Improved process for preparing para aminobenzoic acid-2-ethylhexyl ester

Abstract

The present invention relates to a process for the preparation of para aminobenzoic acid-2-ethylhexyl ester comprising reacting para nitrobenzoic acid-2-ethylhexyl ester with hydrogen in the presence of a catalyst wherein the reaction is carried out in water or in a mixture of water and 2-ethylhexanol. In addition, the present invention relates to para aminobenzoic acid-2-ethylhexyl ester obtained by the method and having high purity.

Description

[0001] The present invention relates to a method for preparing 2-ethylhexyl p-aminobenzoate, which comprises reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst, wherein the reaction is carried out in water or in a mixture of water and 2-ethylhexanol. In addition, the present invention relates to 2-ethylhexyl p-aminobenzoate obtained by the method and having high purity.

[0002] Ethylhexyl triazone (Uvinul T 150, CAS No. 88122-99-0) is a known highly effective UVB filter. Due to its beneficial physical and chemical properties, ethylhexyl triazone is widely used as an ingredient in various cosmetic preparations such as anti-aging facial care products and sunscreens. The superior photostability and absorptivity of ethylhexyl triazone result in high sun protection factors being achieved at only small concentrations. In addition, the polarity of the structure provides good solubility in cosmetic oils and a high affinity for skin keratin.

[0003] Therefore, an economically and environmentally optimal industrial process for the preparation of ethylhexyl triazone is highly desirable. Considering its contact with human skin when used in cosmetic preparations, high purity ethylhexyl triazone is required. Typically, ethylhexyl triazone is prepared in a three-step process starting from the esterification of p-nitrobenzoic acid. The formed p-nitrobenzoic acid-2-ethylhexyl ester is then reduced to p-aminobenzoic acid-2-ethylhexyl ester, which is then reacted with a cyanuric halide to form the final product.

[0004] With regard to the second step, i.e., the reduction of 2-ethylhexyl p-nitrobenzoate to 2-ethylhexyl p-aminobenzoate, EP 3 674 293 A1 discloses the reduction of p-nitrobenzoate by catalytic hydrogenation in a mixture of ethanol and methanol or using a catalyst and a reducing agent in an aprotic organic solvent. Furthermore, protic solvents are considered disadvantageous because these solvents (especially water) may cause unwanted side reactions in the subsequent reaction to form ethylhexyl triazone. The by-products thus produced would need to be removed, which requires an additional purification step.

[0005] CN 112321522 discloses a process for preparing 2-ethylhexyl p-aminobenzoate, wherein isooctyl p-aminobenzoate is reduced by catalytic hydrogenation in isooctyl alcohol.

[0006] In view of the high requirements on the purity of ethylhexyl triazone and also its starting materials, 2-ethylhexyl p-aminobenzoate of optimal product quality is required. Therefore, the object of the present invention is to provide an improved process for preparing 2-ethylhexyl p-aminobenzoate of optimal product quality.

[0007] In this respect, the object is to provide a method which ensures high product purity. In addition, the object is to provide an economically and environmentally advantageous method. In addition, the object is to provide a method which is technically and economically suitable for large-scale industrial applications.

[0008] It has surprisingly been found that at least some of the above objectives can be achieved by the subject matter of the present invention as described below and in the claims.

[0009] In one embodiment, the present invention relates to a method for preparing 2-ethylhexyl p-aminobenzoate, the method comprising reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst, wherein the reaction is carried out in the following:

[0010] (a) in water; or

[0011] (b) In a mixture of water and 2-ethylhexanol.

[0012] The inventors have surprisingly found that reacting in water or in a mixture of water and 2-ethylhexanol provides the desired product with high yield and purity, particularly without a significant amount of residual water.Reacting in water or in a mixture of water and 2-ethylhexanol is advantageous for heat dissipation due to the useful specific heat capacity provided by water.This is particularly applicable because the preparation of p-aminobenzoic acid-2-ethylhexyl according to the present invention is exothermic.In addition, since water forms as a by-product during the hydrogenation reaction, reacting in water is also advantageous, which avoids the additional mixing of the product and simplifies purification and solvent recycling.If reaction (a) is carried out in water, then at the end of the reaction, it is not necessary to remove additional solvent.In addition, there is no additional solvent mixed with water, which reduces complexity, waste and cost, because the solvent mixed with water will have to be wasted or dehydrated for recycling.Since 2-ethylhexanol can be used as a solvent in the previous method step of forming starting material p-nitrobenzoic acid-2-ethylhexyl ester, it is also beneficial to react (b) in a mixture of water and 2-ethylhexanol. In particular, 2-ethylhexyl p-nitrobenzoate can be used directly dissolved in 2-ethylhexanol, which reduces the complexity, waste and cost of the entire process. However, compared with reacting only in 2-ethylhexanol as in the prior art, the mixture with water provides a favorable specific heat capacity and therefore provides a favorable heat dissipation.

[0013] Thus, the present invention provides an environmentally and economically favorable process for preparing 2-ethylhexyl p-nitrobenzoate in high purity and yield, which is suitable for large-scale industrial applications.

[0014] In one embodiment of the present invention, the reaction is carried out in water.

[0015] In one embodiment of the present invention, the catalyst is a noble metal, preferably palladium, Raney nickel, rhodium, platinum or a mixture thereof.

[0016] In one embodiment of the present invention, the reaction is carried out at a temperature of 70°C to 150°C under a hydrogen pressure of up to 100 bar for a period of up to 24 h.

[0017] In one embodiment of the present invention, after the reaction is completed, the reaction mixture is maintained under hydrogen pressure for a aging time of at least 60 min, preferably at least 90 min.

[0018] In one embodiment of the present invention, 2-ethylhexyl p-aminobenzoate is purified by distillation.

[0019] In one embodiment of the present invention, a stabilizer is added for distillation, wherein the stabilizer is selected from ascorbic acid, butylated hydroxytoluene (BHT), tocopherol such as vitamin E, carotenoids, or a mixture thereof.

[0020] In one embodiment of the present invention, the method further comprises preparing 2,4,6-triphenylamino-p-(carbonyl-2'-ethylhexyl-1'-oxy)-1,3,5-triazine having the following chemical formula by reacting cyanuric halide with p-aminobenzoic acid-2-ethylhexyl ester in a non-polar solvent

[0021]

[0022] In one embodiment of the present invention, the method further comprises preparing 2-ethylhexyl p-nitrobenzoate, comprising reacting p-nitrobenzoic acid with 2-ethylhexanol.

[0023] In one embodiment, the present invention is directed to 2-ethylhexyl p-aminobenzoate having a purity of at least 94% by weight.

[0024] In one embodiment, the present invention relates to 2-ethylhexyl p-aminobenzoate, wherein bis(2-ethylhexyl)-4,4'-(diazene-1,2-diyl)(E)-dibenzoate having the following chemical formula

[0025]

[0026] The amount is less than 3000ppm.

[0027] In one embodiment, the present invention relates to 2-ethylhexyl p-aminobenzoate obtained by the process of the present invention.

[0028] Preferred embodiments of the present invention can be found in the claims, the specification and the examples. It should be understood that the above-mentioned features of the subject matter of the present invention and those features to be described below are preferred not only in the respective given combinations, but also in other combinations without departing from the scope of the present invention.

[0029] In conjunction with the above embodiments of the present invention, the following definitions are provided.

[0030] In the context of the present invention, 2-ethylhexyl p-aminobenzoate is obtained by a process comprising reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst, wherein the reaction is carried out (a) in water; or (b) in a mixture of water and 2-ethylhexanol.

[0031] As used herein, "p-aminobenzoic acid-2-ethylhexylester" refers to p-aminobenzoic acid-2-ethylhexylester, which means 4-aminobenzoic acid-2-ethylhexylester.

[0032] As used herein, "p-nitrobenzoic acid-2-ethylhexylester" refers to para-nitrobenzoic acid-2-ethylhexylester, which means 4-nitrobenzoic acid-2-ethylhexylester.

[0033] As used herein, a "catalyst" is a homogeneous or heterogeneous catalyst suitable for a hydrogenation reaction. Exemplary catalysts are catalysts containing palladium, nickel, rhodium, platinum, iridium, ruthenium, iron, or mixtures thereof. Preferably, the catalyst is a noble metal or a mixture thereof. More preferably, the catalyst is palladium, Raney nickel, rhodium, platinum, or a mixture thereof.

[0034] As used herein, "water" refers to deionized water, demineralized water or distilled water, which refers to water purified in a manner such that its (most of) mineral ions and salt ions are removed. As used herein, if reaction (a) is carried out in water or (b) in a mixture of water and 2-ethylhexanol, this refers to water being actively added to the reaction mixture at the start of the reaction, rather than water being present in the amount formed only during the reaction. The method may therefore include adding water or a mixture of water and 2-ethylhexanol to a reactant (i.e. p-nitrobenzoic acid-2-ethylhexyl) or a step in a reaction mixture comprising the reactant at the start of the reaction. Therefore, the inventive method may include the first step of merging p-nitrobenzoic acid-2-ethylhexyl and alternatively a catalyst with a solvent (i.e. water or a water-2-ethylhexanol mixture) before the reaction starts. Then, the reaction may be started by starting hydrogen to feed into the previously formed mixture.

[0035] In various embodiments, the present invention therefore relates to a method for preparing 2-ethylhexyl p-aminobenzoate by reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst, the method comprising

[0036] providing a reaction mixture comprising 2-ethylhexyl p-nitrobenzoate and a catalyst in (a) water or (b) a mixture of water and 2-ethylhexanol; and

[0037] The reaction of 2-ethylhexyl p-nitrobenzoate with hydrogen is carried out in said water or in said mixture of water and 2-ethylhexanol in the presence of a catalyst.

[0038] Preferably, in (b), water is present in a ratio of at least 1:2, more preferably at least 1:1 and even more preferably at least 2:1 relative to 2-ethylhexanol. These ratios are preferably weight ratios, but in some embodiments, can be volume ratios. Both options are therefore covered by the given ratios of at least 2:1, at least 1:1 and at least 1:2. In the preferred mixture (b), the amount of 2-ethylhexanol is the amount of 2-ethylhexanol in which the starting material p-nitrobenzoic acid-2-ethylhexyl ester is dissolved, or the starting material p-nitrobenzoic acid-2-ethylhexyl ester is admixed with 2-ethylhexanol and no additional 2-ethylhexanol is added.

[0039] In some embodiments of the present invention, after the reaction is completed, the reaction mixture is maintained under hydrogen pressure for a slaking time. As used herein, "slaking time" refers to the time period after the reaction is completed, wherein the reaction mixture is maintained under hydrogen pressure. Therefore, the reaction is only carried out for the time required for the reaction to be completed. If a time period is given for the reaction, the time period only refers to such a time range, wherein the reaction is completed depending on given conditions and even if the given time period includes a longer reaction time, the time for the reaction to be carried out does not exceed the time necessary for completing the reaction. For example, if the reaction is carried out for a time period of up to 24h, the reaction is carried out for less than 24h, and if the reaction is completed after 15h, in this case, the reaction is carried out for 15h. Then, the slaking time begins. As used herein, "maintaining under hydrogen pressure" means that hydrogen is not completely released from the reaction vessel / reactor. This includes maintaining a similar, reduced or increased hydrogen pressure compared to the reaction. Preferably, the hydrogen pressure during the slaking time is similar to the hydrogen pressure during the reaction, or refers to the hydrogen pressure generated in the container / reactor after closing the hydrogen valve. When at least one of the reactants is completely converted and / or when the amount of at least one of the reactants no longer changes, the reaction time ends and the aging time begins. In particular, when p-nitrobenzoic acid-2-ethylhexyl is completely converted or the amount of p-nitrobenzoic acid-2-ethylhexyl has reached a minimum value and / or hydrogen consumption has reached a minimum value, the aging time of the inventive method begins. As used herein, "reaching a minimum value" refers to the absolute minimum value that has been reached so that the amount of p-nitrobenzoic acid-2-ethylhexyl or hydrogen consumption no longer changes. In order to determine the completion of the reaction and the beginning of the aging time, methods known to those skilled in the art, such as thin layer chromatography, GC, HPLC or NMR monitoring reactions can be used. If p-nitrobenzoic acid-2-ethylhexyl is no longer detected or the reduction of the amount of p-nitrobenzoic acid-2-ethylhexyl is no longer detected, the reaction is completed, and the aging time begins. In addition, the completion of the reaction and the beginning of the aging time can be determined by monitoring the amount of hydrogen consumption, such as by monitoring the hydrogen flow while maintaining a constant hydrogen pressure. If the hydrogen flow has reached a minimum value while maintaining a constant hydrogen pressure, the reaction is complete and the aging time begins. During the aging time, the reaction mixture is kept under hydrogen pressure. Thus, the aging time ends with the release of excess hydrogen from the reaction vessel / reactor.

[0040] In certain embodiments, the product is purified by distillation, wherein a stabilizer is used. As used herein, "stabilizer" refers to a stabilizer or a mixture of stabilizers for stabilizing the product p-aminobenzoic acid-2-ethylhexyl ester during distillation, for example, by preventing the polymerization and / or oxidation of p-aminobenzoic acid-2-ethylhexyl ester. Therefore, the stabilizer can be an acid and / or a base, such as a carboxylic acid and / or a carboxylic acid salt, to neutralize the acid and / or base present in the mixture, and these acids and / or bases present in the mixture induce the polymerization of p-aminobenzoic acid-2-ethylhexyl ester. In addition, the stabilizer can be an antioxidant. Exemplary stabilizers are ascorbic acid, butylated hydroxytoluene (BHT), tocopherols such as vitamin E, carotenoids or mixtures thereof. A preferred stabilizer is ascorbic acid.

[0041] As used herein, pressure indicated by the pressure unit "bar" refers to relative pressure or gauge pressure, which is zero-referenced to ambient air pressure and is therefore equal to absolute pressure minus atmospheric pressure. Gauge pressure may also be indicated by the pressure unit "bar gauge". Pressure refers to absolute pressure only when the pressure unit "bar (absolute)" is used.

[0042] Preferred embodiments of the method of the present invention are described below.

[0043] The following general considerations apply to this approach.

[0044] Typically, the reaction step is carried out in a reaction vessel commonly used for such reactions, such as a conventional stirred tank reactor. The reaction can be carried out in a continuous, semi-batch or batch mode. Preferably, the method of the present invention is carried out in a batch mode, wherein all reactants are provided in a reaction vessel before starting the reaction.

[0045] The details about reaction pressure and temperature are provided below. If not otherwise specified, these process steps are preferably carried out under atmospheric pressure. The completion of the reaction can be monitored by methods known to those skilled in the art, for example, thin layer chromatography, GC, HPLC or NMR.

[0046] If not indicated otherwise, the reactants can in principle be brought into contact with one another in any desired order.

[0047] Furthermore, it is emphasized that the reaction can be performed on both laboratory and industrial scales.

[0048] In the following, preferred embodiments of the present invention are provided. It should be understood that the preferred embodiments of the present invention are preferred individually or in combination with each other.

[0049] As indicated above, the present invention relates to a method for preparing p-aminobenzoic acid-2-ethylhexyl ester, the method comprises reacting p-nitrobenzoic acid-2-ethylhexyl ester with hydrogen in the presence of a catalyst, wherein the reaction (a) is carried out in water or (b) in a mixture of water and 2-ethylhexyl alcohol. If the reaction is carried out in water or in a mixture of water and 2-ethylhexyl alcohol, water provides a favorable specific heat capacity and therefore a favorable heat dissipation of the reaction mixture, which is particularly relevant for the exothermic preparation of p-aminobenzoic acid-2-ethylhexyl ester. In addition, since water also forms as a by-product during the reaction, the quantity of impurities in the mixture will not increase by adding water to the reaction mixture. If reaction (a) is carried out in water, except that water is used, it is not necessary to remove the solvent impurities. Since water forms as a by-product during the reaction, it must be removed in any case, so the method of the present invention reduces the complexity of product purification and recycling and therefore reduces the waste and cost of the method. Therefore, in one embodiment of the invention, the reaction is carried out in water. It is also possible to use the starting material p-nitrobenzoic acid-2-ethylhexyl ester dissolved in 2-ethylhexanol or mixed with 2-ethylhexanol. This is particularly advantageous, because the previous step of preparing p-nitrobenzoic acid-2-ethylhexyl ester can be carried out in 2-ethylhexanol, so that the step of removing the solvent before the reaction of the present invention can be avoided or reduced, and the complexity, waste and cost of the whole method for preparing p-aminobenzoic acid-2-ethylhexyl ester are positively affected. In this case as well, adding water provides a favorable specific heat capacity as a solvent and therefore provides a favorable heat dissipation of the reaction mixture. Therefore, in one embodiment of the invention, the reaction is carried out in a mixture of water and 2-ethylhexanol. In one embodiment, the reaction is carried out in a mixture of water and 2-ethylhexanol, wherein the weight ratio of water to 2-ethylhexanol is at least 1:2. In another embodiment, the reaction is carried out in a mixture of water and 2-ethylhexanol, wherein the weight ratio of water to 2-ethylhexanol is at least 1:1. In another embodiment, the reaction is carried out in a mixture of water and 2-ethylhexanol, wherein the weight ratio of water to 2-ethylhexanol is at least 2:1. Increasing the amount of water relative to the amount of 2-ethylhexanol increases the specific heat capacity of the reaction mixture, which has a positive effect on heat dissipation. Therefore, in a preferred embodiment, the amount of 2-ethylhexanol in the mixture of water and 2-ethylhexanol is such an amount of 2-ethylhexanol that the starting material 2-ethylhexyl p-nitrobenzoate is dissolved therein, or the starting material 2-ethylhexyl p-nitrobenzoate is admixed with 2-ethylhexanol and no additional 2-ethylhexanol is added.

[0050] In addition, in one embodiment of the invention, before reacting with hydrogen, the pH value is adjusted to a value in the range of 4 to 10. In another embodiment, the pH value is adjusted to a neutral value. In one embodiment, sodium hydroxide is used to adjust the pH value. By adjusting the pH before reacting with hydrogen, the purity of p-aminobenzoic acid-2-ethylhexyl ester can be improved.

[0051] In one embodiment of the invention, the catalyst is a noble metal. Preferably, the catalyst is selected from the group consisting of palladium, Raney nickel, rhodium, platinum and mixtures thereof. In one embodiment, the catalyst is palladium. In another embodiment, the catalyst is palladium carbon (Pd / C). In another embodiment, the catalyst is palladium carbon (Pd / C), wherein the amount of palladium is in the range of 1 weight-% to 10 weight-% palladium. In another embodiment, the catalyst is 2 weight-% palladium carbon (Pd / C). The amount of the catalyst refers to the amount of the noble metal relative to the amount of p-nitrobenzoic acid-2-ethylhexyl ester. In one embodiment, a noble metal of 0.002-0.005 weight-% relative to p-nitrobenzoic acid-2-ethylhexyl ester is used. In another embodiment, a noble metal of 0.003-0.004 weight-% relative to p-nitrobenzoic acid-2-ethylhexyl ester is used.

[0052] The reaction is carried out for a period of time until the reaction is completed. Then, the aging time begins. Therefore, depending on the applied hydrogen pressure and temperature, the reaction time can vary. For example, by reacting under a higher hydrogen pressure, the reaction time can be made shorter. In order to determine the completion of the reaction, the reaction can be monitored by methods known to those skilled in the art, such as thin layer chromatography, GC, HPLC, or NMR. If p-nitrobenzoic acid-2-ethylhexyl ester is no longer detected or the reduction of the amount of p-nitrobenzoic acid-2-ethylhexyl ester is no longer detected, the reaction is completed. In addition, the completion of the reaction can be determined by monitoring the amount of hydrogen consumption, such as by monitoring the hydrogen flow rate while maintaining a constant hydrogen pressure. If the hydrogen flow rate has reached a minimum value while maintaining a constant hydrogen pressure, the reaction is completed. In one embodiment of the present invention, the reaction is carried out at a temperature of 70°C to 150°C under a hydrogen pressure of up to 100 bar for a period of up to 24h. In another embodiment, the reaction is carried out at a temperature of 70°C to 150°C under a hydrogen pressure of 1 to 50 bar for a period of up to 24h. In another embodiment, the reaction is carried out at a temperature of 70°C to 150°C at a hydrogen pressure of 2 to 20 bar for a period of up to 24 h. In another embodiment, the reaction is carried out at a temperature of 70°C to 150°C at a hydrogen pressure of 7 to 10 bar for a period of up to 24 h.

[0053] In one embodiment of the invention, the reaction is carried out at a temperature of 80°C to 120°C at a hydrogen pressure of up to 100 bar for a period of up to 24 hours. In another embodiment, the reaction is carried out at a temperature of 80°C to 120°C at a hydrogen pressure of 1 to 50 bar for a period of up to 24 hours. In another embodiment, the reaction is carried out at a temperature of 80°C to 120°C at a hydrogen pressure of 2 to 20 bar for a period of up to 24 hours. In another embodiment, the reaction is carried out at a temperature of 80°C to 120°C at a hydrogen pressure of 7 to 10 bar for a period of up to 24 hours.

[0054] In one embodiment of the invention, the reaction is carried out at a temperature of 90°C to 100°C at a hydrogen pressure of up to 100 bar for a period of up to 24 hours. In another embodiment, the reaction is carried out at a temperature of 90°C to 100°C at a hydrogen pressure of 1 to 50 bar for a period of up to 24 hours. In another embodiment, the reaction is carried out at a temperature of 90°C to 100°C at a hydrogen pressure of 2 to 20 bar for a period of up to 24 hours. In another embodiment, the reaction is carried out at a temperature of 90°C to 100°C at a hydrogen pressure of 7 to 10 bar for a period of up to 24 hours. In a specific embodiment of the invention, the reaction is carried out at a temperature of 90°C to 100°C at a hydrogen pressure of 2 to 20 bar for a period of 10 hours to 20 hours. In another specific embodiment, the reaction is carried out at a temperature of 90°C to 100°C at a hydrogen pressure of 7 to 10 bar for a period of 13 hours to 17 hours. As described above, the reaction is carried out for no longer than the time necessary to complete the reaction. If a time period is given for a reaction, the time period refers only to the time range in which the reaction is completed depending on the given conditions and even if the given time period includes a longer reaction time, the reaction is carried out for no longer than the time necessary to complete the reaction. For example, if the reaction is carried out for a period of up to 24 hours, the reaction is carried out for less than 24 hours, and if the reaction is completed after 15 hours, in this case, the reaction is carried out for 15 hours. Then, the aging time begins.

[0055] The inventors have surprisingly found that providing an aging time in which the reaction mixture is maintained under hydrogen pressure after the reaction is complete improves the purity of 2-ethylhexyl p-aminobenzoate. In particular, contamination with the azo compound bis(2-ethylhexyl)-4,4'-(diazene-1,2-diyl)(E)-dibenzoate having the formula

[0056]

[0057] As a by-product.

[0058] Therefore, in one embodiment of the invention, after the reaction is completed, the reaction mixture is maintained at a hydrogen pressure for a aging time of at least 60min, preferably at least 90min. In another embodiment, after the reaction is completed, the reaction mixture is maintained at a hydrogen pressure for a aging time of at least 2h. In another embodiment, after the reaction is completed, the reaction mixture is maintained at a hydrogen pressure for a aging time of at least 3h. In another embodiment, after the reaction is completed, the reaction mixture is maintained at a hydrogen pressure for a aging time of 2h to 4h. In another embodiment, after the reaction is completed, the reaction mixture is maintained at a hydrogen pressure for a aging time of 2.5 to 3.5h. Extending the aging time will not negatively affect the formation of azo compounds, reduce or avoid, but reduce the space-time yield, i.e. the yield obtained per space and time in the reactor / container, which increases the cost. In one embodiment, the hydrogen pressure during the aging time is 2 bar to 20 bar. In another embodiment, the hydrogen pressure during the aging time is 7 to 10 bar. In one embodiment, the hydrogen pressure during the aging time is similar to the hydrogen pressure during the reaction or the hydrogen pressure generated in the reactor / container after closing the hydrogen valve. In another embodiment, the hydrogen pressure during the aging time is similar to the hydrogen pressure during the reaction 1.5 to 2h, followed by the hydrogen pressure generated in the reactor / container after closing the hydrogen valve 0.5 to 1.5h. In one embodiment, the temperature during the aging time is 70°C to 150°C. In another embodiment, the temperature during the aging time is 80°C to 120°C. In another embodiment, the temperature during the aging time is 90°C to 100°C. In one embodiment, the temperature during the aging time is similar to the reaction temperature. In another embodiment, the temperature during the aging time is similar to the reaction temperature, and the hydrogen pressure during the aging time is similar to the hydrogen pressure during the reaction for 1.5 to 2h, followed by the hydrogen pressure generated in the reactor / container after closing the hydrogen valve for 0.5 to 1.5h. In another embodiment, the temperature during the aging time is 70°C to 100°C, and the hydrogen pressure during the aging time is 2 bar to 20 bar for 1.5 to 2 hours, followed by the hydrogen pressure generated in the reactor / container after closing the hydrogen valve for 0.5 to 1.5 hours.

[0059] In order to further purify 2-ethylhexyl p-aminobenzoate, the solvent and optionally the reaction byproducts can be removed by distillation. Therefore, in one embodiment of the invention, 2-ethylhexyl p-aminobenzoate is purified by distillation. The solvent removed by distillation can be recycled. In particular, the solvent can be used again in the next process of reducing 2-ethylhexyl p-nitrobenzoate to 2-ethylhexyl p-aminobenzoate. In addition, in one embodiment of the invention, a stabilizer is added for distillation. In particular, the stabilizer can be a compound or more than one compound. In one embodiment, the stabilizer is a compound. Adding a stabilizer improves the yield and purity of 2-ethylhexyl p-aminobenzoate, in particular by preventing the polymerization and / or oxidation of 2-ethylhexyl p-aminobenzoate. Therefore, in one embodiment, the stabilizer is a carboxylic acid and / or a salt of a carboxylic acid to neutralize the acid and / or base present in the mixture, and these acids and / or bases induce the polymerization of 2-ethylhexyl p-aminobenzoate. In another embodiment, the stabilizer is an antioxidant. In another embodiment, the stabilizer is an antioxidant and a carboxylic acid and / or a salt of a carboxylic acid. In one embodiment, the stabilizer is selected from the group consisting of ascorbic acid, butylated hydroxytoluene (BHT), tocopherol, or a mixture thereof. In one embodiment, the stabilizer is ascorbic acid or a mixture with ascorbic acid, preferably, the stabilizer is ascorbic acid.

[0060] In one embodiment of the invention, after reacting with hydrogen, the reaction mixture is filtered to remove the solid catalyst and the phase separation of the filtrate is carried out. In one embodiment, the catalyst is removed with a bag filter. In one embodiment, the phase separation is carried out by adding carbonate. The water content in the organic phase is further reduced by adding carbonate to carry out phase separation. Therefore, the purity of p-aminobenzoic acid-2-ethylhexyl ester in the organic phase is improved. In addition, removing water from p-aminobenzoic acid-2-ethylhexyl ester product is particularly advantageous for subsequent p-aminobenzoic acid-2-ethylhexyl ester to react with cyanuric halide to generate ethylhexyl triazone, because cyanuric halide tends to hydrolyze, produces single-, two- and / or trihydroxy-triazine, which must be removed by additional process steps.

[0061] As indicated above, the process of the present invention provides a process for preparing 2-ethylhexyl p-aminobenzoate, which is an important precursor for preparing the known highly effective UV absorber ethylhexyl triazone (Uvinul T 150, CAS No.: 88122-99-0). The ethylhexyl triazone represents 2,4,6-triphenylamino-p-(carbonyl-2'-ethylhexyl-1'-oxy)-1,3,5-triazine. Therefore, in another embodiment, the process further comprises preparing 2,4,6-triphenylamino-p-(carbonyl-2'-ethylhexyl-1'-oxy)-1,3,5-triazine having the following chemical formula by reacting cyanuric halide with 2-ethylhexyl p-aminobenzoate in a non-polar solvent.

[0062]

[0063] Preferably, cyanuric halide and p-aminobenzoic acid-2-ethylhexyl are reacted in a molar ratio of 1:3 to 1:5. The complete conversion of cyanuric halide is allowed by reacting cyanuric halide and p-aminobenzoic acid-2-ethylhexyl with a molar ratio of at least 1:3, because 3 equivalents of p-aminobenzoic acid-2-ethylhexyl are required to form ethylhexyl triazone relative to 1 equivalent of cyanuric halide. Therefore, the improved method for preparing p-aminobenzoic acid-2-ethylhexyl is also advantageous for the preparation of ethylhexyl triazone. Improve the purity of p-aminobenzoic acid-2-ethylhexyl, reduce the complexity, waste and cost of its preparation simultaneously, and also reduce the overall complexity, waste and cost of preparing ethylhexyl triazone. Considering the high demand for ethylhexyl triazone, this is particularly advantageous because it has multiple applications as UV absorber.

[0064] In addition, p-aminobenzoic acid-2-ethylhexyl is prepared by reacting p-nitrobenzoic acid-2-ethylhexyl with hydrogen. Therefore, in one embodiment of the invention, the method further comprises preparing p-nitrobenzoic acid-2-ethylhexyl, comprising reacting p-nitrobenzoic acid with 2-ethylhexanol. In one embodiment, the p-nitrobenzoic acid-2-ethylhexyl prepared by this method is directly used in subsequent reactions, to prepare p-aminobenzoic acid-2-ethylhexyl, without the need for purification or removal of solvent. If the preparation of p-nitrobenzoic acid-2-ethylhexyl is carried out in water or 2-ethylhexanol or its mixture or in the absence of any solvent, this is particularly applicable.

[0065] As mentioned above, high purity can be obtained by the method of the present invention. Therefore, in one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate, which has a purity of at least 94% by weight or at least 94% as determined by GC (AUC). The purity can be higher, for example at least 95% or at least 96%, or even at least 97% or 98%. In particular, the confounding of azo compound bis (2-ethylhexyl) -4,4'- (diazene -1,2-diyl) (E) - dibenzoate is significantly reduced or even avoided by maintaining the reaction mixture under hydrogen pressure for a continuous aging time after the reaction is completed. Therefore, in one embodiment, the present invention relates to 2-ethylhexyl p-aminobenzoate, wherein there is bis (2-ethylhexyl) -4,4'- (diazene -1,2-diyl) (E) - dibenzoate of the following chemical formula

[0066]

[0067] The amount is less than 3000 ppm, such as less than 2500 ppm or less than 2000 ppm.

[0068] In addition, in one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate, which is obtained by the process of the present invention. This can be characterized by a small amount of the azo compound bis(2-ethylhexyl)-4,4'-(diazene-1,2-diyl)(E)-dibenzoate as described above.

[0069] The present invention is further illustrated by the following examples.

[0070] Examples

[0071] In the examples, GC analysis was performed on an Agilent Technologies 6890N using the following conditions and parameters:

[0072] Detector: FID

[0073] Solvent: Acetonitrile

[0074] Column: Optima 5 (30m, 0.32mm ID, 0.25μm film thickness)

[0075] Carrier gas: Nitrogen

[0076] Example 1: Preparation of 2-ethylhexyl p-aminobenzoate without aging

[0077] 8 kg of 2-ethylhexyl p-nitrobenzoate were added under stirring to a reactor precharged with 0.75 L of deionized water. The pH of the mixture was adjusted to a neutral value using sodium hydroxide (50 weight-% in water).

[0078] Under stirring, add 0.015kg catalyst (2 weight-% palladium carbon) to the reactor. The temperature is adjusted to 95 ℃ and the hydrogen of 9 bar gauge pressure is introduced under vigorous stirring. While maintaining the pressure of 9 bar gauge pressure, the hydrogen flow is always closely monitored. If the hydrogen flow reaches the minimum value, the reaction stops. Then, release the residual hydrogen. Use a bag filter to remove the residual catalyst from the reaction mixture. Stop the agitator to allow the organic phase containing the product to be separated from the aqueous phase. Then the lower layer phase consisting of water is removed from the bottom of the reactor. The organic phase containing the product p-aminobenzoic acid-2-ethylhexyl ester is retained in the reactor and analyzed subsequently. The output is 7.14kg organic phase. Use GC to characterize the final product, and use Karl-Fischer titration to measure the water content. The results are shown in Table 1.

[0079] Table 1

[0080] Water content 2.0 weight-% Azoamino esters 9.4 Area-% 2-Ethylhexyl p-aminobenzoate 85.0 Area-% 2-Ethylhexyl p-nitrobenzoate 0.1 Area-%

[0081] Example 2: Preparation of 2-ethylhexyl p-aminobenzoate with aging

[0082] 8 kg of 2-ethylhexyl p-nitrobenzoate were added under stirring to a reactor precharged with 0.75 L of deionized water. The pH of the mixture was adjusted to a neutral value using sodium hydroxide (50 weight-% in water).

[0083] 0.015 kg of catalyst (2 wt-% palladium on carbon) was added to the reactor with stirring.

[0084] The temperature was adjusted to 95°C and hydrogen was introduced at 9 bar gauge under vigorous stirring. While maintaining a pressure of 9 bar gauge, the hydrogen flow was always closely monitored. Once the hydrogen flow reached a minimum, the hydrogen pressure was maintained for a further 120 minutes. The hydrogen valve was then closed and aging was continued for a further 60 minutes. The residual hydrogen was then released.

[0085] The residual catalyst was removed from the reaction mixture using a bag filter.

[0086] The organic phase of product is separated with water by stopping agitator.Then the lower layer consisting of water is removed from the bottom of the reactor.The organic phase containing product p-aminobenzoic acid-2-ethylhexyl ester is retained in the reactor, and analyzed subsequently.Output is 7.14kg organic phase.GC is used to characterize the final product, and Karl-Fischer titration is used to measure water content.The results are shown in Table 2.

[0087] Table 2

[0088]

[0089]

Claims

1. A method for preparing 2-ethylhexyl p-aminobenzoate, the method comprising reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst, wherein the reaction is carried out in the following steps: (a) in water; or (b) In a mixture of water and 2-ethylhexanol The process comprises adding the water (a) or a mixture of water and 2-ethylhexanol to the reaction mixture at the start of the reaction.

2. The method according to claim 1, wherein: The reaction is carried out in water, and wherein the process comprises adding said water to the reaction mixture at the start of the reaction.

3. The method according to claim 1, wherein: The reaction is carried out in a mixture of water and 2-ethylhexanol, wherein the ratio of water to 2-ethylhexanol is at least 1:2, preferably at least 1:1, more preferably at least 2:1, and wherein the process comprises adding said mixture of water and 2-ethylhexanol to the reaction mixture at the start of the reaction.

4. The method according to any one of claims 1 to 3, wherein: The catalyst is a noble metal, preferably palladium, Raney nickel, rhodium, platinum or a mixture thereof.

5. The method according to any one of claims 1 to 4, wherein: The reaction is carried out at a temperature of 70°C to 150°C under a hydrogen pressure of up to 100 bar for a period of up to 24 h.

6. The method according to any one of claims 1 to 5, wherein: After the reaction is complete, the reaction mixture is kept under hydrogen pressure for an aging time of at least 60 min, preferably at least 90 min.

7. The method according to any one of claims 1 to 6, wherein: The 2-ethylhexyl p-aminobenzoate was purified by distillation.

8. The method according to claim 7, wherein: A stabilizer is added for distillation, wherein the stabilizer is selected from ascorbic acid, butylated hydroxytoluene (BHT), tocopherol such as vitamin E, carotenoids, or mixtures thereof.

9. The method according to any one of claims 1 to 8, wherein: The method further comprises preparing 2,4,6-triphenylamino-p-(carbonyl-2'-ethylhexyl-1'-oxy)-1,3,5-triazine having the following chemical formula by reacting cyanuric halide with p-aminobenzoic acid-2-ethylhexyl ester in a non-polar solvent 10. The method according to any one of claims 1 to 9, wherein: The method further includes preparing 2-ethylhexyl p-nitrobenzoate, comprising reacting p-nitrobenzoic acid with 2-ethylhexanol.

11. 2-Ethylhexyl p-aminobenzoate having a purity of at least 94% by weight or 94% as determined by GC, wherein bis(2-ethylhexyl)-4,4'-(diazen-1,2-diyl)(E)-dibenzoate having the formula The amount is less than 3000ppm.

12. 2-Ethylhexyl p-aminobenzoate according to claim 11, which is obtained by the method according to any one of claims 1 to 7, wherein In the process, after the reaction is completed, the reaction mixture is kept under hydrogen pressure for an aging time of at least 60 min, preferably at least 90 min.

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