CS259635B1 - Method of acrylic and metacrylic acids' esters preparation - Google Patents

Abstract

Process for preparing acrylic esters and methacrylic by re-esterification of methyl, ethyl acrylate or methacrylate with the corresponding alcohols in the presence of a catalyst based on the base alcohol and polymerization inhibitor, are increased temperature and current rectification and distillation releasing lower alcohol so that that the starting molar ratio of methyl-, optionally ethyl acrylate or methacrylate to alcohol is 1.05 to 1.2, is added to the reaction mixture as a polymerization inhibitor 2,6-di-tert-butyl-p-methylphenol, optionally tert-butyl pyrocatechin, optionally a mixture of the two above inhibitors, with the sum of the concentrations of the two inhibitors is at most 0.015 wt. and the concentration of tert-butyl pyrocatechin is preferably less than 0.006% by weight. and reactions a temperature of up to 100 cc per supply of oxygen-containing gas.

Description

259635

The present invention relates to a process for the preparation of acrylic and methacrylic acid esters by re-esterification of methyl or ethyl acrylate or methacrylate with the corresponding alcohols in the presence of magnesium alkoxide as catalyst, hydrocarbon solvent and inhibitor polymerization.

For most applications, particularly in coating, additives and adhesives, as well as from a commercial point of view, the least coloring of the starting monomeric unsaturated esters and the lowest possible content of the inhibitors are required, which cancels the polymerization process of the monomers. The evaluation of monomer color is usually performed by the method according to ČSN 65 0340a and is given in handball units.

The color of unsaturated esters and its stability is dependent on the type and amount of inhibitors used, the nature of the catalyst and the reaction conditions. The catalyst species and reaction conditions directly affect the selection and minimal amount of inhibitor.

The most frequently used inhibitors are mono- and polyvalent phenols and their derivatives such as phenol, cresols, di-tert-butyl-p-ethyl-phenol, hydroquinone, monomethylester of hydroxyquinone, pyrocatechin, tert-butyl-pyro-techin, quinones, aminophenols and aromatic amines such as diphenylamine, hydroxydiphenylamine, phenylenediamine, dinaphthylphenylenediamine, alpha-nitroso-beta-naphthylamine, phenyl-beta-naphthylamine, benzidine, or quinone dyes such as methylene blue, phenothiazine and other less common substances. Of the phenols, the most effective inhibitor is hydroquinone and pyrocatechin. Monovalent phenols and substituted derivatives are substantially less effective. The coloring that the phenols cause the reaction mixture is directly proportional to its efficacy and is particularly evident in the alkaline environment. A reduction in the level of phenolic inhibitors or their complete removal from the prepared esters is in principle simple, it is recommended to extract with alkaline solutions or sorption on ion-exchangers of chinese inorganic active substances. However, the coloration of the mixture resulting from the reaction does not eliminate the extraction and, in addition, ester hydrolysis may occur. However, both in extraction and sorption, there is a considerable problem in industrial realization of the handling and disposal of relatively large amounts of extraction solutions and sorbents.

Aromatic amines are less potent inhibitors and are therefore usually used in larger quantities. They are unstable and in contact with the metal, and in particular light, the products, depending on the amount used, turn pink to brownish red. Removal of these inhibitors of the prepared ester is very difficult.

Therefore, it is clear that in order to achieve a low product color, it is necessary to select less potent inhibitors, use them in small quantities and adapt the reaction conditions.

Acid catalysts such as sulfuric acid or p-toluenesulfonic acid are poorly effective in re-esterification and are therefore used in larger quantities and at temperatures above 100 ° C. This also corresponds to high levels of inhibitors, for example 0.65 wt. nitroso-naphthol (U.S. Pat. No. 289,083) or 0.22% by weight hydroquinone (Pat. MLR 147 212).

Highly efficient catalyst systems containing alkali metal alcoholates required to operate at low temperatures up to 100 ° C in order to reduce side-effect and polymerization reactions. Therefore, either the reduced pressure (Swiss Pat. No. 239,750, U.S. Pat. No. 9,776,304) or dilution with the low boiling solvent (USSR Pat. No. 289,083) is employed, but due to the high catalyst activity, effective inhibitors and relatively large amounts of These catalysts also include stannates (NSR Pat. No. 1,932,625), somewhat less active catalysts with a markedly basic reaction as alkali salts of weak acids (NSR Pat. No. 2,524,970), lithium hydroxide (NSR 2,744,641), metal oxides. BaO, TI2O3, MoOa (NSR 2 637 402) or acetyl acetonates Ca and Zr (NSR 2 805 702) are reused at elevated temperatures up to 130 ° C and in the presence of potent polymerization inhibitors such as methyl ether of hydroquinone, hydroquinone, phenothiazine in In similar conditions, the use of magnesium alcoholates as a catalyst (British Patent 1 174148), NSRpat, 1 568 376) has also been proposed. of ol was at least 1.5: 1 and the concentration of the inhibitor was at least 0.03 wt.

Advances in the preparation of unsaturated esters were the introduction of Ti and Zr alcoholates as esterification catalysts using co-solvent to dilute the reaction mixture and reduce boiling point. The disadvantages of this catalyst include the more difficult ways to separate it after reacting in the esters distillation. (British Patent Nos. 962 928, 960 005, 1 012 817, NSR 2 319 688) or hydrolysis of the titanate at elevated temperature (NSR 2 317 226). In both cases, the ester is heat-expanded to an increased extent, requiring a higher level of inhibition. If a smaller amount of solvent is used, which makes it possible to use a smaller amount of catalyst, the reaction temperatures obtained are again very high, up to 130 ° C. However, larger dilutions of the solvent (USSR 289,083) at reaction temperatures up to 100 ° C still require a larger amount of catalyst, so the reaction conditions do not allow to significantly reduce the amount of polymerization inhibitor in the reaction mixture and the lowest documented level was 0.03 wt%.

Another significant improvement in the unsaturated esters using titanate catalysts was the use of the synergistic effect of 2,6-di-tert-butyl-p-methylphenol (hereinafter DTBMF) and activated charcoal (NSR 2 317 226) and a new method of hydrolysis by water vapor deposition. 259633 solvent and methyl methacrylate vaporities which allowed the concentration of DTBMF in the reaction mixture to be reduced to 0.006 to 0.02 wt%. SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for the preparation of esters of acrylic and methacrylic acids having a particularly low color number, less than 100 and 50, respectively, with a particularly low polymerization inhibition by re-esterification of methyl or ethyl acrylate or methacrylate with the corresponding alcohols, which, in a simpler way of separating the catalyst, would allow the polymerization inhibitors to be reduced in the reaction mixture to less than 0.02% by weight without the addition of charcoal to the mixture to increase stability unsaturated esters. SUMMARY OF THE INVENTION The present invention provides a process for preparing acrylic esters and meta-crystals by re-esterifying methyl or ethyl acrylate or methacrylate with the corresponding alcohols in the presence of a catalyst on magnesium base alcoholate and a polymerization inhibitor at elevated temperature and simultaneously rectifying the lower alcohol releasing distillation characterized in the ratio of methyl or ethyl acrylate or methacrylate of the alcohol is 1.05 to 1.2, adding 2,6-di-tert-butyl-p-methylphenol and / or tert-butylpyrocatechin as the polymerization inhibitor in the reaction mixture, wherein the sum of the concentrations of the two inhibitors is at most 0.015 wt%. and the concentration of tert-butyl pyrocatechin is preferably less than 0.006% by weight. and the reaction is carried out in a hydrocarbon solvent environment at elevated temperatures of up to 100 ° C by introducing an oxygen-containing gas.

By reducing the molar ratio of starting alcohol to ester to 1.05 to 1.2 and diluting the reaction mixture with a hydrocarbon solvent such as cyclohexane, n-hexane, benzene, methylcyclopentane, 2,4-dimethylcyclopentane, 1,2-dichloroethaneapod. the concentration of the predominantly unsaturated ester is significantly reduced in the reaction mixture, which is most readily polymerized, especially at the end of the re-esterification at elevated temperature, thereby increasing the reaction mixture stability, thus allowing an effective amount of polymerization inhibitors to be reduced. Under these conditions, there is virtually no reduction in the rate of esterification in conjunction with the magnesium alkoxy reesterification catalyst, and conversely, the amount of catalyst can be reduced against patent literature data.

Said inhibitors, 2,6-di-tert-butyl-p-methylphenol (hereinafter DTBMF) and tert-butylpyrecatechin (hereinafter TBPK) may be used alone or in combination with each other, preferably so as to the concentration of more potent but less stable TBPK was less than 0.006 wt%. Both inhibitors are inactive compared to hydroquinone and its catalyst derivatives and do not reduce its effectiveness even at a concentration of 0.1% by weight. Therefore, the use of these inhibitors allows to reduce the concentration of magnesium methylate to. values lower than those reported in the patent literature.

The essential component of the inhibitory system, in addition to the above-mentioned compounds, is optionally diluted with nitrogen, which is added to the reaction mixture for the entire heating period of not more than 10 liters per liter of reaction mixture and hour (calculated on the air). The amount of air is determined by the type of starting and emerging esters and their stability. More air is preferred for re-esterification of ethyl acrylate and especially for the preparation of multifunctional esters derived from polyhydric alcohols. On the contrary, in the preparation of alkyl methacrylates, an amount of 0.1 liter / liter may be sufficient. h. It is preferred to recycle the air introduced into the reaction mixture to reduce solvent losses of the starting ester in the gases.

The main effect of the invention is that the reaction conditions are adjusted, the excess of the methacrylic ester starting material is reduced, the reaction mixture is diluted with a solvent, the reaction temperatures are reduced to a maximum of 100 ° C and the magnesium alcoholate is used as a catalyst at low concentrations after conversion to magnesium methylate 0.07 to 0.4% wt. based on the weight of the starting reaction mixture, the suppression of side-reaction and polymerization reactions was achieved by re-esterification to such an extent that it could be used for inhibition. polymerization poorly effective, and color stable inhibitors: 2,6-di-tert-butyl-p-methylphenol and / or tert -butyl-pyro-techinine, at concentrations of at most 0.015 percent by weight. Surprisingly, it was found that the reaction conditions indicated that the rate of reesterification was comparable to that achieved using titanate catalysts. However, unlike these catalysts, it is not necessary to carry out the hydrolysis at a temperature in excess of 100 ° C, but only washing the reaction mixture with dilute acids or precipitating with carbon dioxide gas at normal or slightly elevated temperatures up to 60 ° C is sufficient. This reduces the thermal stress of the reaction mixture and increases the stability of the recovered product to which no additional amounts of inhibitors are required. The products containing only the amount of inhibitors originally added to the reaction mixture during re-esterification are stable storage at temperatures up to 30 ° C for longer than 12 months.

These types of inhibitors do not substantially affect the further processing of the products, the (meth) acrylic monomers, their polymerization, or the properties of the prepared polymer and copolymer compounds. Therefore, the inhibitors need not be removed prior to further processing. This reduces the investment and operating costs associated with removing inhibitors, including the cost of disposing of these operations.

The reaction conditions selected, in particular the low concentration of the starting ester in the reaction mixture and the dilution of the reactants with the hydrocarbon solvent, were also manifested by increased vapor and liquid stability in the re-esterification reactor rectification column and in the condenser, so that condensate and reflux were not required either to the column, or only to such an extent that it does not substantially affect the overall level of the inhibitor mixture and the product. Also re-cycles the solvent which is separated from the reaction mixture after re-esterification and contains about 10% wt. methyl methacrylate or ethyl acrylate, it is not necessary to stabilize with a larger amount of inhibitor than 0.015% by weight, based on the weight of the recycle, whereby the amount of inhibitor added to the reaction mixture can be reduced.

The suppression of side reactions due to the use of mild reaction conditions and the magnesium alcoholate type catalyst in a minimal amount is so effective that even in the case of relatively low boiling types such as butyl acrylate or meta-crylate, it is not necessary to purify the esters by rectification and for their separation is sufficient only to strip the solvent and the excess starting ester after removal of the catalyst. This is reflected in a reduction in equipment costs and in energy consumption. The effect of the invention is monitored by determining the color of the ester of CSN 65 0340, which is expressed in units of Hazen scale (H. H.) and a qualitative test for the presence of polymers, which consists of mixing 1 ml of ester with 98 ml of dry methanol. Do not clear the mixture within 5 minutes.

The main advantage of the process according to the invention is the 10-fold savings in the amount of inhibitor used and, in particular, the saving of equipment, 15% of the total energy investment, 20% of the total energy consumption and at least one workforce that does not need to be removed. a mixture or prepared ester unnecessary amount of an inhibitor which would otherwise prevent further processing thereof.

The invention is further elucidated by the following non-limiting examples. Example 1

In a 1.5 liter Keller flask equipped with a stirrer and heated oil bath, 348 g of 1214 alpha (commercial designation of an industrial mixture of lauryl and myristyl alcohol produced by Condea, Hamburg), 202 g of methyl methacrylate, 345 g of cyclohexane, and 2 ml of an inhibitor solution containing 0.08 g of di-tert-butyl-p-methylphenol (hereinafter "DTBMF") and 0.04 g of tert-butyl pyrocatechin (hereinafter "TBPK"). The column was connected with a reaction flask and a condenser with a reflux condenser, a condenser and a distillate trap, were mounted on top of the column. 1 liter / hour.

The contents of the reaction flask were boiled for 30 minutes and azeotropically dried. After cooling to 70 ° C, a suspension of magnesium methylate in methanol was prepared by dissolving 0.4 g of magnesium magnesium in 13.6 g of methanol. The reaction mixture was boiled again at about 77 ° C and methanol re-esterification was distilled through the rectification column. After 2 hours, more than 85% of the stoichiometric amount of methanol was distilled off and after 4 hours 20 minutes the reesterification was terminated. The end of the esterification was indicated by stopping the boiling point of the reaction mixture and the vapor pressure at the rectification column at 96 and 78 ° C. After decomposition and extraction of the catalyst with a dilute sulfuric acid solution and after stripping the solvent of methyl methacrylate from the organic layer with steam and drying the wet ester, lauryl myristyl methacrylate of at least 1.5% by weight was obtained. % of free alcohols and less than 1.0 wt. methyl methacrylate and solvent. The ester yield based on the starting alcohols was 97.5%. The ester ester color was less than 90 Handball units. Esterbyl free of polymers. The prepared ester was suitable for processing into polymeric lubricating oil additives. Example 2

245 g of n-butanol, 380 g of methyl methacrylate, which was stabilized with 0.02% by weight, were added to the apparatus described in Example 1. DTBMF and 327 g cyclohexane. The contents of the reaction flask were boiled and azeotropically dried for 30 minutes. After cooling to 70 ° C, a suspension of magnesium methylate in methanol was added to the mixture, prepared by dissolving 0.8 g of magnesium metal in 13.6 g of methanol. The reaction mixture was boiled again and methanol was liberated through the rectification column. After 2 hours, more than 93% of the stoichiometric amount of methanol was distilled off. The reesterification was completed after 4 hours at a varus temperature of 95.6 ° C. After decomposition and extraction of the catalyst by treatment with a dilute sulfuric acid solution and stripping the solvent of methyl methacrylate from the organic layer with steam and drying the wet ester, butyl methacrylate was obtained containing less than 0.5 wt. free butanol and less than 1.0 wt. Methyl methacrylate and cyclohexane.

The color of the ester that has not been purified by

Claims (2)

2S9635 10 tilaments were less than 60 handball units. The ester yield was 98%. EXAMPLE 3 41.2 g of 1618 alpha (commercial designation of an industrial mixture of cetyl and stearyl alcohol produced by Condea, Hamburg) were prepared as described in Example 1, 156 g of ethyl acrylate, which was stabilized with 0.025 wt. DTBMF and 0.01% wt TPKK, and 333 g cyclohexane. The contents of the reaction flask were boiled and azeotropically dried for 30 minutes. After cooling to 70 ° C, a suspension prepared by dissolving 0.5 g of metal magnesium oxide in 13.6 g of methanol was added to the mixture. The reaction mixture was boiled again and the releasing methanol was distilled off through the rectification column. After 2 hours, a 90% stoichiometric amount of ethanol was distilled off. After 4 hours, the reesterification was terminated at a boiling point of 97 ° C. After dissolution and extraction of the catalyst by treatment with dilute sulfuric acid solution, after stripping the solvent and ethyl acrylate with water vapor and drying the wet ester, cetostearyl methacrylate containing less than 2 wt. % of free alcohols and less than 1 wt. ethyl acrylate and cyclohexane; The ester color was less than 150 Handball units. The ester yield was 97.8%. EXAMPLE 4 356 g of methyl methacrylate, 164 g of diethylene glycol in the presence of 447 gcyclohexane were esterified in the apparatus described in Example 1. The mixture was stabilized with 2 ml of methyl methacrylate solution containing 0.08 g of DTBMF and 0.04 g of TBPK. The catalyst used was a slurry of magnesium methylate in methanol prepared by dissolving 0.8 g of magnesium metal in 13.6 g of methanol. The esterification was terminated after 5 hours. After decomposition and extraction of the catalyst by treatment with dilute aqueous sulfuric acid, the solvent was stripped off. and methyl methacrylate and drying the wet ester to obtain diethylene glycol dimethyl acrylate containing less than 1.5 wt. Methacrylic acid 2-hydroxy-ethoxyethyl ester. The ester color was less than 180 Handball units. EXAMPLE 5 283 g of benzyl alcohol, 300 g of methyl methacrylate, stabilized with 0.08 g of DTBMF, 390 g of cyclohexane were introduced into the apparatus of Example 1. To the dried mixture was added a slurry of magnesium methylate prepared by dissolving 0.6 g of metallic magnesium in 13.6 g of methanol. The esterification was completed after 3 hours and 40 minutes. After decomposition and extraction of the catalyst by treatment with dilute aqueous acid sulfide solution, stripping off the solvent and methyl methacrylate and drying the wet ester, benzyl methacrylate was obtained which contained less than 2 wt. of free benzyl alcohol and less than 1.2 wt. methyl methacrylate acyclohexane. The ester was free of polymers. The ester color was less than 120 units Handball. The ester yield was 97.5%. The method for preparing acrylic esters of methacrylic acid by re-esterification of methyl, ethyl acrylate or methacrylate with the corresponding alcohols in the presence of a catalyst on a base alcohol and a polymerization inhibitor, at elevated temperature and rectification and distillation of the lower alcohol liberated by wherein the starting molar ratio of methyl or ethyl acrylate or methacrylate of the alcohol is 1.05 to 1.2, and 2,6-di-tert-butyl-p-methylphenol, optionally tert. -butyl-pyrocatechin, optionally a mixture of the two above-mentioned inhibitors, wherein the sum of the concentrations of the two inhibitors is at most 0.015% by weight. and the concentration of tert-butyl pyrocatechin is preferably less than 0.006 wt%. and the re-action is carried out in a hydrocarbon solvent environment at elevated temperature to 100 cc with an oxygen-containing gas feed.