Improved process for preparing p-nitrobenzoic acid-2-ethylhexyl ester

Abstract

The present invention relates to a process for preparing 2-ethylhexyl p-nitrobenzoate, comprising reacting p-nitrobenzoic acid in which excess 2-ethylhexanol acts as a solvent and no additional solvent is added, or in which p-nitrobenzoic acid and 2-ethylhexanol are provided in equimolar amounts and no additional solvent is added, or in which 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added. Furthermore, the present invention relates to 2-ethylhexyl p-nitrobenzoate obtained by this process and having high purity and optimal product properties.

Description

[Technical Field]

[0001] The present invention relates to a process for preparing 2-ethylhexyl p-nitrobenzoate, comprising reacting p-nitrobenzoic acid in which excess 2-ethylhexanol acts as a solvent and no additional solvent is added, or in which p-nitrobenzoic acid and 2-ethylhexanol are provided in equimolar amounts and no additional solvent is added, or in which 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added. Furthermore, the present invention relates to 2-ethylhexyl p-nitrobenzoate obtained by this process and having high purity and optimal product properties. [Background technology]

[0002] Ethylhexyl triazone (Uvinul T150, CAS number: 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 formulations, such as anti-aging face care products and sunscreens. The excellent photostability and absorption properties of ethylhexyl triazone result in very low concentrations being required to achieve a high sun protection factor. Furthermore, the polarity of this structure provides good solubility in cosmetic oils and a high affinity for skin keratin.

[0003] Therefore, an economically and environmentally optimal industrial process for preparing ethylhexyl triazone is highly desirable. Typically, ethylhexyl triazone is prepared in a three-step process starting with the esterification of p-nitrobenzoic acid. The resulting p-nitrobenzoic acid-2-ethylhexyl ester is then reduced to p-aminobenzoic acid-2-ethylhexyl ester, which is then reacted with cyanuric halide to give the final product.

[0004] Regarding the first step, EP 3 674 293 A1 discloses the preparation of p-nitrobenzoic acid-2-ethylhexyl ester by reacting p-nitrobenzoic acid with an alcohol in an organic solvent in the presence of a catalyst such as sulfuric acid, p-toluenesulfonic acid, polyphosphoric acid, or thionyl chloride. However, the use of an organic solvent increases chemical and / or recycling costs and requires an additional purification step to remove the organic solvent.

[0005] Chinese Patent No. 112321522 also discloses a process for preparing 2-ethylhexyl p-nitrobenzoate from p-nitrobenzoic acid and isooctyl alcohol. This process requires washing and liquid separation after the reaction is completed. Furthermore, this process is carried out under reduced pressure. However, the process requires elaborate purification and / or reaction conditions, which is disadvantageous, especially for industrial applications. Summary of the Invention [Problem to be solved by the invention]

[0006] It was therefore an object of the present invention to provide an economically and environmentally improved process for preparing p-nitrobenzoic acid-2-ethylhexyl ester.

[0007] In this regard, it was one object to provide a process that ensures high product purity without the need for purification by washing and phase separation. Furthermore, it was an object to provide a process that does not require expensive reaction conditions, such as vacuum conditions. In another embodiment, it was desired to provide a process that minimizes the excessive use of chemicals in the reaction. Furthermore, it was an object to provide a process that is technically and economically suitable for large-scale applications. [Means for solving the problem]

[0008] Surprisingly, it has been found that at least some of the above-mentioned 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 provides a process for preparing p-nitrobenzoic acid-2-ethylhexyl ester, comprising reacting p-nitrobenzoic acid with 2-ethylhexanol, wherein: (a) excess 2-ethylhexanol acts as the solvent and no additional solvent is added; or (b) providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts without adding additional solvent; or (c) relates to a process that provides 2-ethylhexanol in substoichiometric amounts and does not add additional solvent.

[0010] The present inventors have surprisingly found that the process of the present invention provides the desired product in high yield and purity without the need for additional solvents or for purification of the complex product by washing, phase separation, or distillation. Furthermore, the process has been found to reduce reactor equipment requirements, since elaborate reaction conditions, such as vacuum conditions, are not required. Furthermore, in option (a), only a small excess of 2-ethylhexanol is used as the solvent in the process, and in options (b) and (c), no excess 2-ethylhexanol is used, which is typical of solventless processes. This is particularly surprising given the explosive nature of nitro compounds present in the reaction mixture. However, using a low excess of 2-ethylhexanol has the advantage that less 2-ethylhexanol needs to be removed, disposed of, or recycled after the reaction is complete. These advantages are even more applicable if no excess 2-ethylhexanol is used at all.

[0011] Thus, the present invention provides an environmentally and economically advantageous process for preparing p-nitrobenzoic acid-2-ethylhexyl ester in high purity and high yield that is suitable for large-scale industrial applications, including low reaction and purification complexity in terms of required steps, chemicals, and conditions of use.

[0012] In one embodiment of the present invention, the reaction is carried out in the presence of a catalyst, which is preferably selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, polyphosphoric acid, thionyl chloride, and mixtures thereof.

[0013] In one embodiment of the present invention, in option (a), the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is less than 1.5:1.

[0014] In one embodiment of the present invention, the reaction is not carried out under reduced pressure.

[0015] In one embodiment of the present invention, the product is purified by gas / steam stripping.

[0016] In one embodiment of the present invention, the amount of catalyst is less than 10 mol %, preferably less than 5 mol %.

[0017] In one embodiment of the present invention, the reaction is carried out at a temperature of up to 180° C. for a time period of up to 48 hours.

[0018] In one embodiment of the present invention, the process further comprises preparing p-aminobenzoic acid-2-ethylhexyl ester comprising reacting p-nitrobenzoic acid-2-ethylhexyl ester with hydrogen in the presence of a catalyst.

[0019] In one embodiment of the present invention, the p-nitrobenzoic acid-2-ethylhexyl ester is not purified by washing, distillation or phase separation prior to reaction with hydrogen in the presence of a catalyst.

[0020] In one embodiment of the present invention, the pH value is adjusted to a value in the range of 4 to 10 before reaction with hydrogen.

[0021] In one embodiment of the present invention, after reaction with hydrogen, phase separation is achieved by adding carbonate.

[0022] In one embodiment of the present invention, the process comprises reacting a compound of the formula: [ka] by reacting a cyanuric halide with p-aminobenzoic acid-2-ethylhexyl ester in a non-polar solvent to prepare 2,4,6-trianilino-p-(carbo-2'-ethylhexyl-1'-oxy)-1,3,5-triazine having the formula:

[0023] In one embodiment, the present invention relates to p-nitrobenzoic acid-2-ethylhexyl ester having a purity of at least 94% by weight.

[0024] In one embodiment, the present invention relates to p-nitrobenzoic acid-2-ethylhexyl ester obtained by the process of the present invention.

[0025] In one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate having less than 6% residual 2-ethylhexanol, less than 2% residual p-nitrobenzoic acid, less than 1% residual water, and / or less than 2% residual catalyst.

[0026] In one embodiment, the present invention relates to p-nitrobenzoic acid-2-ethylhexyl ester in the form of a highly viscous fluid.

[0027] Preferred embodiments of the invention can be found in the claims, the description and the examples. It is to be understood that the above-mentioned features of the subject matter of the invention and those further indicated below are preferred not only in each given combination but also in other combinations without departing from the scope of the invention.

[0028] In connection with the above-described embodiments of the present invention, the following definitions are provided.

[0029] In the context of the present invention, p-nitrobenzoic acid-2-ethylhexyl ester is obtained by a process comprising reacting p-nitrobenzoic acid with 2-ethylhexanol, in which reaction (a) excess 2-ethylhexanol acts as the solvent and no additional solvent is added; or (b) providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts without adding additional solvent; or (c) 2-ethylhexanol is provided in substoichiometric amounts and no additional solvent is added.

[0030] As used herein, "p-nitrobenzoic acid 2-ethylhexyl ester" refers to para-nitrobenzoic acid 2-ethylhexyl ester, which represents 4-nitrobenzoic acid 2-ethylhexyl ester.

[0031] As used herein, "p-nitrobenzoic acid" refers to para-nitrobenzoic acid, which stands for 4-nitrobenzoic acid (CAS number: 62-23-7). p-Nitrobenzoic acid is a commercially available, inexpensive compound, making it particularly suitable as a starting material in large-scale processes.

[0032] 2-Ethylhexanol (104-76-7) is also commercially available and inexpensive, making it a suitable starting material for large-scale processes.

[0033] As used herein, the term "excess" refers to any amount that provides a molar ratio greater than 1:1. Specifically, excess 2-ethylhexanol, as used herein, refers to an amount of 2-ethylhexanol that provides a molar ratio of 2-ethylhexanol to p-nitrobenzoic acid greater than 1:1.

[0034] As used herein, the term "equimolar amount" refers to a 1:1 molar ratio. Specifically, p-nitrobenzoic acid and 2-ethylhexanol provided in equimolar amounts refers to a 1:1 molar ratio of 2-ethylhexanol to p-nitrobenzoic acid.

[0035] As used herein, the term "substoichiometric amount" refers to any amount that provides a molar ratio of less than 1:1. Specifically, a substoichiometric amount of 2-ethylhexanol refers to an amount of 2-ethylhexanol that provides a molar ratio of 2-ethylhexanol to p-nitrobenzoic acid of less than 1:1. Preferably, a substoichiometric amount of 2-ethylhexanol refers to an amount of 2-ethylhexanol that provides a molar ratio of 2-ethylhexanol to p-nitrobenzoic acid of 0.5:1 to 1:1. If 2-ethylhexanol is provided in a substoichiometric amount, the yield is calculated based on the applied molar amount of 2-ethylhexanol. In this case, the p-nitrobenzoic acid remaining after the reaction can be separated and reused in the next reaction.

[0036] In some embodiments of the present invention, the reaction is carried out in the presence of a catalyst. The catalyst may be any Lewis acid or Bronsted acid. Preferably, the catalyst is selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, polyphosphoric acid, thionyl chloride, or any other Lewis acid, and mixtures thereof. As used herein, the catalyst may be used in its anhydrous form, as a hydrate, as a solution, or a mixture thereof. If the catalyst is used as a solution, the solution is preferably an aqueous solution. Furthermore, if the catalyst is used as a solution, the percentages indicated with the catalyst refer to the mass percentage of the catalyst, and therefore refer to the percentage of the catalyst mass to the solution mass.

[0037] In some embodiments of the present invention, the reaction is not carried out under reduced pressure. As used herein, the term "reduced pressure" refers to any pressure below atmospheric pressure.

[0038] In some embodiments of the present invention, products are purified by gas / steam stripping. Generally, stripping is a physical separation process that uses a steam stream to remove components from a liquid sample. As used herein, gas / steam stripping is carried out by supplying a reaction product to a vessel or reactor and removing the nonpolar solvent and, optionally, by-products by adding water or a polar solvent, or water vapor or a polar solvent vapor, or a gas, or a mixture thereof, to the vessel or reactor. Thus, gas / steam stripping according to the present invention also includes flashing, which describes a process in which water or a polar solvent is added to the liquid phase from the top of the vessel / reactor. Preferably, gas / steam stripping is carried out by adding water vapor, a polar solvent vapor, a gas, or a mixture thereof from the top or bottom of the vessel / reactor. More preferably, gas / steam stripping is carried out by adding water vapor, a polar solvent vapor, a gas, or a mixture thereof from the bottom of the vessel / reactor. The overhead stream containing the desorbed solvent and optionally reaction by-products can be condensed and separated. As used herein, the term "steam" in connection with gas / steam stripping refers to water vapor or polar solvent vapor, particularly alcohol vapor, preferably ethanol vapor. As used herein, the term "gas" in connection with gas / steam stripping refers to an inert gas that does not undergo chemical reaction, specifically nitrogen gas. As mentioned above, the term gas / steam stripping according to the present invention also includes flashing or flushing with water or a polar solvent, preferably ethanol, in the liquid phase.

[0039] As used herein, pressure denoted 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 denoted by the pressure unit "barg." Only when the pressure unit "bar (abs)" is used does pressure refer to absolute pressure. DETAILED DESCRIPTION OF THE INVENTION

[0040] A preferred embodiment of the process of the present invention is described below.

[0041] The following general considerations apply to the process:

[0042] Generally, the reaction step is carried out in a reaction vessel conventionally used for such reactions, such as a conventional stirred tank reactor. The reaction may be carried out in a continuous, semi-batch, or batch manner. Preferably, the process of the present invention is carried out in a batch manner, wherein all reactants are provided in the reaction vessel prior to initiating the reaction.

[0043] Details regarding reaction pressures and temperatures are provided below. Unless otherwise specified, process steps are preferably carried out under atmospheric pressure. Reaction completion can be monitored by methods known to those skilled in the art, such as thin layer chromatography, GC, HPLC, or NMR.

[0044] Unless otherwise specified, the reactants can in principle be contacted with each other in any desired sequence.

[0045] It is further emphasized that the reaction can be carried out on a laboratory and industrial scale.

[0046] 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 either alone or in combination with each other.

[0047] As indicated above, the present invention provides a process for preparing p-nitrobenzoic acid-2-ethylhexyl ester, comprising reacting p-nitrobenzoic acid with 2-ethylhexanol, wherein: (a) excess 2-ethylhexanol acts as the solvent and no additional solvent is added; or (b) providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts without adding additional solvent; or (c) relates to a process that provides 2-ethylhexanol in substoichiometric amounts and does not add additional solvent.

[0048] By carrying out the reaction without using an additional solvent, the presence of additional chemicals that contaminate the reaction product is avoided, and therefore, more complicated purification steps for removing the additional solvent after the reaction is complete are avoided. In one embodiment of the process of the present invention, excess 2-ethylhexanol acts as a solvent, and no additional solvent is added. Using excess 2-ethylhexanol, i.e., the reactant itself, as a solvent is further advantageous for increasing the conversion rate of p-nitrobenzoic acid and increasing the product yield. The removed excess 2-ethylhexanol can then be reused in the next reaction. Furthermore, if product isolation is not desired and the subsequent reaction can be carried out in 2-ethylhexanol as a solvent, there is no need to remove excess 2-ethylhexanol after the reaction is complete. This applies, for example, to the preparation of p-aminobenzoic acid 2-ethylhexyl ester, which comprises reacting p-nitrobenzoic acid 2-ethylhexyl ester with hydrogen in the presence of a catalyst.

[0049] In another embodiment of the process of the present invention, p-nitrobenzoic acid and 2-ethylhexanol are provided in equimolar amounts, and no additional solvent is added. In this case, the reaction is carried out without the use of any solvent and can be considered solventless. As a result, there is no need to remove, discard, or recycle the solvent after the reaction is complete. In another embodiment of the process of the present invention, 2-ethylhexanol is provided in a substoichiometric amount, and no additional solvent is added. In this case, the reaction is also carried out without the use of any solvent and can be considered solventless. As a result, there is no need to remove, discard, or recycle the solvent after the reaction is complete. Furthermore, excess p-nitrobenzoic acid can be separated and applied to the next reaction. In view of the explosive nature of the nitro compounds present in the reaction mixture, it is particularly surprising that the process of the present invention can be carried out in a small excess of 2-ethylhexanol or without the use of any additional solvent.

[0050] In one embodiment of the process of the present invention, the reaction is carried out in the presence of a catalyst, preferably selected from an acid catalyst, and even more preferably selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, polyphosphoric acid, thionyl chloride, and mixtures thereof. In one embodiment, the catalyst is p-toluenesulfonic acid. The catalyst can be used in its anhydrous form, as a hydrate, as a solution, or a mixture thereof. If the catalyst is used as a solution, the solution is preferably an aqueous solution. Furthermore, if the catalyst is used as a solution, different weight percentages of the catalyst in the solution can be used. In one embodiment, the weight percentage of the catalyst in the solution is greater than 50%. In another embodiment, the weight percentage of the catalyst in the solution is greater than 60%. Regardless of whether the catalyst is used in its anhydrous form, as a hydrate, as a solution, or a mixture thereof, the catalyst can be applied in different amounts relative to the amount of p-nitrobenzoic acid used. If the catalyst is used as a solution, the amount of catalyst refers to the amount of catalyst in the solution.

[0051] In one embodiment of the present invention, the amount of catalyst relative to the amount of p-nitrobenzoic acid is less than 10 mol %, preferably less than 5 mol %. In another embodiment, the amount of catalyst relative to the amount of p-nitrobenzoic acid is 0.1 to 10 mol %, preferably 0.2 to 5 mol %. In another embodiment, the amount of catalyst relative to the amount of p-nitrobenzoic acid is 0.5 to 2.5 mol %. In another embodiment, the amount of catalyst relative to the amount of p-nitrobenzoic acid is 1.0 to 1.5 mol %. Reducing the amount of catalyst used results in less catalyst waste or less catalyst recycling, which is advantageous for both preparation costs and the environment. Furthermore, less catalyst needs to be removed during purification after the reaction is complete.

[0052] As described above, in option (a), in the process of the present invention for preparing p-nitrobenzoic acid 2-ethylhexyl ester, excess 2-ethylhexanol acts as a solvent. This avoids the use of an additional solvent and therefore avoids the need to remove the solvent after the reaction is complete. In one embodiment of the present invention, the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is less than 1.5:1. In another embodiment, the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is 1.01:1 to 1.49:1. In another embodiment, the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is 1.05:1 to 1.3:1. In another embodiment, the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is 1.1:1 to 1.2:1. The use of a low excess of 2-ethylhexanol as the solvent is advantageous in that it reduces costs and chemical waste as well as reducing the amount of solvent that needs to be removed after the reaction is complete.

[0053] In one embodiment of the process of the present invention, the reaction is not carried out under reduced pressure. In another embodiment, the reaction is carried out under atmospheric pressure. Not having to carry out the reaction under reduced pressure provides the advantage of less process complexity and reduced requirements for reactor equipment. This can lead to reduced process costs, especially for large-scale industrial applications. In one embodiment, the reaction is carried out under a nitrogen atmosphere. In another embodiment, the reaction is carried out under a nitrogen atmosphere at atmospheric pressure.

[0054] In one embodiment of the process of the present invention, the catalyst is pre-charged into a vessel or reactor under a nitrogen atmosphere prior to the addition of 2-ethylhexanol and p-nitrobenzoic acid.

[0055] In one embodiment of the process of the present invention, the reaction is carried out under heating. In one embodiment of the process of the present invention, the reaction is carried out under reflux. In one embodiment, the reaction is carried out under reflux at a temperature of up to 180°C for a time period of up to 48 hours. Carrying out the reaction at a temperature below 180°C is advantageous to prevent decomposition of the product, p-nitrobenzoic acid 2-ethylhexyl ester, at excessively high temperatures. Furthermore, an upper limit of 180°C has the advantage of using a temperature below the boiling point of 2-ethylhexanol. In another embodiment, the reaction is carried out under reflux at a temperature of 100°C to 180°C for 1 hour to 24 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 100°C to 180°C for 2 hours to 12 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 100°C to 180°C for 4 hours to 8 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 120°C to 170°C for 1 hour to 24 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 120°C to 170°C for 2 to 12 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 120°C to 170°C for 4 to 8 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 140°C to 160°C for 1 to 24 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 140°C to 160°C for 2 to 12 hours. In another embodiment, the reaction is carried out under reflux at a temperature of 140°C to 160°C for 4 to 8 hours.

[0056] In one embodiment of the process of the present invention, the condensate of the reflux reaction mixture is collected in a second vessel or reactor during the reaction. This allows water to be separated during the reaction. In addition to water, the condensate may optionally contain small amounts of 2-ethylhexanol, catalyst, and / or by-products. Therefore, if the condensate of the reflux reaction mixture is collected in a second vessel or reactor during the reaction, it is preferable to carry out the reaction at a temperature lower than the boiling point of the catalyst. The recovered mixture of water, optionally 2-ethylhexanol, catalyst, and / or by-products can be recycled. The aqueous phase can be separated and the water purified. Alternatively, the catalyst-containing aqueous phase can be separated and reused as a catalyst solution in the following reaction. It is preferable to purify the catalyst-containing aqueous phase before recycling it. Furthermore, 2-ethylhexanol can be separated and reused in the next reaction. It is preferable to purify the 2-ethylhexanol before reuse.

[0057] In one embodiment of the process of the present invention, the product is purified by steam / gas stripping after the reaction is completed. The resulting 2-ethylhexyl p-nitrobenzoate is obtained in high yield and high purity. Therefore, steam / gas stripping is advantageous for effectively removing water, catalyst, optionally excess 2-ethylhexanol, optionally by-products, and optionally remaining reactants from the desired 2-ethylhexyl p-nitrobenzoate. Furthermore, steam / gas stripping has the advantage of being applicable on a large industrial scale. Furthermore, the mixture of water, catalyst, optionally excess 2-ethylhexanol, optionally by-products, and optionally remaining reactants separated by steam / gas stripping can be recycled. In particular, the catalyst-containing aqueous phase can be separated and reused as a catalyst solution in the following reaction. It is preferable to purify the catalyst-containing aqueous phase before recycling it. Furthermore, 2-ethylhexanol can be separated and reused in the next reaction. The 2-ethylhexanol is preferably purified before being reused.

[0058] In one embodiment, stripping is carried out with steam or gas. In another embodiment, stripping is carried out with a gas selected from nitrogen or an alcohol, preferably ethanol in gaseous form. Preferably, the product is purified by stripping with nitrogen.

[0059] In one embodiment of the process of the present invention, the temperature during steam / gas stripping is less than 180°C, preferably less than 170°C. Conducting steam / gas stripping at a temperature less than 180°C is advantageous to prevent decomposition of the product p-nitrobenzoic acid 2-ethylhexyl ester at excessively high temperatures. In another embodiment, the temperature during steam / gas stripping is 100°C to 180°C, preferably 120°C to 170°C. In another embodiment, the temperature during steam / gas stripping is 140°C to 160°C. In one embodiment, stripping is carried out for up to 48 hours. In another embodiment, gas / steam stripping is carried out for 1 to 24 hours. In another embodiment, gas / steam stripping is carried out for 2 to 12 hours. In another embodiment, gas / steam stripping is carried out for 4 to 7 hours.

[0060] In one embodiment of the present invention, the gas / steam pressure during gas / steam stripping is up to 100 bar, preferably up to 20 bar. In another embodiment, the gas / steam pressure during gas / steam stripping is 0.1 bar to 20 bar. In another embodiment, the gas / steam pressure during gas / steam stripping is 0.5 bar to 10 bar. In another embodiment, the gas / steam pressure during gas / steam stripping is 1 bar to 6 bar. In one embodiment, the temperature during gas / steam stripping is 120°C to 170°C, and the gas / steam pressure during gas / steam stripping is 0.1 bar to 20 bar. In one embodiment, the temperature during gas / steam stripping is 120°C to 170°C, and the gas / steam pressure during gas / steam stripping is 0.5 bar to 10 bar. In another embodiment, the temperature during gas / steam stripping is 140°C to 160°C, and the gas / steam pressure during gas / steam stripping is 1 bar to 6 bar. In one embodiment, the temperature during gas / steam stripping is 140°C to 160°C, and the gas / steam pressure during gas / steam stripping is 0.1 bar to 20 bar. In another embodiment, the temperature during gas / steam stripping is 140°C to 160°C, and the gas / steam pressure during gas / steam stripping is 0.5 bar to 10 bar. In another embodiment, the temperature during gas / steam stripping is 140°C to 160°C, and the gas / steam pressure during gas / steam stripping is 1 bar to 6 bar.

[0061] In one embodiment of the process of the present invention, the amount of gas / steam used for gas / steam stripping is at least 25 wt.% relative to the crude product. In another embodiment, the amount of gas / steam used for gas / steam stripping is at least 50 wt.% relative to the crude product.

[0062] In one embodiment, stripping is carried out for up to 48 hours. In another embodiment, stripping is carried out for 1 to 24 hours. In another embodiment, stripping is carried out for 2 to 12 hours. In another embodiment, stripping is carried out for 4 to 7 hours. In another embodiment, the product is purified by nitrogen stripping at atmospheric pressure at a temperature of 150°C to 170°C for up to 48 hours. In another embodiment, the product is purified by nitrogen stripping at atmospheric pressure at a temperature of 150°C to 170°C for 1 to 24 hours. In another embodiment, the product is purified by nitrogen stripping at atmospheric pressure at a temperature of 150°C to 170°C for 2 to 12 hours. In another embodiment, the product is purified by nitrogen stripping at atmospheric pressure at a temperature of 150°C to 170°C for 5 to 7 hours.

[0063] As described above, the process of the present invention provides a process for preparing 2-ethylhexyl p-nitrobenzoate. 2-Ethylhexyl p-nitrobenzoate is a common starting material for the preparation of 2-ethylhexyl p-aminobenzoate. Accordingly, in one embodiment of the present invention, the process further comprises preparing 2-ethylhexyl p-aminobenzoate, which comprises reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst. As described above, high-purity 2-ethylhexyl p-nitrobenzoate can be obtained by the process of the present invention without purification by washing, distillation, or phase separation. Accordingly, in one embodiment of the present invention, the starting 2-ethylhexyl p-nitrobenzoate is not purified by washing, distillation, or phase separation before reaction with hydrogen in the presence of a catalyst to prepare 2-ethylhexyl p-aminobenzoate. Therefore, the improved process for preparing p-nitrobenzoic acid 2-ethylhexyl ester is also advantageous for preparing p-aminobenzoic acid 2-ethylhexyl ester. Furthermore, the purity of p-aminobenzoic acid 2-ethylhexyl ester can be increased by adjusting the pH before the reaction with hydrogen. Therefore, in one embodiment of the present invention, the pH value is adjusted to a value in the range of 4 to 10 before the reaction with hydrogen. In another embodiment of the present invention, after the reaction with hydrogen, phase separation is carried out by adding a carbonate salt. By carrying out phase separation by adding a carbonate salt, the water content is reduced.

[0064] p-Aminobenzoic acid-2-ethylhexyl ester can be reacted with cyanuric halide to obtain the known highly effective UV absorber ethylhexyl triazone (Uvinul T 150, CAS number: 88122-99-0). Said ethylhexyl triazone represents 2,4,6-trianilino-p-(carbo-2'-ethylhexyl-1'-oxy)-1,3,5-triazine. Thus, in another embodiment, the process is carried out by reacting p-aminobenzoic acid-2-ethylhexyl ester ... [ka] The method further comprises preparing 2,4,6-trianilino-p-(carbo-2'-ethylhexyl-1'-oxy)-1,3,5-triazine having the formula: by reacting cyanuric halide with 2-ethylhexyl p-aminobenzoate in a nonpolar solvent. Preferably, the cyanuric halide is reacted with 2-ethylhexyl p-aminobenzoate in a molar ratio of 1:3 to 1:5. Because 3 equivalents of 2-ethylhexyl p-aminobenzoate per equivalent of cyanuric halide are required to form ethylhexyl triazone, the cyanuric halide is reacted with 2-ethylhexyl p-aminobenzoate in a molar ratio of at least 1:3 to ensure complete conversion of the cyanuric halide. Therefore, the improved process for preparing 2-ethylhexyl p-nitrobenzoate is also advantageous for preparing ethylhexyl triazone. Reducing the complexity, waste, and cost of preparing p-nitrobenzoic acid-2-ethylhexyl ester also reduces the overall complexity, waste, and cost of preparing ethylhexyl triazone, which is particularly advantageous in view of the demand for ethylhexyl triazone due to its various uses as a UV absorber.

[0065] As mentioned above, high purity can be obtained by the process of the present invention. Thus, in one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate having a purity of at least 94% by weight. In another embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate having a purity of at least 95% by weight.

[0066] Furthermore, in one embodiment, the present invention relates to p-nitrobenzoic acid-2-ethylhexyl ester obtainable by the process of the present invention.

[0067] In another embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate having a purity of at least 94% by weight or at least 95% by weight and / or obtainable by the process of the present invention, wherein the amount of residual 2-ethylhexanol is less than 6% and / or the amount of residual p-nitrobenzoic acid is less than 2% and / or the amount of residual water is less than 1% and / or the amount of residual catalyst is less than 2%.

[0068] Additionally, 2-ethylhexyl p-nitrobenzoate having a purity of at least 94% by weight, or at least 95% by weight, and / or obtained by the process of the present invention, and / or having a residual 2-ethylhexanol content of less than 6%, and / or a residual p-nitrobenzoic acid content of less than 2%, and / or a residual water content of less than 1%, and / or a residual catalyst content of less than 2%, is in the form of a highly viscous fluid.

[0069] Thus, in another embodiment, the present invention relates to p-nitrobenzoic acid-2-ethylhexyl ester in the form of a highly viscous fluid.

[0070] The present invention is further illustrated by the following examples. [Example]

[0071] The following abbreviations are used: p-NBAE: p-nitrobenzoic acid-2-ethylhexyl ester, 2-EH: 2-ethylhexanol, p-TSA: p-toluenesulfonic acid, p-NBA: p-nitrobenzoic acid.

[0072] In the examples, Karl Fischer titrations were carried out on a Metrohm 890 Titrando with 900 Touch Control and 803TI Stand using a Metrohm 6.0338.100 double PT-Wire electrode.

[0073] In the examples, GC analyses were performed on an Agilent Technologies 7890B using the following conditions and parameters: Detector: FID Solvent: dichloromethane Column: Macherey-Nagel Optima 1701 (25 m, inner diameter 0.53 mm, film thickness 1.00 μm) Carrier gas: Helium 25 mL / min Injector temperature and detector temperature: 250℃ Temperature program: 100° C. for 2 minutes, followed by 10° C. / minute to 150° C., followed by 50° C. / minute to 200° C. and hold at 200° C. for 2 minutes.

[0074] In the examples, HPLC analysis is performed on an Agilent 1260 using the following conditions and parameters: Detector: UV at 220 nm Column: Waters Spherisorb ODS-2 (10 μm, 250 × 4 mm) Flow rate: 1.2mL / min Solvents: acetonitrile containing 0.1% by volume of phosphoric acid (solvent A) and deionized water containing 0.1% by volume of phosphoric acid (solvent B). Gradient Program:

[0075] [Table 1]

[0076] Example 1: Preparation of p-nitrobenzoic acid-2-ethylhexyl ester 17.4 kg of 65% p-toluenesulfonic acid was added to reactor A under an inert nitrogen atmosphere. Then, 495 kg of 2-ethylhexanol and 562.5 kg of solid p-nitrobenzoic acid were added to the same reactor. Esterification was initiated by heating the reactor to a temperature of 160°C for 6 hours while stirring. The reaction was carried out under reflux, and the resulting mixture of 2-ethylhexanol, water, and by-products was collected in a second reactor B. The 2-ethylhexanol from reactor B can be reused after purification for the next reaction. The water and by-products were pumped to a wastewater treatment plant. The remaining 2-ethylhexanol, water, and by-products in reactor A were stripped with nitrogen at 160°C for an additional 6 hours to form the final product, p-nitrobenzoic acid-2-ethylhexyl ester. The purity observed by GC was 95.5%. The final products were characterized using GC (p-NBAE, 2-EH, etc.) and HPLC (p-NBA, p-TSA), and the water content was determined using Karl Fischer titration. The results are shown in Table 1.

[0077] [Table 2]

Claims

1. A method for preparing p-nitrobenzoic acid-2-ethylhexyl ester, comprising reacting p-nitrobenzoic acid with 2-ethylhexanol, wherein in the reaction, (a) Excess 2-ethylhexanol acts as a solvent, and no additional solvent is added; or (b) Provide p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts, without adding any additional solvent; or, (c) A method for providing 2-ethylhexanol in a quasi-stoichiometric amount without adding any additional solvent.

2. The method according to claim 1, wherein the reaction is carried out in the presence of a catalyst, the catalyst is preferably selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, polyphosphate, thionyl chloride, and mixtures thereof.

3. The method according to claim 1 or 2, wherein the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is less than 1.5:

1.

4. The method according to claim 1 or 2, wherein the reaction is not carried out under reduced pressure.

5. The method according to claim 1 or 2, wherein the product is purified by gas / steam stripping.

6. The method according to claim 2, wherein the amount of catalyst is less than 10 mol%, preferably less than 5 mol%.

7. The method according to claim 1 or 2, wherein the reaction is carried out at a temperature of up to 180°C for up to 48 hours.

8. The method according to claim 1 or 2, further comprising preparing p-aminobenzoic acid-2-ethylhexyl ester by reacting the p-nitrobenzoic acid-2-ethylhexyl ester with hydrogen in the presence of a catalyst.

9. The method according to claim 8, wherein the p-nitrobenzoate-2-ethylhexyl ester is not purified by washing, distillation, or phase separation before the reaction with hydrogen in the presence of a catalyst.

10. The method according to claim 8, wherein the pH value is adjusted to a value in the range of 4 to 10 before the reaction with hydrogen.

11. The method according to claim 8, wherein after the reaction with hydrogen, phase separation is carried out by adding a carbonate.

12. The above method is based on the following chemical formula 【Chemistry 1】 The method according to claim 8, further comprising preparing 2,4,6-trianilino-p-(carbo-2'-ethylhexyl-1'-oxy)-1,3,5-triazine having the above p-aminobenzoic acid-2-ethylhexyl ester of halogenated cyanurate in a nonpolar solvent.

13. p-2-ethylhexyl nitrobenzoate having a purity of at least 94% by weight.

14. The p-nitrobenzoate-2-ethylhexyl ester according to claim 13, obtained by the method described in claim 1 or 2.

15. The p-nitrobenzoic acid-2-ethylhexyl ester according to claim 13, wherein the amount of residual 2-ethylhexanol is less than 6%, and / or the amount of residual p-nitrobenzoic acid is less than 2%, and / or the amount of residual water is less than 1%, and / or the amount of residual catalyst is less than 2%.

16. The p-nitrobenzoate-2-ethylhexyl ester according to claim 13 or 15, in the form of a highly viscous fluid.

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