Patentamt JEuropaischesEuropean Patent Office © Publication number: 0 045 637 Office europeen des brevets A1 © EUROPEAN PATENT APPLICATION ©Int CI3: C 07 C 51/09 C 07 C 53/08, C 07 C 53/00 B 01 J 31/22, B 01 J 27/08 © Priority: 04.08.80 US 174824 © Applicant: Exxon Research and Engineering Company 22.06.81 US 275806 P.O.Box 390 200 Park Avenue Florham Park New Jersey 07932(US) © Date of publication of application: © Inventor: Pruett,RoyL 10.02.82 Bulletin 82/6 21 Wellings road New Providence New Jersey(US) © Designated Contracting States: BE DE FR GB IT NL @ Representative: Field, Roger Norton et al, 5 Hanover Square London W1ROHQ(GB) 54) A process for converting formate esters to carboxylic acids. A process for converting formic acid esters or transester- ification products thereof to carboxylic acids comprising contacting a formic acid ester of the formula (HCOO)n-R where R is aliphatic, cycloaliphatic or aralkyl and n is 1 or 2 with a catalytically effective amount of soluble iridium salt and iodine or an iodide as promoter at a temperature of from about 100°C to about 300°C in the presence of an organic solvent containing at least one carboxylic acid. This invention relates to a homogeneous process for the conversion of a formic acid ester or a trans- esterification product thereof to a carboxylic acid. More particularly, the formic acid ester or trans- esterification product is contacted with an iridium salt and an iodide promoter in the presence of an organic solvent containing carboxylic acid. The direct conversion of formic acid esters to carboxylic acids is known. U.S. Patent No. 3,839,428 which was reissued as Re. 29,981 teaches a process for converting formic acid esters to the cor- responding carboxylic acids which comprises contacting the ester with carbon monoxide (CO) at an elevated CO pressure. While the reaction will occur in the absence of a catalyst, Group VIII metals such as iron, cobalt and nickel, Group IIb metals and halogens may be advantageously employed to increase'the conversion rate. U.S. Patent No. 4,194,056 relates to a process for the preparation of acetic acid which comprises heating methyl formate in the presence of a soluble rhodium salt catalyst, halogen promoter and sufficient amounts of carbon monoxide convert the rhodium salt into at to , least a monocarbonyl compound. Other metal salts such as cobalt iodide, nickel iodide and rhenium pentacarbonyl were listed as non-catalysts. Carbon monoxide is stated to be essential. British Patent No. 1,286,224 and German Offen. 2,109,025 disclose a process for producing acetic acid comprising heating methyl formate in the presence of carbon monoxide and a catalyst system containing rhodium and a halogen promoter. U.S. Patent No. 3,798,267 is directed to the isomerization of methyl formate to acetic acid in the presence of carbon monoxide and catalyst system consisting essentially of activated carbon and a halogen promoter. F. J. Bryant et al., preprints Div. of Petr. Chem., 18i 193 (1973) describe the reaction mechanism for the conversion of methyl formate to acetic acid using carbon monoxide, a soluble rhodium complex and methyl iodide at 200°C. The reaction occurs whether or not acetic acid is initially present. U.S. Patent No. 2,508,513 relates to the conversion of methyl formate to acetic acid. The catalysts are carbonyl forming metals or compounds plus halogens. Such catalysts are iron metals, tungsten, vanadium, antimony and bismuth. U.S. Patent No. 2,739,169 discloses the reaction of CO and H20 with olefins, alcohols, esters and ethers to produce acids. Catalysts are stated to be metal carbonyls with typical carbonyl-forming metals being Ni, Co, Fe, Cr, Mo, Ru, Pd, Pt, Re, Os and Ir. Japan Kokai 76/65,703 (Chem. Abstr. 85,93872d) discloses that a mixture of acetic acid and methyl acetate is produced when methyl formate is heated with rhenium catalysts, halides and carbon monoxide. Japan Kokai 73/19,286 (Chem. Abstr. 79,78102k) relates to a hydroformylation reaction wherein methyl formate is heated with a CO/H mixture in N-methylpyrrolidone using CoI2, FeI3, RuI3, RhC13 and bis(butylpyridinium) tetrabromocobaltate as catalysts to produce aldehydes. U.S. Patent 3,488,383 concerns the selective decomposition of formic acid in admixture with another aliphatic acid or ester of an aliphatic acid, e.g., methyl formate. The process comprises contacting the formic acid containing mixture with a soluble complex compound of a Group VIII metal or rhenium. The complex compound is a compound of Pt, Os, Rh, or preferably Ru or Ir. Formate esters are unreactive and may be present as part of the solvent system. Example 1 indicates that at least part of the formic acid is decomposed to H2 and C02. It has been discovered that formic acid esters can be directly converted to their corresponding carboxylic acids without the presence of carbon monoxide. The present process for the preparation of carboxylic acids having the formula R(COOH)n comprises contacting a formic acid ester of the formula (HCOO)nR where R is aliphatic, cycloaliphatic or aralkyl and n is 1 or 2 with a catalytically effective amount of a soluble iridium salt and an iodide promoter at a temperature of from about 100°C to about 300°C in the presence of an organic solvent containing at least one carboxylic acid. In another embodiment, the present carboxylic acids having the formula RCOOH may be prepared by a process which comprises contacting formic acid and an ester of the formula R aCOOR where Ra is aliphatic, cyclo- aliphatic, aralkyl or aryl, and R is aliphatic, cyclo- aliphatic or aralkyl with a catalytically effective amount of a soluble iridium salt and an iodide promoter at-a temperature of from about 100°C to about 300°C in the presence of an organic solvent. As noted above, the process of the invention does not require the presence of carbon monoxide, and the reaction can be carried out at autogenous pressure. Therefore, no special high pressure equipment is needed. Moreover, conversions of 90% or more are attainable in short reaction times. Formate esters may be converted to their cor- responding carboxylic acids according to the reaction (HCOO)nR@R(COOH)n where n is 1 or 2. The radical R is C1-C20 aliphatic, C3-C10 cycloaliphatic or C7-C15 aralkyl, preferably C1-C8 aliphatic, C4-C8 cycloaliphatic or C7-C12 aralkyl, more preferably Cl-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C5-C6 cycloalkyl or C7-C10 aralkyl, and especially C1-C6 alkyl.. Monoformate esters are preferred and methyl formate is especially preferred as the formate ester leading to acetic acid as product. Examples of other carboxylic acids which may be prepared are propionic, butyric, caproic, capric, lauric, cyclo- hexanecarboxylic and phenylacetic. Formate esters also include esters of dicarboxylic acids. An example of the formation of a dicarboxylic acid is the transformation of butanediol diformate to adipic acid according to the equation HCOO(CH2)4OOCH@HOOC(CH2)4COOH. Other examples include the conversion of hydroquinone diformate to terephthalic acid. Suitable catalysts for the conversion of formate ester to carboxylic acid are iridium salts which are soluble in the reaction medium chosen. Iridium salts are simple salts and compounds such as halides or oxides, and complexes containing halides, phosphines, amines including heterocyclic amines, arsines, cyanides, sulfides, esters, beta-diketonates, carboxylates, hydrido, sulfites, nitro and the like as ligands. The complexes may also be organometallic iridium complexes containing both or and π bonded organic ligands, e.g., carbonyl, alkyl, alkenes and alkynes. Examples of iridium salts and complexes are [Ir(cyclooctadiene)Cl]2, Na2IrCl6.XH2O, HIrCO[P(C6H5)3]3, ClIrCO(PEt3)2, IrCl3.XH2O, IrI3. XH2O,Na3Ir(NO2)6.XH2O, K3Ir(CN)6, [(C5H5)2Ir]NO3, Ir4- (CO)12, IrH3[P(C6H5)3]3, 1.2.3-py3IrCl3, trans- [Irpy4Cl2]Cl and (C8H12)2IrSnCl3. Preferred salts are [Ir(cyclooctadiene)Cl]2, IrCl3.XH2O, IrBr3.XH20 and and IrI3·XH2O. [Ir(cyclooctadiene)Cl]2, ZrCl3.XH2O , IrI3.XH2O are especially preferred. The symbol X indicates differing degrees of hydration and varies from 0 to 12. Iodides generally are promoters or co-catalysts for the conversion of formic acid esters to carboxylic acids. Examples of suitable promoters include iodine, HI, alkali metal iodide, alkaline earth metal iodide, organic iodides, and N(R1)4I and P(R1)4I where each R1 is independently hydrogen or Cl-C6 alkyl. Preferred iodides are alkyl iodides of the formula R2I, R2 is R2 C1-C10 alkyl. It is especially preferred to match the group with the R group in starting formate ester, e.g., methyl iodide with methyl formate, ethyl iodide with ethyl formate and so forth. Catalyst concentrations may range from about 0.001 to 15 wt.% of iridium calculated as metal, based on the reaction mixture, preferably from 0.01 to 10 wt.%, especially 0.1 to 2 wt.%. The amount of iodide promoter is not critical, and high iodide:Ir ratios have no significant effect. Amounts in excess of about 0.5 wt.%, based on the reaction mixture may be employed, preferably from about 1 to 15 wt.%. Suitable solvents are organic solvents. The solvent system must, however, contain at least one carboxylic acid as a component thereof. Thus the solvent system may be either a carboxylic acid or a mixture of carboxylic acid with other inert organic solvents. Mixtures of carboxylic acids are also within the scope of the present invention. If the reactants are RaCOOR and formic acid, then formic acid functions as the organic solvent system while at the same time meeting the requirements for the presence of at least one carboxylic acid.