Process for the preparation of 2-(meth)acryloyloxybenzoic acid esters

Abstract

The present invention relates to a solvent-free process for the preparation of 2-(meth)acryloyloxybenzoic acid esters, wherein 2-hydroxybenzoic acid esters are reacted with (meth)acrylic anhydride in the presence of lithium methoxide as catalyst.

Description

[0001] This invention relates to a solvent-free method for preparing 2-(meth)acryloyloxybenzoate, wherein 2-hydroxybenzoate reacts with (meth)acrylic anhydride in the presence of lithium methoxide as a catalyst.

[0002] These polymerizable monomers can be used in a variety of applications, including as reactive diluents in photopolymerization processes, such as lithography-based photopolymerization processes, such as high-temperature lithography processes performed at temperatures above 90°C. These monomers allow for good processability in additive manufacturing technologies and can produce cured products with thermomechanical properties desired for a wide range of applications, including those used to form medical devices and / or intraoral environments, such as intraoral appliances like braces, expanders, or spacers.

[0003] Existing technology WO 2019 / 213588 relates to photopolymerizable monomers and discloses the preparation of certain 2-(meth)acryloyloxybenzoates by reacting 2-hydroxybenzoates with (meth)acryloyl chloride.

[0004] The use of (meth)acrylic anhydride as a reagent for the substrate menthyl salicylate in the presence of DMAP as a catalyst without the use of a solvent is described (see Example 3,

[0185] ).

[0005] The solvent-free preparation of 2-(meth)acryloyloxybenzoate in the presence of lithium methoxide as a catalyst is not described.

[0006] Liska et al. (Journal of Polymer Science 2021 (Hoboken, NJ, USA), Vol. 59, No. 19, pp. 2154-2169) describe a method for producing salicylate methacrylate using stoichiometric amounts of triethylamine and methacryloyl chloride in dichloromethane. The precipitated ammonium chloride was removed by filtration. The filtrate was washed, the organic layer dried over Na₂SO₄, filtered and stabilized, followed by solvent evaporation. The crude product was purified by silica gel chromatography.

[0007] The solvent-free preparation of 2-(meth)acryloyloxybenzoate in the presence of lithium methoxide as a catalyst is not described.

[0008] WO 2019 / 224193 relates to a method for preparing ketone-functionalized aromatic (meth)acrylates by reacting a ketone-functionalized aromatic alcohol or a ketone-functionalized aromatic amine with (meth)acrylic anhydride, wherein the content of (meth)acrylic anhydride is less than 4.5%. An exemplary product is a benzophenone derivative prepared in the presence of a catalytic amount of concentrated sulfuric acid or an aqueous solution of sodium hydroxide.

[0009] The solvent-free preparation of 2-(meth)acryloyloxybenzoate in the presence of lithium methoxide as a catalyst is not described.

[0010] WO 2020 / 035315 relates to a method for preparing (meth)acrylates of primary alcohols, secondary alcohols, tertiary alcohols, and phenols using (meth)acrylic anhydride in the presence of magnesium or rare earth elements.

[0011] There is no description of the preparation of 2-(meth)acryloyloxybenzoate in the presence of lithium methoxide as a catalyst.

[0012] JP 2022-147037 relates to a method for reacting 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone with (meth)acrylic anhydride in the presence of lithium, magnesium, or calcium salts. The preparation of 2-(meth)acryloyloxybenzoate in the presence of lithium methoxide as a catalyst is not described.

[0013] JP 2022-147036 relates to a method for producing benzophenone methacrylate using (meth)acrylic anhydride in the presence of lithium, magnesium, or calcium salts. It does not describe the preparation of 2-(meth)acryloyloxybenzoate in the presence of lithium methoxide as a catalyst.

[0014] One object of the present invention is to provide a solvent-free method for the preparation of 2-(meth)acryloyloxybenzoate in high yield and high purity, which can be used on a large scale and avoids the preparation of equimolar amounts of solid byproducts that must be removed by cumbersome post-treatment to separate the desired product.

[0015] Surprisingly, it was found that, in the presence of lithium methoxide as a catalyst, using (meth)acrylic anhydride as a reagent, sterically hindered alcohol 2-hydroxybenzoate can be converted into the corresponding 2-(meth)acryloyloxybenzoate.

[0016] Due to the steric hindrance of alcohols, the generally known equimolar reactions using known catalysts as described above are not feasible.

[0017] Detailed Description of the Invention This invention relates to a method for preparing 2-(meth)acryloyloxybenzoate of general formula (I). (I), in R represents H or CH3, and R 1 This indicates an unsubstituted C5-7 cycloalkyl group, or one, two, or three substituents selected from straight-chain or branched C1-6 alkyl, straight-chain or branched C1-6 alkoxy, -O(CO)-(C1-6)alkyl, and -COO-(C1-6)alkyl. R 1 Residues representing general formula (II) (II), in R 2 It indicates a straight-chain or branched C1-6 alkyl or a straight-chain or branched C1-6 alkoxy group, and n represents an integer 0, 1, or 2. The method includes the following steps: (a) Reacting a 2-hydroxybenzoate of general formula (III) with a (meth)acrylic anhydride of general formula (IV) in the presence of lithium methoxide as a catalyst and at least one stabilizer: (III), in R 1 As previously defined, (IV), Where R represents H or CH3. The characteristic feature is that the reaction occurs in the absence of any solvent.

[0018] Another object of the present invention relates to a method for preparing 2-(meth)acryloyloxybenzoate of general formula (I), wherein R represents H or CH3, R 1 It represents benzyl, or unsubstituted cyclohexyl, or substituted with one, two, or three substituents selected from straight-chain or branched C1-3 alkyl and straight-chain or branched C1-3 alkoxy groups.

[0019] Another embodiment involves a method further outlined above, wherein the 2-(meth)acryloyloxybenzoate is 3,3,5-trimethylcyclohexylsalicyl (meth)acrylate of general formula (Ia): (Ia), Where R represents H or CH3. The method includes the following steps: (a) To make 3,3,5-trimethylcyclohexyl-2-hydroxybenzoate of formula (IIIa): (IIIa), With general formula (IV) (meth)acrylic anhydride (IV), Where R represents H or CH3. The reaction takes place in the presence of lithium methoxide as a catalyst and at least one stabilizer. The characteristic feature is that the reaction occurs in the absence of any solvent.

[0020] The term "(meth)acrylate" refers to both esters of acrylic acid and esters of methacrylic acid.

[0021] The term "(meth)acrylic anhydride" refers to both acrylic anhydride and methacrylic anhydride.

[0022] The term "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid.

[0023] The C5-7 cycloalkyl group used in this invention can be selected from cyclopentyl, cyclohexyl, and cycloheptyl.

[0024] The straight-chain or branched C1-6 alkyl groups used in this invention can be selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl.

[0025] The straight-chain or branched C1-3 alkyl groups used in this invention can be selected from methyl, ethyl, propyl and isopropyl.

[0026] The straight-chain or branched C1-6 alkoxy groups used in this invention may be selected from methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentoxy, and hexoxy.

[0027] The straight-chain or branched C1-3 alkoxy groups used in this invention may be selected from methoxy, ethoxy, propoxy, and isopropoxy.

[0028] According to the present invention, the amount of lithium methoxide catalyst used is from 3.5 mol% to 10 mol%, preferably from 3.5 mol% to 7 mol%, based on the amount of 2-hydroxybenzoate of general formula (III) or (IIIa) used as the starting material.

[0029] Suitable stabilizers are known to those skilled in the art. These include, for example, phenothiazines, substances having an oxygen group, such as 2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPOL), or 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPOL-(meth)acrylate), and phenol derivatives, such as hydroquinone monomethyl ether (HQME), 2,4-dimethyl-6-tert-butylphenol (DMBP), 2,6-di-tert-butylphenol, or 4-methyl-2,6-di-tert-butylphenol (BHT). Mixtures of different stabilizers may also be used. HQME, DMBP, BHT, phenothiazines, and mixtures thereof are preferred.

[0030] The application of 2-(meth)acryloyloxybenzoate (I) and, in particular, 3,3,5-trimethylcyclohexyl salicylate (Ia) of (meth)acrylate typically requires a colorless product. Therefore, for these unsaturated compounds, non-coloring stabilizers or very small amounts of coloring stabilizers are preferred. The amount of stabilizer used depends on the starting material.

[0031] The amount of stabilizer at the start of the reaction is adjusted to between 1 ppm and 5000 ppm, based on the amount of 2-hydroxybenzoic acid ester of general formula (III) or (IIIa) used as the starting material. Preferably, the amount of stabilizer at the start of the reaction is adjusted to between 1 ppm and 3000 ppm, particularly preferably between 1 ppm and 2000 ppm, based on the amount of 2-hydroxybenzoic acid ester of general formula (III) or (IIIa) used as the starting material.

[0032] The reaction was carried out under air conditions in a suitable reaction vessel equipped with a stirrer and a temperature control system.

[0033] The reaction can be carried out at standard pressure or elevated pressure.

[0034] The reaction temperature is usually in the range of 95℃-115℃, preferably in the range of 100℃-110℃.

[0035] The reaction usually proceeds until all starting materials have reacted (GC controlled).

[0036] According to the present invention, a reaction time of 4 to 15 hours is preferred.

[0037] In order to completely convert the sterically hindered alcohol into the corresponding product, an excess of (meth)acrylic anhydride is required.

[0038] According to the invention, based on the amount of 2-hydroxybenzoate of general formula (III) or (IIIa) used as the starting material, 1.5 to 2.5 molar equivalents, preferably about 2 molar equivalents of (meth)acrylic anhydride, are used.

[0039] During the reaction, (meth)acrylic acid is formed as a byproduct. Therefore, the reaction mixture obtained in step (a) contains not only the desired product of general formula (I) or (Ia), but also (meth)acrylic acid and an excess of (meth)acrylic anhydride.

[0040] Another object of the present invention relates to a process mixture comprising: (a) 45%-70% by weight, preferably 55%-65% by weight, of 2-(meth)acryloyloxybenzoate of general formula (I). (I), in R represents H or CH3, and R 1 This indicates an unsubstituted C5-7 cycloalkyl group, or one, two, or three substituents selected from straight-chain or branched C1-6 alkyl, straight-chain or branched C1-6 alkoxy, -O(CO)-(C1-6)alkyl, and -COO-(C1-6)alkyl. R 1 Residues representing general formula (II) (II) in R 2 Indicates straight-chain or branched C1-6 alkyl or straight-chain or branched C1-6 alkoxy, and n represents 0, 1, or 2; (b) 0%-40% by weight, preferably 12%-30% by weight, of (meth)acrylic anhydride of general formula (IV), wherein R represents H or CH3; (c) 2%-55% by weight, preferably 2%-15% by weight (meth)acrylic acid; and (d) 1 ppm (0.0001 wt%) to 2000 ppm (0.2 wt%) of phenothiazines.

[0041] Another object of the present invention relates to a process mixture comprising: (a) 45% to 70% by weight, preferably 55% to 65% by weight, of compounds of general formula (I), wherein R represents H or CH3, R 1 It represents benzyl, or unsubstituted cyclohexyl, or substituted with one, two or three substituents selected from straight-chain or branched C1-3 alkyl and straight-chain or branched C1-3 alkoxy groups; (b) 0%-40% by weight, preferably 12%-30% by weight, of (meth)acrylic anhydride of general formula (IV), wherein R represents H or CH3; (c) 2%-55% by weight, preferably 2%-15% by weight (meth)acrylic acid; and (d) 1 ppm (0.0001 wt%) to 2000 ppm (0.2 wt%) of phenothiazines.

[0042] Another object of the present invention relates to a process mixture comprising: (a) 45%-70% by weight, preferably 55%-65% by weight, of 3,3,5-trimethylcyclohexyl salicylate of general formula (Ia). (Ia), Where R represents H or CH3; (b) 0%-40% by weight, preferably 12%-30% by weight, of (meth)acrylic anhydride of general formula (IV). (IV), Where R represents H or CH3; (c) 2%-55% by weight, preferably 2%-15% by weight (meth)acrylic acid; and (d) 1 ppm (0.0001 wt%) to 2000 ppm (0.2 wt%) of phenothiazines.

[0043] The contents of each component (a), (b), (c) and (d) are based on the total composition of the process mixture.

[0044] In the specific implementation plan, the total proportions of components (a), (b), (c), and (d) reach 100 by weight.

[0045] The presence of a catalyst leads to sedimentation and polymerization during distillation. Therefore, the catalyst must be removed before the crude product can be further purified.

[0046] To remove the catalyst from the product obtained in step (a) as further outlined above, the process mixture obtained in step (a) can be diluted with water at a ratio of 1:10 to 10:1, preferably 1:1 to 10:1, and stirred for at least 10 minutes.

[0047] Therefore, another object of the present invention relates to a method comprising the steps (a) further outlined above and including the step (b): (b) The process mixture obtained in step (a) is mixed with water at a ratio of 1:10 to 10:1, preferably 1:1 to 10:1, and the resulting mixture is stirred for at least 10 minutes.

[0048] To separate the aqueous phase from the product phase of the mixture obtained in step (b), phase separation can be performed. This phase separation can be carried out by commonly known methods, such as using simple extraction methods or gravity-based methods, like centrifuges, separators, or coalescers. According to the invention, a preferred separation method is the use of a centrifuge.

[0049] Therefore, another object of the present invention relates to a method comprising steps (a) and (b) as further summarized above and further comprising step (c): (c) Separate the aqueous phase of the mixture obtained in step (b) from the product phase to remove the catalyst.

[0050] The product obtained in step (c) may still contain undesirable impurities. In particular, to remove low-boiling-point byproducts such as (meth)acrylic acid and (meth)acrylic anhydride, the product obtained in step (c) may undergo a first distillation to obtain a product with a (meth)acrylic acid and (meth)acrylic anhydride content of less than 1%.

[0051] If the content of undesirable byproducts is still too high, the distillation can be repeated at least a second time.

[0052] Distillation can be carried out under ambient pressure or reduced pressure and at temperatures ranging from 20°C to 150°C, preferably from 70°C to 150°C.

[0053] Therefore, another object of the present invention relates to a method comprising steps (a), (b), and (c) as further summarized above, and further comprising step (d): (d) Distill the product phase obtained in step (c) to obtain the desired product containing less than 1% (meth)acrylic acid and (meth)acrylic anhydride (distillation may have to be repeated at least once).

[0054] To further purify the product obtained in step (d), especially to remove high-boiling-point impurities, the product may undergo a second distillation process to obtain the desired product with a purity of 90% or higher.

[0055] Distillation can be carried out under reduced pressure and at temperatures ranging from 100°C to 200°C, preferably from 120°C to 180°C.

[0056] Therefore, another object of the present invention relates to a method comprising steps (a), (b), (c), and (d) as further summarized above, and further comprising step (e): (e) Optionally, the product obtained in step (d) is then distilled separately to separate it from other impurities (high-boiling compounds).

[0057] Another object of the present invention relates to a method for preparing 3,3,5-trimethylcyclohexyl salicylate of general formula (Ia): (Ia), Where R represents H or CH3. The method includes the following steps: (a) To make 3,3,5-trimethylcyclohexyl-2-hydroxybenzoate of formula (IIIa): (IIIa) With general formula (IV) (meth)acrylic anhydride (IV) Where R represents H or CH3. The reaction takes place in the presence of lithium methoxide as a catalyst and at least one stabilizer. The characteristic feature is that the reaction occurs in the absence of any solvent; (b) The process mixture obtained in step (a) is mixed with water at a ratio of 1:10 to 10:1, preferably 1:1 to 10:1, and the resulting mixture is stirred for at least 10 minutes; (c) Separate the aqueous phase of the mixture obtained in step (b) from the product phase to remove the catalyst; (d) The product phase obtained in distillation step (c) is used to obtain the desired product containing less than 1% (meth)acrylic acid and (meth)acrylic anhydride; and (e) Optionally, the product obtained in step (d) is then distilled separately to separate it from other impurities.

[0058] The present invention is intended to be described in more detail below with reference to embodiments and comparative embodiments, but this does not constitute any limitation.

[0059] Experimental Section abbreviation CE Comparative Example DMAP 4-Dimethylaminopyridine HOMOSALATE (3,3,5-trimethylcyclohexyl-2-hydroxybenzoate) HSMA Humorsalyl Methacrylate = 3,3,5-Trimethylcyclohexylsalicyl methacrylate MA methacrylic acid MAAH methacrylic anhydride Me methyl Analytical Measurement Composition of the process mixture was determined by gas chromatography (GC): To determine the composition of the process mixture, the composition in acetone (20% solution) was studied by gas chromatography. For this purpose, an Agilent 7820 instrument was used with a DB5 type column (length: 30.0 m, diameter: 250.00 µm, film thickness: 0.25 µm). The injection volume was 0.2 μL (split 1:60). The instrument was operated at an injector temperature of 300 °C and a detector temperature of 300 °C. The following temperature program was used: 80 °C for 2 minutes, heated to 300 °C at a heating rate of 16 °C / min, and held at this final temperature for a further 6 minutes.

[0060] Determining the color number: The color number is determined by the method explained in detail in US 2004 / 186311 (color is determined by platinum-cobalt colorimetry; also known as APHA value (APHA number)).

[0061] This method is based on DIN EN ISO 6271. According to the invention, a Cary 100 UV / VIS spectrophotometer from Agilent Technologies is used, which has filters for the 460 nm and 620 nm ranges.

[0062] Example Preparation of stock solutions for use in Examples 3 and 4, and Comparative Examples 1-4, 10-29 and 31 The target molar ratio of homosalate to MAAH is 1:2. 78.7 g of homosalate (0.3 mol) and 92.5 g of MAAH (0.6 mol) were combined with 17.2 mg of phenothiazine (100 ppm) and stirred to obtain a stock solution with a homosalate:MAAH molar ratio of 1:2.

[0063] Preparation of stock solutions for use in Examples 1 and 2, and Comparative Examples 5-9 The target molar ratio of homosalate to MAAH is 1:2.12. 26.2 g of homosalate (0.1 mol) and 32.7 g of MAAH (0.212 mol) were combined with 5.2 mg of phenothiazine (100 ppm) and stirred to obtain a stock solution with a homosalate:MAAH molar ratio of 1:2.12.

[0064] Preparation of stock solutions for comparative examples 30, 32, and 33 The target molar ratio of homosalate to MAAH is 1:1.7. 26.2 g of homosalate (0.1 mol) and 26.2 g of MAAH (0.17 mol) were combined with 5.2 mg of phenothiazine (100 ppm) and stirred to obtain a stock solution with a homosalate:MAAH molar ratio of 1:1.7.

[0065] The general procedures for preparing Examples 3 and 4 and Comparative Examples 1-4 and 7-33 Place 7.0 g of the corresponding stock solution sample into a 15 mL pressure tube equipped with a Teflon® stopper and a magnetic stirrer. Add the catalyst (mol%) as shown in Table 1 to the solution. Seal the pressure tube tightly. Then, place the pressure tube in an aluminum heating block with an integrated magnetic stirrer and stir. The corresponding times and temperatures are listed in Table 1. Filter the sample for GC analysis through a syringe filter unit and dilute with acetone (20% solution) before analysis.

[0066] The general procedure for preparing comparative examples 5 and 6 using 1.5 mol% catalyst A four-necked 2-liter round-bottom flask equipped with a mechanical stirrer, thermometer, and reflux condenser was connected to an air inlet. 262.4 g of homosalate (1.0 mol), 326.8 g of methacrylic anhydride (2.12 mol) (homosalic acid:MAAH molar ratio of 1:2.12), and 569.7 mg of lithium methoxide (15.0 mmol) were added, and the mixture was stabilized with 59 mg of phenotiazine (100 ppm). The reaction mixture was heated to 100 °C, and samples were taken after 4 and 8 hours. The sample for GC analysis was filtered through a syringe filter unit and diluted with acetone (20% solution) before analysis.

[0067] General procedure for preparing Examples 1 and 2 using 3.5 mol% catalyst A four-necked 2-liter round-bottom flask equipped with a mechanical stirrer, thermometer, and reflux condenser was connected to an air inlet. 262.3 g of homosalate (1.0 mol), 326.8 g of methacrylic anhydride (2.12 mol) (homosalic acid:MAAH molar ratio of 1:2.12), and 1.3 g of lithium methoxide (35.4 mmol) were added, and the mixture was stabilized with 59 mg of phenotiazine (100 ppm). The reaction mixture was heated to 100 °C, and samples were taken after 4 and 8 hours. The sample for GC analysis was filtered through a syringe filter unit and diluted with acetone (20% solution) before analysis.

[0068] Table 1: Reaction Conditions

[0069] Examples 1-4 conform to the present invention and disclose the preparation of (meth)acrylate 3,3,5-trimethylcyclohexyl-2-hydroxybenzoate from 3,3,5-trimethylcyclohexyl-2-hydroxybenzoate using lithium methoxide as a catalyst.

[0070] Comparative Examples 1-33 used different catalysts for the same reaction.

[0071] Table 2: Conversion rates of residual homosalate, homosalate methacrylate (HSMA), and high-boiling point impurities (area %) determined by gas chromatography.

[0072] 1 Brown process mixture in conclusion: Table 2 shows that using only at least 3.5 mol% of lithium methoxide, a reaction temperature greater than 90°C and less than 120°C, and a reaction time of 4–8 hours results in the desired product with an acceptable yield, less than 3 wt% of homosalate starting material, and 3 wt% or less of undesirable high-boiling byproducts.

[0073] Pilot-scale production test: Then the following amounts of raw materials were loaded into a 1m 3 The reactor contained: 195 kg of homosalate (0.74 kmol), 243 kg of MAAH (1.58 kmol, homosalate:MAAH molar ratio 1:2.12), 1 kg of lithium methoxide (3.5 mol%), and 48 g of phenothiazine (110 ppm). The reaction mixture was heated to 100 °C for 12 hours. The reaction progress was monitored by GC analysis. Samples were taken at 2, 4, 8, and 12 hours. The corresponding data are reported in Table 3 below.

[0074] Table 3: Reaction progress in pilot-scale production trials: residual homosalate, homosalate methacrylate (HSMA) conversion and high-boiling impurities (area %) determined by gas chromatography.

[0075] After a 12-hour reaction time, the resulting process mixture containing the catalyst was cooled to room temperature.

[0076] Subsequently, storage tests were conducted on the process mixture containing the catalyst at 30°C and 50°C. The results are reported in Tables 4a and 4b below.

[0077] Table 4a: Storage test of process mixtures containing catalyst at 30°C

[0078] Table 4a (continued)

[0079] Table 4b: Storage test of process mixtures containing catalyst at 50°C

[0080] Table 4b (continued)

[0081] in conclusion: Table 4a shows that when stored at 30°C, the process mixture containing the catalyst remained stable for up to 12 months; that is, the purity remained almost constant within the measurement accuracy range. Furthermore, the color number of the process mixture still containing the catalyst only increased from 13 APHA to 15 APHA.

[0082] Table 4b shows that when stored at 50°C, the process mixture containing the catalyst remained stable for at least 6 months; that is, the purity remained almost constant within the measurement accuracy range. Furthermore, the color number of the process mixture still containing the catalyst only increased from 13 APHA to 27 APHA.

[0083] After 6 months of storage, the purity decreased slightly, and the content of the stabilizer phenothiazine also decreased slightly. This is also reflected in the increase in color number.

[0084] Extraction of HSMA process mixtures: The HSMA process mixture obtained from the pilot test was continuously mixed with water (10 parts process mixture to 3 parts distilled water) in a reactor equipped with a stirrer (200 rpm). The residence time was 15 minutes. For phase separation, a centrifuge V02 from CINC was used. The centrifuge was operated with the following parameters: process temperature 25°C, no mixing adapter, 21.59 mm weir, 4800 rpm, and a feed rate of 15 kg / h.

[0085] 433 kg of the process mixture was extracted to obtain 429 kg of extracted process mixture. The extracted process mixture was obtained with a residual water content of 0.0125 wt% and a residual lithium content of 9 μg / g. The extracted process mixture no longer contained catalyst.

[0086] Distillation of HSMA process mixtures: For the distillation of the extracted HSMA process mixture, a thin-film evaporator (length: 300 mm, diameter: 25 mm) was equipped with a condenser to collect the distillate, a Thiele-Anschütz adapter, and a stirrer (IKA RE162, 450 rpm). A vacuum was established using a Leybold rotary vane pump TRIVAC-D 25B, controlled by a Vacuubrand CVC 3000 and VAP5 controller. Temperature was controlled using an oil-operated circulating thermostat.

[0087] The first distillation is to remove low-boiling-point substances (light boilers). 1295.6 g of the extracted HSMA process mixture was fed into a thin-film evaporator over 98 minutes using a jacket temperature of 130 °C and a vacuum of 0.4 mbar. 525.1 g of distillate was removed, yielding 759.3 g of residue.

[0088] A second distillation is performed to remove low-boiling-point substances. Using a jacket temperature of 130°C and a vacuum of 0.8 mbar, 743.4 g of the residue from the first distillation was fed back into the thin-film evaporator over a period of 47 minutes. After removing 3.6 g of distillate, 735.8 g of residue was obtained.

[0089] Final distillation: product distillation Using a jacket temperature of 180°C and a vacuum of 0.5 mbar, 721.6 g of the residue from the second distillation was fed back into the thin-film evaporator over 141 minutes. 476.2 g of final HSMA product (38% distillation yield) was obtained, and 242.1 g of residue was removed.

[0090] Table 5: Gas chromatographic analysis of the final HSMA products:

[0091] Subsequently, storage tests were performed using the final distilled HSMA product at 30°C and 50°C. The results are reported in Tables 6a and 6b below.

[0092] Table 6a: Storage test of the final HSMA product at 30°C

[0093] Table 6a (continued)

[0094] Table 6b: Storage test of the final HSMA product at 50°C

[0095] Measurement error ±5% Table 6b (continued)

[0096] in conclusion: Table 6a shows that when stored at 30°C, the final HSMA product remained stable for up to 12 months; that is, the purity remained almost constant within the measurement accuracy range. Furthermore, the color number of the final HSMA product only slightly increased from 9 APHA to 21 APHA.

[0097] Table 6b shows that when stored at 50°C, the final HSMA product remained stable for at least 6 months; that is, the purity remained almost constant within the measurement accuracy range. Furthermore, the color number of the final HSMA product, still containing the catalyst, only increased from 9 APHA to 38 APHA.

[0098] After 6 months of storage, the purity decreased slightly, and the content of the stabilizer phenothiazine also decreased slightly. This is also reflected in the increase in color number.

Claims

1. A method for preparing 2-(meth)acryloyloxybenzoate of general formula (I) (I)， in R represents H or CH3, and R 1 This indicates an unsubstituted C5-7 cycloalkyl group, or one, two, or three substituents selected from straight-chain or branched C1-6 alkyl, straight-chain or branched C1-6 alkoxy, -O(CO)-(C1-6)alkyl, and -COO-(C1-6)alkyl. R 1 Residues representing general formula (II) (II), in R 2 It indicates a straight-chain or branched C1-6 alkyl or a straight-chain or branched C1-6 alkoxy group, and n represents an integer 0, 1, or 2. The method includes the following steps: (a) Reacting a 2-hydroxybenzoate of general formula (III) with a (meth)acrylic anhydride of general formula (IV) in the presence of lithium methoxide as a catalyst and at least one stabilizer: (III), in R 1 As previously defined, (IV), Where R represents H or CH3. The characteristic feature is that the reaction occurs in the absence of any solvent.

2. The method according to claim 1, wherein R 1 It represents benzyl, or unsubstituted cyclohexyl, or substituted with one, two, or three substituents selected from straight-chain or branched C1-3 alkyl and straight-chain or branched C1-3 alkoxy groups.

3. The method according to claim 1 or 2, wherein the amount of the catalyst used is from 3.5 mol% to 7 mol%, based on the amount of 2-hydroxybenzoic acid ester of general formula (III) used as the starting material.

4. The method according to claim 1, 2 or 3, wherein the stabilizer is selected from phenothiazine, 2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPOL), 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPOL-(meth)acrylate), hydroquinone monomethyl ether (HQME), 2,4-dimethyl-6-tert-butylphenol (DMBP), 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol (BHT) and mixtures thereof.

5. The method according to claim 1, 2, 3 or 4, wherein the stabilizer is selected from phenothiazine, hydroquinone monomethyl ether (HQME), 2,4-dimethyl-6-tert-butylphenol (DMBP), 4-methyl-2,6-di-tert-butylphenol (BHT) and mixtures thereof.

6. The method according to claim 1, 2, 3, 4 or 5, wherein the amount of the stabilizer used is from 1 ppm to 5000 ppm, preferably from 1 ppm to 3000 ppm, more preferably from 1 ppm to 2000 ppm, based on the amount of 2-hydroxybenzoic acid ester of general formula (III) used as the starting material.

7. The method according to claim 1, 2, 3, 4, 5 or 6, wherein the reaction time of step (a) is at least 4 hours, preferably at least 6 hours, more preferably at least 8 hours, and at most 15 hours.

8. The method according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the reaction in step (a) is carried out at a temperature of 95°C-115°C, preferably 100°C-110°C.

9. The method according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein (meth)acrylic anhydride is used in excess based on the amount of 2-hydroxybenzoate of formula (III) used in step (a), in an amount of 1.5 to 2.5 molar equivalents, preferably about 2 molar equivalents.

10. The method according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the 2-(meth)acryloyloxybenzoate is 3,3,5-trimethylcyclohexyl salicylate of general formula (Ia): (I), Where R represents H or CH3. The method includes the following steps: (a) Reaction of 3,3,5-trimethylcyclohexyl-2-hydroxybenzoate of formula (IIIa) with (meth)acrylic anhydride of general formula (IV) in the presence of lithium methoxide as a catalyst (3.5 mol% to 10 mol%) and at least one stabilizer: (IIIa), (IV), Where R represents H or CH3. The characteristic feature is that the reaction occurs in the absence of any solvent.

11. The method according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, further comprising the following steps: (b) The process mixture obtained in step (a) is mixed with water at a ratio of 1:10 to 10:1, preferably 1:1 to 10:1, and the resulting mixture is stirred for at least 10 minutes; (c) Separate the aqueous phase of the mixture obtained in step (b) from the product phase to remove the catalyst; (d) The product phase obtained in distillation step (c) is used to obtain the desired product containing less than 1% (meth)acrylic acid and (meth)acrylic anhydride; and (e) Optionally, the product obtained in step (d) is then distilled separately to separate it from other impurities.

12. The method of claim 11, wherein the phase separation step (c) is performed by using a centrifuge, separator, or coalescer, preferably by using a centrifuge.

13. A process mixture comprising: (a) 45% to 70% by weight of 3,3,5-trimethylcyclohexyl salicylate of general formula (Ia) (I), Where R represents H or CH3; (b) 0%-40% by weight of (meth)acrylic anhydride of general formula (IV) (IV), Where R represents H or CH3; (c) 2%-55% by weight of (meth)acrylic acid; and (d) 1 ppm (0.0001 wt%) to 2000 ppm (0.2 wt%) of phenothiazines.

14. The process mixture according to claim 13, comprising: (a) 55% to 65% by weight of 3,3,5-trimethylcyclohexyl salicylate of general formula (Ia); (b) 12% to 30% by weight of (meth)acrylic anhydride of general formula (IV); (c) 2%-15% by weight of (meth)acrylic acid; and (d) 1 ppm (0.0001 wt%) to 2000 ppm (0.2 wt%) of phenothiazines.

Images