NL8202271A - PROCESS FOR THE PREPARATION OF CARBONIC ACID ESTERS FROM ACYLIUM ANions Formed By CARBONYLATION - Google Patents

Description

* r 7 N.Q. 31110 1 /

Process for the preparation of carboxylic acid esters from acylium anions formed by carbonylation.

The present invention relates to the preparation of carboxylic acid esters by esterification of acyl fluorides and / or acyl chlorides, in particular those compounds formed from carbon monoxide, anhydrous hydrogen fluoride or hydrogen chloride and an olefin with 5 or more double bonds or esters.

The prior art, such as British Patent 942,367, emphasizes aqueous acidic catalyst systems for the preparation of carboxylic acid by carbonylation of compounds with one or more double bonds or esters followed by further hydrolysis of the reaction products with excess water to prepare the carboxylic acids and then the esterification of the acids. In these methods, the aqueous acidic environment is corrosive and expensive equipment is required. The problems of the prior art are overcome by the process for the preparation of carboxylic acid esters.

The accompanying drawing illustrates an embodiment of the ester separation process.

Carboxylic acid esters, for example methyl isobutyrate, are formed by esterification with less than the total amount of alcohol required to react with the total amount of acylium anion product, for example, isobuturyl fluoride, to form the carboxylic acid ester and the anhydrous acid, for example hydrogen fluoride or hydrogen chloride to regenerate. The acylium anion product, although formed by some reaction, is preferably formed by the reaction of carbon monoxide, an anhydrous acid, for example, hydrogen fluoride, and an organic compound capable of reacting with the carbon monoxide and the anhydrous acid , for example, propylene, under conditions where an acylium anion product, for example, isobutyryl fluoride, is formed. In other embodiments of the invention, part or all of the carboxylic acid ester, for example, methyl 30-isobutyrate, is separated from the esterified mixture and the remaining part of the esterified mixture is separated after part or all of the carboxylic acid ester has been separated therefrom (e.g. hydrogen fluoride, unreacted isobutyryl fluoride, unseparated methyl isobutyrate) recycled for reaction with the organic compound (eg propylene) to form more acylium anion product (eg (isobutyryl fluoride). In another embodiment of the invention, the separation and the esterification is 8202271 * - * 2 in time so that side reactions are essentially reduced to a minimum The anhydrous acid is separated and recycled while the acylium anion product is esterified The lower alkyl propionates or isobutyrates, for example methyl isobutyrate , 5 can be oxygenated to 1 other alkyl acrylates or methacrylates, for example methyl methacrylate.

The new process for the preparation of a carboxylic acid ester with an acylium anion product comprises the following step: esterification of a mixture containing an acylium anion product (fluoride or chloride), for example isobutyryl fluoride, in particular an acylium anion product formed by the reaction of carbon monoxide, an acid and contains an organic compound with less than the total amount of alcohol required to esterify the total amount of acylium anion product in the mixture to the carboxylic acid ester, for example methyl isobutyrate. This reaction is carried out under conditions whereby the carboxylic acid ester is formed and the acid is regenerated.

In other embodiments of the invention, the method comprises one or more of the following steps: separation of 1 to 100% of the acid from the esterified mixture and recirculation of 1 to 100% of the separated acid for reaction with carbon monoxide and the organic compound to form more mixture containing the acylium anion product and the anhydrous acid.

In another embodiment of the invention, the process may comprise the following step: separation of 1 to 100% of the carboxylic acid ester from the esterified mixture and recirculation of 1 to 100% of the esterification product mixture remaining after separation of the carboxylic acid ester therefrom, for reaction with carbon monoxide, and the organic compound 30 to form a more mixture containing the acylium anion product.

In another embodiment, the carboxylic acid esters formed by the process, especially the alkyl esters of propionic acid and / or isobutyric acid having a small number of carbon atoms in the alkyl group, such as methyl propionic acid and methyl isobutyric acid, are suitable for direct oxide hydrogenation by known methods to unsaturated alkyl esters with a small number of carbon atoms in the alkyl group such as methyl acrylate and methyl methacrylate.

The acylium anion product, for example isobutyryl fluoride, can be prepared by some method, for example reaction of isobutyryl chloride or bromide with hydrogen fluoride to form 8202271.

»3 of isobutyryl fluoride and regeneration of the hydrogen chloride or hydrogen bromide.

However, a more preferred method is by a carbonylation reaction of carbon monoxide, an anhydrous acid and an organic compound. A preferred carbonylation reaction for the preparation of the acylium anion product is described.

The reagents for forming the acylium anion product can be from any source, but should be free of harmful materials that hinder the process. The total amount of water in the reaction mixture to be esterified must be less than 0.01% by weight to avoid side reactions of the acylium anion product to undesired ethers. Preferably the system is anhydrous.

The carbon monoxide can be from any source, but is preferably substantially free of water to maintain substantially anhydrous reaction conditions. The carbon monoxide can be diluted with other substances that do not hinder the reaction. For example, dry synthesis gas or carbon combustion gas can be used. It is preferred that dry carbon monoxide itself be used.

The organic compounds are those which are capable of reacting with carbon monoxide and the anhydrous acid; i.e., to be carbonylated to form an acylium anion, for example, organic esters or olefins with at least one double bond, which can be carbonylated to an acylium anion product.

The organic esters for the carbonylation reaction are represented by the general formula R-C (= O) -O-R ', wherein R is an alkyl group having up to 20 carbon atoms, such as methyl, ethyl, dodecyl or eicosanyl. Preferably, the alkyl group is methyl, ethyl, propyl or isopropyl, with ethyl and isopropyl being most preferred. Rf 30 is an alkyl group of 2 to 20 carbon atoms such as ethyl, propyl, tert-butyl, dodecyl and eicosanyl. Preferably R 'is ethyl or isopropyl, with isopropyl being most preferred.

When an organic ester is used in the carbonylation process, any of the listed esters can be used. However, it is preferred to use isopropyl isobutyrate (2-propanol-2-methyl propionate), ethyl isobutyrate (ethanol-2-methyl propionate), isopropyl propionate (2-propanol propionate) or ethyl propionate (ethanol propionate) and it is preferable in the especially preferred is to use isopropyl isobutyrate or ethyl propionate.

Examples of organic compounds having at least a double bond 8202271 capable of forming an acylium anion product therewith (carbonylation to an acylium anion product) which can be used in the process are olefins having up to 20 carbon atoms such as ethylene, propylene, butenes, butadiene-1,3 and dodecene. The olefins 5 can be substituted with alkyl groups, aryl groups or cycloalkyl groups or other substituents that do not interfere with the process. Furthermore, the olefins may contain more double bonds in the molecule that do not interfere with the process, such as butadiene-1,3. Preferred olefins are ethylene, propylene, isobutene, butene-1, butene-2 and butadiene-1,3, with ethylene and propylene being particularly preferred.

Although all of the organic compounds described can be used in the process, propylene is particularly preferred, however.

The acids used for the preferred method of preparing the acylium anion should be substantially anhydrous.

The term "anhydrous" as used herein refers to acids which are substantially free of water, for example less than 200 ppm water, or when water is present this should not be the reaction for the formation of the acylium anion or the carboxylic acid ester therefrom hinder.

The anhydrous acids used for the process are: hydrogen fluoride (HF) and hydrogen fluoride (HCl).

The most preferred anhydrous acid for the process is hydrogen fluoride.

The alcohols used for the esterification process can be any primary or secondary alcohol which does not decompose under the esterification and separation conditions and which develop the water-free acid without reaction with the regenerated acid.

Examples of such alcohols are alkanols with up to 20 carbon atoms. Preferred alkanols are those alkanols containing up to 5 carbon atoms. Particularly preferred alcohols are methanol, ethanol and propanol.

Methanol is the most preferred alcohol.

The reaction of carbon monoxide with an organic compound and an anhydrous acid can take place at temperatures from 0 ° C to 100 ° C, the highest temperature being determined by the formation of by-products. For the reaction between the preferred reagents, the temperature may be from 40 ° C to 80 ° C, but the temperature is preferably about 60 ° C. The carbon monoxide pressure can range from 101.3 kPa to about 42000 kPa or up to 70000 kPa, but is generally between 3500 kPa to 35000 kPa and preferably between 10500 kPa and 21000 kPa, increasing the pressure as required for the solubility of the carbon monoxide and in the anhydrous acid and to increase the productivity of the reactor.

The anhydrous acid to organic compound molar ratio should be from 1: 1 to 100: 1, but is generally between 10: 1 and 20: 1, and is preferably about 15: 1. The carbon monoxide to organic compound molar ratio is from 1: 1 to 5: 1 or higher, but is preferably between 1.5: 1 and 1: 1 and the maximum corresponds to the saturation limit of carbon monoxide in the reaction mixture for and at the end of the reaction.

All carbon monoxide and anhydrous acid, for example, anhydrous hydrogen fluoride, which need to be converted to the organic compound, must be thoroughly mixed before contacting the organic compound, for example propylene. The organic compound is then reacted while mixing with the premixed mixture of carbon monoxide and acid. Generally, depending on pressure and temperature, the reaction will take place within minutes to form an acylium anion product, eg, isobutyryl fluoride. The organic compound itself can be diluted with carbon monoxide or inert diluents, for example, methane, ethane or propane before reaction with the anhydrous acid.

The reaction can be carried out in a semi-batch reactor, plug flow reactor, back mixing reactor (CSTR) or other reactor known to those skilled in the art, but the preferred reactor is a plug flow reactor.

The esterification reaction of the acylium anion product, for example isobutyryl fluoride, with an alcohol, in particular methanol, can take place at temperatures from 20 ° C to 150 ° C and at pressures from 100 kPa to 34000 kPa, but usually takes place at temperatures of 40 ° C to 70 ° C and pressures from 330 kPa to 670 kPa. The temperature and pressure are adjusted to avoid decomposition of the intended products and to facilitate product separations.

It is preferred that the reagents be stirred during the esterification. In many cases, when rapid mixing is used, the esterification reaction with simultaneous regeneration of the anhydrous acid, for example HF, can be completed within seconds to minutes. 8202271 6.

The critical feature of the esterification reaction is to maintain the molar ratio of alcohol, for example methanol, on the acylium anion product below 1: 1; that is, the total amount of alcohol reacted with the mixture containing the acylium anion product must be less than the amount of alcohol required for the total amount of the acylium anion product to form the carboxylic acid ester.

The total amount of alcohol can be injected into the mixture containing the acylium anion product, but preferably the alcohol is added in portions to the mixture containing the acylium anion product. The esterification step is exothermic and therefore cooling may be required. The mixture may also contain carbon monoxide, unreacted organic compound, anhydrous acid and carboxylic acid ester. Preferably, the mixture contains anhydrous acid, especially when the acylium anion product is isobutyryl fluoride. When the acylium anion product, such as isobutyryl fluoride, is esterified, the ratio of the amount of anhydrous acid, for example, hydrogen fluoride, to isobutyryl fluoride is in the range of 0.01 to 95.5 parts by weight of anhydrous hydrogen fluoride (AHF) at 99.09 to 4 .5 parts by weight of isobutyryl fluoride (IBF), but preferably from 10.0 to 90.0 parts by weight of AHF to 90 to 10 parts by weight of IBF. The amount of anhydrous acid, for example hydrogen fluoride, in the mixture depends on the effective operation of the process and the ease of separation of the anhydrous acid, for example hydrogen fluoride, from the product mixture containing the acylium anion product, for example isobutyryl fluoride, hydrogen fluoride, carbon monoxide and an alkyl isobutyrate, such as methyl isobutyrate.

After the esterification reaction is complete, depending on the reaction conditions, 1 to 100% of the carboxylic acid ester formed is separated from the product mixture of the esterification reaction. Preferably 80 to 100% of the carboxylic acid ester is separated and the remaining esterified product mixture is recycled for further reaction with the reagents to form more acylium anion product. This recycle stream may contain carbon monoxide and / or anhydrous acid and / or unreacted organic compound and / or the unesterified acylium anion product.

In another embodiment of the invention, 1 to 100% (preferably 80 to 100%) of the anhydrous acid is separated from the esterification product mixture and recycled for reaction 40 to form more acylium anion product. The recycle stream may contain small amounts of unseparated, unesterified acylium anion product and / or carboxylic acid ester and / or unreacted organic compound.

The separation can be by any known separation method, such as distillation or extraction with solvent. Distillation is preferably used.

The preferred embodiment for the preparation of the carboxylic acid ester comprises: esterification of an organic acylium anion product with an alcohol under substantially anhydrous conditions and separation of the carboxylic acid ester, unreacted alcohol, anhydrous acid and unreacted acylium anion product under conditions with the esterification continuing to almost complete.

The process may further involve esterification, while separating 80 to 100% of the anhydrous acid (preferably 90 to 100%) and recycling the separated anhydrous acid to form more acylium anion product.

Preferably, the separation while esterification takes place by distillation of the esterification reaction mixture under conditions, the esterification of the acylium anion product continues to near completion; i.e., 80% to 100% of the acylium anion product is esterified to a carboxylic acid ester, and preferably 90 to 100%. The distillation conditions are such that the formation of by-products is considerably reduced. The distillation conditions are also such that the halogen acids, in particular HF, in particular HF are removed, such that the formation of halogenated by-products is considerably reduced. Preferably, the esterification efficiencies are 80 to 100%, with 90 to 100% being particularly preferred.

A preferred schematic diagram of an esterification and separation device is shown in Figure 1 which is adapted for the esterification process described herein, but is particularly suitable for esterification of isobutyryl fluoride with methanol to methyl isobutyrate. The acylium anion product, for example an isobutryryl fluoride source 20, is passed through line 30 through the metering pump 32 through line 34, valve 36 and line 38 into the esterification reactor 40 where it reacts with the alcohol, for example methanol. The alcohol is passed from the alcohol supply source 42 through the metering pump 44 to the esterification reactor 40 through line 46, valve 48 and line 50. The feed of the acylium anion product (e.g., isobutyryl fluoride) 40 and alcohol (e.g., methanol) enter the esterification reactor 40 8202271 8 through dispersion nozzles (not shown), respectively. connected to lines 38 and 50. The esterification reactor may be equipped with dividers or other devices to ensure rapid mixing of the reagents. The reaction mixture from the esterification reactor 40 enters the distillation column 52 through a conduit 42 at point 56 which is located between the entry point 58 of the refluxed product and above the point of removal 60 of the liquid phase. The distillation column 52 is operated to remove the unconverted organic carbon monoxide acid anion, for example, isobutyryl-10 fluoride, the unreacted alcohol, for example, methanol, and the regenerated acid, for example, hydrogen fluoride, and to initiate the esterification reaction the esterification reactor 40 to be completed within the distillation column 52. This distillation column 52 shown in Fig. 2, with its feed and discharge points, is particularly applicable to the substantially anhydrous methanol esterification of isobutyryl fluoride. However, the feed and discharge points can be easily modified, as known to those skilled in the art, to be adapted to anhydrous esterification by other alcohols. For example, when the boiling point of the ester is below that of the anhydrous acid, the ester effluent will be at the top of the column, while that of anhydrous acid will be below.

The liquid phase, containing unconverted alcohol (methanol) and / or ammonium anion addition product (for example isobutyryl fluoride) and / or hydrogen fluoride and / or ester (for example methyl isobutyrate), is removed at outlet point 60 and passes through line 62 to the heat output exchanger 64, where it is cooled if necessary and passes through line 66 to the metering pump 68 through line 70 in the esterification reactor 40. The acylium anion product, for example, isobutyryl fluoride, combines with the alcohol, for example, methanol, during the distillation operation, which takes place between the supply point 56 and the discharge point 60 of the liquid stream, so that it is mainly converted to the ester, for example methyl isobutyrate, which moves down through the distillation section and is removed from the distillation column at the discharge 72 and through line 74 to the storage tank 76 35. A portion of the impure product passing through line 74 can be recycled through line 78 through heat exchanger 80 and line 82 to re-enter distillation column 52 at 84. The anhydrous acid (e.g. hydrogen fluoride), which is regenerated by the esterification reaction, goes up through the distillation column 52 and is removed at the top at the outlet 86 and passes 8202271 t 9 through line 88 in the heat exchanger 90, where it partially or is completely condensed and passes through line 92 to separator 94. The anhydrous acid (e.g., hydrogen fluoride) passes through line 96 to storage unit 98 or 102 for reuse to prepare 5 more acylium anion product. The separator bottoms exit the separator bottom through line 96 and return partially or wholly through line 98 to the distillation column at reflux point 58. The operation of the condenser and separator may be specified by those skilled in the art to assist in the removal of the impurities and / or by-products which are more or less volatile than hydrogen fluoride.

In another embodiment of the invention, it is possible to add a second solvent through line 104 to act as a stripping agent to enhance the removal of the acylium anion addition product (eg, isobutyryl fluoride) from the ester, eg, methyl isobutyrate, eliminating the exchanger and the total energy load is placed on the exchange 90.

In another embodiment, the height of point 60 can be chosen to eliminate exchanger 64 and place the total energy load on exchanger 90.

In another embodiment of the invention, a solvent in direct current with the alcohol, for example, methanol, is added to the esterification reactor 40 to dilute and mix the alcohol in the reaction mixture and to strip the regenerated anhydrous acid (eg, HF ) and is removed by the blower 102. The solvent used is inert to the reagents under the conditions of the reaction and separation and does not form an azeotrope with the ester, for example methyl iso-30 butyrate or the anhydrous acid, hydrogen fluoride, and has a boiling point that is between that of the anhydrous acid, for example hydrogen fluoride and the ester, for example methyl isobutyrate, so that the separation is increased; preferably the solvent has a low heat of evaporation. Suitable solvents for the esterification and separation of isobutyryl fluoride which has been esterified with methanol are the hydrofluoroalkanes with up to 20 carbon atoms, but preferably those with up to 5 carbon atoms.

Examples

The following examples will illustrate the invention.

The following method was used to examine the esterification of isobutyl-8202271 * 10 methyl fluoride based on less than the amount of methanol required to esterify all isobutyryl fluorides to methyl isobutylate under semi-adiabatic conditions.

A 2 1 Hastelloy C Parr reactor, equipped with a methanol-5 delivery system (using nitrogen and 3500 kPa), a thermocouple, which is connected to a continuous temperature recorder and an air motor and stirrer set to run at 1000 revolutions per minute to rotate, was charged with a weighed amount of anhydrous hydrogen fluoride (if used) and isobutyryl-10 fluoride (maintained at the temperature of dry ice-acetone). After filling, the reagents and the reactor are brought to the preselected temperature and the temperature recorder is operated. The weighed amount of methanol (less than the amount required for reaction of all isobutyryl fluoride) is then injected into the reactor. The initial temperature of the methanol was at room temperature. After esterification was completed, the mixture was analyzed by gas chromatography. Temperature increases were noted from the temperature-time recording. Generally, the first was attributed to the mixed heat and the second was attributed to the esterification reaction.

Example I

419.3 g (4.66 mol) isobutyryl fluoride (IBP) were esterified at 26 ° C by injection of 131.2 g of methanol (at 21 ° C). The temperature of the reaction mixture initially dropped and then rose to 64.6 ° C for the next 5.25 min. The reaction was completed and gas chromatographic analysis showed only anhydrous hydrogen fluoride (132 g, 4.1 mol) and methyl isobutyrate formed (418.2 g, 4.1 mol) with 50.30 g (0.56 mol) isobutyryl fluoride that had not reacted.

Example II

A mixture of 46.6 g of anhydrous hydrogen fluoride (10 wt. Z) and 422.6 g of isobutyryl fluoride (90 wt. Z) was esterified at 29.3 ° C with 133 g of methanol at 21 ° C (the methanol was dissolved in βδη portion added). A temperature rise of 20.7 ° C was observed, followed by a temperature increase at 128 ° C for the next 38.4 sec. The reaction was completed and the gas chromatographic analysis showed 416.0 g of methyl isobutyrate, 134.3 g of anhydrous hydrogen fluoride and 51.8 g of unreacted isobutyryl fluoride.

Example III

A mixture of 540.4 g of anhydrous hydrogen fluoride and 59.9 g of iso-40 butyryl fluoride was esterified at 30 ° C by adding 18.6 g of methanol (from 22 ° C) in SSn portion. Under these conditions rose after 1.5 sec. the temperature continuously from 30 ° C to 49.5eC. The reaction was completed and the analysis showed that 58.2 g of methyl isobutyrate had been obtained. shaped. The amount of anhydrous hydrogen fluoride was 552.7 g and the unreacted isobutyryl fluoride was 8.0 g.

Example IV

The following continuous procedure can be performed to prepare methyl isobutyrate according to the described procedure.

A plug flow reactor is used to form isobutyric acid from propylene. The reactor consists of a tube with a length of 1220 cm and an internal diameter of 12.7 mm with a pre-mixing section of approximately 150 cm and equipped with injection points at intervals of -150 cm and a heating device. The carbonylation reaction is carried out at 50 ° C and 21600 kPa with propylene, anhydrous hydrogen fluoride and carbon monoxide in a molar ratio of 1:14: 1.3 at a flow rate of 1.52 kg per hour. The anhydrous hydrogen fluoride and the carbon monoxide are injected into the premix section, in which they are thoroughly mixed and the propylene is injected into the mixture of anhydrous hydrogen fluoride and carbon monoxide at 150 cm intervals, the final addition taking place at 900 cm from the beginning of the reactor. After the reaction is complete, methanol is injected at the 1050 cm injection point into the reactor, the esterification preferably taking place at the rate at which the esterification takes place and methyl isobutyrate is formed. The amount of injected methanol is less than the amount of isobutyryl fluoride formed. This section of the reactor, where the esterification is taking place, is maintained at about 40 ° C and a pressure of 700 kPa. The methyl isobutyrate is separated from the final product mixture by simple distillation and the remaining isobutyryl fluoride, carbon monoxide and anhydrous hydrogen fluoride are recycled with the carbon monoxide and anhydrous hydrogen fluoride which are injected into the premix section of the reactor.

In another embodiment of the continuous reaction, prior to esterification, the product mixture containing the acylium anion product (isobutyryl fluoride) is passed to a separation unit in which the excess carbon monoxide and 10 to 90% of the excess anhydrous hydrogen fluoride are removed. and recycle while the residual product mixture, preferably with 10 parts by weight of anhydrous hydrogen fluoride to 90 parts by weight of isobutyryl fluorine-40, is esterified as described, followed by the separation of 8202271 12 methyl isobutyrate and the recycle of the remaining product mixture. of unreacted isbuturyl fluoride and anhydrous hydrogen fluoride. Formation of methacrylic acid or methyl methacrylic acid.

The methyl ester of the propionic or isobutyric acid formed from acylium anion product, for example propionyl fluoride or isobutyryl fluoride, can be oxidized after esterification as described herein by the method described in U.S. Patents 3,585,248, 3,585,249, 3,585,250, 3,634,494, 3,652,654, 3,660,514, 3,766,191, 3,781,336, 3,784,483, 3,855,279, 3,917,673, 3,948,959, 10 3,968,149, 3,975,301, 4,029,695, 4,061 .673, 4,081,465, 4,088,602 and British Patent 1,447,593.

Preferably, the catalyst is composed of iron, phosphorus and oxygen, as defined by the empirical formula FePxOz, in which, based on an atom of iron, x represents 0.25 to 3.5 atoms of phosphorus and z represents the number of oxygen atoms is required to meet the valence needs of the catalyst. More preferred catalysts are those described in U.S. Pat. No. 3,948,959 which contain a promoter proposed by Mey, wherein Me is the promoter of Li, Na, K, Kb, Ce, 20 Mg, Ca, Sr , Ba represents mixtures thereof and y represents the number of promoter atoms relative to an atom of iron and is 0.01 to 2.0. The methyl acrylate or methyl methacrylate is then separated by techniques known per se, for example distillation in the presence of a polymerization inhibitor or by extraction.

8202271

Claims (21)

1 13 CONCLUSIONS. 1. Process for preparing a carboxylic acid ester from an acylium anion product, characterized in that a mixture containing an acylium anion product is esterified with less than the amount of an alcohol required for the esterification of all acylium anion product in the mixture into the carboxylic acid ester under anhydrous conditions, whereby the carboxylic acid ester is formed and the acid is regenerated from the anion, which alcohol is selected from the group consisting of a primary alcohol of at most 20 carbon atoms and a second alcohol of at most 20 carbon atoms, wherein the acylium anion product is formed from the reaction of carbon monoxide, an anhydrous acid, an organic compound which can react with the carbon monoxide and an anhydrous acid is selected from the group consisting of hydrogen fluoride and hydrogen chloride, which organic compound is selected from the group consisting of from (1) an ester represented by the general formula RC (= 0) -0-Rr, wherein R is an alkyl group with at most 20 carbon atoms and R 'is an alkyl-20 group with 2 to 20 carbon atoms and (2) an olefin with at most 20 carbon atoms with at least € §n double bond, which can form an acylium anion product therewith, which esterification is carried out within a temperature range of from 20 ° C to 150 ° C and pressures from 1 bar to 340 bar in the presence of the anhydrous acid, the initial amount of the anhydrous acid on acylium anion product is within the range of 0.01 to 95.5 parts by weight of anhydrous acid to 99.0 to 4.5 parts by weight of acylium anion product. 2. Process according to claim 1, characterized in that the organic compound used is an ester selected from the group consisting of isopropyl isobutyrate, ethyl isobutyrate, isopropyl propionate and ethyl propionate. 3. Process according to claim 1, characterized in that the organic compound used is an olefin with at most 20 carbon atoms with at least ββη double bond which can form an acylium anion product therewith. 4. Process according to claim 1, characterized in that ethylene is used as the olefin. Process according to claim 1, characterized in that propylene is used as the alkene. Process according to one or more of claims 1 to 5, characterized in that 8202271 is characterized in that methanol is used as the alcohol. 7. Process according to claim 6, characterized in that further 1 to 100% of the amount of anhydrous acid from the esterification product mixture containing the carboxylic acid ester formed is removed, the separated anhydrous acid is recycled for reaction with carbon monoxide and organic compound to form more acylium anion product. 8. Process according to claim 6, characterized in that 1 to 100% of the amount of the carboxylic acid ester is separated from the esterification product mixture and 1 to 100% of the amount of the esterification product mixture which remains after separation of the carboxylic acid star therefrom, recycle to form more acylium anion product. 9. Process according to claim 6, characterized in that hydrogen fluoride is used as anhydrous acid fluoride. Process according to claim 9, characterized in that the starting amount of anhydrous hydrogen fluoride on acylium anion product (acyl fluoride) is 10 to 90 parts by weight of anhydrous hydrogen fluoride on 90 to 10 parts of acyl anion product (acyl fluoride). Process according to claim 7, characterized in that hydrogen fluoride as anhydrous acid is used. 12. Process according to claim 8, characterized in that hydrogen fluoride is used as anhydrous acidic fluoride. 13. Process according to claim 1, characterized in that a mixture containing carbon monoxide, anhydrous hydrogen fluoride and isobutyryl fluoride is used as the alcohol, methanol is used, the amount of methanol initially added being 70 to 99% of the amount of isobutyryl fluoride and the amount of anhydrous hydrogen fluoride in the mixture to be esterified is generally within the range of from 10 to 20 moles of anhydrous hydrogen fluoride to 1 mole of isobutyryl fluoride. Process according to claim 13, characterized in that the esterification reaction is carried out mainly within a pressure range from 3.3 bar to 6.7 bar and a temperature range from 40 ° C to 70 ° C. 15. Process according to claim 14, characterized in that a distillation step is further carried out for the separation of 808 to 100% of the isobutyric acid, which is formed from the esterification product mixture. Process according to claim 15, characterized in that the distillation and esterification steps are carried out simultaneously. Process according to claim 16, characterized in that 90 to 40 100% of the methyl isobutyric acid is removed from the esterification product mixture. 18 * Process for preparing an unsaturated carboxylic acid ester selected from the group consisting of methyl acrylate and methyl methacrylate, characterized in that a mixture containing an acylium anion product is esterified with less than the amount of methanol required to form the esterify acylium anion product to the corresponding ester selected from the group consisting of methyl propionate and methyl isobutyrate under anhydrous conditions, whereby the carboxylic acid ester is formed and the acid is regenerated from the anion, the ester is stripped off, the ester in the vapor phase oxydehydrogenates to the corresponding unsaturated carboxylic acid ester ( methyl acrylate or methyl methacrylate), the acylium anion product being formed from the reaction of carbon monoxide, an olefin selected from the group consisting of ethylene and propylene and an anhydrous acid under conditions to produce an acylium anion product, the anhydrous acid being selected from the group consisting of hydrogen fluoride and hydrogen chloride. 19. Process according to claim 18, characterized in that anhydrous acidic hydrogen fluoride is used. 20. Process according to claim 18 or 19, characterized in that propylene is used as the olefin. 21. Process according to one or more of claims 18 to 20, characterized in that in the oxide hydrogenation step a catalyst is used, which contains iron, phosphorus and oxygen, which catalyst is defined by the empirical formula FePxO2, in which on an iron atom x represents 0.25 to 3.5 atoms of phosphorus and z represents the number of oxygen atoms required to meet the valence needs of the catalyst. 30 ----- 8202271