CA1156256A

CA1156256A - Production of carboxylic esters from acylium anions formed by carbonylation

Info

Publication number: CA1156256A
Application number: CA000404471A
Authority: CA
Inventors: Ralph F. Pascoe; Richard V. Norton
Original assignee: Ashland Oil Inc
Current assignee: Ashland LLC
Priority date: 1981-07-10
Filing date: 1982-06-04
Publication date: 1983-11-01
Also published as: FR2509293B1; DE3221175A1; AT390056B; ATA220382A; DE3249675A1; BE893416A; CH657845A5; AU535364B2; AU8460782A; GB2101592A; CH656872A5; GB2101592B; JPS6227055B2; IT1195929B; NL187015C; DE3249675C2; DE3221175C2; NL8202271A; JPS5810538A; KR840000469A

Abstract

ABSTRACT OF THE DISCLOSURE
Carboxylic esters, e.g. methyl isobutyrate, are formed by esterifying an acylium anion product, e.g., iso-butyryl fluoride, with less than the total amount of alcohol, e.g., methanol, required to react with the acylium anion product under conditions whereby the anhydrous acid e.g., hydrogen fluoride, is regenerated.

Description

1 15~256 FORMED BY CARBONYLATION

BACKGROUND OF THE INVENTION
-A. Field of the Invention The invention relates to formation of carboxylic esters by esterifying acyl fluoriaes and/or chlorides especially those formed from carbon monoxide, anhydrous hydrogen fluoride or hydrogen chloride, and an olefin with one or more double bonds or esters.

B Descri tion of the Prior Art P
The prior art such as GB 942,367 stresses aqueous acid catalyst systems for production of carboxylic acid by carbonylation of compounds having one or more double bonds, or esters followed by further hydrolysis of the reaction products with excess water to produce carboxylic acids and then esterifying acids. In these processes, the aqueous acid medium is corrosive and expensive equipment is reauired.
TXe prior art problems are overcome by the process described herein for forming carboxylic esters.

: 20 BRIEF DESCRIPq~ION OF T~IE DRAWING
~ The drawing illustrates one embodiment of the ; esterification-separation process described herein.

SUMMARY OF THE INVENTION
Carboxylic esters, e.g., methyl isobutyrate, are formed by esterifying with less than the total amount of alcohol required to react with all of an acylium anion product, e.g., isobutyryl fluoride, to form the carboxylic acid ester and to regenerate the anhydrous acid, e.g., hydrogen fluoride or hydrogen chloride, The acylium anion 1 15~256 product, although formed by any reaction, i9 preferably formed by the reaction of carbon monoxide, an anhydrous acid described here, e.g., hydrogen fluoride, and an organic compound capable of reacting with carbon monoxide and the anhydrous acid, e.g., propylene, under conditions whereby an acylium anion product, e.g., isobutyryl fluoride, forms. In other embodiments of the invention, part or all of the carboxylic acid ester, e.g., methyl isobutyrate, is separated from the esterified mixture and the remaindçr of the esterified mixture after part or all of the carboxylic acid ester is separated therefrom ~e.g., hydrogen fluoride, unreacted isobutyryl fluoride, unseparated methyl isobuty-rate) is recycled to react with the organic compound (e.g., propylene) to form more acylium anion product ~e.g., isobutvryl fluoride). In another embodiment of the inven-tion, the separation and esterifying are concurrent so that side reactions are substantially minimized. The anhydrous acid is separated and is recycled while the acylium anion product is being esterified. The lower alkyl propionates or isobutyrates, e.g., methyl isobutyrate, may be oxydehydro-genated to lower alkyl acrylates or methacrylates, e.g., methyl methacrylate.

DESCRIPTION OF T~E INVENTION
The no~el discovered process for producing a carboxylic acid ester from an acylium anion product com-prises the step of:
esterifying a mixture comprised of an acylium anion product (fluoride or chloride), e.g., isobutyr~l fluoride, especially an acylium anion product formed by the reaction of carbon monoxide, an acid described hereln and an organlc compound described herein with less than the total amount of alcohol described herein required for esterifying all of the acylium anion product in the mixture to the carboxylic acid ester, e.g., methyl isobutyrate. This reaction is carried 1 15~2~6 out under conditions whereby the carboxylic acid ester forms and the acid is regenerated as described herein.
In other embodiments of the invention, the process further comprises the step or steps of:
S separating from one ~1) to one hundred (100) percent of the acid from the esterified mixture and recycling from one (1) to one hundred (100) percent of the separated acid for reaction with carbon monoxide and the or~anic compound described herein to form more of the mixture comprised of the acylium anion product and the anhydrous acid.
In another embodiment of the invention, the process can comprise the step of:
separating from one (1) to one hundred (100) percent of the carboxylic acid ester from the esterified mixture, and recycling from one (1) to one hundred (100) percent of the esterification product mixture remaining after separation of the carboxylic acid ester therefrom, for reaction with carbon monoxide and the organic compound described herein to form more of the mixture comprised of the acylium anion product.
In another embodiment, the carboxylic esters, formed by the process described herein, particularly the lower chain alkylesters of propionic acid and/or isobutyric acid, such as methyl-propionic acid and methyl isobutyric acid, are suitable for direct oxydehydroqenation by known processes to lower alkyl unsaturated esters; such as methyl acrylate and methyl methacrylate.

REACTANTS TO FORM THE AcyLI~tM ANION PRODUCT
; The acylium anion product described herein, e.g., isobutyryl fluoride, may be made by any process, for example, reaction of isobutyryl chloride or bromide with hydrogen fluoride to form isobutyryl fluoride, and regeneration of the hydrogen chloride or hydrogen bromide.
However, a more preferred method is by a carbonyla-tion reaction of carbon monoxide, an anhydrous acid herein, 1 15~256 and an organic compound described herein. A preferred carbonylation reaction for making the acylium anion product is described herein.
The reactants to form the acylium anion product may be from any source, but must be free from deleterious materials which interfere with the process described herein.
The total amount of water in the reaction mixture to be esterified must be less than 0.01 weight ~ to prevent side reactions of the acylium anion product to.form undesirable ethers. Preferably the system is anhydrous.
The carbon monoxide may be from any source, but is preferably substantially free from water so as to maintain substantially anhydrous reaction conditions. The carbon monoxide may be diluted with other substances which do not interfere with the reaction. For example, dry synthesis gas or coal combustion gas may 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, that is, carbonylated to form an acyLium anion, for example, organic esters described herein or olefins having at least one double bond capable of carbonylating to an acylium anion product described herein.
The organic esters for the carbonylation reaction o are represented by the general formula R - C - O - R', wherein R is an alkyl of up to twenty carbon atoms, such as methyl, ethyl, dodecyl, eicosanyl. Preferably the alkyl is methyl, ethyl, propyl, or isopropyl, with ethyl and isopropyl being the most preferred. R' is an alkyl of from two to twenty carbon atoms, such as ethyl, propyl, t-butyl, dodecyl, eicosanyl. Preferably R' is ethyl or isopropyl, with isopropyl being the most preferred.
When an organic ester is used in the carbonylation process described herein, any one of the esters mentioned 1 15~256 herein may be used. It is preferable, however, to use iso-propyl isobutyrate (2-propanol 2-methylpropionate), ethyl isobutyrate (ethanol 2-methylpropionate), isopropyl pro-pionate (2-propanol propionate) or ethyl propionate (ethanol propionate), and it is especially preferred to use lsopropyl isobutyrate or ethyl propionate.
Examples of organic compounds having at least one double bond capable of forming an acylium anion product therewith (carbonylating to an acylium anion product) which lQ may be used in the process described herein are olefins of up to twenty carbon atoms, such as ethylene, propylene, butenes, 1,3-butadiene, and dodecene. The olefins may be substituted with alkyl, or aryl, or cycloalkyls, or other substituents which do not interfere in the process described herein. Furthermore, the olefins may have multiple double ~onds within the molecule which does not interfere in the process described herein such as 1,3-butadiene. Preferred olefins are ethylene, propylene, isobutene, l-butene, 2-butene, and 1,3-butadiene, and ethylene and propylene are hi~hly preferred.
Although all of the organic compounds described herein may be ùsed in the process described herein, propylene, however, is especially preferred.
The acids used for the preferred process to make the acylium anion described herein should be substantially 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 200 ppm of water, or if water is oresent, 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) tHF) and hydrogen chloride (hydrochloric acid) tHCl).

1 15~256 The most preferred anhydrous acld for the process described herein is hydroaen fluoride (hydrofluoric acid).

ALCOHOLS FOR ESTERIFYING THE ACYLIUM ANION PRODUCT

The alcohols used for the esterification process described herein may be any primary or secondary alcohol which does not decompose under the esterification and separa-tion conditions, and which generates the anhydrous acid without reacting with the regenerated acid. Examples of such alcohols are alkanols of up to twenty aarbon atoms.
Preferred alkanols are those having up to five carbon atoms.
Highly preferred alcohols are methanol, ethanol, and propanol.
The most preferred alcohol is methanol.

REACTION CONDITIONS TO FORM THE ACYLIUM ANION PRODUCT
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 Centi-grade (0C) to one hundred degrees Centigrade ~100C), the upper temperature bein~ determined by side product formation.
For the reaction between the preferred reactants described herein, the temperature can be from forty degrees Centiarade (40C) to eighty degrees Centigrade (80C), but preferably it is at about sixty degrees Centigrade (60C). The carbon monoxide pressure can vary from 14.? psia to about 6,000 psia, or to 10,000 psia, but generally it is from 500 psia to 5,000 psia, and preferably from l,500 psia to 3,000 psia, the pres-sure being increased as required for the solubility of carbon monoxide in the anhydrous acid and to incrsase the productivity of the reactor.
The mole ratio of anhydrous acid to the organic compound described herein should be from ~:l to 100:1, but generally it is from 10:1 to 20:1 and preferably about 15:1.
The mole ratio of carbon monoxide to the organic compound described herein is from l:l to 5:1 or higher, but preferably 1 15~256 it is from 1.5:1 to 1:1 and the maximum correspondc to the saturation limit of carbon monoxide in the reaction mixture during and at the end of the reaction.
All of the carbon monoxide and anhydrous acid, e.g., anhydrous hydrogen fluoride, which is to be reacted with the organic com~ound, should be thoroughly mixed prior to contacting with the organic compound descxibed herein, e.g., propylene. The organic compound is then reacted while mixing with the premixed carbon monoxide and acid. 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 inert diluents, e.g., methane, ethane, propane, prior to reaction with the anhydrous acid.
The reaction can be conducted in a semi-batch reactor, plu~ flow reactor, back mix reactor ~CSTR), or other reactor known to those skilled in the art, ~ut the preferred reactor is a plug flow reactor.

THE ESTERIFICATION PROCESS mo FORM THE CAR~OXYLIC ACID ~STERS
The esterification reaction of the acylium anion product, e.g., isobutyryl fluoride, with an alcohol, particu-larly, methanol, can occur at temperatures from twenty degrees - Centigrade (20C) to one hundred fifty degrees Centigrade (150~C) and at pressures from one (1) bar (14.7 psia) to three hundred forty (340) bars (5,000 psia), but normally it occurs at temperatures from forty degrees Centigrade (40C) to seventy degrees Centigrade (70~C) and pressures at three and three tenths (3.3) bars (50 psia) to six and seven tenths (6.7) bars (100 psia). The temperature and pressure beinq 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, .
115~256 the esterification reaction with the concurrent regeneration of the anhydrous acid, e.g., HF, can be completed within seconds to minutes.
The critical feature of the esterification reaction S is maintaining the mole ratio of alcohol, e.g., methanol, to the acyLium anion product below 1:1; that is, the total amount of alcohol reacted with the mixture comprised of the acylium anion product must be less than the amount of alcohol required for all of the acylium anion product to form the carboxylic acid ester.
The total amount of alcohol may be injected into the mixture comprised of the acylium anion product, but preferably the alcohol is added in partial amounts into the mixture comprised of the acylium anion product. The esteri-fication step is exothermic, and thus cooIing 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, particularly 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, e.g., hydrogen fluoride, to isobutyryl fluoride is in the range from 0.01 to 95.5 parts by weight of anhydrous hydrogen fluoride (AHF) to 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 lO parts by weight of I9F. The amount of anhydrous acid, e.g., hydrogen fluoride, in the mixture is dependent upon the efficient operation of the process, and the ease o~ se~arating the anhydrous acid, e.~., hydrogen fluoride, from the product mixture comprised of the acylium anion product, e.g., isobutyryl fluoride, hydrogen fluoride, carbon monoxide, and alkyl isobutyrate, such as methyl iso~utyrate.
After the esterification reaction is complete, ; 35 which depends upon the reaction conditions from one (1) to 1 15~256 g one hundred ~100) percent of the carboxylic acid ester formed is separated from the product mixture of the esteri-fication reaction. Preferably from eighty (80) to one hundred (100) percent of the carboxylic acid ester is separated, and the remaining esterified product mixture is recycled for further reaction with the reactants 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, 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 and ; 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 preferred embodiment for producing the carboxy}ic acid esters described herein comprises: Esteri-fying an organic acylium anion product, described herein, with an alcohol, described herein, under substantially anhydrous conditions and separating the carboxylic acid ester, unreacted alcohol, anhydrous acid, and unreacted acylium anion product under conditions whereby the esterification continues to substantial completion.
The process can further comprise esterifying while separating eighty ~80) percent to one hundred ~100) percent of the anhydrous acid ~preferably ninety ~0) percent to one hundred ~100) percent) and recycling the separated anhydrous acid to form more acylium anion product.

The process preferably can further comprise esteri-fying while separating from the esterification mixture from ninety (90) percent to one hundred (100) percent of the carboxylic acid ester, and from eighty (80) percent to one hundred (100) percent of the anhydrous acid, and recycling the separated anhydrous acid to form more acylium anion product.
Preferably the separating while esterifying occurs by distilling the esterification reaction mixture under conditions whereby the esterification of the acyLium anion product continues to substantial completion; that is, from eighty (80) percent to one hundred (100) percent of the acylium anion product is esterified to a carboxylic acid ester, and preferably from ninety (90) percent to one hundred (100) percent. The distilling conditions are such that the formation of side products is substantially reduced. Also the distilling conditions are such that the halogen acids especially HF are removed so as to substantially reduce the formation of halogenated side products. Preferably the esterification yields are substantially from eighty (80) percent to one hundred (100) percent, with ninetv (90) percent to one hundred (100) percent being highly preferred.

ESTERIFICATION REACTOR AMD SEPARATOR
A schematic diagram of a preferred esterification and separation apparatus is shown in Figure 1, which is adaptable to the esterification process described herein, but is especially useful for the esterification of isobutyryl fluoride with methanol to methyl isobutyrate. The acylium anion product, e.g., isobutyryl fluoride source 20, is fed 30 by line 30 through the metering pump 32 via line 34, valve 36 and line 38, into the esterification reactor 40 where it reacts with the alcohol, e.g., methanol. The alcohol is fed from the alcohol feed source 42 through the metering pump 44 '

2 5 6 to the esterification reactor 40 via lines 46, valve 48, and line 50. The feed of the acylium anion product (e.g., isobutyryl fluoride) and alcohol (e.g., methanol) enter the esterification reactor 40 through dispersion nozzles (not shown) connected to lines 38 and S0 respectively. The esterification reactor 40 can be equipped with baffles or other means for insuring rapid mixing of the reactants.
The reaction mixture from the esterification reactor 40 enters the distillation column 52 via line 42 at point 56 which is located between the reflux entry point 58 and above the removal point 60 of the liquid phase. The distillation column 52 is operated to remove the unreacted organic carbon monoxide acid anion, e.g., isobutyryl fluoride, the unreacted alcohol, e.g., methanol, and the regenerated acid, e.g., lS hydrogen fluoride, and to cause the esterification reaction which begins in the esterification reactor 40 to be completed within the distillation column 52. This distillation column 52 shown in Figure 2 with its feed and take off points is particularly applicable to the substantially anhydrous methanol esterification of isobutyryl fluoride. However, the feed and take off points can readily be modified as known to those skilled in the art so as to be adaoted to anhydrous esterification by other alcohols. For example, if the boiling point of the ester is below that of the anhydrous acid, the take off of ester would be at the top of the column while that of the anhydrous acid would be below.
The liquid phase containing unreacted alcohol (methanol) and/or acylium anion addition product (e.g., isobutyryl fluoride) and/or hydrogen fluoride and~or ester (e.g., methyl isobutyrate) is removed at take off point 60 and passes through line 62 into the heat exchanger 64 where it is cooled if necessary and passes through line 66 into ; metering pump 68 through line 70 into the esterification reactor 40. The acylium anion product, e.g., isobutyryl fluoride, combines to react with the alcohol, e.g., methanol, 1 15~256 during the stripping operation which occurs between the feedpoint 56 and the liquid stream take ofC point 60, so that it is substantially converted to the ester, e.g., methyliso-butyrate, which moves downward through the stripping section and is removed from the distillation column 52 at outlet 72 and passes through line 74 into storage container 76. A
slip of the crude product passing through line 74 can be returned via line 78 through heat exchanger 80 and line a2 to reenter at 84 into the distillation column 52. The anhy-drous acid (e.g., hydrogen fluoride) which is regenerated bythe esterification reaction passes up and through the distil-lation column S2 and is removed overhead at outlet 86, and passes through line 88 in the heat exchanger 90 where it is partially or totally condensed, and passes through line 92 into separator 94. The anhydrous acid (e.g., hydrogen fluoride) passes through line 96 into storage unit 98 or 102 for reuse to make more acylium anion product. The separator bottoms pass out of the separator bottom via line 96 and part or all return via line 9~ to the distillation column at point 58 for reflux. Operation of the condenser and separator can be specified by those ski~lled in the art to assist in the removal of impurities and/or side products which are either more or less volatile than hydrogen fluoride (HF).
In another embodiment of the invention, it is possible to add via line 104 a secondary solvent to act as stripping agent to enhance the removal of the acylium anion addition product (e.g., isobutyryl flu!oride) from the ester, e.g., methyl isobutyrate, thereby eliminating the exchanger 64 and placing the entire energy load on exchanger 90.
In anotner embodiment o~ the invention, the level of point 60 can be selected so as to eliminate exchanger 64 and placing the entire energy load on exchanger 90.
In another embodiment of the invention, a solvent is added co-currently with the alcohol, e.g., methanol, into the esterification reactor 40, to assist in diluting and mixing the alcohol in the reaction mixture and to enhance the stripping of the regenerated anhydrous acid ~e.g., HF), and is removed through purge 102. The solvent used is inert to the reactants under the reaction and separation condi-tions, and does not azeotrope with the ester, e.g., methyl-isobutyrate or the anhydrous acid, hydrogen fluoride, andhas a boiling point which is intermediate between the anhy-drous acid, e.g., HF, and the ester, e.g., methyl isobutyrate, so that separation is enhanced, preferably the solvent has a low heat of vaporization. Useful solvents for the esteri-fication and separation of isobutyryl fluoride esterifiedwith methanol are the hydrofluoroalkanes, having up to twenty carbon atoms, but preferably those of up to five carbon atoms.

EXAMPLES
, .
The following examples will illustrate the inven-tion described herein.
The following procedure was used to study theesterification of isobutyryl fluoride based on less than the amount of methanol required to esterify all of the iso-butyryl fluoride to methyl isobutyrate, under semiadiabatic conditions.
A two-liter Hastello~ C Parr reactor, equipped with a methanol delivery system (used nitrogen at 500 psia), a thermocouple connected to a continuous temperature recorder, and an air motor and stirrer adjusted to rotate at 1,000 revolutions per minute, was charged with a weighed amount of reactant anhydrous hydrogen fluoride (if used) and isobutyryl fluoride (maintained at dry ice-acetone temperature). After charging, the reactants and reactor are brought to the pre-selected temperature, and the temperature recorder i9 star~ed.
The weighed amount of methanol (less than the amount required for reaction of all of the isobutyryl fluoride) is then injected into the reactor. The initial temperature of the methanol was at room temperature. After esterification was complete, the mixture was analyzed by gas chromatography.

* Trade Mark i 1 15625~

From the temperature-time recording, the temperature rises were noted. Generally, the first was attributed to the heat of mixing, and the second was attributed to the esterifica-tion reaction.
s Example I
isobutyryl fluoride, IBF (419.3 arams; 4.66 moles) at 26C was esterified by injecting 131.2 grams of methanol (at 21 a C). The reaction mixture temperature initially dropped then rose to 64.6C over the next 5.25 minutes. The reaction was complete, and GC analysis showed only anhydrous hydrogen fluoride tl82 grams; 4.1 moles) and methyl isobuty-rate (418.2 grams; 4.1 moles) formed, with 50.3 grams (0.56 moles) of isobutyryl fluoride was unreacted.
Example II
A mixture of 46.6 grams of anhydrous hydrogen fluoride (10 wt. percent) and 422.6 grams of isobutyryl fluoride (90 wt. percent) at 29.3C was esterified with 133 grams of methanol at 21C. ~The methanol was added in one slug.) A temperature rise of 20.7C was obser~ed, followed 20 by temperature to 128C over the next 38.4 seconds. The reaction was complete, the GC analvsis showed methyl isobuty-rate (416.0 grams), anhydrous HF (134.3 grams), and unreacted ; isobutyryl fluoride (51.8 grams).
Example III
A mixture of 540.4 grams anhydrous hydrogen fluoride and 59.9 grams isobutyryl fluoride at 30C Centigrade was esterified by adding 18.6 grams of methanol (at 22C) in one slug. Under these conditions, after 1.5 9econds, the temperature rose continuously from 30C to 49.5~C. The reaction was complete, the analysis showed that 58.2 grams of methyl isobutyrate was formed. The amount of anhydrous HF wa~ 552.7 grams, and the unreacted iso~utyryl fluoride was 8.0 grams.

.

Example IV
The following continuous process can be conducted to produce methyl isobutyrate by the process described herein.
A plug flow reactor is used for the ormation of isobutyric acid _rom propene. It is formed from a forty (40) foot tube having a one-half (1/2) inch internal diameter, with a premix section of about five (5) feet and equipped with injection points at five-foot inter~als and a heater.
The carbonylation reaction is conducted at 50C and 2,800 psig, with propene, anhydrous hydrogen fluoride and carbon monoxide in a mole ratio of 1.0:14:1.3, at a flow rate of

3.2 lbs per hour (1.52 kilograms per hour). The anhydrous hydrogen fluoride and carbon monoxide is injected into the premix section where they are thoroughly mixed, and the propene is injected into the mixture of anhydrous hydrogen fluoride and carbon monoxide at five-foot intervals, with the final addition being 30 feet from the beginning of the reactor. After the reaction is complete, at the 35-foot injection point, methanol is injected into the reactor where the esterification occurs preferably at the rate at which esterification occurs and methyl isobutyrate is formed. The amount of methanol injected is less than the amount of iso-butyryl fluoride formed. This section of the reactor where the esterification occurs is maintained at approximately 40C
and at a pressure of 100 psig. The methylisobutyrate is separated from the final product mixture by simple distilla-tion, and the remaining isobutyryl fluoride, carbon monoxide and anhydrous hydrogen fluoride is recycled with the carbon monoxide and anhydrous hydroqen fluoride that are being in~ected into the premix section o.f 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 where the excess carbon monoxide and from ten to ninety percent of the excess anhydrous hydrogen 1uoride is removed, and recycled, while the remaining product mixture preferably having 10 part~ by weight of anhydrous hydrogen fluoride to 90 parts by weight of iso-butyryl fluoride is esterified as described herein followedby separation of methylisobutyrate and recycling of the remaining product mixture of unreacted isobutyryl fluoride and anhydrous hydrogen fluoride.

FORMATION OF METHYLACRYLIC ACID OR METHYL METHAC~YLIC ACID
The methyl ester of the carboxylic acid of propionic acid or isobutyric acid formed from acylic anion product, e.g., propionyl fluoride or isobutyryl fluoride, after esterification, as described herein, can be oxydehydro-genated by the process described in U.S. patents 3,585,248;
3,585,249; 3,585,250; 3,634,494; 3,6~2,654, 3,660,514;
3,766,191; 3,781,336; 3,7~4,483; 3,855,279, 3,91~,673;
3,948,959; 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 comprised of iron, phosphorous, and oxygen as defined by the empirical formula, Fe Px z~ where relative to one (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. More preerred catalysts are those described in U.S. patent 3,948,959, which have a promoter represented by Mey wherein Me represents the promoter of Li, Na, R, Rb, Ce, Mg, Ca, Sr, Ba, and mixtures thereof, and y represents the number of promoter atoms relative to one atom o iron and is from 0.01 to 2Ø The methyl acrylate or methyl methacrylate is then separated by techniques known in the art, e.g., distillation in the presence of a polymerization inhibitor, or by extraction.
, While the invention has been described with refer-ence to specific details of certain illustrative embodiments, 1 15~256 it is not intended that it shall be limited thereby except insofar as such details appear in the accompanying claims.

Claims

The embodiments of the invention in which an exclusive property of privilege is claimed, are defined as follows:

1. A process for producing a carboxylic ester from an acylium anion product which comprises:
esterifying a mixture comprised of an acylium anion product with less than the amount of an alcohol required for esterifying all of the acylium anion product in the mixture to the carboxylic ester under anhydrous conditions whereby the carboxylic ester forms and the acid is regenerated from the anion;
said alcohol being selected from the group con-sisting of a primary alcohol of up to twenty carbon atoms and a secondary alcohol of up to twenty carbon atoms;
the acylium anion product being formed from the reaction of carbon monoxide, an anhydrous acid, an organic compound capable of reacting with the carbon monoxide and an anhydrous acid is selected from the group consisting of hydrogen fluoride (HF) and hydrogen chloride (HCl);
said organic compound being selected from the group consisting of (1) an ester represented by the general ?
formula R - C - O - R', wherein R is an alkyl of up to twenty carbon atoms and R' is an alkyl of from two to twenty carbon atoms; and (2) an olefin of up to twenty carbon atoms having at least one double bond capable of forming an acylium anion product therewith;
said esterification being conducted within a temperature range of from twenty (20) degrees Centi-grade to one hundred fifty (150) degrees Centigrade and pressures from one (1) bar (14.7 psia) to three hundred forty (340) bars (5,000 psia) in the presence of said anhydrous acid, the initial amount of said anhydrous acid to acylium anion product being within the range of from 0.01 to 95.5 parts by weight of anhy-drous acid to 99.09 to 4.5 parts by weight of acylium anion product.

2. The process as recited in Claim 1 wherein the organic compound is an ester selected from the group consisting of isopropyl isobutyrate, ethyl isobutyrate, isopropyl propionate, and ethyl propionate.

3. The process as recited in Claim 1 wherein the organic compound is an olefin of up to twenty carbon atoms having at least one double bond capable of forming an acylium anion product therewith.

4. The process as recited in Claim 1 wherein the olefin is ethylene.

5. The process as recited in Claim 1 wherein the olefin is propylene.

6. The process as recited in Claim 1 wherein the alcohol is methanol.

7. The process as recited in Claim 6 which further com-prises the step of separating from one (1) percent to one hundred (100) percent of the amount of anhydrous acid from the esterification product mixture containing the formed carboxylic ester, and recycling the separated anhydrous acid to react with carbon monoxide and organic compound to form more acylium anion product.

8. The process as recited in Claim 6 which further com-prises the step of separating from the esterification product mixture from one (1) percent to one hundred (100) percent of the amount of carboxylic ester, and recycling from one (1) percent to one hundred (100) percent of the amount of the esterification product mixture remaining after separation of the carboxylic ester therefrom to form more acylium anion product.

9. The process as recited in Claim 6 wherein the anhydrous acid is hydrogen fluoride.

10. The process as recited in Claim 9 wherein the initial amount of anhydrous hydrogen fluoride to acylium anion product (acyl fluoride) is from ten (10) to ninety (90) parts by weight of anhydrous hydrogen fluoride to ninety (90) to ten (10) parts by weight of acylium anion product (acyl fluoride).

11. The process as recited in Claim 7 wherein the anhydrous acid is hydrogen fluoride.

12. The process as recited in Claim 8 wherein the anhydrous acid is hydrogen fluoride.

13. The process as recited in Claim 1 wherein the mixture comprises carbon monoxide, anhydrous hydrogen fluoride and isobutyryl fluoride, the alcohol is methanol, said amount of methanol initially added being from seventy (70) to ninety-nine (99) percent of the amount of isobutyryl fluoride, and the amount of anhydrous hydrogen fluoride in the mixture being esterified is substan-tially within the range of from ten (10) to twenty (20) moles of anhydrous hydrogen fluoride to one (1) mole of isobutyryl fluoride.

14. The process as recited in Claim 13 wherein the esteri-fication is conducted substantially within a pressure range of from three and three tenths (3.3) bars (50 psia) to six and seven tenths (6.7) bars (100 psia) and a temperature range of from forty (40) degrees Centi-grade to seventy (70) degrees Centigrade.

15. The process as recited in Claim 14 which further com-prises the step of distilling to separate from eighty (80) percent to one hundred (100) percent of the iso-butyric acid formed from the esterification product mixture.

16. The process as recited in Claim 15 wherein the steps of distilling and esterification occur concurrently.

17. The process as recited in Claim 16 wherein from ninety (90) to one hundred (100) percent of the methyliso-butyric acid is separated from the esterification product mixture.

18. A process for producing an unsaturated carboxylic ester selected from the group consisting of methyl acrylate and methyl methacrylate which comprises:
esterifying a mixture comprised of an acylium anion product with less than the amount of methanol required to esterify the acylium anion to the corres-ponding ester selected from the group consisting of methyl propionate and methyl isobutyrate under anhydrous conditions whereby the carboxylate ester forms and the acid is regenerated from the anion;
separating the ester, oxydehydrating the ester in the vapor phase to the corresponding unsaturated carboxylic ester of methyl acrylate or methyl meth-acrylate;
the acylium anion product is formed from the reaction of carbon monoxide, an olefin selected from the group consisting of ethylene and propylene and an anhydrous acid under conditions whereby an acylium anion product forms; the anhydrous acid being selected from the group consisting of hydrogen fluoride (HF) and hydrogen chloride (HCl).

19. The process as recited in Claim 18 wherein the anhy-drous acid is hydrogen fluoride.

20. The process as recited in Claim 19 wherein the olefin is propylene.

21. The process as recited in any of Claims 18, 19, or 20 wherein the step of oxydehydrogenating uses a catalyst comprised of iron, phosphorous, and oxygen defined by the empirical formula Fe Px Oz where relative to one (1) atom of Fe, x represents from 0.25 to 3.5 atoms of P, and z represents the number of oxygen atoms required to satisfy the valence requirements of the catalyst.

22. A process for producing a lower carboxylic ester from isobutyryl fluoride, which comprises:
reacting an anhydrous mixture comprised of isobutyryl fluoride, hydrogen fluoride, and an alcohol selected from the group consisting of methanol, ethanol and propanol, at a temperature of from twenty (20) to one hundred and fifty (150) degrees Centigrade, and at a pressure sufficient to maintain the reacting mixture in the liquid phase; the initial amount of hydrogen fluoride and isobutyryl fluoride being within the range of from 0.01 to 95.5 parts by weight of hydrogen fluoride, and 4.5 to 99.99 parts by weight of isobutyryl fluoride, and the mole ratio of alcohol to isobutyryl fluoride in the reacting mixture being less than one (1.0), said reaction being conducted until substantially all of the alcohol reacts to form the corresponding isobutyryl ester.

23. The process as recited in Claim 22, wherein the initial mole percent of alcohol based on isobutyryl fluoride in the reacting mixture is from seventy (70) to ninety-nine (99) mole percent, and initial amount of anhydrous hydrogen fluoride in the reacting mixture is within the range of from ten (10) to twenty (20) moles of anhydrous hydrogen fluoride to one (1) mole of isobutyryl fluoride.

24. The process as recited in Claim 23, wherein the pressure is from three and three-tenths (3.3) bars (50 psia) to six and seven-tenths (6.7) bars (100 psia) and the temperature is from forty (40) degrees Centigrade to seventy (70) degrees Centigrade.

25. The process as recited in claim 22 wherein the alcohol is methanol, and the corresponding ester is methylisobutyrate.

26. The process as recited in claim 25, which further comprises the step of distillation to separate the corresponding isobutyrate ester from the reaction mixture.

27. The process as recited in claim 26, wherein the steps of distillation and esterification occur concurrently.