CH656872A5 - METHOD FOR PRODUCING CARBONIC ACID ESTERS. - Google Patents

Description

The present invention relates to a process for the preparation of carboxylic acid esters, in which a carboxylic acid chloride or fluoride is reacted with a primary or secondary alcohol or a mixture of such alcohols in the presence of anhydrous hydrofluoric acid or hydrochloric acid while observing certain temperature and pressure conditions.

This process is also suitable for the preparation of acrylic acid esters and methacrylic acid esters by using that of propionic acid or isobutyric acid as the carboxylic acid chloride or fluoride and subjecting the separated ester to oxydehydrogenation in a vapor phase.

In previous, prior art publications, such as. B. in British Patent No. 942 367, it was emphasized that aqueous acidic catalyst systems for the production of carboxylic acids by carbonylation of compounds which have one or more double bonds or of esters are suitable, followed by a hydrolysis reaction of the products with a Excess water was carried out to produce the corresponding carboxylic acids, which were then subjected to an esterification reaction to produce the corresponding esters. In these previously known production processes, the aqueous acidic medium was corrosive and expensive equipment was required for the production process.

The aim of the present invention was to avoid the disadvantages of previously known production processes in the production of carboxylic acid esters.

A preferred embodiment of the method described here is explained with reference to the drawing.

The process according to the invention for the preparation of carboxylic acid esters is characterized in that a mixture of carboxylic acid chloride or fluoride in a primary alcohol with up to 20 carbon atoms, a secondary alcohol with up to 20 carbon atoms or a mixture of such alcohols at 20 to 150 ° C and a pressure of 1 to 340 bar in the presence of anhydrous hydrofluoric acid or hydrochloric acid or a mixture thereof, the initial amount of these anhydrous acids being from 0.01 to 95.5 parts by weight of anhydrous acid to 99.09 is up to 4.5 parts by weight of carboxylic acid chloride or fluoride and the amount of alcohol used is measured such that not the entire amount of carboxylic acid chloride or fluoride is converted to the respective ester.

Carboxylic acid esters, such as. B. the isobutyric acid methyl ester are prepared according to the invention by carrying out an esterification with a smaller amount than the total amount of alcohol required to convert the entire amount of the acylium anion product, in this case isobutyric acid fluoride, to form the corresponding carboxylic acid ester and to implement to regenerate the anhydrous acid, i.e. hydrofluoric acid or hydrochloric acid, if the isobutyric acid chloride is used. While the acylium anion product cannot be made by any manufacturing method, it is preferably formed by

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one carbon monoxide, the anhydrous acid described here, such as. As hydrofluoric acid, and an organic compound, the organic compound used must be able to react with carbon monoxide and the anhydrous acid under such conditions that an acylium anion product is formed. Propylene may be mentioned as an example of a preferred organic compound suitable for this purpose, and the isobutyric acid fluoride is formed with the anhydrous hydrogen fluoride. In other embodiments, part or all of the carboxylic acid esters, for example methyl isobutyrate, can be separated from the esterified mixture and the remainder of the esterified mixture that remains after part or all of the carboxylic acid ester has been separated from this mixture then returned to the process and subjected to renewed reaction with the organic compound to form additional amounts of the acylium anion product. The esterified mixture which remains after all or part of the carboxylic acid ester has been separated off can contain, for example, hydrofluoric acid, unreacted isobutyric acid fluoride and unseparated methyl isobutyrate and, if it is returned to the production process, this mixture can be reacted, for example, with further amounts of propylene are, with further amounts of isobutyric acid fluoride forming as the acylium anion product.

According to another embodiment of the present invention, the separation reaction and the esterification reaction take place simultaneously or as competitive reactions, so that the occurrence of any side reactions is substantially reduced to a minimum. The anhydrous acid is preferably separated and returned to the process while the acylium anion product can be esterified. The lower alkyl propionates or the lower alkyl isobutyrates, such as methyl isobutyrate, can be subjected to oxydehydrogenation to form the lower alkyl esters of acrylic acid or methacrylic acid, such as methyl methacrylate.

Acrylic acid methyl ester and methacrylic acid methyl ester are prepared by carrying out the esterification according to the invention as described above and using as a mixture of carboxylic acid chloride or fluoride and alcohol with up to 20 carbon atoms propionic acid or isobutyric acid chloride or the respective fluoride and methanol and the formed propionate or methyl isobutyrate in the vapor phase of an oxydehydrogenation.

The inventive method thus relates to the esterification of a mixture containing an acylium anion product, such as. B. contains an acylium fluoride or acylium chloride, the isobutyric acid fluoride being mentioned as an example. The mixture to be esterified preferably contains an acylium anion product which could be produced by the reaction of carbon monoxide, an acid mentioned here and an organic compound mentioned here. The esterification of the acylium anion product is carried out with a smaller amount of alcohol than the total amount of alcohol which would be required to esterify the entire amount of acylium anion products of the mixture to form the corresponding carboxylic acid ester, taking as an example of a carboxylic acid ester which can be prepared in this way the methyl isobutyrate should be mentioned. The reaction is preferably carried out under conditions under which the carboxylic acid ester forms and the acid is regenerated, as will be explained in more detail below.

1-100% of the acid can be separated from the esterified reaction mixture and this amount of the separated acid can be returned to the reaction with the carbon monoxide and the organic compound mentioned

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to produce further amounts of a mixture which contains the acylium anion product which is used as the starting product in the process according to the invention and the anhydrous acid.

One can also separate 1-100% of the carboxylic acid ester from the esterified mixture and 1-100% of the mixture of the esterification product which remains after the carboxylic acid ester has been separated from this mixture, returned to the reaction and reacted with the carbon monoxide and the organic compound mentioned , forming further amounts of the mixture containing the acylium anion product.

As already mentioned above, carboxylic acid esters obtained, in particular the short-chain alkyl esters of propionic acid and / or isobutyric acid, such as. B. methyl propionate or methyl isobutyrate are subjected to a direct oxydehydrogenation process according to known process steps to produce the corresponding unsaturated lower alkyl esters, such as. B. methyl acrylate or methyl methacrylate.

The starting materials for making the acylium anion product are the following:

The acylium anion product described here, e.g. Isobutyric acid fluoride, can be prepared by any method, such as. B. by reacting isobutyric acid chloride or bromide with hydrofluoric acid, isobutyric acid fluoride being formed and the hydrochloric acid or hydrobromic acid formed thereby being recovered. However, the acylium anion product is preferably prepared by the process described in Swiss Patent No. 656872 (Application No. 3478 / 82-0).

In the process according to the invention, anhydrous hydrofluoric or hydrochloric acid are used. These acids are said to be substantially free of water, i.e. H. they should be in anhydrous form. The term "anhydrous" as used herein means that the compounds in question are essentially free of water, i. H. that there is less than 200 parts per million of water in them or that when water is present, this does not interfere with the reaction to form the carboxylic acid ester.

The most preferred anhydrous acid for carrying out the process according to the invention is hydrofluoric acid.

45 The alcohols that can be used to esterify the acylium anion product are described in more detail below:

The alcohols that are used to carry out the esterification process described are primary alcohols or secondary alcohols, each with up to 20 carbon-50 atoms, which do not decompose under the esterification conditions and the separation processes used, and the anhydrous acid is supplied without a reaction with the recovered anhydrous acid occurs. Preferred alkanols are those which have 55 to 5 carbon atoms per molecule. Alcohols which are particularly preferred are methanol, ethanol and propanol. The most preferred alcohol is methanol.

The esterification process for the preparation of the carboxylic acid esters is explained in more detail below. 60 The esterification reaction of the acylium anion product, for example the isobutyryl fluoride with an alcohol, in particular methanol, is carried out at temperatures in the range from 20 to 150 ° C. and at pressures in the range from 1 to 340 bar. In general, the esterification reaction is carried out at temperatures in the range from 40 to 70 ° C. and at pressures in the range from 3.3 to 6.7 bar. The temperature and the pressure are chosen so that the products to be manufactured are not decomposed

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and that the separation of the products will be facilitated.

It is preferred that the reactants be stirred during the esterification. In many cases where a rapid mixing process is carried out, the esterification reaction with the concurrent recovery of the anhydrous acid, such as hydrofluoric acid, can be carried out within seconds or minutes.

The critical variable in carrying out the esterification reaction is the maintenance of the molar ratio of alcohol, for example methanol, to the acylium anion product and this molar ratio must be below the value 1: 1. That is, the total amount of alcohol that is reacted with the mixture containing the acylium anion product must be less than the amount of alcohol that is required to react the entire acylium anion product to form the carboxylic acid ester.

The entire amount of alcohol can be injected into the mixture containing the acylium anion product. However, the alcohol is preferably added in smaller portions to the mixture containing the acylium anion product.

The esterification step is an exothermic reaction and cooling may be necessary. The mixture supplied to the esterification can also contain carbon monoxide, unreacted organic compound, anhydrous acid and carboxylic acid ester. The mixture preferably contains anhydrous acid, particularly when the acylium anion product is the isobutyric acid fluoride. When an acylium anion product such as isobutyric acid fluoride is esterified, the ratio of the amount of anhydrous acid such as hydrofluoric acid to isobutyric acid fluoride is in the range of 0.01-95.5 parts by weight of anhydrous hydrofluoric acid 99.09-4.5 parts by weight of isobutyric acid fluoride. However, the ratio is preferably in the range of 10.0-90.0 parts by weight of anhydrous hydrofluoric acid to 90-10 parts by weight of isobutyric acid fluoride. The amount of anhydrous acid, for example hydrofluoric acid, in the mixture depends on the efficiency of the operation of the process and the ease with which the anhydrous acid is separated from the product mixture. The anhydrous acid can be hydrofluoric acid and the product mixture containing the acylium anion product can be, for example, a mixture of isobutyric acid fluoride, hydrofluoric acid, carbon monoxide and the isobutyric acid alkyl ester, for example the isobutyric acid methyl ester.

After the esterification reaction is complete, depending on the reaction conditions, 1-100% of the carboxylic acid ester formed can be separated from the product mixture of the esterification reaction. Preferably 80-100% of the carboxylic acid ester is separated and the esterified product mixture remaining after this separation is preferably reintroduced into the process for the preparation of the acylium ion and subjected to a further reaction with the reactants in order to supply further amounts of the acylium anion product. This recycle product stream may contain carbon monoxide and / or anhydrous acid and / or unreacted organic compound and / or the unesterified acylium anion product.

However, 1-100% and preferably 80-100% of the anhydrous acid can also be separated from the mixture of the esterification products and this anhydrous acid is preferably returned to the process in order to form further amounts of the acylium anion product there. This recycle product stream may contain small amounts of undissolved unesterified acylium anion product and / or carboxylic acid ester and / or unreacted organic compound.

The separation can be carried out by any of the known separation methods, for example by distillation or solvent extraction. Distillation is preferably used.

A preferred embodiment of the process for the preparation of the carboxylic acid esters comprises the following steps: An esterification of an organic acylium anion product, as described here, is carried out with an alcohol, which is described here, maintaining essentially anhydrous conditions and the Carboxylic acid esters, unreacted alcohol, the anhydrous acid and the unreacted anion product are separated under those conditions under which the esterification proceeds essentially completely.

In the process, the esterification can also take place while 80-100% of the anhydrous acid and preferably 90-100% of the anhydrous acid are separated off and this separated anhydrous acid is preferably returned to the process for the preparation of the acylium anion product.

From the esterification mixture obtained, z. B. also separate 90 to 100% of the carboxylic acid ester and 80 to 100% of the anhydrous acid, this anhydrous acid usually being returned to the process for the preparation of the acylium anion.

Preferably, the separation is carried out during the esterification by distilling the mixture of the esterification reaction under conditions under which the esterification of the acylium anion product continues until it is substantially complete. This means that B. 80 to 100% of the acylium anion product can be esterified to form the carboxylic acid ester and preferably 90-100% can be converted into the ester. The distillation conditions are usually chosen so that the formation of by-products is significantly reduced. Furthermore, the distillation conditions should also be set so that the halogen acids can be removed so that the formation of halogenated by-products is significantly reduced.

The yields in the esterification reaction are preferably essentially in the range from 80-100%, with yields which can be found in the range from 90-100% being very preferred.

The reaction vessel for carrying out a preferred esterification and a separation apparatus is described in more detail below:

1 shows a schematic diagram of a preferred esterification apparatus and a preferred separation apparatus. This device can be used to carry out the esterification processes described herein, but is particularly useful when the esterification of isobutyric acid fluoride with methanol is to be carried out to form the methyl isobutyrate. The product which contains the acylium anion, for example the material which provides the isobutyric acid fluoride, is shown in the drawing at 20 and it is fed through line 30 via measuring pump 32 and via line 34, tap 36 and line 38 into the Reaction vessel 40 introduced, in which the esterification is carried out. In the esterification reaction vessel 40, the acylium anion product is reacted with the alcohol, for example with methanol. The alcohol is introduced from the storage container 42 via the measuring pump 44 into the esterification reaction container 40 via the line 46, the tap 48 and the line 50. The feeds for the acylium anion product, for example the isobutyric acid fluoride and the alcohol, for example the methanol, enter the esterification reaction vessel 40 through dispersing nozzles, not shown here, which are connected to line 38 and line 50, respectively. The esterification reaction container 40 can be equipped with resistance bodies, baffles or other devices.

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genes that ensure rapid mixing of the reactants 96, and part or all of which will ensure about the. The reaction mixture, which comes from the Vereste line 98 into the distillation column at point 58, is introduced into the reaction vessel 40 via line 42 and is further distilled there under reflux.

position 56 in the distillation column 52. The point 56 of the operation of the cooling devices and the separating

The distillation column is located between the reflux devices and can be set by the person skilled in the art in this area 58 of this distillation column and above that that with the aid of these devices the

Point 60 of the column at which the liquid phase removes removal of impurities and / or by-products,

becomes. The distillation column 52 is operated in such a way that it is either more volatile or less volatile than the set anion of the organic acid, for example isobutene hydrofluoric acid.

ryl fluoride is removed and also unconverted alcohol, 10 According to a further embodiment of the present, for example, methanol and also the regenerated acid, the invention, it is possible via line 104 another, for example hydrofluoric acid. Furthermore, the distilla solvent, that is, a so-called secondary solvent ion column, is operated in such a way that the esterification reaction which is to be added serves as an evaporation agent and the removal of the

Esterification reactor 40 had started, within the distilla acylium anion addition product, for example the isobutene

tion column 52 runs completely. 15 tersäurefluorides from the ester, for example the isobutter

This distillation column 52 is lightened in FIG. 1 with its methyl acid ester. In this case the heat

Inlet and outlet points are shown and it is particularly omitted exchanger 64 and the entire thermal energy is well applicable to the exchanger 90 is introduced essentially under anhydrous conditions.

esterification of the isobutyric acid fluoride with methane. In another embodiment, the height of the point can be carried out. However, it should be pointed out that in 20 60 are selected such that the heat exchanger 64 is omitted from this column, the addition and removal points easily and the total thermal energy in the exchanger 90

can be modified as introduced by a person skilled in the art.

is known in the art to adapt the column to the anhydrous. In another embodiment, a solvent is esterification with alcohols other than methanol. together with the alcohol, for example methanol, into the If, for example, the boiling point of the ester is introduced below the esterification reaction vessel 40, which is because of the anhydrous acid, then the withdrawal point must be thinner to dilute and mix the ester The upper end of the column is while the alcohol is used with the reaction mixture and also for the removal point for the anhydrous acid to be below the removal and evaporation of the recovered anhydrous acid, at the point for the ester. for example, to facilitate hydrofluoric acid. The liquid phase, which contains unreacted alcohol, for example solvent, is then removed via the cleaning device 102, such as methanol and / or the acylium anion addition product. The solvent used must be inert towards, for example, isobutyric acid fluoride and / or hydrogen fluoride reactants and the reaction conditions and separation acid and / or the ester, for example the isobutyric acid conditions, and it may contain, with the ester formed, methyl ester at the withdrawal point 60 which is removed, for example, from the methyl isobutyrate and also with the column 52 and this liquid phase is introduced via line 35 into the heat exchanger 64 via the anhydrous acid, for example hydrofluoric acid, and there does not form an azeotrope. Furthermore, the boiling point of the solution must be cooled. Then it is fed via line 66 to the medium between that of the anhydrous acid, for example measuring pump 68, and introduced via line 70 into the esterified form of hydrofluoric acid and the ester, for example reaction reaction vessel 40. The acylium anion pro- des isobutyric acid methyl ester, so that the separation duct, for example isobutyric acid fluoride, then reacts with 40 is promoted. The solvent preferably has a low alcohol, for example methanol, during the heat of vaporization. Solvent used in the evaporation process which occurs between the addition point 56 of esterification and also to facilitate separation and point 60 where the liquid stream is withdrawn from the isobutyric acid fluoride esterified with the methanol. Thus, during the evaporation process, the acylium net is, such fluorohydrocarbons, in particular anionic product, are essentially converted into the ester, for example with 43 fluorinated alkanes which have up to 20 carbon atoms, are esterified to give the methyl isobutyrate, but are particularly preferred are those that have up to 5 carbon atoms - these esters are located in the column downwards through the evaporation atoms.

area and the ester is then removed from the distillation. The invention is now to be removed using the following examples column 52 via the outlet 72 and then explained in more detail.

the line 74 is conveyed into the storage container 76. A 50 In the examples, the following working method was a small fraction of the crude product which is used through line 74 to conduct the esterification of the isobutyric acid fluoride, can be examined via line 78 through the heat exchange, the esterification according to the invention being carried out with a shear 80 and the line 82 are returned, and this less amount of methanol has been carried out than the portion then returns to the distillation king at point 84, which would be required for the total amount of isobutyric acid column 52. 55 refluoride to form the methyl isobutyrate to ver- The anhydrous acid, for example hydrofluoric acid, esters. The esterification was further under semiadiabatic which is recovered in the esterification reaction, conditions increase e.g. B. performed as follows:

through the distillation column 52 upwards and becomes a 2 liter reaction vessel, namely a Hastelloy

Top end removed at outlet 86, and this anhydrous acid C Parr reactor, was equipped with a system for adding methanol, then via line 88 into heat exchanger 90 60, and nitrogen was introduced at a pressure of 34 bar, where it was partially or fully condensed is used. The reaction vessel was also equipped with a

and then it is fitted via line 92 into the pre-separating element, which has a continuously recorded

direction 94 introduced. The anhydrous acid, for example, was connected to the temperature recorder and that

Hydrofluoric acid, is then via line 96 in the reaction vessel was also with an air motor and

Storage container 98 passed or it enters the container 102, 65 stirrer, which was set so that it turned 1000 and is rotated to produce more amounts of the acylium revolutions per minute. The anion product filled into the reaction vessel was reused. The material formed at the bottom of the separating device enters the reaction participants in a directional direction and emerges from the bottom via the line, namely of anhydrous hydrofluoric acid, if this

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was applied, and to isobutyric acid fluoride. keeping it at a temperature of a cooling bath of dry ice and acetone.

After the reaction vessel has been filled, the reaction participants and the reaction vessel are brought to a predetermined temperature and the automatic temperature display is put into operation.

The weighed amount of methanol, and less than that required to convert all of the isobutyric acid fluoride, is then injected into the reaction vessel. The initial temperature at which the methanol was introduced was room temperature. Once the esterification reaction was complete, the mixture was analyzed using gas chromatography.

The temperature increases could be observed from the temperature recording. In general, the first temperature rise was attributed to the heat of mixing and the second temperature rise to the esterification reaction.

example 1

419.3 g (4.66 moles) of isobutyric acid fluoride at 26 ° C was esterified by injecting 131.2 g of methanol at 21 ° C. The temperature of the reaction mixture initially dropped and then rose to 64.6 ° C over the next 5.25 min. The reaction was complete and analysis by gas chromatography showed that only anhydrous hydrofluoric acid and methyl isobutyrate had formed and that unreacted isobutyric acid fluoride remained. The amounts of the ingredients were as follows:

182 g (4.1 moles) of anhydrous hydrofluoric acid, 418.2 g (4.1 moles) of methyl isobutyrate and 50.3 g (0.56 moles) of unreacted isobutyric acid fluoride.

Example 2

A mixture of 46.6 g of anhydrous hydrofluoric acid (10% by weight) and 422.6 g of isobutyric acid fluoride (90% by weight), which had a temperature of 29.3 ° C., was mixed with 133 g of methanol, which was a temperature owned by 21 ° C, esterified. The methanol was added in a single portion. A temperature increase of 20.7 ° C was observed and then the temperature rose to 128 ° C over the next 38.4 seconds. The reaction was complete. Analysis by gas chromatography showed that 416.0 g of methyl isobutyrate and 134.3 g of anhydrous hydrofluoric acid had formed and that 51.8 g of unreacted isobutyric acid fluoride remained.

Example 3

A mixture of 540.4 g of anhydrous hydrofluoric acid and 59.9 g of isobutyric acid fluoride, which was at a temperature of 30 ° C., was esterified by adding 18.6 g of methanol, which was at a temperature of 22 ° C., in a single portion . Under these conditions, the temperature rose continuously from 30 ° C to 49.5 ° C after 1.5 seconds. The reaction was complete and the analysis showed that 58.2 g of methyl isobutyrate had formed. The amount of anhydrous hydrofluoric acid was 552.7 g and 8.0 g of unreacted isobutyric acid fluoride was present.

Example 4

A continuous process for the preparation of the methyl isobutyrate is described using this example.

A plug flow reaction container was used. This reaction vessel was manufactured from a tube with a length of 12.19 m and an inner diameter of 1.27 cm. This pipe had a premixing zone 1.52 m long and was provided with spots. into which could be injected and which were at a distance of 1.5 m from each other. The tube was also equipped with a heater.

The carbonylation reaction was carried out at a temperature 5 of 50 ° C. and a pressure of approx. 108 bar, the propene, the anhydrous hydrofluoric acid and the carbon monoxide being added in a molar ratio of 1.0: 14: 1.3. The flow rate was 1.52 kg per hour.

10 The anhydrous hydrofluoric acid and the carbon monoxide are injected into the premixing zone and thoroughly mixed there, and then the propene is injected into the mixture of the anhydrous hydrofluoric acid and the carbon monoxide at intervals of 1.52 m, the last 15 additions at a distance of 9.14 m from the start of the reaction vessel. After the reaction is complete, methanol is injected into the reaction vessel at the injection site 10.66 m from the beginning of the tube, and esterification takes place at this point. The methanol is preferably added at the rate at which the esterification takes place and the methyl isobutyrate forms. The amount of methanol injected is less than the amount of previously formed isobutyric acid fluoride.

The section of the reaction vessel in which the esterification takes place is kept at a temperature of about 40 ° C. and a pressure of about 6.8 bar. The methyl isobutyrate is separated from the mixture of the end products by simple distillation and the remaining iso-30 butyric acid fluoride, the carbon monoxide and the anhydrous hydrofluoric acid, together with the carbon monoxide and the anhydrous hydrofluoric acid, which are injected into the premixing zone of the reaction vessel, are returned to the reaction.

In another embodiment of the continuous reaction before the esterification is carried out, the mixture containing the acylium anion product, for example isobutyric acid fluoride, is passed through a separation unit in which the excess of carbon monoxide and 10-90% of the excess of anhydrous hydrofluoric acid are removed and then the recycling takes place while the remaining product mixture, which preferably contains 10 parts by weight of anhydrous hydrofluoric acid and 90 parts by weight of isobutyric acid fluoride, is esterified according to the process 45 described here, followed by the separation of the isobutyric acid methyl ester and the recycling of the following remaining product mixture of unreacted isobutyric acid fluoride and anhydrous hydrofluoric acid.

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Example 5

The production of methyl acrylate or methyl methacrylate is explained below.

The methyl ester of propionic acid or isobutyric acid, which have been prepared from the corresponding acyclic anion product, such as, for example, from propionic acid fluoride or isobutyric acid fluoride, can be subjected to oxydehydrogenation by the esterification process described here, for example by those processes which are described in US Pat. 3 585 248: 3 585 249 - 3 585 250: 3 634 494: 3 652 654; 3 660 514: 3 766191: 3 781336: 3 784 483: 3 855 279: 3 917 673; 3,948,959: 3,968149: 3,975,301; 4,029,695: 4,061,673; 4 081465 and 4088 602 in British Patent No. 1447 593.

Preferably, the catalyst used for this contains iron, phosphorus and oxygen, and it can be represented by the following empirical formula

Fe P, O ,,

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are illustrated, in which per 1 atom of iron x represents the value of 0.25-3.5 atoms of phosphorus and z means the number of oxygen atoms which are required to saturate the remaining valences of the catalyst. Particularly preferred catalysts are those described in U.S. Patent No. 3,948,959 that contain a chemical accelerator. This chemical accelerator can do the formula

Mey, in which Me / Me represents the accelerator atoms Li, Na, K, Rb, Ce, Mg, Ca, Sr, Ba or mixtures of two or more such accelerator atoms and y illustrates the number of accelerator atoms per atom of iron. This value y is in the range of 0.01-2.0.

The methyl ester 5 of acrylic acid or methyl ester of methacrylic acid formed in this oxydehydrogenation is then separated off by separation processes described in the literature, for example by distillation in the presence of an inhibitor for the polymerization or else by extraction.

i ° Although the present invention has been explained on the basis of specific examples with the specification of special conditions, it is nevertheless not intended to be restricted in any way by these special working methods.

M

1 sheet of drawings

Claims (13)

656 872 PATENT CLAIMS 1. A process for the preparation of carboxylic acid esters, characterized in that a mixture of carboxylic acid chloride or fluoride in a primary alcohol with up to 20 carbon atoms, a secondary alcohol with up to 20 carbon atoms or a mixture of such alcohols at 20 to 150 ° C and a pressure of 1 to 340 bar in the presence of anhydrous hydrofluoric acid or hydrochloric acid or a mixture of these, the initial amount of these anhydrous acids to the carboxylic acid chloride or fluoride in the range of 0.01 to 95.5 wt. Parts of anhydrous acid to 99.09 to 4.5 parts by weight of carboxylic acid chloride or fluoride and the amount of alcohol used is measured such that not the entire amount of carboxylic acid chloride or fluoride is converted to the respective ester. 2. The method according to claim 1, characterized in that methanol is used as the alcohol in the esterification. 3. The method according to claim 1, characterized in that ethanol or propanol is used as the alcohol in the esterification. 4. The method according to claim 1, 2 or 3, characterized in that hydrogen fluoride is used as the anhydrous acid. 5. The method according to claim 4, characterized in that the initial amount of anhydrous hydrofluoric acid to carboxylic acid fluoride is 10-90 parts by weight of the anhydrous hydrofluoric acid to 90-10 parts by weight of carboxylic acid fluoride. 6. The method according to claim 1, characterized in that isobutyric acid fluoride is used as the carboxylic acid fluoride and methanol is used as the alcohol and the reaction is carried out in the presence of anhydrous hydrofluoric acid, the amount of methanol added at the beginning being in the range from 70-99% of The amount of isobutyric acid fluoride is and the amount of anhydrous hydrofluoric acid present in the mixture being esterified is in the range of 10-20 moles of anhydrous hydrofluoric acid per 1 mole of isobutyric acid fluoride. 7. The method according to claim 6, characterized in that one carries out the esterification at a temperature of 40-70 ° C and a pressure of 3.3-6.7 bar. 8. The method according to claim 7, characterized in that one carries out a distillation step in order to remove 80-100% of the isobutyric acid formed from the product mixture obtained in the esterification. 9. The method according to claim 8, characterized in that the process steps of distillation and esterification take place simultaneously. 10. The method according to any one of claims 6-9, characterized in that 90-100% of the methyl ester of isobutyric acid is removed from the mixture of the esterified products. 11. A process for the preparation of methyl acrylate and methyl methacrylate, characterized in that the esterification is carried out according to the process according to claim 1 and as a mixture of carboxylic acid chloride or fluoride and alcohol up to 20 C atoms of propionic acid or isobutyric acid chloride or the respective fluoride and methanol is used and the methyl propionate or methyl isobutyrate formed is subjected to an oxydehydrogenation in the vapor phase. 12. The method according to claim 11, characterized in that hydrofluoric acid is used as the anhydrous acid. 13. The method according to claim 11 or 12, characterized in that one carries out the step of oxydehydrogenation using a catalyst. which is composed of iron, phosphorus and oxygen and which is the following empirical formula Fe Px Oz, in which x has a value of 0.25-3.5, so that 0.25-3.5 atoms of phosphorus are present on an iron atom present in the compound and z illustrates the number of oxygen atoms, which are needed to saturate the still free valences of the catalyst.