetic resins, ion exchangers, textile auxiliaries, dyes, vulcanization accelerators, emulsifiers and / or as starting materials for the production of ureas and polyureas.