Process for producing N-long-chain acyl acidic amino acids or salts thereof

Abstract: There is provided an industrially advantageous process for producing an N-long chain acyl acidic amino acid from an acidic amino acid and a long chain fatty acid halide. The desired product is obtained in a high yield without the problems of odour and safety which may arise when solvents and catalyst remain in the desired product. The equipment for removal of the solvents is reduced, and production is simplified. According to the process of the invention an N-long-chain acyl acidic amino acid is produced by condensing an acidic amino acid with a long chain fatty acid halide in water in the presence of an alkali, and the reaction is performed in the presence of a polyhydric alcohol.

Description: The present invention relates to a process for producing N-long-chain acyl acidic amino acids or salts thereof. More specifically, the present invention relates to a process for producing N-long-chain acyl acidic amino acids or salts thereof by reacting an acidic amino acid such as glutamic acid, aspartic acid or its salt with a long-chain fatty acid halide. N-long-chain acyl acidic amino acids, for example, an N-long-chain acyl glutamic acid, N-long-chain acyl aspartic acid or salts thereof such as sodium salts, potassium salts and triethanolamine salts have been used in various agents such as detergents, dispersing agents, emulsifying agents and antibacterial agents because they have surface activating action and sterilizing action. Especially, these have low irritancy towards the skin and the hair, and have therefore found wide acceptance in detergent compositions such as hair shampoo and body shampoo. As a method of forming an N-long-chain acyl acidic amino acid, for example an N-long-chain acyl glutamic acid, a method is known in which glutamic acid is condensed with a long chain fatty acid halide in a solvent of water in the presence of an alkali (e.g., see Reference Example at the beginning of column 7 in Japanese Patent Publication No. 35,058/1973). However, this prior art method is not said to be a method which can satisfactorily be used industrially because of the low yield. As a method of producing an N-long chain acyl acidic amino acid in a high yield, a method is known in which the reaction is conducted in a solvent of water using a tertiary amine or a quaternary ammonium salt as a catalyst (Japanese Patent Publication No. 35,058/1973). However, since these catalysts involve safety problems such as irritation of the skin and a problem of odour of the catalyst used, a procedure and equipment for removing catalyst remaining in a desired product are required. Thus, this method is not said to be an industrially satisfactory method. As another method to increase the yield, a method is known in which a mixed solvent of an organic solvent such as acetone, methyl ethyl ketone, dioxane or tetrahydrofuran and water is used as a reaction solvent (Japanese Patent Publication No. 8,685/1971). However, when these organic solvents are used, problems occur because of the potential effect of the solvents on the working environment. In order to satisfy safety regulations, such as fire laws, special equipment has to be provided requiring plant investment. Further, in view of other safety problems such as those related to skin irritation and problems related to odour of the solvent, a procedure and equipment for removing solvents remaining in the desired product are needed. Likewise, a method is known in which a hydrous lower alcohol is used as a reaction solvent to increase the yield (Japanese Patent Publication No. 38,681/1976). However, this method also involves problems such as the odour of lower alcohol remaining in the desired product, and a procedure and equipment for removing the same are required. Desirably, embodiments of the present invention provide a process in which an N-long chain acyl acidic amino acid can be produced from an acidic amino acid and a long chain fatty acid halide in a high yield without the above-mentioned problems. The present inventors have found that it is advantageous to use a mixed solvent of a polyhydric alcohol and water as a reaction solvent in a process for producing an N-long-chain acyl acidic amino acid by condensing an acidic amino acid or its salt with a long-chain fatty acid halide in the presence of an alkali. This finding has led to the completion of the present invention. That is, the present invention relates to a process for producing an N-long chain acyl acidic amino acid or its salt, characterized in that when an acidic amino acid or its salt is reacted with a long chain fatty acid halide containing from 8 to 22 carbon atoms in water in a presence of an alkali, a reaction is performed in the presence of a polyhydric alcohol. With respect to the acidic amino acid or its salt as one of the starting materials in the process of the present invention may be selected from glutamic acid, aspartic acid or salts thereof. These may be the optically active substances or racemic compounds. As examples of the salts alkali metal salts such as the sodium salt and the potassium salt can be mentioned. The long-chain fatty acid halide to be condensed with the acidic amino acid or its salt is a saturated or unsaturated fatty acid halide containing from 8 to 22 carbon atoms. Examples thereof include saturated or unsaturated fatty acid chlorides of a single composition, such as nonanoyl chloride, undecanoyl chloride, lauroyl chloride, tridecanoyl chloride, myristoyl chloride, palmitoyl chloride, stearoyl chloride and oleyl chloride; and mixture fatty acid chlorides such as coconut oil fatty acid chloride, tallow fatty acid chloride, hardened tallow fatty acid chloride, soybean fatty acid chloride and cottonseed fatty acid chloride. Examples of the polyhydric alcohol used as a component of the reaction solvent in the present invention include glycerol, ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, sorbitol, mannitol, erythritol and pentaerythritol. Further, a polymer of the above-mentioned, such as polyethylene glycol is also available. Still further, non-reductive disaccharide containing plural hydroxyl groups, such as trehalose and sucrose can also be included in the polyhydric alcohol of the present invention. Even if these polyhydric alcohols remain in a desired product, it is not problematic as regards safety, such as the skin irritation. Further, most of these polyhydric alcohols are ordinarily used as an ingredient which is incorporated into toiletries or surfactants. It is considered that the removal of these slightly remaining polyhydric alcohols is scarcely required. Further, the problem of the odour of the desired product has been much improved. Accordingly, great industrial merits such as the simplification of the procedure and the equipment for removing the remaining solvent and catalyst are provided. Among the above-mentioned polyhydric alcohols, preferable one include glycerol, ethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol. From the aspects of the reaction yield and the low cost, ethylene glycol, propylene glycol and dipropylene glycol are especially preferable in industrially practising the process. In the present invention, the reaction is conducted in the presence of an alkali. In a particularly preferred reaction procedure, the amino acid or its salt is first dissolved in the polyhydric alcohol solution in the presence of an alkali, then the long-chain fatty acid halide is added. From the standpoint of increasing the reaction yield, the pH of the reaction solvent is preferably between 10 and 13. Further, it is advisable to conduct the reaction by maintaining the pH within this range until the reaction is completed. The alkali to be used is not particularly limited. Examples thereof include sodium hydroxide, potassium hydroxide, sodium carbonate and ammonia. Sodium hydroxide is especially practical. The polyhydric alcohol in the reaction solvent used in the present invention can be used in a relatively wide range of a concentration. The concentration before the addition of the fatty acid halide is preferably between 5 and 80% in terms of % by weight, more preferably between 5 and 50%. When it is less than 5%, the reaction yield is less increased. When it exceeds 80%, the acidic amino acid as a starting material is hardly dissolved in the reaction solvent. The reaction temperature in the present invention is not particularly limited. The reaction is ordinarily performed at the range of from 0°C to 50°C. However, in order to proceed with the reaction in a high yield, it is preferably from 0°C to 40°C, more preferably from 5°C to 30°C. With respect to the ratios of the acidic amino acid or its salt and the long chain fatty acid chloride, it is preferable that the former is used in an equimolar or larger amount relative to the latter for obtaining the desired product in a high yield. Within this range, the larger the amount of the former, the more the yield is improved. Practically preferable is that the ratio (molar ratio) of the acidic amino acid or its salt relative to the long chain fatty acid chloride is between 1.0 and 1.5. The concentration of the acidic amino acid or its salt is not particularly limited. In view of the increase in the reaction yield, it is preferably between 10 and 60% in terms of percent by weight before the addition of the fatty acid halide, and it is especially preferably between 15 and 50%. In the reaction, it is preferable in the aspect of the increase in the reaction yield that the acidic amino acid or its salt is dissolved in a mixed solvent of water and a polyhydric alcohol, and a fatty acid halide is then gradually added to the solution while being stirred. The reaction time varies depending on conditions. The time of the addition of the fatty acid halide is usually between 1 and 6 hours, and the reaction time after the addition is usually between 10 minutes and 4 hours. After the completion of the reaction, the reaction mixture is acidified with a mineral acid such as sulfuric acid or hydrochloric acid, and the N-long chain acyl acidic amino acid precipitated is separated through filtration. The N-long chain acyl acidic amino acid separated through filtration is neutralized with a sodium hydroxide solution or a potassium hydroxide solution, and water is then distilled off under reduced pressure to obtain an N-long chain acyl acidic amino acid salt. Examples Embodiments of the present invention are illustrated specifically by referring to the following Examples. Example 1 Sodium L-glutamate monohydrate (175 g, 0.93 mols) was suspended in 230 ml of a 13% (by weight) dipropylene glycol aqueous solution, and 145 g of a 25% (by weight) sodium hydroxide aqueous solution were added thereto to prepare an aqueous solution having a pH of 12. (The concentration of dipropylene glycol is 9% by weight). To this aqueous solution were added 158 g (0.72 mols) of lauroyl chloride and a 25% (by weight) sodium hydroxide aqueous solution simultaneously over the course of 2 hours with stirring while maintaining the pH of 12 and a temperature of 10°C. Further, the reaction was conducted for 2 hours. After the completion of the reaction, the reaction mixture was adjusted to a pH of 1 with 15% (by weight) sulfuric acid, and crystals were precipitated with the addition of cold water. The crystals were collected through filtration, and dried at 25°C for 24 hours. As a result, the amounts of the crystals were 220 g. By analysing through HPLC, the yield of N-lauroyl glutamate was 89 mol% (relative to lauroyl chloride). Example 2 Sodium L-glutamate monohydrate (175 g, 0.93 mols) was suspended in 230 ml of a 13% (by weight) polyethylene glycol aqueous solution, and 145 g of a 25% (by weight) sodium hydroxide aqueous solution were added thereto to prepare an aqueous solution having a pH of 12. (The concentration of polyethylene glycol is 9% by weight). The reaction was conducted as in Example 1. The crystals were collected through filtration, and dried at 25°C for 24 hours. As a result, the amounts of the crystals were 220 g. By analysing through HPLC, the yield of N-lauroyl glutamate was 85 mol% (relative to lauroyl chloride). Example 3 Sodium L-glutamate monohydrate (175 g, 0.93 mols) was suspended in 250 ml of a 20% (by weight) polyethylene glycol aqueous solution. 145 g of a 25% (by weight) sodium hydroxide aqueous solution were added thereto to prepare an aqueous solution having a pH of 12 (the concentration of polyethylene glycol is 14% by weight). The reaction was conducted as in Example 1. The crystals were collected through filtration, and dried at 25°C for 24 hours. As a result, the amounts of the crystals were 223 g. By analysing through HPLC, the yield of N-lauroyl glutamate was 91 mol% (relative to lauroyl chloride). Example 4 Sodium L-glutamate monohydrate (175 g, 0.93 mols) was suspended in 230 ml of a 7.5% (by weight) sucrose aqueous solution. 145 g of a 25% (by weight) sodium hydroxide aqueous solution were added thereto to prepare an aqueous solution having a pH of 12. (The concentration of sucrose is 5% by weight). The reaction was conducted as in Example 1. The crystals were collected through filtration, and dried at 25°C for 24 hours. As a result, the amounts of the crystals were 223 g. By analysing through HPLC, and the yield of N-lauroyl glutamate was 82 mol% (relative to lauroyl chloride). Example 5 Sodium L-glutamate monohydrate (175 g,- 0.93 mols) was suspended in 240 ml of a 15% (by weight) propylene glycol aqueous solution. 140 g of a 25% (by weight) sodium hydroxide aqueous solution were added thereto to prepare an aqueous solution having a pH of 11. (The concentration of propylene glycol is 10% by weight). The reaction was conducted as in Example 1 with a pH of 11 at 20°C using 170 g (0.78 mols) of lauroyl chloride. The crystals were collected through filtration, and dried at 25°C for 24 hours. As a result, the amounts of the crystals were 235 g. By analysing through HPLC, the yield of N-lauroyl glutamate was 90 mol% (relative to lauroyl chloride). Example 6 Sodium L-glutamate monohydrate (175 g, 0.93 mols) was suspended in 240 ml of 15% (by weight) glycerol aqueous solution. 145 g of a 25% (by weight) sodium hydroxide aqueous solution were added thereto to prepare an aqueous solution having a pH of 12. (The concentration of glycerol is 10% by weight). The reaction was conducted as in Example 1. The crystals were collected through filtration, and dried at 25°C for 24 hours. As a result, the amounts of the crystals were 200 g. These crystals were analysed through HPLC, and the yield of N-lauroyl glutamate was 81 mol% (relative to lauroyl chloride). Example 7 Propylene glycol was added to 200 ml of water, and a plurality of reaction solvents which were different in the concentration of propylene glycol were prepared. Sodium L-glutamate monohydrate (175 g, 0.93 mols) was suspended in each of the reaction solvents. Then, the reaction was conducted as in Example 1 using 160.9 g (0.72 mols) of coconut oil fatty acid chloride. The relationship between the concentration of propylene glycol before the addition of coconut oil fatty acid chloride and the yield of N-cocoyl glutamic acid is shown in Table 1. Concentration of propylene glycol (weight %) Yield of N-cocoyl glutamic acid (mol%) 0 74 7 79 13 88 15 91 17 92 50 94 Example 8 Organoleptic evaluation of an odour The reaction was conducted as in Example 1 using a 13% ethanol aqueous solution as a reaction solvent to obtain crystals of N-lauroyl glutamate. These crystals were used as Comparative Example. One hundred grams of N-lauroyl glutamate obtained in each of Examples 1, 2, 3, 4, 5 and 6 and Comparative Example were dissolved in a 25% sodium hydroxide aqueous solution to prepare 450 g of a surfactant solution having a pH of 7.3. The odour was evaluated at 25°C on this surfactant solution. The evaluation scores were given to the surfactant solutions by ten panelists according to the following standards, and the average values are shown in Table 2. Score No odour is given at all. 0 Slight odour is given. 1 Odour is given. 2 Strong odour is given. 3 In summary, embodiments of the present invention facilitate production of an acyl acidic amino acid or its salt in high yield, and mean fewer safety precautions, eg fire precautions, are required. Equipment and procedures for removal of remaining solvents or catalyst can be simplified. Thus, the process can be practised industrially advantageously.

Claims: A process for producing N-long-chain acyl acidic amino acids or salts thereof, when an acidic amino acid or a salt thereof is reacted with a long chain fatty acid halide containing from 8 to 22 carbon atoms in water in the presence of an alkali, characterized in that the reaction is performed in the presence of a polyhydric alcohol. A process according to claim 1 wherein the amino acid or salt thereof is first dissolved in the polyhydric alcohol solution in the presence of an alkali, and the long chain fatty acid halide is then added. A process according to claim 2 wherein the concentration of polyhydric alcohol in the polyhydric alcohol solution, before the addition of the fatty acid halide is between 5 and 80% by weight. A process according to anyone of the preceding claims wherein the reaction is carried out at a pH between 10 and 13. A process according to any one of the preceding claims wherein the polyhdric alcohol is selected from glycerol, ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, sorbitol, mannitol, erythritol and pentaerythritol.

Inventors: HATTORI TATSUYA, HIRAI KIYOMIKI, HATTORI, TATSUYA, HIRAI, KIYOMIKI, HATTORI, TATSUYA, TOKAI PLANT, AJINOMOTO CO., INC., HIRAI, KIYOMIKI, TOKAI PLANT, AJINOMOTO CO., INC.
Applicants: AJINOMOTO KK, AJINOMOTO CO., INC.
Application year: 1998
Main classification: C07C231
IPC codes: C07C233, C07C231