Process for Producing Carboxylic Acids and/or Esters Thereof

This invention relates to a process for producing carboxylic acids and/or esters thereof by reacting alcohols or ethers with carbon monoxide.

A typical known method for producing carboxylic acids by the carbonylation of alcohols is the production of acetic acid from methanol and carbon monoxide. For example, U.S. Pat. Nos. 2,729,651 and 2,727,902 and German Pat. Nos. 921,938, 933,148 and 947,469 disclose a so-called Reppe method which comprises reacting alcohols, ethers or esters with carbon monoxide using a transition metal such as iron, cobalt or nickel and a compound of a halogen such as iodine or bromine as a catalyst.

These methods, however, require severe high-temperature high-pressure conditions, and many of them do not give satisfactory yields. In an attempt to overcome these disadvantages, methods have recently been developed which involve the use of a complex of a platinum-group metal typified by rhodium as a catalyst (Japanese Patent Publications Nos. 3331 to 3337/1972 which correspond to U.S. applications Ser. Nos. 701,637 to 701,639, 628,577, 628,578, 628,581 and 628,591). These methods which are catalyzed by platinum-group metal complexes can effect carbonylation under milder conditions than the Reppe method, and can give better yields with less amounts of by-products. Since rhodium and other noble metals used as catalyst in these methods are very expensive, it is necessary in commercial practice to take a measure against the loss of the catalyst by, for example, preventing the noble metal complex from being reduced to the metal in a reducing atmosphere [Chemistry and Industry, 29 (5), p. 376 (1960)].

Accordingly, it is an object of this invention to eliminate the defects of the prior art methods, and provide a process for producing carboxylic acids and/or their esters by the carbonylation of alcohols or ethers under mild conditions using an inexpensive catalyst.

The object of the invention is achieved by a process for producing a carboxylic acid and/or its ester, which comprises reacting an alcohol or ether with carbon monoxide in the presence of elemental nickel or a nickel compound, iodine or an iodine compound and an organic compound of a trivalent nitrogen-group element; wherein the iodine or iodine compound is selected from the following formulae (I) to (IV),

wherein R represents a hydrogen atom or an alkyl or alkylene group, X represents an iodine or bromine atom, and n is an integer of 1 to 3, at least one of n.multidot.X's being an iodine atom,

wherein R represents an alkyl group,

wherein M represents an alkaline earth metal, and the amount of the iodine or iodine compound is such that the amount of the free iodine or iodine compound not chemically bonded to the nickel or nickel compound or the organic compound of a nitrogen-group element is at least 0.2 mole as elemental iodine per mole of the nitrogen-group element compound and at least 0.2 mole as elemental iodine per mole of the nickel or nickel compound.

Alcohols and ethers which can be advantageously used as starting materials in the present invention are aliphatic alcohols having 1 to 20 carbon atoms, aliphatic ethers having 2 to 30 carbon atoms, aromatic alcohols having 7 to 20 carbon atoms, and aromatic ethers having 7 to 30 carbon atoms. Specific examples of these alcohols and ethers include methanol, ethanol, propanol, butanol, pentanol, hexanol, decanol, ethylene glycol, propylene glycol, butanediol, hexanediol, cyclohexanol, benzyl alcohol, phenethyl alcohol, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, cyclohexyl methyl ether, anisole, phenetole, methyl benzyl ether, methyl cellosolve, butyl cellosolve, monoglyme and diglyme.

Elemental nickel and organic or inorganic nickel compounds can be used as the nickel or nickel compounds (nickel component) which is one catalyst component. There can be used, for example, nickel powder, and various nickel compounds such as nickel acetate, nickel iodide, nickel acetyl acetone, nickel carbonyl, nickel dicarbonyl, nickel dicarbonyl bistriphenyl phosphine, and nickel tetramethyl ammonium iodide.

The iodine and iodine compound (iodine component) is selected from substances represented by the formulae (I) to (IV). Specific examples include I.sub.2, KI.sub.3, HI, CH.sub.3 I, C.sub.2 H.sub.5 I, C.sub.3 H.sub.7 I, C.sub.4 H.sub.9 I, CH.sub.2 I.sub.2, C.sub.2 H.sub.4 I.sub.2, CH.sub.2 IBr, CHI.sub.3, C.sub.2 H.sub.4 IBr, CH.sub.3 COI, C.sub.2 H.sub.5 COI, and CaI.sub.2.

The organic compound of a trivalent nitrogen-group element (nitrogen-group component) used in this invention denotes an organic compound of trivalent nitrogen, phosphorus, arsenic or antimony. Examples of the organic nitrogen compound are organic nitrogen compounds of the formula (V) ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are identical or different, and each represents a hydrogen atom, an alkyl or aryl group, such as monomethylamine, dimethylamine, butylamine, trimethylamine, diethylamine, aniline and dimethylaniline; and organic nitrogen compounds represented by the following formula (VI) ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 are identical or different, and each represents a hydrogen atom or an alkyl or aryl group, such as dimethyl acetamide and methyl phenyl acetamide. Heterocyclic nitrogen compounds such as pyridine, hydroxyquinoline and imidazole, nitriles such as acetonitrile, propionitrile, adiponitrile and benzonitrile, or ammonium salts such as ammonium acetate can also be used.

Examples of the phosphorus, arsenic or antimony compounds are those resulting from substituting P, As or Sb for N in the compounds of formula (V) above, such as trimethylphosphine, tributylphosphine, diphenylphosphine, triphenylphosphine, methyldiphenylphosphine, triphenylarsine, and triphenylstibine. Complexes of these with nickel or nickel carbonyl can also be utilized.

Some of the catalysts comprising the three components are known (for example, see U.S. Pat. No. 2,729,651 cited hereinabove). The catalyst used in this invention, however, is characterized by the fact that it should be used in such a proportion that the amount of the free iodine or iodine compound which does not react with either the nickel component or the nitrogen-group component is at least 0.2 mole, preferably at least 0.5 mole, more preferably at least 1 mole, as elemental iodine per mole of each of the organic nitrogen-group component and the nickel component.

In some cases, the iodine or iodine compound used in this invention reacts with the other catalyst ingredients used. For example, there is a possibility that CH.sub.3 I reacts with P.phi..sub.3 (wherein .phi. represents a phenyl group) to form an onium iodide compound, (CH.sub.3 P.phi..sub.3)I. In this case, it is necessary to use CH.sub.3 I in such an amount that the difference resulting from substracting the amount of CH.sub.3 I that reacts with P.phi..sub.3 from the total amount of CH.sub.3 I used is at least 0.2 mole, preferably at least 0.5 mole, more preferably at least 1 mole, as elemental iodine per mole of each of the organic nitrogen-group component and the nickel component.

In other words, the iodine or iodine compound of formula (I), (II), (III) or (IV) should be present as such in the above-specified amount.

When the organic nitrogen-group compound is a nitrile, the iodine or iodine compound is considered to be not reactive with the nitrogen-group compound. Thus, the total amount of the iodine or iodine compound used can be regarded as the amount of the free iodine compound.

It is obvious to those skilled in the art whether or not the iodine or iodine compound reacts with a given species of the organic nitrogen-group compound used in this invention.

When the iodine compound is HI, I.sub.2, I.sub.3.sup.- or RCOI, it is assumed that the compound is reactive with the nickel or nickel compound used in this invention. Thus, the amount of the free iodine compound is the difference resulting from subtracting the amount of the iodine compound which is assumed to react with the nickel or nickel compound from the total amount of the iodine compound. Other iodine compounds are not assumed to be reactive with the nickel or nickel compound, and the total amount of such an iodine compound used will be regarded as the amount of the free iodine compound.

Compounds which are formed by the reaction of the iodine or iodine compound with the other catalyst components, for example a nickel compound such as NiI.sub.2 or [(CH.sub.3).sub.4 N].sub.2 NiI.sub.4 or an onium iodide compound such as (CH.sub.3 P.phi..sub.3)I are not included within the definition of the iodine compounds of the invention represented by formulae (I) to (IV).

If the amount of the free iodine compound is less than the above-specified amount, high yields cannot be achieved under mild reaction conditions.

When the nickel compound used in this invention is concurrently a nitrogen-group compound, for example such a compound as nickel dicarbonyl bistriphenyl phosphine or nickel tetramethyl ammonium iodide, it can be used both as a nickel component and a nitrogen-group component. Hence, so long as such a compound is used in the required amounts, another nitrogen-group compound or nickel compound need not be used. In many cases, such a compound is a coordination compound of nickel and the nitrogen-group compound.

The amount of the nickel component used in this invention is generally 10.sup.-6 to 1 mole, preferably 10.sup.-4 to 10.sup.-1 mole, per liter of the starting materials and a solvent (as will be described hereinbelow, the reaction in accordance with this invention can be performed in the presence of solvent) combined. The amount of the nitrogen-group compound required to form a stoichiometric coordination compound with nickel is 10.sup.-6 to 10 moles, preferably 10.sup.-4 to 5 moles, per liter of the starting materials and a solvent combined. As stated hereinabove, the amount of the iodine component is such that the amount of the free iodine or iodine compound is at least 0.2 mole, preferably at least 0.5 mole, more preferably at least 1 mole, as elemental iodine per mole of each of the nickel component and the nitrogen-group component. The concentration of the iodine or iodine compound per liter of the starting materials and a solvent combined is 10.sup.-6 to 20 moles, preferably 10.sup.-4 to 10 moles, as elemental iodine. When the concentration of the catalyst is high, the rate of the reaction tends to increase.

The reaction in accordance with the process of this invention is carried out at a temperature of 50.degree. to 300.degree. C., preferably 100.degree. to 240.degree. C., and a carbon monoxide partial pressure of 0 to 1000 kg/cm.sup.2 .multidot.G, preferably 2 to 200 kg/cm.sup.2 .multidot.G, more preferably 4 to 70 kg/cm.sup.2 .multidot.G.

Carbon monoxide needs not be of high purity, and may contain hydrogen, carbon dioxide, methane, nitrogen, rare gases, water, etc. Hydrogen does not hamper the reaction, and rather tends to stabilize the catalyst. Carbon monoxide of extremely low purity, however, is not preferred because it will increase the pressure of the reaction system.

The use of a solvent is not essential, but preferable, in the process of this invention. Examples of solvents that can generally be used in this invention include organic acids such as acetic acid, propionic acid, butyric acid, octanoic acid, phthalic acid and benzoic acid, organic acid esters such as methyl acetate, ethyl acetate, dimethyl adipate, methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, dioctyl phthalate, phenyl acetate and tolyl acetate, hydrocarbons such as dodecane, hexadecane, benzene, naphthalene and biphenyl, inorganic acid esters such as triphenyl phosphate, tricresyl phosphate, dibutylphenyl phosphate, tetramethyl ortho-silicate and tetrabutyl silicate, ketones such as acetophenone, propiophenone and benzophenone, and phenols such as phenol, cresol, chlorophenol and nitrophenol.

In particular, the organic acids, organic acid esters and phenols tend to increase the affinity of the starting material with the catalyst. Above all, the organic acid phenyl ester has an effect of preventing the generation of water, hydrogen halide, etc. in the reaction and thus the formation of a corrosive atmosphere, and increasing the yield of the final product.

The alcohol as a starting material in this invention can also act as a solvent. However, when methanol, for example, is used, a volatile substance such as dimethyl ether forms at the early stage of reaction. Furthermore, the affinity of the starting material with the catalyst sometimes changes and the condition of the reaction system will be aggravated.

According to the present invention, carboxylic acids or esters thereof can be obtained in good yields by the carbonylation of the corresponding alcohols or ethers (for example, acetic acid from methanol, nonanoic acid from octanol, ethyl propionate from diethyl ether, and phenyl acetate from anisole) under milder reaction conditions than in the prior art methods, and its advantage is very great.

The following examples illustrate the invention more specifically.

A reaction vessel was charged with 4.2 g of NiI.sub.2.6H.sub.2 O, 35.5 g of CH.sub.3 I, 5.8 g of triphenylphosphine (P.phi..sub.3), 107.7 g of phenyl acetate as a solvent and 21.1 g of methanol as a starting material. The inside of the reactor was pressurized with carbon monoxide to a total pressure of 42 kg/cm.sup.2 .multidot.G (the partial CO pressure 30 kg/cm.sup.2 .multidot.G), and at this pressure and a temperature of 180.degree. C., the reaction was performed to afford a reddish violet solution containing 38.2 g of acetic acid. This corresponded to a yield of 96.1% based on the starting material. Methyl acetate derived from the starting methanol was formed in trace as an impurity, but no substantial amounts of aldehyde, ether, carboxylic acid (except acetic acid), methane, CO.sub.2 and other impurities formed. The time (the half period; abbreviated t) which was required to convert 50% of the starting methanol to acetic acid was 80 minutes. The results are shown in Table 1 together with the reaction conditions, the starting material, solvent and catalyst.

The procedure of Example 1 was repeated except that the starting materials, solvents, catalysts and reaction conditions shown in Table 1 were employed (in Example 5, a gaseous mixture of CO and H.sub.2 was used). The results are shown in Table 1. Formation of by-products was not noted. (In Example 3, however, 74% of methyl acetate used as a solvent changed to acetic anhydride.)

The reaction mixture obtained by the reaction of Example 5 was distilled to remove volatile components. Methyl iodide and anisole were added to the distillation residue, and the same reaction as in Example 5 was performed. The results are shown in Table 1.

The reaction mixture obtained by the reaction of Example 6 was distilled to remove volatile components. Methyl iodide and anisole were added to the distillation residue, and the same reaction as in Example 6 was performed. The results are shown in Table 1.

The reaction mixture obtained by the reaction of Example 7 was distilled to remove volatile components. Methyl iodide, acetic acid and methanol were added to the distillation residue, and the same reaction as in Example 7 was performed. The results are shown in Table 1.

The procedure of Example 1 was repeated except that the starting materials, solvents, catalysts and reaction conditions shown in Table 1 were employed. Formation of by-products was not observed.

Diethylene glycol dimethyl ether as a starting material was reacted by the same procedure as in Example 1 using the catalyst and the reaction conditions shown in Table 1. In 300 minutes after the initiation of the reaction, 10.3 g of ethylene glycol diacetate, 57.7 g of diethylene glycol monomethyl ether monoacetate and 57.8 g of diethylene glycol diacetate were obtained. The results are shown in Table 1.

A reactor was charged with acetic acid as a solvent and the catalyst components indicated in Table 1, and maintained at the temperature and pressure shown in Table 1. Then, 32 g of methanol as a starting material was fed continuously into the reactor over the course of 4 hours at the above temperature and pressure. Two hours later, the reactor was cooled, and the product was analyzed. It was found that 56.3 g (excluding that added as solvent) of acetic acid was obtained. Formation of by-products such as aldehyde, dimethyl ether and high-boiling carboxylic acids was not observed. The results are shown in Table 1.

The same procedure as in Example 1 was repeated employing the starting materials, solvents, catalysts and reaction conditions shown in Table 1. The reaction time was 3 hours in Comparative Examples 1 and 3, and 5 hours in Comparative Example 2. Reaction conditions Catalyst Partial CO Nitrogen- Free I/ pressure Half Starting Nickel Iodine group Free I/Nitrogen- Total (partial H.sub.2 period, material Solvent compound compound compound Ni group Temperature pressure pressure) t Yield, g Example (g) (g) (g) (g) (g) compound compound (.degree.C.) (kg/cm.sup.2 . G) (kg/cm.sup.2 . G) (minutes) (%) By-product 1 Methanol Phenyl NiI.sub.2 . 6H.sub.2 O CH.sub.3 I P.phi..sub.3 22.8 10.3 180.degree. C. 42 30 80 38.2g Substantially 21.1 acetate 4.2 35.5 5.8 (96.1%) absent 107.7 2 Methanol Phenyl Ni(CO).sub.2 (P.phi..sub.3).sub.2 CH.sub.3 I 23.3 11.6 200 31 10 70 58.0 Substantially 32 acetate 6.3 35.5 (96.7) absent 107.8 3 Methanol Methyl Ni powder CH.sub.3 I P.phi..sub.3 22.7 9.0 200 73 43 140 47.0 Substantially 25.6 acetate 0.58 35.5 6.6 (97.9) absent 59.2 4 Methanol Phenyl Ni powder CH.sub.3 I P.phi..sub.3 23.0 10.3 200 50 32 60 110.5 Substantially 32 acetate 0.58 35.5 5.8 (95.5) absent 51.6 acetic acid 53.2 5 Anisole -- Ni powder CH.sub.3 I P.phi..sub.3 18.0 3.7 200 55 45 62 122.1 Substantially 100 0.58 32 12.5 (5) (97.0) absent6 Anisole -- -- CH.sub.3 I -- 60 119.6 Substantially 100 32 (95.0) absent 7 Anisole -- -- CH.sub.3 I -- 61 123.4 Substantially 100 26 (98.0) absent 8 Methanol Acetic -- CH.sub.3 I -- 200 60 30 70 111.2 Substantially 28 acid 23 (15) (95.0) absent 61.3 9 Methanol Phenyl Ni powder CH.sub.3 I P.phi..sub.3 23.0 10.3 200 32 10 35 57.6 Substantially 32 acetate 0.58 35.5 5.8 (96.0) absent 107.7 10 Anisole -- Ni powder CH.sub.3 I P.phi..sub.3 18.0 3.7 160 55 50 240 125 Substantially 100 0.58 32 12.5 (99.3) absent 11 Anisole -- Ni powder CH.sub.3 I P.phi..sub.3 6.6 1.4 200 55 50 120 123 Substantially 100 0.58 16 12.5 (97.7) absent 12 Methanol Phenyl Ni powder CaI.sub.2 P.phi..su b.3 23.0 10.3 200 42 30 70 37.8 Substantially 21.2 acetate 0.58 36.8 5.8 (95.1) absent 124.5 13 Methanol Phenyl NiI.sub.2 . 6H.sub.2 O CH.sub.3 I (C.sub.2 H.sub.5).sub.3 N 4.0 10.3 180 41 30 170 37.4 Substantially 21.2 acetate 24.2 35.5 2.23 (94.1) absent 124.0 14 Methanol Phenyl Nickel CH.sub.3 I Pyridine 20.6 4.7 200 45 30 120 48.2 Substantially 26.8 acetate acetyl- 35.5 3.5 (95.9) absent 114 acetone 2.57 15 Methanol Phenyl Nickel CH.sub.3 I (n-C.sub.4 H.sub.9).sub.3 P 22.8 10.5 200 45 30 35 48.7 Substantially 26.8 acetate acetyl- 35.5 4.4 (96.9) absent 114 acetone 2.57 16 Methanol P-Tolyl Nickel CH.sub.3 I P.phi..sub.3 22.8 10.2 200 45 30 25 48.2 Substantially 26.8 acetate acetyl- 35.5 5.83 (95.9) absent 114.0 acetone 2.57 17 Methanol -- Ni powder CH.sub.3 I P.phi..sub.3 20.2 4.0 180 55 40 185 57 Substantially 32 0.58 35.5 13.1 (95) absent Anisole 55 46 (96) 18 Methanol Phenyl Nickel CH.sub.3 I (C.sub.2 H.sub.5).sub.2 NH 16.2 1.9 200 47 30 75 48.0 Substantially 26.8 acetate acetyl- 35.5 6.4 (95.5) absent 114 acetone 2.57 19 Methanol Phenyl Nickel CH.sub.3 I Ammonium 16.2 1.8 200 46 30 100 47.8 Substantially 26.8 acetate acetyl- 35.5 acetate (95.1) absent 114 acetone 6.8 2.57 20 Methanol P-Tolyl Nickel CH.sub.3 I Aniline 16.2 1.8 200 46 36 45 46.2 Substantially 25.6 acetate acetyl 35.5 8.2 (96.3) absent 114 acetone 2.57 21 Methanol Phenyl Nickel CH.sub.3 I Dimethyl 16.2 1.8 200 46 30 100 48.1 Substantially 26.8 acetate acetyl- 35.5 acetamide (95.7) absent 114 acetone 7.7 2.57 22 Methanol Phenyl Nickel CH.sub.3 I Sb.phi..sub.3 22.8 10.3 200 46 30 65 44.7 Substantially 26.8 acetate acetyl- 35.5 7.8 (89.0) absent 114 acetone 2.57 23 Methanol Phenyl Nickel CH.sub.3 I As.phi..sub.3 23.0 11.4 200 46 30 70 43.7 Substantially 26.8 acetate acetyl- 35.5 6.2 (86.9) absent 114 acetone 2.57 24 Octanol Phenyl Nickel CaI.sub.2 P.phi..sub.3 22.8 10.3 200 33 30 32.1 Substantially 65 acetate acetyl- 36.8 5.8 absent 68 acetone 2.57 25 Methanol Phenyl Nickel CH.sub.3 I Adipo- 25.0 6.3 200 48 30 47.4 Substantially 26.8 acetate acetyl- 35.5 nitrile (94.3) absent 114 acetone 4.3 2.57 26 Di- Ni powder CH.sub.3 I P.phi..sub.3 23.0 10.3 200 36 30 10.3 Substantially ethylene 0.58 35.5 5.8 57.7 absent glycol 57.8 dimethyl ether 107.2 27 Methanol Acetic Ni powder CH.sub.3 I P.phi..sub.3 23.0 10.3 200 41 30 56.3 Substantially 32 acid 0.58 35.5 5.8 (93.8) absent 60 28 Anisole Ni powder CH.sub.3 I P.phi..sub.3 3.0 0.5 200 55 50 310 116.0 Substantially 100 0.50 10.4 12.5 (92.1) absent 29 Diethyl Propio- Nickel C.sub.2 H.sub.5 I P.phi..sub.3 22.8 10.3 200 44 30 210 66.5 Substantially ether nic acetyl- 39 5.8 (93.1) absent 51.8 acid acetone 51.8 2.57 30 Methanol Phenyl Nickel CH.sub.3 I PH.phi..sub.2 22.8 10.4 200 44 30 36 46.2 Substantially 25.6 acetate acetyl- 35.5 4.1 (96.3) absent 108.8 acetone 2.57 31 Anisole -- Ni powder CH.sub.3 I P.phi..sub.3 1.3 0.23 200 54 50 480 111.8 Substantially 100 0.50 8.3 12.5 (88.8) absent 32 Methanol Acetic Nickel CH.sub.3 I Tributyl- 10.0 4.5 200 57 30 45 28.8 Substantially 16.0 acid acetyl- 16.2 amine (10) (96.0) absent 40 acetone 3.83 Aceto- 2.41 phenone 41 33 Methanol Aceto- Nickel CH.sub.3 I n-Butyl- 10.1 5.1 200 59 30 100 28.4 Substantially 16.0 phenone acetyl- 16.2 amine (10) (94.7) absent 81.6 acetone 1.37 2.41 34 Methanol Phenyl Nickel CH.sub.3 I Dimethyl- 10.1 5.1 200 55 30 100 28.1 Substantially 16.0 acetate acetyl- 16.2 aniline (10) (93.7) absent 81.6 acetone 2.27 2.41 35 Methanol Phenyl Nickel CH.sub.3 I 2-Hydroxy- 8.2 2.0 200 45 20 50 28.4 Substantially 16.0 acetate acetyl- 16.2 pyridine (10) (94.7) absent 81.6 acetone 3.57 2.41 36 Methanol Acetic Nickel CH.sub.3 I Tri-n- 10.0 4.5 200 57 30 45 28.3 Substantially 16.0 acid acetyl- 16.2 hexylamine (10) (94.3) absent 40 acetone 5.55 Aceto- 2.41 phenone 41 37 Methanol Phenyl Nickel CH.sub.3 I n-Hexyl- 9.9 4.5 200 59 30 110 28.2 16.0 acetate acetyl- 16.2 amine (10) (94.0) 81.6 acetone 2.10 2.41 Comp. Methanol -- Nickel (CH.sub.3 P.phi..sub.3)I 0.0 0.0 200 73 50 Reacted Not formed Large amount Ex. 1 100 acetyl- 8.5 for substan- of dimethyl- acetone 3 hrs. tially ether 2.57 Comp. Methanol Nickel (CH.sub.3).sub.4 NI P.phi..sub.3 0 0 180 64 50 Reacted Not formed Ex. 2 100 acetyl- 75.4 27 for substan- acetone 5 hrs. tially 2.57 Comp. Methanol Propionic Nickel P.phi..sub.3 . CH.sub.3 I P.phi..sub.3 0 0 200 64 50 Reacted Not formed Ex. 3 32 acid acetyl- 60.6 12.6 for substan- 74 acetone 3 hrs. tially 2.42