CROSS REFERENCE TO RELATED APPLICATIONS

The present application is US national stage of international application PCT/EP2019/063084, which had an international filing date of May 21, 2019, and which was published on Nov. 28, 2019. The PCT application claims priority to European application EP 18173839.4, filed on May 23, 2018. The contents of each of these applications is hereby incorporated by reference in its entirety.

The invention relates to a method for preparing keto-functionalized aromatic (meth)acrylates.

The prior art contains a method for preparing [(meth)acryloyloxy]benzophenone starting from (meth)acrylic anhydride (JP2003261506, Mitsubishi Rayon). Triethylamine is used as catalyst and reagent. Since the amine forms a salt with the methacrylic acid produced during the reaction, the amine must be made equimolar with the hydroxybenzophenone. Correspondingly, equimolar amounts of salt are obtained, and have to be disposed of as waste. The economics of the process are therefore poor. In addition, the work is carried out at very moderate temperatures (30° C.), which, despite high catalyst amounts, leads to long reaction times of >5 h. Thus, the method is also disadvantageous taking into account the space-time yield.

In a more recent application WO2017/146444, an enzymatic reaction of (meth)acrylic esters (e.g. vinyl acrylate) with 4-hydroxybenzophenone is described. The reaction takes place at moderate temperatures around 60° C., the reaction times are 8 h. For isolation, drying is carried out for several days at 50° C. Thus, reaction times and the expenditure for isolation are uneconomical. The high yields achievable and high product purity are mentioned to justify the excessive expenditure.

In WO 2017/147040, the reaction in a microflow reactor between 4-hydroxybenzophenone and methacryloyl chloride in the presence of superstoichiometric amounts of triethylamine is described. The amounts of salt formed, which must be removed or reworked, make the method uneconomical and expensive.

Other methods in the prior art are the reaction of (meth)acryloyl chloride with hydroxy-functional benzophenones, and the reaction of this raw material with glycidyl methacrylate. When handling (meth)acryloyl chloride, the corrosive and caustic properties must be borne in mind and in addition stoichiometric amounts of a base, for example triethylamine, are always used. This makes such a method very expensive. The use of glycidyl methacrylate is disadvantageous on account of the high toxicity.

WO2010/072479 describes the preparation of [(meth)acryloyloxy]benzophenone in the presence of catalytic amounts of sulfuric acid. When reaction is at an end, the catalyst has to be neutralized with aqueous sodium hydroxide solution, and removed by filtration as sodium sulfate. While this method is technically feasible, the long residence times of 4-8 hours however mean that the space-time yields are not advantageous. Despite the long residence time, the hydroxybenzophenone conversions are incomplete, which is disadvantageous for the subsequent use in the form of a polymer, e.g. as additive for paints and dyes. As is known, residual monomers and other molecules which are not covalently incorporated into the polymer migrate over the lifetime of the application and can thus be released into the environment, which is undesirable. No mention is made of further by-products which cannot be bonded as monomer in a polymer.

WO2015/049200 describes a method for preparing [(meth)acryloyloxy]benzophenone in the presence of catalytic amounts of basic salts. In this case, long residence times, customarily of 5 h at 90° C., are required for the reaction. In addition, the method described therein requires high concentrations of stabilizer of more than 2600 ppm Topanol A (based on 4-hydroxybenzophenone), which entails a high concentration of stabilizer of more than 800 ppm in the product. Here, the by-products of the reaction are also quantified, namely unreacted 4-hydroxybenzophenone and 4-acetoxybenzophenone, which are of the order of magnitude of a few percent in each case relative to the target products, and which remain in the product. In terms of space-time yields, and also the product quality which can be achieved, this method is therefore not optimal.

DE 1720603 describes a method for preparing aqueous dispersions of readily crosslinkable polymers. This involves copolymerizing acrylic and methacrylic esters with photoactive, olefinically unsaturated monomers, with optional accompanying use of photoactive, nonionic emulsifiers.

EP0346788 describes a method for preparing radiation-sensitive carbamoylbenzo- and -acetophenones having at least one methacrylate or acrylate end group. This involves reacting isocyanatoalkyl (meth)acrylates with hydroxyacetophenones or hydroxybenzophenones, using a basic catalyst. It is necessary here to operate in the absence of moisture. Moreover, only dried, non-nucleophilic solvents can be used.

It was an object to provide an improved method for preparing keto-functionalized aromatic (meth)acrylates.

The object was achieved by a method for the preparation of keto-functionalized aromatic (meth)acrylates by reacting keto-functionalized aromatic alcohols or keto-functionalized aromatic amines and (meth)acrylic anhydride, in which reactants, products and catalyst are present together in the reaction matrix at a reaction temperature between 50° C. and 120° C., characterized in that the residence time of the reactants, products and catalysts is restricted from 0.1 to at most 4 hours and (meth)acrylic anhydride is used at a content of (meth)acrylic acetic anhydride of <4.5%.

Surprisingly, it has been found that high conversions are achieved, and the amount of by-products is greatly reduced, with the method according to the invention.

It has been found that the inventive method is only burdened with a small salt load, which was either used as catalyst or is formed when the catalyst acid is neutralized during work-up. The (meth)acrylic acid generated as a by-product can be used in the subsequent polymerization of the keto-functionalized aromatic (meth)acrylate monomers as comonomer or can be recycled for preparing new (meth)acrylic anhydride.

Keto-Functionalized Aromatic (Meth)Acrylates

Keto-Functionalized Aromatic (Meth)Acrylates

A=alkyl, aryl, heteroaryl, substituted with any desired selection from H, alkyl, aryl, halides, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2R1, R2, R3, R4, R5=different or identical to one another, selected from H, alkyl, halide, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2

with a ring closure also being explicitly included between A and one of the radicals R1-5, e.g. as fluorenone derivative

with one of the substituents R1-5being described by the following formula

n=0-10, preferably n=1-6R=alkyl, aryl, oligoether, COR′═H, MeX═O, S, NHY═O, NH

Preferred:

Keto-Functionalized Aromatic (Meth)Acrylates

A=alkyl, aryl, heteroaryl, substituted with any desired selection from H, alkyl, aryl, halides, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2R1, R2, R3, R4, R5=different or identical to one another, selected from H, alkyl, halide, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2with a ring closure also being explicitly included between A and one of the radicals R1-5, e.g. as fluorenone derivative

with one of the substituents R1-5being described by the following formula

R′═H, MeY═O, NH

More Preferred:

Keto-Functionalized Aromatic (Meth)Acrylates

A=alkyl, aryl, heteroaryl, substituted with any desired selection from H, alkyl, aryl, halides, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2R1, R2, R3, R4, R5=different or identical to one another, selected from H, alkyl, halide, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2

with one of the substituents R1-5being described by the following formula

R′═H, MeY═O, NH

Furthermore Preferred:

Keto-Functionalized Aromatic (Meth)Acrylates

A=alkyl, aryl, substituted with any desired selection from H, alkyl, aryl, halides, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2R1, R2, R3, R4, R5=different or identical to one another, selected from H, alkyl, halide, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2
with one of the substituents R1-5being described by the following formula

R′═H, MeY═O, NH

Particularly Preferred:

Keto-Functionalized Aromatic (Meth)Acrylates

A=aryl, substituted with any desired selection from H, alkyl, aryl, halides, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2R1, R2, R3, R4, R5=different or identical to one another, selected from H, alkyl, halide, OAlkyl, NO2, OH, sulfonyl, NH2, NAlkyl2

with one of the substituents R1-5 being described by the following formula

R′═H, MeY═O, NH

Most Particularly Preferred:

Keto-Functionalized Aromatic (Meth)Acrylates

A=aryl, substituted with any desired selection from H, alkyl, halides, OAlkyl, sulfonyl, NAlkyl2R1, R2, R3, R4, R5=different or identical to one another, selected from H, alkyl, halide, OAlkyl, sulfonyl, NAlkyl2

with one of the substituents R1-5being described by the following formula

R′═H, MeY═O, NH

Especially Preferred:

Keto-Functionalized Aromatic (Meth)Acrylates

A=aryl, substituted with any desired selection from H, alkyl, halides, OAlkyl, sulfonyl, NAlkyl2R1, R2, R3, R4=different or identical to one another, selected from H, alkyl, halide, OAlkyl, sulfonyl, NAlkyl2R′═H, MeY═O, NH

Exemplary, Non-Limiting Representatives of Keto-Functionalized Aromatic (Meth)Acrylates



The notation “(meth)acrylate” here means both methacrylate, for example methyl methacrylate, ethyl methacrylate, etc., and acrylate, for example methyl acrylate, ethyl acrylate, etc., and mixtures of the two.

Keto-Functionalized Aromatic Alcohols and Keto-Functionalized Aromatic Amines

The keto-functionalized aromatic alcohols or keto-functionalized aromatic amines used are characterized in that they have a keto function directly adjacent to an aromatic system and additionally have either an NH2or OH group on the aromatic system (phenylamine/aniline; phenylalcohol/phenol) or a spacer with a free NH2or OH group (e.g. benzylamine, benzylalcohol). The spacer unit may be or comprise oligoethers, alkyl-, aryl-, -ethers, -thioethers-amines, -esters, -thioesters, or -amides. Preference is given to keto-functionalized aromatic alcohols or amines which have an NH2or OH group on the aromatic system. Furthermore, preference is given to derivatives in which the two substituents of the keto function are not directly connected to one another. Moreover, preference is given to those keto-functionalized aromatic alcohols or amines which do not contain any heteroatoms. Particularly preferred representatives of the keto-functionalized aromatic alcohols or amines are benzophenone derivatives, most particularly preferably benzophenone derivatives which are substituted with H, alkyl, halide, alkoxy, sulfonyl or dialkylamine groups. Preference is especially given here to benzophenone derivatives, the NH2or OH function of which is in the para position relative to the keto function. Most particularly preferred keto-functionalized alcohols or amines are represented by the corresponding compounds which, according to the inventive reaction, lead to the inventive keto-functionalized aromatic (meth)acrylates. The keto-functionalized aromatic alcohols or amines are usually characterized by a purity of >96%. This degree of purity can contribute to achieving a low colour index in the product.

Catalyst

The reaction of keto-functionalized aromatic alcohols or keto-functionalized aromatic amines and (meth)acrylic anhydride can take place in the presence of acids, preferably customary strong inorganic or organic acids having a pKavalue of <2 and particularly preferably in the presence of sulfuric acid or alkyl- or arylsulfonic acids. Alternatively, bases have also proved to be suitable catalysts. Preferred bases in this case are carboxylate salts or else stronger bases having a pKbvalue of <9, for example sodium hydroxide, sodium methoxide or potassium hydroxide and mixtures thereof, since these generate the corresponding (meth)acrylate salt in situ by reaction with (meth)acrylic anhydride.

Preferably, the reaction is carried out in the presence of catalytic amounts of concentrated sulfuric acid or aqueous sodium hydroxide solution. The catalytic amounts are preferably between 0.01 and 3 mol % based on the (meth)acrylic anhydride used and particularly preferably between 0.2 and 1.5 mol % based on the (meth)acrylic anhydride used.

Stabilizer

Suitable stabilizers are known to those skilled in the art. They include, for example, phenothiazine, substances having an oxyl radical, such as 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPOL) or 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPOL-(meth)acrylate) and also 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 can also be used. Preference is given to using sterically hindered phenols; particular preference is given to using HQME, DMBP, BHT and also mixtures of these substances. The applications of keto-functionalized aromatic (meth)acrylates generally require colourless products. Therefore, for unsaturated compounds, preference is given to non-colouring stabilizers or colouring stabilizers in very small amounts. The amount used of stabilizer is dependent on the starting materials. The amount of stabilizer at the start of the reaction is adjusted to be between 0 and 5000 ppm based on the keto-functionalized aromatic alcohols or amines used. Preferably, the amount of stabilizer at the start of the reaction is adjusted to be between 0 and 3000 ppm based on the keto-functionalized aromatic alcohols or amines used, particularly preferably between 50 and 2000 ppm.

(Meth)Acrylic Anhydride

The (meth)acrylic anhydride is added in a small excess to the keto-functionalized aromatic alcohols or amines. In this case, a molar ratio of alcohol or amine to (meth)acrylic anhydride of 1:1.01 to 1:4, preferably between 1:1.03 to 1:2, particularly preferably between 1:1.05 to 1:1.5 is chosen. The (meth)acrylic anhydride is used with a purity of >93%, preferably >94%, particularly preferably >96%, most particularly preferably >98%.

Both acetoxy derivative and remaining alcohol or amine are not reacted in the radical polymerization and are therefore present in the polymer in unbound form. These substances can migrate and are therefore detrimental to the adjustment of the properties of the polymer. In addition, toxic substances may potentially be released into the environment in this way. Therefore, a high conversion of the alcohol or amine used is critical. As a result, the above purity requirement is directly applicable to the (meth)acrylic anhydride. The acetoxy derivative in turn originates from the mixed anhydride of (meth)acrylic acid and acetic acid, which is a typical impurity of (meth)acrylic anhydride. This species preferably transfers the acetyl radical. In order to limit the content of acetoxy derivative in the product, the (meth)acrylic anhydride used must have a content of mixed anhydride of (meth)acrylic acid and acetic acid, hereinafter referred to as (meth)acrylic acetic anhydride, of <4.5 wt %, preferably <3 wt %, particularly preferably <1.5 wt %.

Reaction Conditions

The reaction is carried out at temperatures between 50° C. and 120° C., preferably 60° C. to 95° C., particularly preferably between 70° C. and 90° C., with a residence time of 0.1 to 4 hours, preferably of 1 to 3 hours.

In order to avoid the formation of undesired by-products, the reaction is interrupted at a conversion of >90%, preferably >95%, particularly preferably >97% of the reactant used.

Neutralization and Work-Up

In the case of acids being used catalytically, the neutralization is carried out with aqueous bases, preferably with aqueous alkali metal hydroxide solution or ammonia solution. Basic catalysts do not have to be neutralized. By treating the catalyst, in the simplest case a neutralization, a colour change may arise.

The keto-functionalized aromatic (meth)acrylates prepared in high purity can be directly dissolved from the crude product in customary organic solvents, (meth)acrylic esters, preferably methyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and/or styrene and also subsequently stored and further reacted.

Preference is given to a mixture of 10-50 wt % of the keto-functionalized aromatic (meth)acrylate in 30-80 wt % of methyl methacrylate in the presence of <15 wt % of (meth)acrylic acid; particular preference is given to a mixture of 25-35 wt % of the keto-functionalized aromatic (meth)acrylate in 55-65 wt % of methyl methacrylate in the presence of 8-12 wt % of (meth)acrylic acid.

The subsequent work-up of the crude monomer may be carried out by adding water. In this case, the keto-functionalized aromatic (meth)acrylate precipitates by addition of excess water and is isolated in solid form by filtration. It is just as possible to introduce the crude monomer into water. In this way, the (meth)acrylic acid forming in the course of the reaction, the catalyst and the salts from the neutralization thereof, and other water-soluble impurities, are separated off. In accordance with expectations, however, a significant depletion of the unreacted reactant or the acetylated by-product is not achieved in this way, which emphasizes the fact that, in order to obtain a particularly pure product, a (meth)acrylic anhydride with as low as possible a content of mixed anhydride of (meth)acrylic acid and acetic acid must be used.

An alternative work-up of the crude monomer can be carried out by addition of organic solvents to the crude product at elevated temperatures, for example between 60 and 100° C. The crude monomer can also be added to an organic solvent with the same result. Possible solvents are organic esters, for example methyl methacrylate or butyl acetate, linear or cyclic alkanes, preferably methylcyclohexane, or aromatic compounds, preferably toluene. In this case, the keto-functionalized aromatic (meth)acrylate is firstly dissolved and precipitates upon subsequent cooling to room temperature. The target product is isolated in solid form by filtration. The methacrylic acid and also the catalyst or salts from the neutralization thereof are separated off in this way. In addition, a slight depletion in the by-product 4-(acetoxy)benzophenone is observed.

Also proceeding from the worked-up pure product, corresponding solutions can be prepared in customary organic solvents, (meth)acrylic esters, preferably methyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and/or styrene.

Preferred Method Variants1. Method for the preparation of keto-functionalized aromatic (meth)acrylates by reacting keto-functionalized aromatic alcohols or amines and (meth)acrylic anhydride, in which reactants, products and catalyst are present together in the reaction matrix at a reaction temperature between 50° C. and 120° C., characterized in that the residence time of the reactants, products and catalysts is restricted from 0.1 to at most 4 hours, (meth)acrylic anhydride is used at a content of (meth)acrylic acetic anhydride of <4.5%, the amount of stabilizer at the start of the reaction is adjusted to be between 0 and 5000 ppm based on the keto-functionalized aromatic alcohols or amines used, and (meth)acrylic anhydride is used with a purity of >93%.2. Method for the preparation of keto-functionalized aromatic (meth)acrylates by reacting keto-functionalized aromatic alcohols or aminess and (meth)acrylic anhydride, in which reactants, products and catalyst are present together in the reaction matrix at a reaction temperature between 50° C. and 120° C., characterized in that the residence time of the reactants, products and catalysts is restricted from 0.1 to at most 4 hours, (meth)acrylic anhydride is used at a content of (meth)acrylic acetic anhydride of <4.5%, the amount of stabilizer at the start of the reaction is adjusted to be between 0 and 5000 ppm based on the keto-functionalized aromatic alcohols or amines used, and the reaction is interrupted at a conversion of >90% of the reactant used.3. Method for the preparation of keto-functionalized aromatic (meth)acrylates by reacting keto-functionalized aromatic alcohols or amines and (meth)acrylic anhydride, in which reactants, products and catalyst are present together in the reaction matrix at a reaction temperature between 50° C. and 120° C., characterized in that the residence time of the reactants, products and catalysts is restricted from 0.1 to at most 4 hours, (meth)acrylic anhydride is used at a content of (meth)acrylic acetic anhydride of <4.5%, the amount of stabilizer at the start of the reaction is adjusted to be between 0 and 5000 ppm based on the keto-functionalized aromatic alcohols or amines used, and the reaction is carried out in the presence of catalytic amounts of acid.4. Method for the preparation of keto-functionalized aromatic (meth)acrylates by reacting keto-functionalized aromatic alcohols or amines and (meth)acrylic anhydride, in which reactants, products and catalyst are present together in the reaction matrix at a reaction temperature between 50° C. and 120° C., characterized in that the residence time of the reactants, products and catalysts is restricted from 0.1 to at most 4 hours, (meth)acrylic anhydride is used at a content of (meth)acrylic acetic anhydride of <4.5%, the amount of stabilizer at the start of the reaction is adjusted to be between 0 and 5000 ppm based on the keto-functionalized aromatic alcohols or amines used, and the keto-functionalized aromatic (meth)acrylate precipitates by addition of water or of an organic solvent into the reaction mixture and is isolated in solid form by filtration.5. Method for the preparation of keto-functionalized aromatic (meth)acrylates by reacting keto-functionalized aromatic alcohols or amines and (meth)acrylic anhydride, in which reactants, products and catalyst are present together in the reaction matrix at a reaction temperature between 50° C. and 120° C., characterized in that the residence time of the reactants, products and catalysts is restricted from 0.1 to at most 4 hours, (meth)acrylic anhydride is used at a content of (meth)acrylic acetic anhydride of <4.5%, the amount of stabilizer at the start of the reaction is adjusted to be between 0 and 5000 ppm based on the keto-functionalized aromatic alcohols or amines used, and the keto-functionalized aromatic (meth)acrylate is prepared by addition of a liquid (meth)acrylic ester or styrene into the product mixture as solution in said ester or in styrene.

In the application for coatings and paints, the Hazen colour index (also known as Pt—Co colour index) of the raw materials used is of critical importance. The colour index of the products described here can be reduced by using adsorbents, preferably activated carbon. Suitable in principle are different adsorbents which reduce the Pt—Co colour index after the reaction is carried out; these adsorbents are added to the crude mixture as slurry and are later removed again or, in an alternative embodiment, operate as fixed bed. Thus, when using 10 wt % of activated carbon, a reduction of the colour index by approximately 100 APHA is achieved within less than 2 h. Since the activated carbon cannot be directly reused, such a method is very expensive. It is therefore advantageous to keep the colour index low even during the reaction, such that further work-up is not required. To this end, the method steps according to Claims1-3and5-13of the inventive method are preferably combined such that the Pt—Co colour index of a 30 wt % solution of the reaction product, after neutralization of the catalyst with a base in 60 wt % MMA and 10 wt % methacrylic acid, is adjusted to <500 APHA, preferably to <400 APHA, particularly preferably to <350 APHA.

Keto-functionalized aromatic (meth)acrylates can, for subsequent photocrosslinking of polymers by daylight or UV light, also be used as polymeric photoinitiators (as described in WO2010112474A1 and the references cited therein).

The keto-functionalized aromatic (meth)acrylates can additionally be used as comonomer for polymerization reactions.

The examples given below better illustrate the present invention, without however restricting the invention to the features disclosed therein.

