PROCESS FOR PRODUCTION OF CARBOXYLIC ACID ESTERS

Abstract: Carboxylic acid esters, industrially important compounds, are efficiently obtained by reacting carboxylic acid amides with formic acid esters in the presence of an inorganic solid acid catalyst.

Description: 1. Field of the Invention The present invention relates to a process for the efficient production of carboxylic acid esters which comprises reacting a carboxylic acid amide and a formic acid ester in the presence of a catalyst. 2. Description of Related Arts Carboxylic acid esters are industrially important compounds. These carboxylic acid esters can be produced from carboxylic acid amides. For example, methyl acetate is produced from acetic acid amides; methyl methacrylate is produced from methacrylic acid amide; methyl acrylate is produced from acrylic acid amide; and methyl α-hydroxyisobutyrate is produced from α-hydroxyisobutyric acid amide. For producing carboxylic acid esters from carboxylic acid amides, a method of reacting carboxylic acid amides with alcohols in the presence of sulfuric acid is already known. This method is widely employed for industrial production of methyl methacrylate. This method, however, has disadvantages in that a large amount of acidic ammonium sulfate results as a by-product, leading to a marked increase in production costs owing to its disposal, and an expensive corrosion-resistant apparatus is also required. In order to overcome the above problems, a method of producing carboxylic acid esters by reacting carboxylic acid amides and alcohols without the use of sulfuric acid has been proposed. According to JP-A-3015/1977, 141216/1978 and 144524/1978, for example, this reaction is carried out in a liquid phase in the presence of e.g. metal salts or metal alcoholates. On the other hand, according to JP-A-67534/1982 and 49338/1983, this reaction is carried out in a gas phase in the presence of a solid acid catalyst. These methods, however, have disadvantages in that the yield of the desired carboxylic acid ester or its selectivity is low and thus are not satisfactory in commercial practice thereof. Moreover, in commercial practice, they suffer from problems in that: (1) the reaction should be carried out at high temperatures, (2) in case of the liquid phase reaction, high pressure is needed, (3) a large amount of ammonia is produced during the reaction and thus its recovery and separation is needed, and (4) the reaction of the ammonia with carboxylic acids as by-product leads to the formation of ammonium salts thereof. From JP-A-55444/1983 and 78937/1985 a method of producing carboxylic acid esters and formamide by reacting carboxylic acid amides with formic acid esters in the presence of a catalyst is already known. In JP-A-55444/1983 a main catalyst consisting of a metallic compound of groups Ib, IIa, IIb, IIIb, IVa, IVb, VIa, VIIb and VIII in the periodic table and a promotor consisting of a nitrogen or phosphorus-containing organic compound are used in combination. In one of the examples, the reaction was carried out at 185 to 250°C for 2 to 4,5 hours, and the desired carboxylic acid ester was obtained in a yield of 16,3 to 78,9%. This yield, however, cannot be said to be sufficiently high, and moreover the catalyst system is expensive. In JP-A-78937/1985, a catalyst system is used, and the reaction is carried out under pressure of carbon monoxide. The used catalyst is, for example, a combination of amidine, tertiary amine, a mixture thereof and metal carbonyl. However, although the selectivity of the carboxylic acid ester is relatively high, this method has disadvantages in that high pressure is needed for the reaction, highly toxic metal carbonyl is used, and the catalyst system is expensive. US-A-4 161 609 describes a process based on heterogeneous catalysis wherein the reactants (amide and alcohol or phenol) are used in the vapor phase. Also in this case high pressure is needed for the reaction and the selectivity of the carboxylic acid ester is low. SUMMARY OF THE INVENTION Therefore, the object of the present invention is to provide a new process for producing carboxylic acid esters from carboxylic acid amides and formic acid esters in the presence of cheaper catalysts which allows higher yields and does not require the presence of high pressures of carbon monoxide which are necessary in the alternative to the process of JP-A-55 444/1983 proposed by JP-A-78 937/1985. Surprisingly, it has been found that an inorganic solid acid catalyst, e.g. silica, alumina, silica-alumina or zeolite, is effective for producing carboxylic acid esters, and that if such a solid acid catalyst is used, it is not necessary to maintain the reaction system under the pressure of carbon monoxide. In the case of such a solid acid catalyst, recovery of the catalyst and its reuse are very easy and, therefore, the process of the present invention is extremely significant for industrial use. Subject-matter of the present invention is a process for the production of carboxylic acid esters which comprises reacting a carboxylic acid amide and a formic acid ester in the presence of a catalyst which is characterized in that a) said catalyst is at least one inorganic solid acid catalyst selected from silica, alumina, silica-alumina, titania, zirconia, solid phosphoric acid, zeolite, and composite compounds thereof optionally comprising a carrier, and b) said process is conducted in an autoclave at a reaction temperature of 170 to 250 °C. According to a preferred embodiment of the present invention the carboxylic acid amide is an aliphatic carboxylic acid amide, an aromatic carboxylic acid amide, an aliphatic α-hydroxyl carboxylic acid amide, an aromatic α-hydroxylcarboxylic acid amide, an aliphatic α-aminocarboxylic acid amide or an aromatic α-aminocarboxylic acid amide, preferably at least one compound selected from the group consisting of acetamide, lactic acid amide, acrylic acid amide, methacrylic acid amide, α-hydroxyisobutyric acid amide, benzamide, valine amide and alanineamide. According to a further preferred embodiment of the present invention the formic acid ester is at least one compound prepared by reacting formic acid with aliphatic alcohols having 1 to 10 carbon atoms or alicyclic alcohols having 4 to 10 carbon atoms, and the amount of the formic acid ester is preferably 1 to 10 moles per mole of the carboxylic acid amide. DESCRIPTION OF PREFERRED EMBODIMENTS Carboxylic acid amides to be used in the present invention include aliphatic or aromatic carboxylic acid amides, and α-hydroxy or α-aminocarboxylic acid amides. These amides can be prepared by hydrolyzing nitriles, or by reacting amines and carbon monoxide. Specific examples are acetamide, lactic acid amide, acrylic acid amide, methacrylic acid amide, α-hydroxyisobutyric acid amide, benzamide, valine amide and alanineamide. Formic acid esters to be used in the present invention are those prepared from formic acid, and aliphatic alcohols having 1 to 10 carbon atoms or alicyclic alcohols having 4 to 10 carbon atoms. Specific examples of aliphatic alcohols are methanol, ethanol, propanol, butanol and octanol. Specific examples of the alicyclic alcohols are cyclohexanol and cycloheptanol. The catalyst to be used in the present invention is a catalyst generally called an "inorganic solid acid catalyst", which is selected from the group consisting of silica, alumina, silica-alumina, titania, zirconia, solid phosphoric acid,zeloites, composite compounds of the above compounds, and composite compounds comprising the above compounds and a carrier. This catalyst can be used in the state of suspension or flow in the reaction system as a powder. It can be also used in a suitable size of molding made of the above compound as a fixed bed catalyst. The reaction of the present invention is an equilibrium reaction, and the conversion greatly varies according to the molar ratio of formic acid ester to carboxylic acid amide. From an industrial production viewpoint of carboxylic acid ester, the amount of the formic acid ester is preferably 1 to 10 moles per mole of carboxylic acid amide. Carboxylic acid amides are generally in solid state at room temperature. Since the solubility of carboxylic acid amide in formic acid ester is low, in may cases it is desirable to use a suitable solvent in the present invention. An alcohol constituting the formic acid ester is preferably used for the solvent. The reaction conditions and period of time can be chosen from a wide range depending on the kind of the starting material, the amount of the catalyst charged, and the conversion objective. The reaction is carried out in an autoclave and the reaction temperature is 170 to 250°C, preferably 190 to 230°C. The reaction period of time is preferably 0,1 to 5 hours and more preferably 0,2 to 3 hours. The present invention is described in greater detail with reference to the following examples. EXAMPLE 1 6.2 g (0.06 mole) of α-hydroxyisobutyric acid amide, 18 g (0.3 mole) of methyl formate, 9.6 g (0.3 mole) of methanol, and 2 g of a silica-alumina catalyst (N631H produced by Nikki Chemical Co., Ltd.) powder which had been calcined at 800°C for 3 hours were placed in a 100-milliliter stainless steel autoclave, and the mixture thus obtained was reacted at 200°C for 3 hours. After completion of the reaction, the reaction mixture was cooled to room temperature and then the catalyst was removed by filtration. The product was subjected to a gas chromatographic analysis. This analysis showed that the conversion of α-hydroxyisobutyric acid amide was 56.5%, the selectivity into methyl α-hydroxyisobutyrate was 94.1%, and the selectivity into formamide (based on the reacted α-hydroxyisobutyric acid amide) was 88.5%. EXAMPLE 2 The procedure of Example 1 was repeated with the exception that 3.5 g (0.06 mole) of acetic acid amide was used as the carboxylic acid amide. The conversion of acetic acid amide was 60.5%, the selectivity into methyl acetate was 96.5% and the selectivity into formamide (based on the reacted acetic acid amide) was 90.9%. EXAMPLE 3 The procedure of Example 1 was repeated with the exception that 7.3 g (0.06 mole) of benzamide was used as the carboxylic acid amide. The conversion of benzamide was 55.1%, the selectivity into methyl benzoate was 95.1% and the selectivity into formamide was 87.6%. EXAMPLE 4 The procedure of Example 1 was repeated with the exception that an alumina catalyst (N612 produced by Nikki Chemical Co., Ltd.) was used as the catalyst, and that the reaction temperature and time period of time were changed to 220°C and 1 hour, respectively. The conversion of α-hydroxyisobutyric acid amide was 59.4%, the selectivity into methyl α-hydroxyisobutyrate was 92.8% and the selectivity into formamide was 85.2%. EXAMPLE 5 The procedure of Example 1 was repeated with the exception that 30.6 g (0.3 mole) of butyl formate was used as the formic acid ester and that 22.2 g (0.3 mole) of butanol was used as the alcohol. The conversion of α-hydroxyisobutyric acid amide was 54.3%, the selectivity into butyl α-hydroxyisobutyrate was 90.9% and the selectivity into formamide was 86.5%. COMPARATIVE EXAMPLE 1 The procedure of Example 1 was repeated with the exception that the catalyst was not used. The conversion of α-hydroxyisobutyric acid amide was 24.8%, the selectivity into methyl α-hydroxyisobutyrate was 87.6% and the selectivity into formamide was 84.7%.

Claims: A process for the production of carboxylic acid esters which comprises reacting a carboxylic acid amide and a formic acid ester in the presence of a catalyst, characterized in that a) said catalyst is at least one inorganic solid acid catalyst selected from silica, alumina, silica-alumina, titania, zirconia, solid phosphoric acid, zeolite, and composite compounds thereof optionally comprising a carrier, and b) said process is conducted in an autoclave at a reaction temperature of 170 to 250 °C. The process as claimed in Claim 1, wherein the carboxylic acid amide is aliphatic carboxylic acid amide, aromatic carboxylic acid amide, aliphatic α-hydroxyl carboxylic acid amide, aromatic α-hydroxylcarboxylic acid amide, aliphatic α-aminocarboxylic acid amide or aromatic α-aminocarboxylic acid amide. The process as claimed in Claim 1, wherein the carboxylic acid amide is at least one compound selected from the group consisting of acetamide, lactic acid amide, acrylic acid amide, methacrylic acid amide, α-hydroxyisobutyric acid amide, benzamide, valine amide and alanineamide. The process as claimed in Claim 1, wherein the formic acid ester is at least one compound prepared by reacting formic acid with aliphatic alcohols having 1 to 10 carbon atoms or alicyclic alcohols having 4 to 10 carbon atoms. The process as claimed in Claim 1, wherein the amount of the formic acid ester is 1 to 10 moles per mole of the carboxylic acid amide.

Inventors: HIDEO, IKARASHI MITSUBISHI GAS CHEMICAL CO. INC., HIROYUKI, HIRAYAMA MITSUBISHI GAS CHEMICAL CO. INC, SEIJI, NAGASAWA MITSUBISHI GAS CHEMICAL CO. INC., YOSHIO, KAWAI MITSUBISHI GAS CHEMICAL CO. INC.
Applicants: MITSUBISHI GAS CHEMICAL COMPANY, INC.
Application year: 1989
Main classification: C07C67
IPC codes: B01J21, C07C69, C07B61, B01J29, C07C67