Preparation of (meth)acrylates

Abstract

The invention relates to a process for the preparation of (meth)acrylates from (meth)acrylic anhydrides.

Description

Technical Field

[0001] This invention relates to a method for preparing (meth)acrylates from (meth)acrylic anhydride. Background Technology

[0002] (Meth)acrylates are commonly used as monomers for the preparation of various poly(meth)acrylates and corresponding copolymers. Accordingly, various methods for obtaining (meth)acrylates are known. These methods particularly include transesterification reactions, in which methyl methacrylate reacts with an alcohol. Another common possibility is the acylation of the alcohol with (meth)acrylic anhydride.

[0003] The process of alcohol acylation using (meth)acrylic anhydride, particularly methacrylic anhydride, is typically carried out in the presence of acids, such as sulfuric acid. Under these conditions, undesirable reactions, such as polymerization of the anhydride, often occur, resulting in only moderate yields of (meth)acrylate products. Furthermore, the preparation of (meth)acrylates from sterically hindered alcohols is known to be hampered by low reaction yields because these alcohols are not only poorly reactive with (meth)acrylic anhydride but also tend to undergo undesirable dehydration under the commonly used reaction conditions.

[0004] For these reasons, (meth)acrylic anhydride is often used in large excesses to achieve reasonable conversion rates of hindered alcohols and phenols. This is disadvantageous from both an economic and environmental perspective, as (meth)acrylic anhydride is quite expensive and the recovery of unreacted excess (meth)acrylic anhydride is difficult.

[0005] In the past, quite a few methods have been developed for the acylation of alcohols using non-polymerizable acid anhydrides, such as acetic anhydride. However, these methods are generally ineffective for (meth)acrylic anhydride because the reactivity and chemical behavior of (meth)acrylic anhydride are significantly different from those of acetic anhydride.

[0006] US 4,540,743A describes the acylation of polyvinyl alcohol by esterification with activated (meth)acrylic anhydride in the presence of a tertiary amine. This procedure requires a relatively large amount of tertiary amine. Therefore, the tertiary amine needs to be separated from the product mixture in a separate washing step, which generates a considerable amount of aqueous waste. Summary of the Invention

[0007] In view of the aforementioned technical problems of the prior art, the object of the present invention is to develop a more efficient, industrially applicable method for preparing (meth)acrylates from (meth)acrylic anhydride. Such a method should ideally provide the following advantages:

[0008] High product yield and high conversion rate of (meth)acrylates

[0009] Short reaction time

[0010] Low excess of (meth)acrylic anhydride

[0011] • A small amount of acylation catalyst can be easily separated from the resulting product if needed.

[0012] In addition, this method should be suitable for the efficient and cost-effective preparation of di- or poly(meth)acrylates on an industrial scale.

[0013] This invention is based on a surprising discovery—that (meth)acrylic anhydride can be activated efficiently by using magnesium salts or salts of rare earth elements as catalysts.

[0014] Accordingly, one aspect of the present invention relates to a method for preparing (meth)acrylates, the method comprising at least the following step (a):

[0015] (a) The reaction between (meth)acrylic anhydride of formula (I) and the substrate in the presence of magnesium salts or rare earth element salts.

[0016]

[0017] Where R1 is a hydrogen atom or a methyl group,

[0018] This results in a mixture of products containing (meth)acrylates.

[0019] As used herein, the terms “(meth)acrylate” and “(meth)acrylate series” can refer to acrylate and methacrylate. The (meth)acrylic anhydride of formula (I) can be acrylic anhydride (R1 is a hydrogen atom) or methacrylic anhydride (R1 is a methyl group).

[0020] The first catalyst used in step (a) catalyzes the reaction between (meth)acrylic anhydride of formula (I) and the substrate. According to the invention, the first catalyst comprises a magnesium salt or a salt of a rare earth element.

[0021] As used herein, the term "rare earth element" refers to an element selected from cerium, dysprosium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, and yttrium. In a particularly preferred embodiment, the term "rare earth element" refers to an element selected from lanthanum, ytterbium, yttrium, and scandium.

[0022] In principle, virtually any magnesium salt or salt of the rare earth elements listed above is suitable as the first catalyst in this invention. However, the catalytic activity of the first catalyst is particularly high if the salt is selected from fluorides, chlorides, bromides, iodides, acetates, sulfates, perchlorates, and trifluoromethanesulfonates. In a particularly preferred embodiment, the salt may be selected from chlorides, bromides, iodides, and trifluoromethanesulfonates.

[0023] Accordingly, the catalytic activity of the first catalyst is particularly high when it contains halides of magnesium or rare earth elements, perchlorates of magnesium or rare earth elements, or trifluoromethanesulfonates of magnesium or rare earth elements. In particular, if the first catalyst is selected from magnesium bromide, magnesium iodide, magnesium chloride, bis-(trifluoromethanesulfonyl)imide magnesium, magnesium perchlorate, lanthanum(III) trifluoromethanesulfonate, ytterbium(III) trifluoromethanesulfonate, yttrium(III) trifluoromethanesulfonate, and scandium(III) trifluoromethanesulfonate, the yield of the (meth)acrylate product formed in reaction step (a) is particularly high.

[0024] The first catalyst can be used in anhydrous form or as a hydrate.

[0025] Surprisingly, even when the first catalyst is present in a relatively low amount, the reaction between the (meth)acrylic anhydride of formula (I) and the substrate in reaction step (a) proceeds smoothly. Nevertheless, by using a higher amount of the first catalyst, the reaction time in reaction step (a) can be further reduced. Depending on the reactivity of the substrate, the total amount of the first catalyst in step (a) is typically selected based on the amount of substrate, between 0.001 mol% and 10 mol%, more preferably between 0.01 mol% and 1.0 mol%, and even more preferably between 0.1 mol% and 0.5 mol%.

[0026] The reaction solvent used in step (a) is not particularly limited, provided that the solvent does not chemically react with the (meth)acrylic anhydride of formula (I) and its boiling point allows step (a) to be carried out at the desired temperature. However, advantageously, step (a) is carried out in the absence of any solvent.

[0027] The order in which the reagents are added in step (a) is not particularly restricted. Thus, in one embodiment, the first catalyst is first dispersed in the substrate, followed by the addition of (meth)acrylic anhydride of formula (I). Alternatively, the first catalyst may be first dispersed in (meth)acrylic anhydride of formula (I), followed by the addition of the substrate to the resulting dispersion.

[0028] In some implementations, a mixture of (meth)acrylic anhydride of formula (I) and the substrate may be prepared first, and the reaction may be initiated by adding a first catalyst thereto. However, this procedure is generally more difficult to use on an industrial scale.

[0029] Those skilled in the art can readily adjust the optimal reaction temperature in step (a) based on the reactivity of the substrate and the (meth)acrylic anhydride of formula (I). Typically, the reaction temperature in step (a) is maintained between 20°C and 140°C, preferably between 40°C and 110°C, and more preferably between 60°C and 90°C.

[0030] Due to the high catalytic activity of the first catalyst, the reaction time of step (a) is typically between 10 minutes and 10 hours, and usually between 30 minutes and 4 hours. As will be readily apparent to those skilled in the art, the reaction time of step (a) can also be adjusted by changing the reaction temperature and the amount of the first catalyst.

[0031] The substrates suitable for the methods of the present invention are not particularly limited and can be selected from substantially any primary, secondary, tertiary, and phenolic alcohols. For example, in one embodiment of the invention, the substrate can be selected from primary, secondary, tertiary, and phenolic alcohols having one or more hydroxyl groups. For example, the substrate can be advantageously selected from primary, secondary, and tertiary alcohols having one hydroxyl group. The use of these substrates readily results in the production of the corresponding (meth)acrylate monoesters in good stoichiometry.

[0032] The molar ratio of (meth)acrylic anhydride to substrate in step (a) is not particularly limited and can be adjusted according to the reactivity of the substrate and (meth)acrylic anhydride. For example, the molar ratio of (meth)acrylic anhydride to substrate in step (a) can be selected between 5:1 and 1:5, preferably between 3:1 and 1:3, more preferably between 2:1 and 1:2, and even more preferably between 1.5:1 and 1:1.5.

[0033] The reaction between the (meth)acrylic anhydride of formula (I) in step (a) is typically carried out in the presence of a slight excess of (meth)acrylic anhydride, for example, at least 10 mol% or at least 20 mol% excess based on the amount of substrate. To separate the unreacted excess (meth)acrylic anhydride from the resulting (meth)acrylate, an auxiliary alcohol may be added to the product mixture obtained in step (a). Under these conditions, a product mixture comprising the desired methacrylate and the auxiliary alcohol is formed. Subsequently, the methacrylate of the auxiliary alcohol can be separated from this product mixture, typically by distillation.

[0034] Therefore, in this embodiment, the method of the present invention can be carried out as follows:

[0035] (a) The reaction between (meth)acrylic anhydride of formula (I) and substrate in the presence of a first catalyst, thereby forming a product mixture containing (meth)acrylate;

[0036] (b) Adding an auxiliary alcohol to the product mixture obtained in step (a), thereby forming a product mixture comprising the (meth)acrylate and the auxiliary alcohol; and

[0037] (c) Remove the auxiliary alcohol (meth)acrylate from the product mixture obtained in step (b).

[0038] The auxiliary alcohol is typically a primary or secondary alcohol. Due to its high reactivity, the auxiliary alcohol readily reacts with the unreacted (meth)acrylic anhydride of formula (I) after step (a), thereby forming the (meth)acrylate of the auxiliary alcohol. For easy separation of the (meth)acrylate of the auxiliary alcohol by distillation in process step (c), the auxiliary alcohol preferably has a boiling point of no more than 150°C, more preferably no more than 120°C, and more preferably no more than 80°C, measured at a pressure of 105 Pa. For example, the auxiliary alcohol may advantageously be selected from methanol, ethanol, n-propanol, isopropanol, or mixtures thereof, with methanol being particularly preferred.

[0039] Finally, another aspect of the invention is the use of magnesium salts or salts of rare earth elements as catalysts in the reaction between (meth)acrylic anhydride of formula (I) and the substrate.

[0040]

[0041] Where R1 is a hydrogen atom or a methyl group;

[0042] The reaction produces a mixture of products containing (meth)acrylates, wherein

[0043] The substrates are selected from primary alcohols, secondary alcohols, tertiary alcohols, and phenols.

[0044] The present invention will be illustrated by the following examples, but they are not intended to constitute a limitation in any way. Detailed Implementation

[0045] Example

[0046] Examples 1-82: Evaluation of the catalytic activity of the first catalyst

[0047] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the study investigated the acylation of menthol via methacrylic anhydride.

[0048] Preparation of raw material solutions of menthol and methacrylic anhydride

[0049] 156 g (1.0 mol) of natural menthol and 161.9 g (1.05 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0050] General procedures for Examples 1-67:

[0051] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst based on menthol was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 50°C oil bath with an integrated magnetic stirrer and stirred for 3 hours.

[0052] A sample without any catalyst (Example 35) in an oil bath at 50°C served as a reference sample and a reaction control, while another starting material solution sample was kept at room temperature. After 3 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0053] The results of Examples 1-67 are summarized in Table 1 below:

[0054] Table 1. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride

[0055]

[0056]

[0057] The data presented in Table 1 indicate that various catalysts commonly used for the acylation of alcohols with acetic anhydride (Lewis acids, Brønsted acids, tertiary amines) are not suitable for (meth)acrylic anhydride. Under the tested reaction conditions, the use of these catalysts resulted in a maximum conversion of 18%.

[0058] Surprisingly, magnesium salts and rare earth element salts exhibited significantly higher catalytic activity under the same reaction conditions.

[0059] The data in Table 1 further demonstrate that the properties of the anions also significantly influence the catalytic activity of the tested salts. Contrary to the inventors' expectations, no correlation was found between the Lewis acid strength of the anions in the tested salts and their catalytic activity. Surprisingly, magnesium halides and rare earth metal trifluoromethanesulfonates exhibited the highest catalytic activity in the acylation using (meth)acrylic anhydride. Perchlorates of the aforementioned metals also showed good catalytic activity.

[0060] Reference Scale 68-76: Evaluation of the catalytic activity of the first catalyst

[0061] As a reference for evaluating the catalytic activity of the first catalyst, the study investigated the acylation of menthol with acetic anhydride.

[0062] Preparation of raw material solutions of menthol and methacrylic anhydride

[0063] 37.8 g (0.17 mol) of natural menthol and 161.9 g (0.1785 mol) of acetic anhydride were combined. The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0064] General procedures for Examples 68-76

[0065] Place a 7g sample of the raw material solution in a container with The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst (based on menthol) was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 50°C oil bath with an integrated magnetic stirrer for 3 hours (unless otherwise specified) with stirring.

[0066] After 3 hours, the contents (area %) of acetic acid, acetic anhydride, menthol, and product were determined by gas chromatography. Based on these data, the reaction conversion rates based on acetic anhydride and menthol were calculated.

[0067] The results of Examples 68-76 are summarized in Table 2 below:

[0068] Table 2. Evaluation of the catalytic activity of the first catalyst when using acetic anhydride

[0069]

[0070] The data in Table 2 confirm that commonly used acylation catalysts, such as 4-dimethylaminopyridine, exhibit excellent catalytic activity when using acetic anhydride. However, these catalysts surprisingly fail when using methacrylic anhydride (see Table 1 above). This suggests that common knowledge about the catalytic behavior of typical acylation catalysts does not apply to acylation using (meth)acrylic anhydride.

[0071] Examples 77-95: Evaluation of the catalytic activity of the first catalyst at 90°C

[0072] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the study investigated the acylation of menthol with methacrylic anhydride at 90 °C.

[0073] Preparation of raw material solutions of menthol and methacrylic anhydride

[0074] 156 g (1.0 mol) of natural menthol and 161.9 g (1.05 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0075] General procedures for Examples 77-95:

[0076] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst based on menthol was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 90°C oil bath with an integrated magnetic stirrer and stirred for 3 hours.

[0077] A catalyst-free sample (Example 93) in an oil bath at 90°C was used as a reference sample. After 3 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0078] The results of Examples 77-95 are summarized in Table 3 below:

[0079] Table 3. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride at 90 °C

[0080]

[0081] The experimental data in Table 3 confirm that lanthanum(III) salts exhibit excellent catalytic activity at 90 °C, even exceeding that of magnesium bromide at this temperature. The data also indicate that these catalysts can be used as both anhydrous salts and hydrates without significant loss of catalytic activity.

[0082] In Reference Example 93, the conversion rate was 38.90% in the absence of any catalyst. Surprisingly, the use of strong Lewis acids, such as zinc chloride (see Example 94), did not result in an improvement of more than 38.90% in conversion rate.

[0083] Examples 96-103: Evaluation of the catalytic activity of the first catalyst when using glycerol carbonate

[0084] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the study investigated the acylation of glycerol carbonates by methacrylic anhydride at 80 °C.

[0085] Preparation of raw material solutions of glycerol carbonate and methacrylic anhydride

[0086] 118 g (1.0 mol) of glycerol carbonate and 162.0 g (1.05 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0087] General procedures for Examples 96-103:

[0088] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. A first catalyst, at 0.1 mol% (unless otherwise specified) based on glycerol carbonate, was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in an 80°C oil bath with an integrated magnetic stirrer and stirred for 6 hours.

[0089] A sample without any catalyst (Example 96) was used as a reference sample in an oil bath at 80°C. After 6 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0090] The results of Examples 96-103 are summarized in Table 4 below:

[0091] Table 4. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride and glycerol carbonate at 80 °C

[0092]

[0093] The results in Table 4 show that the conversion rate was as low as 6.00% in the absence of any catalyst (Example 96). The use of known acylation catalysts, such as 4-dimethyl-aminopyridine (Example 100) and zinc chloride (Example 103), did not provide any improvement. On the contrary, the product conversion rates in these examples were even lower than in the absence of any catalyst.

[0094] In the presence of zinc perchlorate (reference 99) or sulfuric acid (reference 102), unwanted polymers form. Therefore, the desired product cannot be detected.

[0095] Finally, the use of the catalyst according to the invention allows for the preparation of the desired product in moderate to excellent yields.

[0096] Examples 104-111: Evaluation of the catalytic activity of the first catalyst when using isopropanol

[0097] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the isopropanol was acylated by methacrylic anhydride at 90 °C.

[0098] Preparation of raw material solutions of isopropanol and methacrylic anhydride

[0099] 30.1 g (0.50 mol) of isopropanol and 108.0 g (0.7 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0100] General procedures for Examples 104-111:

[0101] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst (based on isopropanol) was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 90°C oil bath with an integrated magnetic stirrer and stirred for 6 hours.

[0102] A catalyst-free sample (Example 104) was used as a reference sample in a 90°C oil bath. After 6 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0103] The results of Examples 104-111 are summarized in Table 5 below:

[0104] Table 5. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride and isopropanol at 90 °C

[0105]

[0106] The results in Table 5 show that the conversion rate is 46.60% in the absence of any catalyst (reference 104). The use of the known acylation catalyst 4-dimethylaminopyridine (reference 109) only brings about a modest improvement.

[0107] In the presence of zinc perchlorate (reference example 108), unwanted polymers are formed and the desired product cannot be detected.

[0108] Examples 112-119: Evaluation of the catalytic activity of the first catalyst when using hexafluoroisopropanol

[0109] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the study investigated the acylation of hexafluoroisopropanol by methacrylic anhydride at 90 °C.

[0110] Preparation of raw material solutions of hexafluoroisopropanol and methacrylic anhydride

[0111] A mixture of 50.4 g (0.30 mol) hexafluoroisopropanol and 64.8 g (0.42 mol) methacrylic anhydride was stabilized with 2000 ppm 2,4-dimethyl-6-tert-butylphenol, 1000 ppm hydroquinone monomethyl ether, and 10 ppm 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0112] General procedures for Examples 112-119:

[0113] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst based on hexafluoroisopropanol was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 90°C oil bath with an integrated magnetic stirrer and stirred for 6 hours.

[0114] A catalyst-free sample (reference 112) was used as a reference sample in a 90°C oil bath. After 6 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0115] The results of Examples 112-119 are summarized in Table 6 below:

[0116] Table 6. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride and hexafluoroisopropanol at 90 °C

[0117]

[0118] The results in Table 6 show that the conversion rate was 43.80% in the absence of any catalyst (reference 112).

[0119] In zinc perchlorate (reference ratio 116) and In the presence of M31 (reference example 113), unwanted polymers are formed and the desired product cannot be detected.

[0120] Examples 120-127: Evaluation of the catalytic activity of the first catalyst when using tert-butanol

[0121] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the study investigated the acylation of tert-butanol by methacrylic anhydride at 90 °C.

[0122] Preparation of raw material solution of tert-butanol and methacrylic anhydride

[0123] 37.1 g (0.50 mol) of tert-butanol and 107.9 g (0.70 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0124] General procedures for Examples 137-127:

[0125] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst based on tert-butanol was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 90°C oil bath with an integrated magnetic stirrer and stirred for 6 hours.

[0126] A catalyst-free sample (reference sample 120) was used as a reference sample in a 90°C oil bath. After 6 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0127] The results of Examples 120-127 are summarized in Table 7 below:

[0128] Table 7. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride and tert-butanol at 90 °C

[0129]

[0130] The results in Table 7 show that, in the absence of any catalyst (reference ratio 120), the conversion rate is as low as 7.50%.

[0131] In zinc perchlorate (reference ratio 124) and In the presence of M31 (reference example 121), unwanted polymers are formed. Therefore, the desired product cannot be detected.

[0132] Magnesium bromide (Example 122) and magnesium perchlorate (Example 123), i.e., the use of catalysts according to the invention, enable a significant improvement in yield.

[0133] Examples 128-137: Evaluation of the catalytic activity of the first catalyst when using 4-hydroxybenzophenone

[0134] As a benchmark reaction for evaluating the catalytic activity of the first catalyst, the acylation of 4-hydroxybenzophenone by methacrylic anhydride was studied at 90 °C.

[0135] Preparation of raw material solution of 4-hydroxybenzophenone and methacrylic anhydride

[0136] 3.35 g (0.017 mol) of 4-hydroxybenzophenone and 3.65 g (0.024 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0137] General procedures for Examples 128-137:

[0138] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with a stopper and a magnetic stirrer. 0.1 mol% (unless otherwise specified) of the first catalyst based on tert-butanol was added to this solution, and the pressure tube was sealed. The pressure tube was then placed in a 90°C oil bath with an integrated magnetic stirrer and stirred for 6 hours.

[0139] A catalyst-free sample (reference 128) was used as a reference sample in a 90°C oil bath. After 6 hours, the conversion and product yield (area %) were determined by gas chromatography.

[0140] The results of Examples 128-137 are summarized in Table 8 below:

[0141] Table 8. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride and 4-hydroxybenzophenone at 90 °C

[0142]

[0143] The results in Table 8 show that the conversion rate is 30.9% in the absence of any catalyst (reference 128).

[0144] In the presence of zinc perchlorate (reference example 133), unwanted polymers are formed. Therefore, the desired product cannot be detected.

[0145] The use of various catalysts according to the present invention enables a significant improvement in yield.

[0146] Examples 138-155: Catalytic activity of the first catalyst at different dosages

[0147] As a benchmark reaction for evaluating the catalytic activity of the first catalyst at different dosages, the study investigated the acylation of menthol with methacrylic anhydride at 90 °C.

[0148] Preparation of raw material solutions of menthol and methacrylic anhydride

[0149] 78.1 g (0.50 mol) of natural menthol and 107.9 g (0.70 mol) of methacrylic anhydride were combined and stabilized with 2000 ppm of 2,4-dimethyl-6-tert-butylphenol, 1000 ppm of hydroquinone monomethyl ether, and 10 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (ppm based on the total mass of the anhydride and alcohol). The resulting mixture was gently heated in the absence of any catalyst to obtain a clear feed solution.

[0150] General procedures for Examples 138-155:

[0151] Place a 7.0 g sample of raw material solution in a container with... The solution was placed in a 15 mL pressure tube with an integrated magnetic stirrer. The first catalyst was added to this solution, and the pressure tube was sealed. Subsequently, the pressure tube was placed in a 90°C oil bath with an integrated magnetic stirrer and stirred.

[0152] A catalyst-free sample (Reference Example 138) was used as a reference sample in a 90°C oil bath. Conversion and product yield (area %) were determined by gas chromatography after the times indicated in Table 9.

[0153] The results of Examples 138-155 are summarized in Table 9 below:

[0154] Table 9. Evaluation of the catalytic activity of the first catalyst when using methacrylic anhydride and menthol at 90 °C

[0155]

[0156] The data in Table 9 indicate that the optimal amount of the first catalyst is typically between about 0.1 mol% and about 0.5 mol% based on the amount of substrate.

Claims

1. A method for preparing (meth)acrylates, said method comprising at least the following step (a): (a) The reaction between (meth)acrylic anhydride of formula (I) and the substrate in the presence of a first catalyst. Where R1 is a hydrogen atom or a methyl group; This results in a mixture of products containing (meth)acrylates; The method is characterized by: The substrate is selected from primary, secondary, and tertiary alcohols having one hydroxyl group; and The first catalyst contains magnesium halides; During step (a), the temperature is maintained between 60°C and 90°C.

2. The method according to claim 1, wherein the first catalyst is selected from magnesium bromide, magnesium iodide and magnesium chloride.

3. The method according to claim 1 or 2, wherein the total amount of the first catalyst in step (a) is between 0.001 mol% and 10 mol% based on the amount of substrate.

4. The method according to claim 1 or 2, wherein the total amount of the first catalyst in step (a) is between 0.01 mol% and 1.0 mol% based on the amount of substrate.

5. The method according to claim 1 or 2, wherein the total amount of the first catalyst in step (a) is between 0.1 mol% and 0.5 mol% based on the amount of substrate.

6. The method according to claim 1 or 2, wherein the molar ratio of (meth)acrylic anhydride to substrate in step (a) is between 5:1 and 1:

5.

7. The method according to claim 1 or 2, wherein the molar ratio of (meth)acrylic anhydride to substrate in step (a) is between 3:1 and 1:

3.

8. The method according to claim 1 or 2, wherein the molar ratio of (meth)acrylic anhydride to substrate in step (a) is between 2:1 and 1:

2.

9. The method according to claim 1 or 2, wherein the method further comprises the following steps (b) and (c) performed after step (a): (b) Adding an auxiliary alcohol to the product mixture obtained in step (a), thereby forming a product mixture comprising the (meth)acrylate and the auxiliary alcohol; and (c) Remove the (meth)acrylate of the auxiliary alcohol from the product mixture obtained in step (b); The auxiliary alcohol is a primary or secondary alcohol having a boiling point of not more than 150°C as measured at 105 Pa.

10. The method of claim 9, wherein the auxiliary alcohol has a boiling point of not more than 120°C as measured at 105 Pa.

11. The method of claim 9, wherein the auxiliary alcohol has a boiling point of not more than 80°C as measured at 105 Pa.

12. The method of claim 9, wherein the auxiliary alcohol is selected from methanol, ethanol, n-propanol, isopropanol, or mixtures thereof.

13. The method of claim 9, wherein the auxiliary alcohol is methanol.

14. Use of the first catalyst as a catalyst in the reaction between (meth)acrylic anhydride of formula (I) and the substrate. Where R1 is a hydrogen atom or a methyl group; The reaction produces a product mixture containing (meth)acrylates, wherein the substrate is selected from primary, secondary, and tertiary alcohols having one hydroxyl group. The first catalyst contains magnesium halides.

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