Improved process for preparation of p-nitrobenzoic acid-2-ethylhexyl ester

Abstract

The present invention relates to a process for the preparation of p-nitrobenzoic acid-2-ethylhexyl ester comprising reacting p-nitrobenzoic acid with excess 2-ethylhexanol acting as a solvent and without adding additional solvent, or providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts and without adding additional solvent, or 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added. In addition, the present invention relates to p-nitrobenzoic acid-2-ethylhexyl ester obtained by this process and having high purity and optimal product properties.

Description

[0001] The present invention relates to a process for preparing 2-ethylhexyl p-nitrobenzoate, which comprises reacting p-nitrobenzoic acid, wherein an excess of 2-ethylhexanol serves as solvent and no additional solvent is added, or p-nitrobenzoic acid and 2-ethylhexanol are provided in equimolar amounts and no additional solvent is added, or 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.

[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. 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] Regarding the first step, EP 3 674 293 A1 discloses the preparation of 2-ethylhexyl p-nitrobenzoate 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 organic solvents increases chemical and / or recycling costs and requires an additional purification step to remove the organic solvent.

[0005] CN 112321522 also discloses a method for preparing 2-ethylhexyl p-nitrobenzoate from p-nitrobenzoic acid and isooctyl alcohol. This method requires washing and liquid separation after the reaction is completed. In addition, the method is carried out under reduced pressure. However, methods that require elaborate purification and / or reaction conditions are disadvantageous, particularly for industrial applications.

[0006] It is therefore an object of the present invention to provide an economically and environmentally improved process for the preparation of 2-ethylhexyl p-nitrobenzoate.

[0007] In this respect, an object is to provide a method for ensuring high product purity without the need for purification by washing and phase separation. In addition, an object is to provide a method that does not require expensive reaction conditions, such as a method for reduced pressure conditions. In another embodiment, it is desirable to provide a method for minimizing the excessive use of chemicals in the reaction. In addition, an object is to provide a method that is technically and economically suitable for large-scale 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-nitrobenzoate, which comprises reacting p-nitrobenzoic acid with 2-ethylhexanol, wherein

[0010] (a) excess 2-ethylhexanol acts as the solvent and no additional solvent is added; or

[0011] (b) providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts without adding additional solvent; or

[0012] (c) 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added.

[0013] The inventors have surprisingly found that the method of the present invention provides the desired product with high yield and purity without the need for additional solvent or complex product purification by washing, phase separation or distillation. In addition, it has been found that the method does not require delicate reaction conditions, such as reduced pressure conditions, which also reduces the requirements for the reaction setting. In addition, in option (a), only a small amount of excessive 2-ethylhexanol is used as a solvent in the method, or in options (b) and (c), excessive 2-ethylhexanol is not used, representing a solvent-free method. Considering the explosive tendency of the nitro-compounds present in the reaction mixture, this is particularly unexpected. However, using a relatively low amount of excessive 2-ethylhexanol has the advantage of less 2-ethylhexanol, which must be removed, discarded or recycled after the reaction is completed. If excessive 2-ethylhexanol is not used, these advantages are even more applicable.

[0014] Thus, the present invention provides an environmentally and economically advantageous process for preparing 2-ethylhexyl p-nitrobenzoate in high purity and yield, which is suitable for large-scale industrial applications. This includes low reaction and purification complexity in terms of the required steps, chemicals, and conditions used.

[0015] 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.

[0016] 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.

[0017] In one embodiment of the present invention, the reaction is not carried out under reduced pressure.

[0018] In one embodiment of the invention, the product is purified by gas / steam stripping.

[0019] In one embodiment of the present invention, the amount of catalyst is less than 10 mol%, preferably less than 5 mol%.

[0020] In one embodiment of the present invention, the reaction is carried out at a temperature of up to 180°C for a period of up to 48 hours.

[0021] In one embodiment of the present invention, the method further comprises preparing 2-ethylhexyl p-aminobenzoate, comprising reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst.

[0022] In one embodiment of the present invention, 2-ethylhexyl p-nitrobenzoate is not purified by washing, distillation or phase separation before reacting with hydrogen in the presence of a catalyst.

[0023] In one embodiment of the present invention, the pH is adjusted to a value in the range of 4 to 10 before reacting with hydrogen.

[0024] In one embodiment of the present invention, after the reaction with hydrogen, phase separation is performed by adding carbonate.

[0025] 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

[0026]

[0027] In one embodiment, the present invention is directed to 2-ethylhexyl p-nitrobenzoate having a purity of at least 94% by weight.

[0028] In one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate obtained by the process of the present invention.

[0029] In one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate, 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%.

[0030] In one embodiment, the present invention is directed to 2-ethylhexyl p-nitrobenzoate in the form of a high viscosity fluid.

[0031] 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.

[0032] In conjunction with the above embodiments of the present invention, the following definitions are provided.

[0033] In the context of the present invention, 2-ethylhexyl p-nitrobenzoate is obtained by a process comprising reacting p-nitrobenzoic acid with 2-ethylhexanol, wherein

[0034] (a) excess 2-ethylhexanol acts as the solvent and no additional solvent is added; or

[0035] (b) providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts without adding additional solvent; or

[0036] (c) 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added.

[0037] As used herein, "p-nitrobenzoic acid-2-ethylhexylester" refers to para-nitrobenzoic acid-2-ethylhexylester, which means 4-nitrobenzoic acid-2-ethylhexylester.

[0038] As used herein, "p-nitrobenzoic acid" refers to para-nitrobenzoic acid, which represents 4-nitrobenzoic acid (CAS No.: 62-23-7). Para-nitrobenzoic acid is a commercially available, inexpensive compound and is therefore particularly suitable as a starting material in large-scale processes.

[0039] 2-Ethylhexanol (104-76-7) is also commercially available and inexpensive and is therefore also suitable as starting material in large-scale processes.

[0040] As used herein, the term "excess" refers to any amount that provides a molar ratio exceeding a 1: 1 molar ratio. In particular, excess 2-ethylhexanol as used herein refers to an amount of 2-ethylhexanol that provides a molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid exceeding a 1: 1 molar ratio.

[0041] As used herein, the term "equimolar amount" refers to a 1: 1 molar ratio. In particular, p-nitrobenzoic acid and 2-ethylhexanol provided in equimolar amounts means that the molar ratio of 2-ethylhexanol to p-nitrobenzoic acid is 1:1.

[0042] As used herein, the term "substoichiometric amount" refers to any amount that provides a molar ratio of less than 1:1. In particular, 2-ethylhexanol provided in a substoichiometric amount refers to an amount of 2-ethylhexanol that provides a molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid of less than 1:1. Preferably, 2-ethylhexanol provided in a substoichiometric amount refers to an amount of 2-ethylhexanol that provides a molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid between 0.5:1 and 1:1. If 2-ethylhexanol is provided in a substoichiometric amount, the yield is calculated relative to 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.

[0043] In some embodiments of the present invention, the reaction is carried out in the presence of a catalyst. The catalyst can 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 can be used in its anhydrous form, as a hydrate, as a solution, or with its mixture. If the catalyst is used as a solution, it is preferably an aqueous solution. In addition, if the catalyst is used as a solution, the percentage given with the catalyst refers to the weight percentage of the catalyst and therefore refers to the catalyst mass relative to the mass of the solution.

[0044] 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.

[0045] In some embodiments of the present invention, product is purified by gas / steam stripping.Generally, stripping is to use vapor stream to remove the physical separation process of component from liquid sample.As used herein, gas / steam stripping is to feed the reaction product into container or reactor and to strip non-polar solvent and alternatively by-product by adding water or polar solvent or steam or gas of water vapor or polar solvent or its mixture into container or reactor.Therefore, gas / steam stripping according to the present invention also comprises flash distillation (flashing) or flash distillation (flash), which describes the process of adding water or polar solvent in liquid phase from the top of container / reactor.Preferably, gas / steam stripping is to carry out by adding water vapor, steam, gas or its mixture of polar solvent from the top or bottom of container / reactor.More preferably, gas / steam stripping is to carry out by adding water vapor, steam, gas or its mixture of polar solvent from the bottom of container / reactor.Can be by comprising the solvent of desorption and alternatively the overhead flow of byproduct of reaction condensation and separation. As used herein, the term "steam" in connection with gas / steam stripping refers to water vapor or vapor of a polar solvent, in particular vapor of an alcohol, preferably vapor of ethanol. As used herein, the term "gas" in connection with gas / steam stripping refers to an inert gas, in particular nitrogen, which does not undergo a chemical reaction. As mentioned above, the term gas / steam stripping according to the present invention also includes flashing or flashing with water or a polar solvent, preferably ethanol, in the liquid phase.

[0046] 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.

[0047] Preferred embodiments of the method of the present invention are described below.

[0048] The following general considerations apply to this approach.

[0049] 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.

[0050] 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.

[0051] If not indicated otherwise, the reactants can in principle be brought into contact with one another in any desired order.

[0052] Furthermore, it is emphasized that the reaction can be performed on both laboratory and industrial scales.

[0053] 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.

[0054] As indicated above, the present invention relates to a process for preparing 2-ethylhexyl p-nitrobenzoate, which comprises reacting p-nitrobenzoic acid with 2-ethylhexanol, wherein

[0055] (a) excess 2-ethylhexanol acts as the solvent and no additional solvent is added; or

[0056] (b) providing p-nitrobenzoic acid and 2-ethylhexanol in equimolar amounts without adding additional solvent; or

[0057] (c) 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added.

[0058] Carrying out this reaction in the absence of additional solvent avoids the existence of the additional chemicals that contaminate the reaction product, and therefore avoids the more complicated purification of removing the additional solvent after the reaction is completed. In one embodiment of the inventive method, excessive 2-ethylhexyl ester serves as solvent, and does not add additional solvent. Using excessive 2-ethylhexanol (i.e. reactant itself) as solvent further helps to increase the transformation efficiency of p-nitrobenzoic acid and therefore increase the product yield. The excessive 2-ethylhexanol removed can be reused in the next reaction subsequently. In addition, if it is not necessary to carry out product separation and subsequent reaction can be carried out in the 2-ethylhexanol as solvent, then after the reaction is completed, it is not necessary to remove excessive 2-ethylhexanol. This is applicable to the preparation of for example p-aminobenzoic acid-2-ethylhexyl ester, comprising making p-nitrobenzoic acid-2-ethylhexyl ester react with hydrogen in the presence of a catalyst.

[0059] In another embodiment of the inventive method, 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 any solvent and can therefore be considered as solvent-free. Therefore, after the reaction is completed, it is not necessary to remove, discard or recycle any solvent. In another embodiment of the inventive method, 2-ethylhexanol is provided in a substoichiometric amount, and no additional solvent is added. Also in this case, the reaction is carried out without any solvent and can therefore be considered as solvent-free. Therefore, after the reaction is completed, it is not necessary to remove, discard or recycle any solvent. In addition, excess p-nitrobenzoic acid can be separated and applied to the next reaction. In view of the explosive tendency of the nitro compounds present in the reaction mixture, it is particularly unexpected that the method of the present invention can be carried out in a small amount of excess 2-ethylhexanol or even in the absence of any additional solvent.

[0060] In one embodiment of the inventive method, the reaction is carried out in the presence of a catalyst, which is 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 in its mixture. If the catalyst is used as a solution, it is preferably an aqueous solution. In addition, 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 higher than 50%. In another embodiment, the weight percentage of the catalyst in the solution is higher than 60%. Whether the catalyst is used in its anhydrous form, as a hydrate, as a solution, or in its mixture, 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 the catalyst refers to the amount of the catalyst in the solution.

[0061] In one embodiment of the invention, the amount of catalyst is less than 10 mol%, preferably less than 5 mol%, relative to the amount of p-nitrobenzoic acid. In another embodiment, the amount of catalyst is 0.1 mol% to 10 mol%, preferably 0.2 mol% to 5 mol%, relative to the amount of p-nitrobenzoic acid. In another embodiment, the amount of catalyst is 0.5 mol% to 2.5 mol%, relative to the amount of p-nitrobenzoic acid. In another embodiment, the amount of catalyst is 1.0 mol% to 1.5 mol%, relative to the amount of p-nitrobenzoic acid. Reducing the amount of catalyst used results in less catalyst waste or less catalyst recycling, which is beneficial both for production costs and environmental aspects. In addition, the amount of catalyst that must be removed during purification after the reaction is completed is lower.

[0062] As described above, in option (a), excess 2-ethylhexanol acts as a solvent in the method for preparing 2-ethylhexyl p-nitrobenzoate of the present invention. This avoids the use of additional solvents and therefore avoids removing them after the reaction is complete. In one embodiment of the present invention, the molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid is less than 1.5:1. In another embodiment, the molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid is 1.01:1 to 1.49:1. In another embodiment, the molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid is 1.05:1 to 1.3:1. In another embodiment, the molar ratio of 2-ethylhexanol relative to p-nitrobenzoic acid is 1.1:1 to 1.2:1. Using a small amount of excess 2-ethylhexanol as a solvent is advantageous in reducing costs and chemical waste and reducing the solvent that must be removed after the reaction is complete.

[0063] In one embodiment of the inventive method, the reaction is not carried out under reduced pressure. In another embodiment, the reaction is carried out under atmospheric pressure. It is not necessary to react under reduced pressure to provide the advantages of less method complexity and less requirements for reaction unit. This can be associated with the method cost reduced, particularly 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.

[0064] In one embodiment of the process of the present invention, the catalyst is pre-charged into a container or reactor under a nitrogen atmosphere before adding 2-ethylhexanol and p-nitrobenzoic acid.

[0065] In one embodiment of the method of the present invention, the reaction is carried out under heating. In one embodiment of the method 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 period of up to 48 hours. It is advantageous to carry out the reaction at a temperature below 180°C in order to prevent the product p-nitrobenzoic acid-2-ethylhexyl ester from decomposing at too high a temperature. In addition, the 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 a period of 1h to 24h. In another embodiment, the reaction is carried out under reflux at a temperature of 100°C to 180°C for a period of 2h to 12h. In another embodiment, the reaction is carried out under reflux at a temperature of 100°C to 180°C for a period of 4h to 8h. In another embodiment, the reaction is carried out under reflux at a temperature of 100°C to 180°C for a period of 1h to 24h. In another embodiment, the reaction is carried out at a temperature of 120°C to 170°C under reflux for a period of 2h to 12h. In another embodiment, the reaction is carried out at a temperature of 120°C to 170°C under reflux for a period of 4h to 8h. In another embodiment, the reaction is carried out at a temperature of 140°C to 160°C under reflux for a period of 1h to 24h. In another embodiment, the reaction is carried out at a temperature of 140°C to 160°C under reflux for a period of 2h to 12h. In another embodiment, the reaction is carried out at a temperature of 140°C to 160°C under reflux for a period of 4h to 8h.

[0066] In one embodiment of the inventive method, the condensate of the reflux reaction mixture is collected in a second container or reactor during the reaction. Thus, water is separated during the reaction. In addition to water, the condensate can also optionally contain a small amount of 2-ethylhexanol, catalyst and / or by-product. Therefore, preferably, if the condensate of the reflux reaction mixture is collected in a second container or reactor during the reaction, the reaction is carried out at a temperature lower than the boiling point of the catalyst. The collected water and optionally the mixture of 2-ethylhexanol, catalyst and / or by-product can be recycled. The aqueous phase can be separated, and the water can be purified. Alternatively, the aqueous phase containing the catalyst can be separated and reused in subsequent reactions as a catalyst solution. Preferably, the aqueous phase containing the catalyst is purified before reuse. In addition, the 2-ethylhexanol can be separated and reused in subsequent reactions. Preferably, the 2-ethylhexanol is purified before reuse.

[0067] In one embodiment of the inventive method, after the reaction is completed, the product is purified by steam / gas stripping. The obtained p-nitrobenzoic acid-2-ethylhexyl ester is obtained with high yield and high purity. Therefore, steam / gas stripping is advantageous, so as to effectively remove water, catalyst, optionally excessive 2-ethylhexanol, optionally by-products and optionally remaining reactants from the desired p-nitrobenzoic acid-2-ethylhexyl ester. In addition, steam / gas stripping has the advantage of being applicable to large industrial scale. In addition, the mixture of water, catalyst, optionally excessive 2-ethylhexanol, optionally by-products and optionally remaining reactants separated by steam / gas stripping can be recycled. In particular, the aqueous phase containing catalyst can be separated and reused in subsequent reactions as catalyst solution. Preferably, the aqueous phase containing catalyst is purified before reuse. In addition, 2-ethylhexanol can be separated and reused in subsequent reactions. Preferably, 2-ethylhexanol is purified before reuse.

[0068] In one embodiment, the stripping is carried out with water vapor or gas. In another embodiment, the 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.

[0069] In one embodiment of the process of the present invention, the temperature during the steam / gas stripping is less than 180°C, preferably less than 170°C. It is advantageous to carry out the steam / gas stripping at a temperature below 180°C in order to prevent the product p-nitrobenzoic acid-2-ethylhexyl ester from decomposing at too high a temperature. In another embodiment, the temperature during the steam / gas stripping is 100°C to 180°C, preferably 120°C to 170°C. In another embodiment, the temperature during the steam / gas stripping is 140°C to 160°C. In one embodiment, the stripping is carried out for a period of up to 48 hours. In another embodiment, the gas / steam stripping is carried out for a period of 1 to 24 hours. In another embodiment, the gas / steam stripping is carried out for a period of 2 to 12 hours. In another embodiment, the gas / steam stripping is carried out for a period of 4 to 7 hours.

[0070] In one embodiment of the invention, the pressure of the gas / steam during the gas / steam stripping is up to 100 bar, preferably up to 20 bar. In another embodiment, the pressure of the gas / steam during the gas / steam stripping is 0.1 bar to 20 bar. In another embodiment, the pressure of the gas / steam during the gas / steam stripping is 0.5 bar to 10 bar. In another embodiment, the pressure of the gas / steam during the gas / steam stripping is 1 bar to 6 bar. In one embodiment, the temperature during the gas / steam stripping is 120°C to 170°C, and the pressure of the gas / steam during the gas / steam stripping is 0.1 bar to 20 bar. In one embodiment, the temperature during the gas / steam stripping is 120°C to 170°C, and the pressure of the gas / steam during the gas / steam stripping is 0.5 bar to 10 bar. In another embodiment, the temperature during the gas / steam stripping is 140°C to 160°C, and the pressure of the gas / steam during the 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 pressure of the gas / steam 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 pressure of the gas / steam 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 pressure of the gas / steam during gas / steam stripping is 1 bar to 6 bar.

[0071] In one embodiment of the process of the invention, the amount of gas / steam used for gas / steam stripping is at least 25% by weight relative to the crude product. In another embodiment, the amount of gas / steam used for gas / steam stripping is at least 50% by weight relative to the crude product.

[0072] In one embodiment, stripping is performed for a period of up to 48 hours. In another embodiment, stripping is performed for a period of 1 to 24 hours. In another embodiment, stripping is performed for a period of 2 to 12 hours. In another embodiment, stripping is performed for a period of 4 to 7 hours. In another embodiment, the product is purified by stripping with nitrogen at a temperature of 150°C to 170°C at atmospheric pressure for a period of up to 48 hours. In another embodiment, the product is purified by stripping with nitrogen at a temperature of 150°C to 170°C at atmospheric pressure for a period of 1 to 24 hours. In another embodiment, the product is purified by stripping with nitrogen at a temperature of 150°C to 170°C at atmospheric pressure for a period of 2 to 12 hours. In another embodiment, the product is purified by stripping with nitrogen at a temperature of 150°C to 170°C at atmospheric pressure for a period of 5 to 7 hours.

[0073] As indicated above, the method of the present invention provides a method for preparing 2-ethylhexyl p-nitrobenzoate. 2-ethylhexyl p-nitrobenzoate is a common starting material for preparing 2-ethylhexyl p-aminobenzoate. Therefore, in one embodiment of the invention, the method further comprises preparing 2-ethylhexyl p-nitrobenzoate, comprising reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst. As mentioned above, 2-ethylhexyl p-nitrobenzoate of high purity can be obtained by the method of the present invention without purifying by washing, distillation or phase separation. Therefore, in one embodiment of the invention, 2-ethylhexyl p-nitrobenzoate of raw material is not purified by washing, distillation or phase separation before reacting with hydrogen in the presence of a catalyst for preparing 2-ethylhexyl p-nitrobenzoate. Therefore, the improved method for preparing 2-ethylhexyl p-nitrobenzoate is also advantageous for the preparation of 2-ethylhexyl p-aminobenzoate. In addition, the purity of p-aminobenzoic acid-2-ethylhexyl ester can be improved by adjusting pH before reacting with hydrogen. Therefore, in one embodiment of the invention, before reacting with hydrogen, the pH value is adjusted to a value within the range of 4 to 10. In another embodiment of the invention, after reacting with hydrogen, phase separation is performed by adding carbonate. Phase separation is reduced by adding carbonate to reduce water content.

[0074] 2-Ethylhexyl p-aminobenzoate can be reacted with cyanuric halide to obtain the known high-efficiency 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'-oxyl)-1,3,5-triazine. Therefore, in another embodiment, the method further includes preparing 2,4,6-triphenylamino-p-(carbonyl-2'-ethylhexyl-1'-oxyl)-1,3,5-triazine having the following chemical formula by reacting cyanuric halide with 2-ethylhexyl p-aminobenzoate in a non-polar solvent:

[0075]

[0076] Preferably, cyanuric halide and p-aminobenzoic acid-2-ethylhexyl are reacted in a molar ratio of 1:3 to 1:5. Reacting cyanuric halide and p-aminobenzoic acid-2-ethylhexyl in a molar ratio of at least 1:3 allows the complete conversion of cyanuric halide, 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-nitrobenzoic acid-2-ethylhexyl is also advantageous for the preparation of ethylhexyl triazone. Reducing the complexity, waste and cost of the preparation of p-nitrobenzoic acid-2-ethylhexyl also reduces the overall complexity, waste and cost of the preparation of ethylhexyl triazone. Considering the high demand for ethylhexyl triazone, this is particularly advantageous because it has multiple applications as a UV absorber.

[0077] As mentioned above, high purity can be obtained by the process of the present invention. Therefore, 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.

[0078] Furthermore, in one embodiment, the present invention relates to 2-ethylhexyl p-nitrobenzoate, which is obtained by the process of the present invention.

[0079] 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 obtained 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%.

[0080] Furthermore, 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 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% - is in the form of a high-viscosity fluid.

[0081] Thus, in another embodiment, the present invention is directed to 2-ethylhexyl p-nitrobenzoate in the form of a high viscosity fluid.

[0082] The present invention is further illustrated by the following examples.

[0083] Examples

[0084] The following abbreviations are used: p-NBAE: 2-ethylhexyl p-nitrobenzoate, 2-EH: 2-ethylhexanol, p-TSA: p-toluenesulfonic acid, p-NBA: p-nitrobenzoic acid.

[0085] In the examples, Karl Fischer titration was performed on a Metrohm 890 Titrando with 900 Touch Control and 803 TI stage using a Metrohm 6.0338.100 double PT-wire electrode.

[0086] In the examples, GC analysis was performed on an Agilent Technologies 7890B using the following conditions and parameters:

[0087] Detector: FID

[0088] Solvent: dichloromethane

[0089] Column: Macherey-Nagel Optima 1701 (25 m, 0.53 mm ID, 1.00 μm film thickness)

[0090] Carrier gas: Helium 25mL / min

[0091] Injector temperature and detector temperature: 250°C

[0092] Temperature program: 100°C for 2 min, then 10°C / min until 150°C, then 50°C / min until 200°C, and hold at 200°C for 2 min.

[0093] In the examples, HPLC analysis was performed on an Agilent 1260 using the following conditions and parameters:

[0094] Detector: UV at 220 nm

[0095] Column: Waters Spherisorb ODS-2 (10 μm, 250×4 mm)

[0096] Flow rate: 1.2mL / min

[0097] Solvents: Acetonitrile with 0.1 vol% phosphoric acid (Solvent A) and deionized water with 0.1 vol% phosphoric acid (Solvent B)

[0098] Gradient Program:

[0099]

[0100] Example 1: Preparation of 2-ethylhexyl p-nitrobenzoate

[0101] Under an inert nitrogen atmosphere, 17.4 kg of 65% p-toluenesulfonic acid was added to reactor A. Then, 495 kg of 2-ethylhexanol and 562.5 kg of solid p-nitrobenzoic acid were added to the same reactor. Esterification was started by heating the reactor to a temperature of 160° C. for a period of 6 hours under stirring. The reaction was carried out under reflux, and the mixture of 2-ethylhexanol, water and by-products produced was collected in a second reactor B. The 2-ethylhexanol in reactor B can be reused in subsequent reactions after purification. Water and by-products are pumped to a wastewater treatment plant. The remaining 2-ethylhexanol, water and by-products in reactor A are stripped with nitrogen at a temperature of 160° C. for an additional period of 6 hours to form the final product of p-nitrobenzoic acid-2-ethylhexyl ester. The purity observed with GC is 95.5%. The final products were characterized using GC (p-NBAE, 2-EH, others) and HPLC (p-NBA, p-TSA), and the water content was measured using Karl-Fischer titration. The results are shown in Table 1.

[0102] Table 1.

[0103]

[0104] Other = substances not identified from GC peaks

Claims

1. A method for preparing 2-ethylhexyl p-nitrobenzoate, 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) 2-ethylhexanol is provided in a substoichiometric amount and no additional solvent is added.

2. The method according to claim 1, wherein: The reaction is carried out in the presence of a catalyst, preferably selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, polyphosphoric acid, 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 any one of claims 1 to 3, wherein: The reaction was not carried out under reduced pressure.

5. The method according to any one of claims 1 to 4, wherein: The product was purified by gas / steam stripping.

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

7. The method according to any one of claims 1 to 6, wherein: The reaction is carried out at a temperature of up to 180°C for a period of up to 48 hours.

8. The method according to any one of claims 1 to 7, wherein: The method further includes preparing 2-ethylhexyl p-aminobenzoate, comprising reacting 2-ethylhexyl p-nitrobenzoate with hydrogen in the presence of a catalyst.

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

10. The method according to claim 8 or 9, wherein: Prior to the reaction with hydrogen, the pH is adjusted to a value in the range of 4 to 10.

11. The method according to any one of claims 8 to 10, wherein: After reaction with hydrogen, phase separation is carried out by adding carbonate.

12. The method according to any one of claims 8 to 11, 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 13. 2-Ethylhexyl p-nitrobenzoate having a purity of at least 94% by weight.

14. 2-Ethylhexyl p-nitrobenzoate according to claim 13, which is obtained by the process according to any one of claims 1 to 12.

15. 2-Ethylhexyl p-nitrobenzoate according to claim 13 or 14, 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. 2-Ethylhexyl p-nitrobenzoate according to any one of claims 13 to 15, which is in the form of a high viscosity fluid.

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