PROCESS FOR THE PREPARATION OF CARBOXYLIC ACIDS

Abstract: A process for the preparation of a carboxylic acid of the general formula RCOOH wherein R represents an alkyl, cycloalkyl, or aralkyl group by heating an ester of formic acid of the general formula HCOOR wherein R is as defined above in the presence of carbon monoxide, a soluble palladium catalyst, a nickel co-catalyst, an iodide and/or bromide source and an organic nitrogen compound containing a group or a sulphone.

Description: PROCESS FOR THE PREPARATION OF CARBOXYLIC ACIDS The present invention relates to a process for the preparation of carboxylic acids by heating a formic acid ester in the presence of carbon monoxide, a soluble palladium catalyst and an iodide and/or bromide source. The invention relates in particular to a process for the preparation of acetic acid from methyl formate. UK Patent Specification 1,293,193 discloses a process for the preparation of a carboxylic acid by heating a formic acid ester in the presence of carbon monoxide, a catalyst comprising a metal of Group VIII or Group IIb of the Periodic Table and an amide, heterocyclic amine, nitrile or ketone as solvent. The disclosed process requires the use of high temperatures and pressures or of high amounts of catalyst. Processes in which acetic acid is produced from methyl formate in the presence of carbon monoxide at moderate reaction conditions of temperature and pressure using a rhodium catalyst are for example disclosed in UK Patent Specification 1,286,224 and US Patent Specification 4,194,056. Because rhodium is very expensive it is attractive to develop processes in which less expensive catalysts can be used at moderate temperatures and pressures. German Offenlegungsschrift 3,046,899 discloses a process for the preparation of acetic acid in which methyl formate is isomerized at moderate conditions in the presence of carbon monoxide, a palladium, iridium or ruthenium catalyst, a halogen promotor, and optionally a secundary organic promotor such as an amine, phosphine, amide or nitrile. Palladium and ruthenium catalysts are much cheaper than rhodium catalysts. However, for the production of carboxylic acids on a large scale it is important that even when a relatively cheap catalyst is used, the activity of the catalytic system formed in the reaction mixture by interaction of the metal compound, the halogen containing promotor and other compounds present be as high as possible. The production rate of carboxylic acid can be expressed as grams of carboxylic acid produced per gram of metal per gram of halogen present in the halogen containing promotor per hour. The production rate expressed in this way is a suitable measure for the activity of the catalytic system formed in the reaction mixture because the reaction is accelerated in proportion to both the amount of metal catalyst and the amount of halogen containing promotor. It has now surprisingly been found that the activity of a catalytic system based on a palladium catalyst and an iodine or bromine containing promotor can considerably be enhanced by the simultaneous presence of a nickel co-catalyst and an amide group containing compound or a sulphone. The present invention therefore relates to a process for the preparation of a carboxylic acid of the general formula RCOOH wherein R represents an alkyl, cycloalkyl or aralkyl group by heating an ester of formic acid of the general formula HCOOR wherein R is as defined above in the presence of carbon monoxide, a soluble palladium catalyst and an iodide and/or bromide source in which a nickel co-catalyst and an organic nitrogen compound containing a group EMI2.1 or a sulphone are present in the reaction mixture. By means of the process of the invention production rates are attained which are very high in comparison to production rates calculated from prior art processes. Consequently smaller quantities of expensive palladium catalysts and iodide and/or bromide containing promotors, which are generally corrosive, are needed to obtain satisfactory results. The formic acid ester used as starting material in the process according to the invention has the general formula HCOOR wherein R represents an alkyl group having preferably 1-20 and in particular 1-6 carbon atoms, a cycloalkyl group having preferably 3-10 and in particular 5 or 6 carbon atoms or an aralkyl group having preferably 7-15 and in particular 7-10 carbon atoms. The process of the invention is suitable for the preparation of carboxylic acids such as for example propionic acid, n-butyric acid, iso-butyric acid, lauric acid, cyclohexyl carboxylic acid, phenylacetic acid and in particular acetic acid. Suitable soluble palladium compounds which can be used as catalyst in the process of the invention are soluble palladium salts such as for example palladium chloride, palladium bromide, palladium chloride dihydrate, palladium iodide, palladium nitrate, palladium formate, palladium acetate, palladium propionate, palladium iso-butyrate or soluble palladium complexes such as for example palladium acetylacetonate. Na2PdCl4, K2PdCl4, K2PdJ4, [Pd(CO)C12]2, Pd[(C6H5)3P]232, [(n-C4Hg)4P]2[PdC14], Pd[(C6H5)3P]2(CO)Br and PdL(n-c4H9)32]2J2 The amount of palladium catalyst used in the process of the invention is not critical and any amount which exerts catalytic activity can be used. The catalyst is preferably used in an amount of 1O-21O-6 and in particular of 10-3-10'5 gram-atoms, based on palladium, per mol formic acid ester. The iodide and/or bromide source used in the process of the invention may be for example elemental iodine or bromine, or hydrogen iodide or bromide, or an alkali metal or an alkaline earth metal iodide or bromide such as for example lithium iodide, sodium iodide, potassium iodide, rubidium iodide, cesium iodide, lithium bromide, sodium bromide, potassium bromide, rubidium bromide, cesium bromide, calcium iodide, calcium bromide, magnesium iodide, magnesium bromide, or an ammonium, phosphonium, arsonium or stibonium iodide or bromide such as for example triphenylphosphonium iodide, methyltriphenyl phosphonium iodide, tetramethylammonium iodide and tetrabutylammonium iodide. Further bromide and/or iodide sources are organic compounds of general formula R1(CO)nHal wherein n=O or 1, Hal represents Br or J and R1 represents an alkyl group having up to 1-12 carbon atoms or an aryl, aralkyl or alkaryl group having up to 12 carbon atoms such as for example CH3Br, C2H5J, C4HgJ, C8H17J and in particular CH3J. The use of an alkali metal iodide or a mixture of an alkali metal iodide and an alkyl iodide, in particular CH3J, is preferred. The total amount of the iodide and/or bromide source present in the reaction mixture is equivalent to 1-1000, preferably 3-500 and in particular 10-300 gram-atoms iodine and/or bromine per gram-atom palladium. Suitable nickel co-ctatalysts which can be used in the process of the present invention are for example soluble nickel compounds such as nickel chloride, nickel chloride hexahydrate, nickel iodide, nickel nitrate or nickel acetate or nickel complexes such as for example bishalobisphosphino or bissalicylaldiminato complexes of nickel. The amount of nickel compound used is generally equivalent to 2-100, preferably 5-70 and in particular 10-50 gram-atoms nickel per gram atom palladium. The organic nitrogen compound containing a group EMI4.1 or the sulphone used in the process of the invention forms a solution with the reacting materials and/or formed products under the reaction conditions. Very suitable organic nitrogen compounds containing a group EMI4.2 are amides, carbamates urea and urea derivatives which are fluids at the temperatures and pressures applied during the reaction. Suitable amides are for example amides of the general formula EMI4.3 wherein R2 represents H or an alkyl, cycloalkyl, aryl, alkaryl or aralkyl group having up to 10 carbon atoms, R3 and R4 each represent H or an alkyl, aryl, alkaryl or aralkyl group, which may contain a group ,C-O, having up to 10 carbon atoms, or R3 and R4 together with the nitrogen atom form a cyclic group having up to 5 carbon atoms or R2 and R3 or R4 together with the nitrogen atom form a cyclic group having up to 5 carbon atoms. Specific examples of these amides are formamide, acetamide, N-methylacetamide, N-ethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-N-ethylacetamide, N,N-dimethylcyclohexyl carboxamide, N,N-dimethylbenzamide, N-phenylacetamide, N,N-diphenylacetamide, N-methylpyrolidone, N-formylmorpholine, N-acetylmorpholine, N-formylpiperidine, N-acetylpiperidine and N-acetyl-N'-methylpiperazine. Especially suitable are N,N-dimethylacetamide and Nmethylpyrrolidone. Amides of the above general formula also include diamides, triamides such as diacetamide, triacetamide, dibenzamide, tribenzamide and N-methyldibenzamide and imides such as succinimide, 1,2 cyclohexane dicarboximide and N-phenylphthalimide. Suitable carbamates are for example carbamates of the general formula EMI5.1 wherein R5 represents an alkyl, aryl, aralkyl or alkaryl group having up to 10 carbon atoms and R6 and R7 each repsent H or an alkyl, aryl, aralkyl or alkaryl group having up to 10 carbon atoms. Specific examples of these carbamates are methyl carbamate, ethyl carbamate, phenyl carbamate, methyl N-methylcarbamate, methyl N-ethylcarbamate, methyl N-phenylcarbamate, ethyl N-methylcarbamate, ethyl N-ethylcarbamate, phenyl N-ethylcarbamate, phenyl N-phenylcarbamate, methyl N,N-dimethylcarbamate, methyl N,N-diethylcarbamate, methyl N,N-diphenylcarbamate, ethyl N,N-dimethylcarbamate, ethyl N,N-diethylcarbamate, ethyl N,N-diphenylcarbamate, phenyl N,N-dimethylcarbamate, phenyl N,N-diethylcarbamate, phenyl N, N-diphenylcarbamate, methyl N-methyl-N-ethylcarbamate and ethyl N-methyl-N-ethylcarbamate. Urea and urea derivatives which can be used in the process of the invention have the general formula EMI6.1 wherein R8, R9, R10 and R11 each represent H or an alkyl, aryl, aralkyl, or alkaryl group having up to 10 carbon atoms. Specific examples of these compounds are urea, 1,3-dimethylurea, 1,3-diethylurea, 1,3-diphenylurea, 1, 1-dimethylurea, 1, 1-diphenylurea and 1, 1,3, 3-tetramethyl- urea. Suitable sulphones are for example sulphones of the general formula EMI6.2 wherein R12 and R13 each represent an alkyl, aryl, aralkyl or alkaryl group having up to 10 carbon atoms or R12 and R13 together with the sulfur atom form a cyclic group having up to 5 carbon atoms. Specific examples of these sulphones are dimethyl sulphone, diethyl sulphone, methylethyl sulphone, methylbutyl sulphone, butylphenyl sulphone, dibenzyl sulphone, 4,4'-ditolyl sulphone, 4,4'-diacetamidodiphenyl sulphone, sulpholane, 2-methyl sulpholane, 3-methyl sulpholane or 2mathyl-4-butyl sulpholane. The use of sulpholane or a methyl substituted sulpholane is preferred. In general the organic nitrogen compound containing a group EMI6.3 or the sulphone is present in the reaction mixture in an amount of at least 0.01 mol per mol formic acid ester and preferably in an amount in the range of 0.05-3 mol per mol formic acid ester. If desired, the process according to the invention may be carried out in the presence of an additional promotor. Suitable additional promotors are organic phosphorus compounds represented by the general formula EMI6.4 in which n is 0 or 1, either a, b and c are 0 or 1 and R14, R15 and R16 are similar or dissimilar optionally substituted hydrocarbon groups, or a and b are 0 and c is O or 1 and R14 and R15 form together with P a heterocyclic group. Preference is given to compounds represented by the above general formula in which a, b, and c are 0. In these compounds the group R14, R15 and R16 are preferably similar or dissimilar alkyl groups containing 1-12 carbon atoms or cycloalkyl, aryl or alkaryl groups containing 5-12 carbon atoms optionally substituted with groups which are substantially inert in the reaction medium such as chlorine, alkoxy groups, caboxylic ester groups or oxo groups. Very suitable additional promotors are tertiary phosphines and the oxides thereof such as tri-n-butylphosphine, tri-n-butylphosphine oxide, triethylposphine, triethylphosphine oxide, tricyclohexylphosphine, tricyclohexylphosphine oxide, triphenylphosphine, triphenylphosphine oxide, tri-p-tolylphosphine oxide, tri-p-chlorophenylphosphine and 1-phenylphospholane oxide. Most preferred are triphenylphosphine and triphenylphosphine oxide. The amount of additional promotor which can be used in the process of the invention is not critical and may be in the range of from 0.01 to 200 mols organic phosphorus compound per gram-atom palladium. It will be appreciated that in the reaction mixture salts or complexes may be formed by the reaction of the organic phosphorus compounds with the iodine or bromine compound(s) present. An example of such a complex is [(C6Hs)3Po-H-oP(C6Hs)3]+J3 . Consequently the use of such salts or complexes as additional promotors when prepared separately is within the scope of the present invention. Furthermore it will be appreciated that the oxides of the phosphines can be formed in situ from the corresponding phosphines by carrying out the reaction in the presence of molecular oxygen or hydrogen peroxide. The process according to the present invention can be carried out using a temperature in the range of 50 C to 250QC. Preference is given to a temperature in the range of 1100C to 2250C and particularly in the range of 1250C to 2000C. In general the reaction is carried out at a partial pressure of carbon monoxide of 0.5 bar to 70 bar. Higher pressures as high as 1000 bar can L- applied, but they are generally not economical because of the investments and energy costs involved. Partial pressures of carbon monoxide in the range of 10 bar to 60 bar are preferred. The carbon monoxide used in the process of the invention may contain inert gases such as for example nitrogen, noble gases, carbon dioxide or methane. Mixtures of carbon monoxide and hydrogen i.e. synthesis gas can also be used. Synthesis gas has the advantage that it is easily available. The molar ratio of hydrogen to carbon monoxide may be in the range of O to 3 and preferably in the range of O to 1. The process of the invention is carried out in the liquid phase. Usually there is no need for the use of an (additional) solvent since the formic acid ester used as starting material and/or the formed carboxylic acid have sufficient degree of solvent activity. Other components of the reaction mixture, for example a liquid iodide source or a liquid phosphine (oxide) may also be active as solvents. If desired, additional quantities of these compounds may be added to the reaction mixture. Suitable (additional) solvents are preferably carboxylic acids or esters such as for example, acetic acid, propionic acid, butyric acid, lauric acid, methyl acetate or butyrolactone. The process of the invention is preferably carried out under anhydrous conditions. Small quantities of water such as present in commercially available starting materials can be allowed. The process according to the invention may be carried out continuously or batch-wise. The reaction mixture obtained may be worked-up with the aid of known techniques, such as fractional distillation. Furthermore, the process may be integrated into existing processes for preparing the starting material or for further processing the carboxylic acid obtained. Example I A magnetically stirred 300-ml Hastelloy C autoclave (Hastelloy is a trade mark) was charged with 35 ml methyl formate, 35 ml N-methylpyrrolidone, 0.1 mmol palladium acetate, 2.4 mmol NiC12-6H20 and quantities of further ingredients as indicated in Table A. The vessel was flushed with carbon monoxide and then pressurized with a mixture of carbon monoxide and hydrogen to 45 bar (partial pressure of carbon monoxide 30 bar, partial present of hydrogen 15 bar). The autoclave was then heated to 1700C and kept at this temperature during 3 hours. After the reaction time the reaction mixture was cooled and analyzed by gas-liquid chromatography. The production rate of acetic acid was expressed as grams of acetic acid per gram palladium per gram iodine per hour. When experiment 3 was repeated with either pyridine or diglyme as solvent in stead of Nmethylpyrrolidone and 10 ml methyl formate in stead of 35 ml methyl formate, only traces of acetic acid were produced. When experiment 2 was repeated except that no nickel co-catalyst was present, the production rate of acetic acid was 160 gr acetic acid per gram palladium per gram iodine per hour. Example II A magnetically stirred 300-ml Hastelloy C autoclave (Hastelloy is a trade mark) was charged with 10 ml methyl formate, 35 ml sulpholane and quantities of further ingredients as indicated in Table B. The vessel was flushed with carbon monoxide and then pressurized with a mixture of carbon monoxide and hydrogen to 45 bar. (partial pressure of carbon monoxide 30 bar, partial pressure of hydrogen 15 bar). The autoclave was then heated to 1700C and kept at this temperature during a number of hours as indicated in Table B. The further procedure was as described in Example I. The comparative experiments 2 and 3 show that by using either a palladium catalyst or a nickel inferior results are obtained. TABLE A Experiment Methyl Alkali. Triphenyl Production rate nr. iodide metal phosphine g acetic acid/gr Pd iodine oxide /gr J/h mmol mmol mmol 1 12.5 LiJ 18 210 2 12.5 LiJ 18 12 227 3 KJ 18 12 362 TABLE B Experiment Palladium NiCl2-6H2O Methyl Alkali Triphenyl Reaction Production rate nr. acetate iodine metal phosphine time h f acetic acid/ iodine oxide g Pd/g J/h mmol mmol mmol mmol mmol 1 0.1 2.4 KJ 18 12 1 199 2 0.1 18 LiJ 12 12 2.5 46 3 2.4 18 LiJ 12 12 3 3* * calculated on Ni.

Claims: CLAIMS 1. A process for the preparation of a carboxylic acid of the general formula RCOOH wherein R represents an alkyl, cycloalkyl, or aralkyl group by heating an ester of formic acid of general formula HCOOR wherein R is as defined above in the presence of carbon monoxide, a soluble palladium catalyst and an iodide and/or bromide source characterized in that a nickel co-catalyst and an organic nitrogen compound containing a group EMI12.1 a sulphone are present in the reaction mixture. 2. A process according to claim 1 characterized in that the organic nitrogen compound containing a group EMI12.2 or the sulphone is present in an amount of at least 0.01 mol per mol formic acid ester and preferably in an amount in the range of 0.05-3 mols per mol formic acid ester. 3. A process according to claim 1 or 2 characterized in that the organic nitrogen compound EMI12.3 <tb> containing <tb> <SEP> 0 <SEP> R3 <tb> RL-C-N, <SEP> <tb> <SEP> R4 <tb> a group EMI12.4 is an amide of the general formula wherein R2 represents H or an alkyl, cycloalkyl, aryl, alkaryl or aralkyl group having up to 10 carbon atoms, R3 and R4 each represent H or an alkyl, aryl, alkaryl or aralkyl group which may contian a group ,C-O, having up to 10 carbon atoms, or and R4 together with the nitrogen atom form a cyclic group having up to 5 carbon atoms or R2 and R3 or R4 together with the nitrogen atom form a cyclic group having up to 5 carbon atoms. 4. A process according to any one of claims 1-3 characterized in that the amide is N-methylpyrrolidone. 5. A process according to claim 1 or 2 characterized in that the organic nitrogen compound containing a group EMI12.5 is a carbamate of the general formula EMI13.1 wherein R5 represents an alkyl, aryl, aralkyl or alkaryl group having up to 10 carbon atoms and R6 and R7 each represent H or an alkyl, aryl, aralkyl or alkaryl group having up to 10 carbon atoms. 6. A process according to claim 1 or 2 characterized in that the organic nitrogen compound containing a group EMI13.2 is urea or an urea derivative of the general formula EMI13.3 wherein R8, R9, R10 and R11 each represent H or an alkyl, aryl aralkyl or alkaryl group having up to 10 carbon atoms. 7. A process according to claim 1 or 2 characterized in that the sulphone is a sulphone of the general formula EMI13.4 wherein R12 and R13 each represent an alkyl, aryl, aralkyl or alkaryl group having up to 10 carbon atoms or R12 and R13 together with the sulfur atom form a cyclic group having up to 5 carbon atoms. 8. A process according to any one of claims 1, 2 or 7 characterized in that the sulphone is sulpholane or a methyl substituted sulpholane. 9. A process according to any one of claims 1-8 characterized in that the iodide and/or bromide source is elemental iodine or bromine, hydrogen iodide or bromide, an alkali metal iodide or bromide, an alkaline earth metal iodide or bromide or an organic compound having general formula R1(CO)n Hal wherein n-O or 1, Hal represents Br or J and R1 represents an alkyl group having 1-12 carbon atoms or an aryl, aralkyl or alkaryl group having up to 12 carbon atoms. 10. A process according to any one of claims 1-9 characterized in that the iodide and/or bromide source is an alkali metal iodide or a mixture of an alkali metal iodide and an alkyl iodide. 11. A process according to any one of claims 1-10 characterized in that the iodize and/or bromide source is present in a total amount equivalent to 1-1000, preferably 3-500 and in particular 10-300 gram-atoms iodine and/or bromine per gram-atom palladium. 12. A process according to any one of claims 1-10 characterized in that a tertiary phosphine or an oxide thereof is present as additional promotor. 13. A process according to any one of claims 1-12 characterized in that the additional promotor is triphenylphosphine or triphenylphosphine oxide. 14. A process according to any one of claims 1-13 characterized in that the reaction is carried out at a partial pressure of carbon monoxide of 0.5 bar to 70 bar and preferably 10 bar to 60 bar.

Inventors: DRENT, EIT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1984
Main classification: C07C51
IPC codes: C07C51, C07C53, C07C67, B01J31, C07B61