AMIDOACIDS BY ALKALI HYDROLYSIS OF AMIDOESTERS

Abstract: A process for the alkali hydrolysis of an amido ester to the corresponding amido acid is disclosed. The process is characterized by the steps of: A) hydrolyzing, in an aqueous alkaline media, an amido ester represented by formula (I), wherein R is selected from C1-20 alkyl, R1 is selected from C2-14 alkylene and C2-14 alkenylene, and R2 is selected from hydrogen and alkyl, aryl and aralkyl groups containing 1-10 carbon atoms, and R3 is selected from C1-8 alkyl; with at least one equivalent of an alkali metal salt per mole of amido ester at 20-160 C to produce an amido acid salt; and B) acidifying the amido acid salt with at least 1.0 equivalents of a strong acid, per mole of amido acid salt at, 20-160 C to produce an amido acid. The process gives a high yield and a good selectivity for the amido acid.

Description: A idoacids by Alkali Hydrolysis of Amidoesters This invention relates to a process for the preparation of amido acids by hydrolysis of amido esters and to a process for drying such amido acids. In particular, the present invention relates to a process for the preparation of amido acids of the formula III from amido alkyl esters: 0 R? 0 0 I II II R - N - C - Rι - C - 0 - H (III) wherein R is selected from Cι_20 alkyl; Ri is selected from C2-14 alkylene and C2-14 alkenylene; and R 2 is selected from hydrogen and C alkyl, aryl and aralkyl groups containing 1-10 carbon atoms. Such amido acids and a method for their preparation are known-from European patent application 0445096. In the process of this patent application, these amido acids are prepared by the hydrolysis of the Q amido monoalkyl ester under conditions which avoid transition metal contamination of the amido acids. The hydrolysis process is described as being conventional. While the patent application does not give further details, one can conclude that by conventional is meant an acid hydrolysis process since acid hydrolysis is the industrially 5 preferred method to produce pure acids and in this application an analogous process, namely hydrolysis of diamide by-products of the reaction to produce the monoalkyl ester, is carried out with an inorganic acid. Hydrolysis under alkaline conditions is nowhere suggested. 0 Production of the amido acids by acid hydrolysis resulted in a low selectivity for the amido acid and, therefore, substantial quantities of undesirable by-products. The formation of these by-products not only reduced the yield of the desired amido acid, but also gave problems in the purification of the amido acid. It was found that this problem could be reduced by continuously removing alkanol from the reactor during the hydrolysis reaction, but such alkanol removal proved to be impractical for large-scale production. In addition, problems were encountered when drying the amido peracids, particularly when scaling-up the production process. A drying process such as that disclosed in DE 3539036, i.e. vacuum drying at 30°C is unsuitable for large scale continuous production due to limitations on throughput rate as well as the requirement for an extremely large drying apparatus. Accordingly, an alternative process was sought which provides a higher selectivity to the desired amido acid and which does not require the continuous removal of alkanol from the reactor. In addition, an alternative drying method was sought which could be used in large- scale production. These and other objects of the invention will be apparent from the summary and detailed description which follows. The present invention relates to a process for the alkali hydrolysis of an amido ester to the corresponding amido acid characterized by the steps of: (A) hydrolyzing, in an aqueous alkaline media, an amido ester represented by the formula I: R 2 0 0 I II II R - N - C - R1 - C - O - R3 (i) wherein R is selected from Cχ_20 alkyl, Ri is selected from C 2 -i4 alkylene and C2-14 alkenylene, and R 2 is selected from hydrogen and alkyl, aryl and aralkyl groups containing 1-10 carbon atoms, and R3 is selected from Cι_8 alkyl; with at least one equivalent of an alkali metal salt per mole of amido ester, at a temperature of 20-160°C to produce an amido acid salt represented by the formula II: R 2 0 0 I II II R - N - C - Rι - C - 0 - X (II) wherein R, Rj, and R 2 are as defined above and X is an alkali metal; and (B) acidifying the amido acid salt with at least 1.0 equivalents of a strong acid, per mole of amido acid salt, at a temperature of 20-160°C to produce an amido acid represented by the formula III: R 2 0 0 I II II R - N - C - Rι - C - 0 - H (III) wherein R, R]_, and R are as defined above. In a second embodiment, the present invention also relates to a process for the drying of an amido acid represented by the formula III, characterized in that the amido acid is dried in a two-stage flash evaporator wherein the first stage operates at 130-140°C, 1.0-2.0 bar and for a time period sufficient to reduce the water content of the amido acid to 1.5 -3.0% by weight, and the second stage operates at 110-135°C, a pressure lower than that used in the first stage, and for a time period sufficient to further reduce the water content of the amido acid to <0.5 by weight. All percentages appearing in this text refer to percent by weight, unless otherwise specified. With respect to the first embodiment of the present invention, it is known from European Patent Application 0 240 138 to prepare cinnamic acid from cinnamic ester by starting the hydrolysis of the ester with an alkali and using water as a solvent in a heterogeneous binary-phase liquid system to obtain an aqueous solution of an alkali cinnamate and then precipitating cinnamic acid by acidifying the aqueous alkaline solution with a mineral acid to maintain the pH at less than 4 in the resulting liquid. However, cinnamic ester lacks an amido functionality and thus is not analogous to the present amido esters. Japanese Laid-Open number 102614/74 also discloses an alkali hydrolysis process for the hydrolysis of cinnamate esters. This process employs an organic solvent which leads to attendant difficulties in separating the cinnamic acid from the solvent media. The amido esters used as reactants in the process of the present invention can be obtained by esterifying a polycarboxylic acid of the formula IV: 0 0 H - 0 - C ii - Rι - C - - O - H (IV) wherein Ri is as defined above, with a Cι_8 alkanol followed by reacting the ester thereby obtained with a monoalkylamine of the formula RNH 2 , wherein R is as defined above. Such a process is described in detail in European Patent Application 0445 096. Examples of some amido esters which may be employed in the process of the present invention include, but are not limited to, N-n-nonylamido methyl adipate, N-n-octylamido methyl adipate, N-n-decylamido methyl adipate, N-n-nonylamido methyl succinate, N-n-octylamido methyl succinate, N-n-decylamido methyl succinate, as well as the amido esters of the formula I wherein R3 is methyl, R is octyl , nonyl or decyl , Ri is trans-C 2 alkenylene and R is hydrogen, and the amido esters wherein R3 is methyl, R is octyl, decyl, dodecyl or mixtures thereof, Ri is C4 alkylene, and R 2 is hydrogen. The hydrolysis employed in the present invention is an alkali hydrolysis process. In the process, an amido ester of the formula I is reacted with an alkali metal salt in an aqueous alkaline media to produce an alkali metal amido acid salt represented by the formula II. Typically, a molar ratio of amido ester to alkali metal salt of 1-2 is employed, more preferably 1-1.4, and most preferably only a slight excess of alkali metal salt is employed giving a mole ratio of 1-1.1. Of course, sufficient aqueous media must be present for provision of the water necessary for the hydrolysis, as well as to dissolve the amido acid salt. Alkali metal salts useful in the process of the present invention include, but are not limited to, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, potassium carbonate, sodium carbonate, lithium bicarbonate, potassium bicarbonate, sodium bicarbonate and mixtures thereof. Most preferred of the alkali metal salts are the hydroxides and most particularly, sodium hydroxide. The hydrolysis step may be carried out at a temperature of 20-160°C. Of course, the lower the temperature, the longer the reaction time. Accordingly, temperatures of 60-100°C are preferred, particularly since these temperatures are often above the melting point of the amido esters, thus easing stirring of the reaction mixture. The most preferred temperature range is 70-95°C which gives a good balance between stirrability, reaction rate and minimization of amido acid salt decomposition. Temperatures above 100°C can be employed so long as a pressure of, for example, 2-6 bar is employed. The reaction is normally carried out at atmospheric pressure though higher pressures can be employed when using higher reaction temperatures. The reaction time depends upon the reaction temperature and pressure and is preferably in the range of 1 minute to 4 hours. In this regard, a preferred embodiment of the invention is a process whereby at least 99.5% of the amido ester is hydrolyzed to the amido acid salt. Accordingly, in this embodiment, the reaction will be continued for as long as is necessary to achieve this level of conversion. Vigorous stirring is employed in the process of the invention in order to achieve complete mixing and contact between the alkali metal salt and the amido ester. Alkanols generated in the process of the invention may be recovered by, for example, distillation. The alkali hydrolysis process of the present invention is advantageous since it can produce substantially 100% conversion of the amido ester to the amido acid while retaining an extremely high selectivity. The corresponding acid hydrolysis, for example, leads to significant quantities cf unwanted by-products. Further, in the acid hydrolysis it is necessary to remove the formed al anol from the reactor during the hydrolysis process in order to achieve a satisfactory yield. Such alkanol removal is impractical for large-scale production. The alkali hydrolysis process of the present invention does not require alkanol removal during the hydrolysis step. In the second step of the process of the invention, the amido acids can be precipitated by acidifying the resultant aqueous alkaline solution with a strong acid such as mineral acid so that the amido acid can be separated from the reaction mixture by, for example, filtration, decantation, centrifugation, and the like. If precipitation of the amido acid is desired, the acidification step should be carried out at a temperature below the melting point of the amido acid. Such temperatures are typically in the range of about 20-85°C. Water soluble mineral acids such as, for example, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, sodium bisulfate, sodium biphosphate and mixtures thereof may be used in the process. Typically, at least 1.0 equivalents of mineral acid per mole of amido acid salt are employed. More preferably, about 1.0-2.0 equivalents per mole of amido acid salt are used, and, most preferably, 1.0-1.2 equivalents of mineral acid per mole of amido acid salt, are employed. Higher yields of precipitate are obtained by acidification to a pH of about 2-4 to ensure complete precipitation of the amido acid. In the process of the invention, the mineral acid may be added to the amido acid salt solution or vice versa, or the two materials can be continuously fed to a single reactor. The reaction mixture must be maintained sufficiently fluid to permit effective stirring. This can be ensured by, for example, adding the amido acid salt solution to the mineral acid, or by adding water during the acidification step. There is no limit on the reaction time for the acidification step except that an inordinately long reaction time, which could result in some acid-catalysed esterification of the amido acid by the alkanol, should be avoided. The amido acid is then separated from the reaction mixture by filtration, centrifugation or the like, preferably washed with aqueous media which may be acidified water with a pH of 2-4, to remove residual alkanol, amines and alkali metal salts and dried by, for example, air at 20-60°C for up to 24 hours at a pressure of 0.1-1.0 bar in a drying oven. Finally, if desired, the amido acid can be flaked by a drum flaker using conventional means. A second, more preferred, method for carrying out the acidification step of the present process is to maintain the reaction mixture at a temperature above the melting point of the amido acid. Since the amido acid salt is water soluble and the amido acid is essentially water-insoluble, the result is the formation of a two-layer liquid which can be easily separated. Other than the higher temperature required, the remaining details of the acidification step are the same as for the precipitation method described above. Typical temperatures for acidification in this manner are 85-160°C and more preferably 90-95°C. Of course the lower limit may vary depending on the melting point of the amido acid. The upper temperature limit is dictated by the tendency of the amido acid to esterify in the presence of strong acid and/or decompose at higher temperatures. One may use temperatures in excess of 160°C, but generally the result will be a lower yield and formation of some undesirable by-products. Separation of the liquid system is accomplished by removing the alkanol, water and alkali metal salt-containing layer at a temperature above the melting point of the amido acid, preferably 85-110°C, and more preferably 90-95 β C. The remaining amido acid-containing layer is preferably washed with an aqueous media such as acidified water of pH of 2-4, to remove substantially all of the residual alkanol therefrom. The alkanol can be separated from the alkali metal salt by, for example, distillation at a temperature of about 100-105°C and employed or sold as a second product of the reaction. The obtained amido acid can be flaked and/or dried in any order. In one embodiment, the amido acid is first flaked by a drum flaker and subsequently dried at 20-75°C for a period of up to 24 hours in a drying oven at a low pressure of, for example 0.05-0.5 bar. It is generally desirable to dry the amido acid to a water content of <2.0% and, more preferably, <0.5%. The flaking operation is a conventional process wherein the material is formed into flakes by a rotating drum flaker which is externally cooled with water to solidify the amido acid. Another possibility is to first dry the amido acid and then to flake it. This is the most preferred process since it offers the possibilility of drying the amido acid in the melt form, in a relatively short time period and in a manner suitable for large-scale continuous production. Due to the tendency of the amido acid to decompose at higher temperatures, drying of the solid form is generally a long, slow operation. More particularly, the preferred drying apparatus for drying the molten amido acid is a flash evaporator. The amido acid can be dried to a water content of <2.0% in a single step at, for example, 140-180°C and a pressure of one bar. The dried product may then be flaked in a drum flaker. This single stage drying operation in a flash evaporator provides acceptable results but suffers from the disadvantage that a significant amount of the amido acid decomposes during drying due to the extremely high temperature or long residence time necessary to achieve the desired low water content. For example, in order to dry in ten seconds at atmospheric pressure, a temperature of 160-180°C is needed. At lower temperatures, a significantly lower pressure is required. It has been found that if the drying operation in the flash evaporator is performed in two distinct stages, it can be accomplished in a short time period and at a temperature such that significantly less amido acid decomposes than in a comparable single stage drying process. More particularly, a first drying step is carried out at a 130-140°C and 1.0-2.0 bar to lower the water content to 1.5-3.0%. Subsequently, a second drying step is carried out at a lower temperature and pressure to further reduce the water content to <0.5%. The second drying stage is generally carried out at a temperature of 110-135°C and a pressure of from 0.05-0.5 bar. The first drying stage generally takes about 10 seconds whereas the second stage takes about 5 seconds. Though the total residence time is longer than that for the single stage drying, the milder temperatures required apparently result in significantly less decomposition of the amido acid. Of course, minor variations in the temperature, pressure and drying time are possible within the scope of the invention, depending on the total water content of the amido acid coming from the reactor and the particular amido acid being made. The following examples of the invention are provided for the purpose of illustration and description only and are not to be construed as limiting the scope of the invention in any way. The scope of the invention is to be determined from the claims appended hereto. Example 1 A reaction vessel is charged with 136.8 grams of the methylester of the nonylamide of adipic acid and 632 grams of water. This mixture is heated to 80°C and 42.3 grams of a 50% aqueous solution of caustic soda is dosed over a 30 minute period. After a post-reaction time of 15 minutes, the pH of the reaction mixture is adjusted to 3.5 with a 50% aqueous solution of sulfuric acid and the temperature is allowed to rise to 90°C. The water layer is drained and the organic layer is washed with 320 grams of water. After separation, the organic layer is flaked and dried. The amount of formed nonylamidoadipic acid is 126.5 grams with an assay of 98.5% and having a melting point of 106-107°C. Exampl e 2 The process as described in Example 1 is repeated using 228 grams of methylester of the nonylamide of adipic acid, 360 grams of water and 89.6 grams of 50% aqueous solution of caustic soda. This mixture is warmed with stirring to 90-95°C and maintained at this temperature for about 90 minutes (at about 60°C melting of the ester is observed). The reaction mixture is then acidified to pH 3.0 with about 120 grams of 50% aqueous solution of sulfuric acid. The water layer is separated and the organic layer is washed with 150 grams of water over a 15 minute period at 90-93°C. After separation, the organic layer is flaked and dried. In this manner, 215 grams of nonylamidoadipic acid is obtained with an assay of 97.5%. Comparative Examples 2A-2B The process of Example 2 was repeated except that initially 400 g. water was employed and in place of NaOH, 96% sulfuric acid solution (53 g) were used to carry out acid hydrolysis. In Example 2A methanol was removed by distillation during the reaction and an additional 500 grams of water were required. The reaction time was 225 minutes and an assay of 96% was achieved. In Example 2B, steam injection was employed and 1000 g extra water was required. The reaction time was 240 minutes and the assay was only 90%. Example 3 The nonylamidoadipic acid obtained by the process of Example 1 was dried in a flash evaporator in two stages. The first stage was carried out at a temperature of 135-140°C, a pressure of 1 bar and for a period of 10 seconds and the second stage was carried out at a temperature of 135-110°C and a pressure of 0.2 bar for a period of 2 seconds. An assay of 98% nonylamidoadipic acid was obtained having a water content of <0.5%. Comparative Example 3A The nonylamidoadipic acid obtained by the process of Example 1 was dried in a flash evaporator in one step at a temperature of 160-180°C, a pressure of 1 bar and for a period of 10 seconds. A yield of 96.5% nonylamidoadipic acid was obtained having a water content of <0.5%. Example 3 and Comparative Example 3A demonstrate the unexpected advantages of the preferred drying process of the present invention, namely that it can be carried out in seconds on a large-scale and without significant decomposition of the amido acid.

Claims: What is claimed is: 1. A process for the alkali hydrolysis of an amido ester to produce an amido acid characterized by the steps of: (A) hydrolyzing, in an aqueous alkaline media, an amido ester represented by the formula I: R 2 0 0 R - N I - C ll - R1 - C ll - O - R3 (I) wherein R is selected from Cι_ 2 o alkyl, Ri is selected from C2-14 alkylene and C2-14 alkenylene, R 2 is selected from hydrogen and alkyl, aryl and aralkyl groups containing 1-10 carbon atoms and R3 is selected from Cι_8 alkyl; with at least one equivalent of an alkali metal salt per mole of amido ester at 20-160 β C to produce an amido acid salt; and (B) acidifying the amido acid salt with at least 1.0 equivalents of a strong acid, per mole of amido acid salt, at 20-160°C to produce an amido acid. 2. A process in accordance with claim 1 wherein hydrolysis step (A) is carried out until >99.5%, of the amido ester is converted to the corresponding amido acid salt. 3. A process in accordance with any one of claims 1-2 further comprising the steps of: (C) precipitating the amido acid from the aqueous reaction media of step (B), (D) isolating the amido acid solid precipitate, (E) washing the amido acid solid precipitate with a sufficient amount of an aqueous media to remove substantially all residual alkanol therefrom, and (F) drying the washed amido acid solid precipitate at a temperature of 20-95°C. 4. A process in accordance with any one of claims 1-2 wherein step (B) is carried out at a temperature above the melting point of the amido acid, and further comprising the steps of: (C) separating the liquid phase containing the amido acid at a temperature above the melting point of the amido acid, and (D) washing the liquid phase containing the amido acid with a sufficient amount of an aqueous media to remove substantially all residual ethanol therefrom. 5. A process in accordance with claim 4 further comprising the steps of: (E) drying and flaking the amido acid, characterized in that the drying and flaking steps may be performed in any order and that the drying step reduces the water content of the amido acid to <2.0%, by weight. A process in accordance with claim 5 wherein the drying step is performed prior to the flaking step and the drying step comprises drying the amido acid in a flash evaporator at 110-180°C. A process in accordance with claim 6 wherein the drying step is performed in a two-stage flash evaporator, the first stage operating at 130-140°C, 1.0-2.0 bar and for a time period sufficient to reduce the water content of the amido acid to 1.5-3.0% by weight, and the second stage operating at a lower temperature and pressure than was used in the first stage and for a time period sufficient to further reduce the water content of the amido acid to <0.5% by weight. 8. A process for the drying of an amido acid represented by the formula III: R 2 0 0 I II II R - N - C - Rι - C - 0 - H (III) wherein R is selected from CI_ 2 Q alkyl, Ri is selected from C 2 _i4 alkylene and C 2 -i4 alkenylene; and R 2 is selected from hydrogen and alkyl, aryl and aralkyl groups containing 1-10 carbon atoms; characterized in that the amido acid is dried in a two-stage flash evaporator wherein the first stage operates at 130-140°C, 1.0-2.0 bar and for a time period sufficient to reduce the water content of the amido acid to 1.5%-3.0% by weight, and the second stage operates at a pressure lower than that used in the first stage and for a time period sufficient to further reduce the water content of the amido acid to <0.5% by weight. 9. A process as claimed in claim 8 wherein the second stage of drying is carried out at a temperature which is lower than the temperature used in the first drying stage. 10. A process as claimed in any one of claims 8-9 wherein the amido acid is obtained by hydrolysis of an amido ester.

Inventors: BOUWMEESTER JOHANNES GERHARDUS, EDELIJN HERMAN JOHANNES, GERRITSEN HANS GIOVANNI, MEIJER JOHN, VAN DE BEEK THEODORUS WILHELMU, VAN DOORN MARCELLINUS ALEXANDE, BOUWMEESTER, JOHANNES, GERHARDUS, BERNARDUS, EDELIJN, HERMAN, JOHANNES, GERRITSEN, HANS, GIOVANNI, MEIJER, JOHN, VAN DE BEEK, THEODORUS, WILHELMUS, JOZEF, VAN DOORN, MARCELLINUS, ALEXANDER
Applicants: AKZO NV, BEEK THEODORUS WILHELMUS JOZEF, BOUWMEESTER JOHANNES GERHARDUS, DOORN MARCELLINUS ALEXANDER VA, EDELIJN HERMAN JOHANNES, GERRITSEN HANS GIOVANNI, MEIJER JOHN, AKZO N.V.
Application year: 1993
Main classification: C07C231
IPC codes: C07C231, C07C233