GB2101591A - Production of acyl halides and carboxylic acids and esters therefrom - Google Patents

Abstract

In a carbonylation process for a producing acyl halides, e.g. acyl fluorides, the carbon monoxide and anhydrous acid such as hydrogen fluoride are premixed to form a single liquid phase which is reacted in a second reactor with an organic compound, i.e. an ester or an olefin, e.g. propylene, to produce an acyl halide, e.g., isobutyryl fluoride. In the second reactor the temperature is 0- 90 DEG C and the pressure 34-340 bars. The mole ratio of anhydrous acid to organic compounds is 1-100 moles of anhydrous acid per mole of organic compound and the mole ratio of carbon monoxide to organic compound is 1 to 5 moles of carbon monoxide per mole of organic compound. The acyl halide product may be hydrolysed to form the corresponding carboxylic acid which may in turn be oxydehydrogenated in the organic phase to form the corresponding unsaturated acid, e.g., acrylic acid or methacrylic acid.

Description

SPECIFICATION Production of an acylium anion product and carboxylic acids and esters therefrom This invention relates to the production of an acylium anion product and carboxylic acids and esters therefrom.

More particularly the invention relates to the liquid phase production of an acylium anion.

product, e.g., isobutyryl fluoride, by reacting a premixed carbon monoxide saturated anhydrous acid solution and an organic compound capable of adding carbon monoxide thereto.

The prior art such as British Patent 942,367 and German Offenlegungsschrift 2,750,719 as a whole stresses the requirement of gas-liquid phase systems and an aqueous acid catalyst reaction medium for production of carboxylic acids from compounds having one or more double bonds, or esters following by further hydrolysis of ,the reaction products to produce carboxylic acids.

In these processes, serious irreversible polymerization occurs and the aqueous acid medium is corrosive so that expensive equipment is required.

For example, in the prior art, such as in U. S.

Patent No. 2,831,877 (Koch), acid fluorides can be formed by reacting an olefin with carbon monoxide and anhydrous hydrogen fluoride. This reaction is a dual phase reaction with the carbon monoxide in the gaseous state and the olefin and hydrogen fluoride remaining in the liquid state. As with most dual phase reactions, problems arise due to the requirement of additional mixing and replenishing the carbon monoxide into the liquid as it is used up. This is extremely significant in that the olefin dimerizes or polymerizes under these conditions.

The problems of the prior art can be overcome by the use of a liquid phase anhydrous system to form the acylium anion product by the process or reaction conditions described herein, or the carboxylic acids by the process described herein.

Carbon monoxide and an anhydrous acid described herein, e.g., hydrogen fluoride, are premixed in a first reactor to form a liquid phase preferably saturated with carbon monoxide which is rapidly reacted in a second reactor with an organic compound described herein capable of adding carbon monoxide thereto, e.g., propylene, under reaction conditions of a liquid phase whereby an acylium anion product forms, e.g., isobutyryl fluoride, in substantial yields. The acylium anion product, e.g., isobutyryl fluoride, may be further reacted with excess water to form carboxylic acid, e.g., idobutyric acid. The acid can be oxydehydrogenated to an unsaturated acid, e.g., methacrylic acid as described herein.

In the accompanying drawings: Fig. 1 is a diagram of the solubility of carbon monoxide in anhydrous hydrogen fluoride.

Fig. 2 is a schematic diagram of a reactor for the process of the present invention.

The process according to the invention for producing an acylium anion product and/or a carboxylic acid and/or ester therefrom comprises the following steps: (a) forming in a first reactor a liquid mixture comprising carbon monoxide dissolved in an anhydrous acid described herein, e.g., hydrogen fluoride, preferably the anhydrous acid is saturated with carbon monoxide.

(b) reacting in the liquid phase in a second reactor under conditions whereby an acylium anion product forms the liquid mixture from the first reactor of CO dissolved in the anhydrous acid with a liquid mixture comprising an organic compound capable of adding carbon monoxide thereto, described herein, e.g., propylene, to form a product mixture comprised of the acylium anion product, e.g., isobutyryl fluoride.

In one embodiment of the invention, the process further comprises the step of hydrolyzing the acylium anion product, e.g., isobutyryl fluoride, to form the corresponding carboxylic acid, e.g., isobutyric acid, under conditions whereby the carboxylic acid forms and the anhydrous acid is regenerated. Preferably the carboxylic acid is separated from the hydrolyzed mixture, and the remaining hydrolyzed mixture, absent of any deleterious amount of water and other deleterious materials comprised of anhydrous acid, e.g., hydrogen fluoride, and/or carbon monoxide, and/or unreacted acylium anion product, e.g., isobutyryl fluoride, is recycled to the liquid mixture of anhydrous acid and carbon monoxide.

In another embodiment of the invention, acrylic acid and/or methacrylic acid is produced from the propionic acid and/or isobutyric acid by oxydehydrogenation as described herein in the vapor phase, in the presence of an oxygencontaining gas, air or oxygen itself, and water, at a temperature from 300 to 5000 C, and at a pressure from 0.5 atmospheres to two (2) atmospheres in the presence of a catalyst described herein comprised of iron, phosphorous, and oxygen defined by the empirical formula FePx02, where relative to one (1) atom of iron, x represents from 0.25 to 3.5 atoms of phosphorous and zrepresents the number of oxygen atoms required to satisfy the valence requirements of the catalyst.Methyl or other alkyl esters of acrylic acid and/or methacrylic acid can be formed by esterifying the acrylic and/or methacrylic acid.

The carbon monoxide may be from any source, but must be substantially free from water; that is, contain less than 1 ,000 ppm of water. The carbon monoxide may be diluted with other substances which do not interfere with the reaction. For example, dry synthesis gas may be used or dry coal combustion gases may be used. It is preferred that dry carbon monoxide itself be used.

The organic compound capable of reacting with carbon monoxide and the anhydrous acid may contain other compounds and/or very small amounts of water, e.g., less than 1 ,000 ppm of water, which do not interfere with the liquid phase reaction and/or cause a dual phase to occur. The organic compounds may be organic esters or isopropanol described herein which split to form the acid and an acylium anion product or organic compounds having at least one unsaturated bond capable of adding carbon monoxide thereto as described herein.

Examples of these organic esters are represented by the general formula

wherein R is an alkyl group having up to five carbon atoms; such as methyl, ethyl or pentyl.

Preferably the alkyl group is methyl, ethyl, propyl or isopropyl, with ethyl and isopropyl being highly preferred, and isopropyl being especially preferred. R' is an alkyl group having from two to five carbon atoms, such as ethyl, propyl or pentyl.

Preferably R' is ethyl or isopropyl, with isopropyl being the most preferred.

Although any one of the esters mentioned herein may be used, it is preferable if an ester is used to use isopropyl, isobutyrate (2-propanol 2methylpropionate), ethyl isobutyrate (ethanol 2methylpropionate), isopropyl p-ropionate (2propanol propionate) or ethyl propionate (ethanol propionate). But isopropyl isobutyrate (2-propanol 2-methylpropionate) is especially preferred when an ester is used in the process described herein.

Examples of organic compounds having at least one unsaturated bond capable of adding carbon monoxide thereto which may be used in the process described herein are olefins having up to twenty carbon atoms having at least one double bond capable of adding carbon monoxide thereto, such as: ethylene, propylene, butenes, dodecene, 1,3-butadiene, 1,4-pentadiene, 1,5hexadiene. Ethylene and propylene are preferred, and propylene is highly preferred. The alkenes may be substituted with alkyl, aryl or cycloalkyl, or other substitutes which do not interfere in the process described herein.

Although all of the organic compounds described herein may be used in the process described herein, propylene is especially preferred.

The acids used for the preferred process to the acylium anion described herein should be susbstantially free from water; that is, anhydrous.

The term "anhydrous" as used herein and in the claims refers to acids which are substantially free from water, e.g., less than 1,000 ppm of water, or if water is present, it does not interfere with the reaction to form the acylium anion, or the carboxylic ester therefrom.

The anhydrous acids which may be used for the described process are: hydrogen fluoride (hydrofluoric acid) (HF) hydrogen chloride (hydrochloric acid) (HCI) hydrogen fluoride-boron trifluoride (HF BF3) or mixtures thereof; but preferably the individual acids.

Preferably the anhydrous acid for the process described is anhydrous hydrogen fluoride or an hydros hydrogen chloride. However, the most preferred anhydrous acid for the process described herein is hydrogen fluoride (hydrofluoric acid).

The reaction of carbon monoxide, with an organic compound described herein and an anhydrous acid described herein, can occur at temperatures of from zero degree Centigrade (0 C) to ninety degrees Centigrade (900C), the upper temperature being determined by side product formation. For the reaction between the preferred reactants described herein, the temperature can be from forty degrees Centigrade (400 C) to sixty degrees Centigrade (600C), but preferably it is at about fifty degrees Centigrade (50"C). The carbond monoxide pressure can vary from thirty-four (34) bars (500 psia) to three hundred forty (340) bars (5,000 psia), and preferably it is from 2,500 psia to 2,000 psia.The pressure being increased as required for the solubility of carbon monoxide in the anhydrous acid, as for example, shown in Figure 1, which shows the increase in the amount of carbon monoxide dissolved in anhydrous hydrogen fluoride as the pressure and temperature increases.

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

All of the carbon monoxide (CO) and anhydrous acid, e.g., anhydrous hydrogen fluoride, which is to be reacted with the organic compound, e.g., propylene, should be thoroughly mixed in the first reactor to form a liquid mixture in which the CO is dissolved therein, preferably the liquid mixture is saturated with the CO prior to reacting with the organic compound described herein, e.g., propylene, then the organic compound in the liquid phase is rapidly reacted, while mixing with the premixed carbon monoxide and acid in the second reactor. Generally, the reaction, depending upon the pressure and the temperature, will occur within minutes to form an acylium anion product, e.g., isobutyryl fluoride.

The organic compound itself can be diluted with carbon monoxide or other inert diluents, e.g., methane, ethane or propanol, in the liquid phase to form a liquid mixture comprising the organic compound, e.g., propylene, and CO, and /or inerts prior to reaction with the liquid mixture of anhydrous acid diluted with carbon monoxide.

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

After the reaction to form the acylium anion is complete, which depends upon the reaction conditions as known to those skilled in the art, from one (1 ) to one hundred (100) percent of the acylium anion product formed is separated from the product mixture. Preferably, from eighty (80) to one hundred (100) percent of the acylium anion product is separated, and the remaining product mixture is recycled to the first or second reactor; that is, carbon monoxide, anhydrous acid, and the organic compound described herein.Or, from one (1) to one hundred (100) percent (preferably from eighty (80) to one hundred (100) percent), of the anhydrous acid is separated from the product mixture containing the acylium anion product after the reaction to form the acylium anion is complete and the separated anhydrous acid is recycled back to the first reactor for further mixing with carbon monoxide.

The separation can be by any of the known methods of separation, such as distillation.

The hydrolysis reaction of the acylium anion ,addition product, e.g., isobutyryl fluoride, with excess water can occur at a temperature from twenty degrees Centigrade (200 C) to one hundred and fifty degrees Centigrade (-1500C) and at a pressure from 14.7 psia to 5,000 psia, but norm-ally it occurs at a temperature from forty degrees Centigrade (400C) to seventy degrees Centigrade (700C) and a pressure from 500 psia to 3,000 psia. The temperature and pressure are set to avoid the decomposition of the intended products.

The total amount of water to be added, may be injected into the reaction mixture after the reaction to form acylium anion is complete. The hydrolysis step is exothermic; and, thus, cooling may be required.

The esterification reaction of the acylium anion product, e.g., isobutyryl fluoride, with an alcohol, particularly, can occur at a temperature from twenty degrees Centigrade (200C) to one hundred fifty degrees Centigrade (1 500C) and at a pressure from 14.7 psia to 5,000 psia, but normally it occurs at a temperature from forty degrees Centigrade (400C) to seven-ty degrees Centigrade (700 C) and a pressure from 50 psia to 100 psia. The temperature and pressure are set to avoid the decomposition of the intended products, and to facilitate product separations.

It is preferred that the reactants be stirred during esterification. In many cases, when rapid mixing is used, the esterification reaction with the concurrent regeneration of the anhydrous acid, e.g., HF, can be completed within seconds to minutes.

From one (1) to one hundred (100) percent (preferably from eighty (80) to one hundred (100) percent) of the anhydrous acid is separated from the esterification product mixture and is recycled back for reaction 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 of the known methods of separation, such as distillation or solvent extraction. Preferably, distillation is used.

The carboxylic acid or propionic acid or isobutyric acid formed from acylic anion product, e.g., propionyl fluoride or isobutyryl fluoride, after hydrolysis as described herein can be oxyde hydrogenated for example by the process described in U. S. Patents 3,585,248; 3,585,249; 3,585,250; 3,634,494; 3,652,654; 3,660,5t4; 3,766,191; 3,781,336; 3,784,483; 3,855,279; 3,917,673; 3,948,959; 3,968,149; 3,975,301; 4,029,695; 4,061,673; 4,081,465; 4,088,602; British Patent 1,447,593.

The reaction forming the acylium anion product can be carried out in any reactor which has a means for forming a liquid phase mixture of carbon monoxide and anhydrous acid, e.g., a pressurized mixing tank, and a means for separately contacting the liquid phase mixture of carbon monoxide and anhydrous acid with a liquid phrase comprised of an organic compound and reacting (e.g., a tubular reactor) so as to form a product mixture containing an acylium anion product.It can further comprise either a means for separating the acylium anion product from the product mixture, e.g., a distillation column, our a means for separating the acylium anion product from the product mixture, and separately hydrolyzing or esterifying the separated acylium anion product from-the product mixture to a carboxylic acid or ester (e.g., a distillation column connected to a reactor) or a means for separately hydrolyzing or esterifying the acylium anion product in the product mixture to a carboxylic acid or ester. A means for separating the carboxylic acid or ester can be attached to the reactor (e.g., distillation column). Means for introducing the reactants to reactor (e.g., pumps) can be attached to the reactor.

Figure 2 shows a schematic diagram of a typical reaction system for use in the present invention. Such a system should include a source of the acid, e.g., hydrofluoric acid, 10, a source of carbon monoxide 11 and a source of the organic compound, e.g., propylene, 12. The carbon monoxide is metered-by metering means such as a metering valve 13 through line 14 into a pressurized mixing tank 1 5 which is maintained under pressure.The acid, e.g., hydrofluorie id is injected into the mixing tank through line 16 by inserting means such as pump 1 7. The pressurized mixing tank 1 5 should also be equipped with agitation means such as a stirrer 1 8. The pressurized mixing tank may generally have a liquid phase 19 and a gaseous phase 20 wherein the carbon monoxide not dissolved in the acid, e.g., hydrogen fluoride, is maintained.

The liquid phase comprises a mixture of carbon monoxide and hydrogen fluoride. This mixture is transferred through line 21 under pressure to the inlet of a reactor such as a plug flow or tubular reactor 22.

The organic compound, such as propylene, is transferred through a line 23 into the reactor inlet via a liquid-liquid mixing nozzle. A metering pump 24 should also be used to inject the organic compound at the desired rate and at the pressure of the reaction.

The reactor of the present invention must be capable of maintaining the hydraulic pressure of the system and must allow sufficient residence time for the reaction to occur. The reaction time generally will vary based on the reaction temperature. Increased temperature increases the rate of reaction. Generally, the reaction time should take no longer than approximately 120 seconds although it will be within the competence of one of ordinary skill in the art to determine exactly what the preferred reaction time should be for particular reagents, temperatures and pressures.

The reagent mixture comprising the acid, hydrogen fluoride-carbon monoxide solution and the organic compound passes through the reactor and exits through a pressure release valve or let down valve 25.

This is a simple schematic diagram of a reaction system suitable for the present invention.

Various types of reactors could be used for the present invention and one of ordinary skill in the art would have no trouble in designing a particular reactor suitable for the particular intended purpose.

After the reactants have passed the let down valve 25, the additional step of hydrolysis or esterification of the acylium anion product, such as an acyl fluoride, e.g., isobutyryl fluoride can be conducted in a second reactor 26 or in an extension of the tubular reactor 22. The hydrolysis is conducted simply by adding water to the stable organic carbon monoxide acid anion product, e.g., the acid fluoride e.g., isobutyryl fluoride. This produces the carboxylic acid, e.g., isobutyric acid, and acid, e.g., hydrogen fluoride, which then can be separated by means such as a distillation apparatus 27 and used again if desired to produce additional stable organic carbon monoxide acid anion addition product. The acid can also be reacted with other compounds such as an alcohol to form an ester.

It is extremely important in the present invention to maintain the proper amount of carbon monoxide in solution. From the chart in Figure 1 the amount of carbon monoxide which can be dissolved in anhydrous hydrogen fluoride can be determined. This data was determined empirically and one of ordinary skill in the art should be able to likewise determine the solubility of carbon monoxide in any anhydrous or substantially anhydrous acid at a particular temperature and a particular pressure. Based on the molar amount of the organic compound which is intended to be reacted, the amount of carbon monoxide needed for the reaction can be determined.For example, as stated above, the desired range of molar ratios of organic compound to carbon monoxide to acid is 1 :1-5: 1-100 and in the preferred ratio 1:1.1:15, particularly for propylene, carbon monoxide, anhydrous hydrogen fluoride.

Other information required is the reaction conditions desired, e.g., the pressure and the temperature of the reactor. From this the molar percentage of carbon monoxide dissolved in the acid, e.g., hydrogen fluoride, can be determined.

From this, the amount of acid, e.g., hydrogen fluoride, solution required to supply sufficient carbon monoxide to react with the organic compound can also be determined.

For example, if the intended reaction conditions are 5,000 psig and 800C, it is known from Figure 1 or it could be determined empirically that under these conditions 14 Ibs. of carbon monoxide will dissolve in 100 Ibs. of anhydrous hydrogen fluoride.

More specifically, take for example the formation of isobutyryl fluoride from propene where the intended flow rate of propene is 226 Ib-moles/hr. or 9,515 Ib/hr. It is preferable to have about a 10 percent excess of carbon monoxide to ensure sufficient carbon monoxide availability for the olefin. Therefore, approximately 248 Ibmole/hr. (6,963 Ib/hr.) of carbon monoxide is required. Since the solubility of carbon monoxide is hydrogen fluoride at the reaction conditions is 14 lb. CO/1 00 lbs. HF it is known that 49,736 Ibs/hr. of HF is sufficient to dissolve the carbon monoxide needed to react with the propene. This equals 2,486 lb. mole/hr. making a molar ratio of hydrogen fluoride to propene of 11:1.

At 3,000 psig and 800 C, 9 Ibs. of carbon monoxide would be dissolved in 100 Ibs. of hydrogen fluoride. Therefore, the minimum mole ratio in this situation calculates to 17:1 HF to propene.

Once the proper proportions of organic compound and acid carbon monoxide solutions are determined the carbon monoxide and acid solution is injected into the mixing vessel at the desired reaction conditions. The solution of carbon monoxide in acid, e.g., hydrogen fluoride, which is formed in the mixing vessel is metered into the reactor. The mixing vessel must be maintained at a high enough temperature and pressure to keep the carbon monoxide in solution.

The desired amount of organic compound, e.g., propylene, is also metered into the reactor whe-re it contacts and mixes with the solution of carbon monoxide in acid, e.g., hydrogen fluoride.

The reagents are passed through the reactor while maintaining the pressure and temperature.

Since this reaction is generally exothermic, cooling jackets may be required for the reactor.

Thus, for carbon monoxide, hydrogen fluoride, propylene reaction this is particularly important since this reaction should be conducted at less than 900C.

The reagents once having passed through the reactor are released through a let down valve and further purified and if required, further reacted. A typical reaction as described previously would be the hydrolysis of the stable organic carbon monoxide and anion addition product, e.g., acid fluoride to form a carboxylic acid and the acid, e.g., hydrogen fluoride.

The following examples will illustrate the process and reactor scheme described herein.

Example The reactor in the present example comprises a 1-litre Monel autoclave equipped with a turbine blade stirrer with two inlets and a bottom outlet connected to a reactor. The reactor was a tubular reactor comprising a 1/2-inch (12.7 mm) diameter tube 40 feet (12.19 m) in length connected at one end to the outlet of the autoclave and at the exhaust end to a let down valve. The reaction temperature was maintained at approximately 300C and the pressure was maintained at 3,000 psig.

In this reaction propene was reacted to form isobutvryl fluoride. The carbon monoxide was injected into the autoclave at a rate of 3.5 g.

mole/hr. and the hydrogen fluoride was injected at a rate of 55 g. mole/hr. and mixed therein to form a liquid phase of carbon monoxide in hydrogen fluoride which was injected into the tubular reactor. The flow rate of propene into the tubular reactor was 2.6 g. mole/hr. The total flow rate of reagents through the tubular reactor was 1,198 g. per hr. Using this method 2.05 g.

mole/hr. of isobutyryl fluoride was formed.

Remaining in the effluent were 1.0 g. mole/hr.

carbon monoxide, 52.4 g. mole/hr. hydrogen fluoride and a trace of propene. The remaining effluent comprised other undesirable organics.

The selectivity of this reaction to isobutyryl fluoride was approximately 75 percent.

While the invention has been described with reference to specific details of certain illustrative embodiments, it is not intended that it shall be limited thereby except insofar as such details appear in the accompanying claims.

Claims (14)

Claims

1. A process for the carbonylation of olefins and organic esters which comprises: (a) forming in a first reactor at a temperature in the range of from zero (0) degree Centigrade to one hundred (100) degrees Centigrade and a pressure in the range from fourteen (14) bars (206 psia) to six hundred eighty-two (682) bars (10,000 psia) a liquid mixture of carbon monoxide in an anhydrous acid; (b) reacting in the liquid phase in a second reactor the liquid mixture of carbon monoxide in an anhydrous acid and an organic compound for a time sufficient to form the corresponding acylium anion product at a temperature within the range of from zero (0) degree Centigrade to ninety (90) degrees Centigrade, and at a pressure within the range of from thirty-four (34) bars (500 psia) to three hundred forty (340) bars (5,000 psia);; the anhydrous acid being hydrogen fluoride (HF), hydrogen chloride (HCI), hydrogen fluoride boron trifluoride, or a mixture thereof; the organic compound being an olefin having up to twenty (20) carbon atoms and having at least one double bond capable of adding carbon monoxide thereto, or an organic ester represented by the formula

wherein R is an alkyl group having up to five (5) carbon atoms, and R' is an alkyl group having from two (2) to five (5) carbon atoms; the mole ratio of anhydrous acid to the organic compound being within the range of from one (1) mole to one hundred (100) moles of anhydrous acid to one (1) mole of organic compound; and the mole ratio of carbon monoxide to the organic compound being from one (1) mole to five (5) moles of carbon monoxide to one (1) mole of organic compound.

2. A process as claimed in Claim 1 wherein the organic compound is isopropyl isobutyrate, ethyl isobutyrate, isopropyl propionate, or ethyl propionate.

3. A process as claimed in Claim 1 wherein the organic compound is isopropyl isobutyrate.

4. A process as claimed in Claim 1 wherein the organic compound is an olefin having up to twenty carbon atoms and having at least one double bond capable of adding carbon monoxide thereto.

5.'A process as claimed in Claim 1 wherein the organic compound is ethylene or propylene

6. A process as claimed in Claim 1 wherein the organic compound is propylene.

7. A process as claimed in any of Claims 1 to 6, wherein the anhydrous acid is hydrogen fluoride.

8. A process as claimed in Claim 7 wherein the acylium anion formed is substantially separated from the reaction mixture.

9. A process as claimed in Claim 8 wherein the acylium anion is further reacted with water at a temperature of from twenty (20) degrees Centigrade to one hundred fifty (150) degrees Centigrade and at a pressure from one (1) bar (14.7 psia) to three hundred and forty (340) bars (5,000 psia).

10. A process for producing acrylic acid or methacrylic acid which comprises: (a) forming in a first reactor a liquid mixture comprising carbon monoxide dissolved in an anhydrous acid; (b) reacting in the liquid phase in a second reactor under conditions whereby an acylium anion product forms, the liquid mixture of carbon monoxide dissolved in the anhydrous acid and a liquid comprising ethylene or propylene, the anhydrous acid being hydrogen fluoride (HF), hydrogen chloride (HCI), hydrogen fluoride boron trifluoride (HF.BF3), or a mixture thereof.

(c) hydrolyzing the acylium anion product under conditions whereby a carboxylic acid forms; (d) separating the carboxylic acid from the hydrolyzed mixture; (e) oxydehydrogenating in the vapor phase a mixture comprising the carboxylic acid, water, and oxygen, at a temperature from 300 to 5000C, at a pressure from 0.5 atmospheres to two (2) atmospheres, in the presence of a catalyst comprising iron, phosphorous, and oxygen, defined by the empirical formula Fe Px Oz, where relative to 1 atom of Fe, x represents from 0.25 to 3.5 atoms of phosphorous, and z represents the number of oxygen atoms required to satisfy the valence requirements of the catalyst, for a time sufficient to produce the corresponding unsaturated carboxylic acid acrylic acid or methacrylic acid.

11. A process as claimed in Claim 10 wherein the catalyst further comprises a promoter represented by Me, wherein Me represents the promoter and y represents the number of promoter atoms relative to one atom of iron and is from 0.01 to 2.0, the promoter Me being Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, or a mixture thereof.

12. A process as claimed in Claim 10 or 11 wherein the anhydrous acid is hydrogen fluoride, and the olefin is propylene.

1 3. A process for the carboxylation of olefins and organic esters substantially as described with particular reference to the example and/or the accompanying drawings.

14. An acylium anion product when prepared by a process as claimed in any of Claims 1 to 9 or 13.

1 5. Acrylic acid or methacrylic acid when prepared by a process as claimed in any of Claims lotto 12.