PROCESS FOR OBTAINING DERIVATIVES OF ACETIC ACID

Abstract: Method for obtaining derivatives of acetic acid (I) wherein R₁ and R₂ are H or groups -CH₂-COOH by oxidation of (II) wherein R and R' are H or groups -CH₂-CH₂OH with O₂ or a gas containing it, in the presence of alkali, demineralized water and Cu-Raney. The reaction takes place while maintaining constant a partial pressure of O₂ inside the reactor lower than 20kg/cm². The acids (I) obtained as soluble salts may be isolated and purified by chemical or electrochemical process. Examples of acids (I) are Gly, IDA and NTA useful as nutrients (Gly) and in the synthesis of herbicides (IDA, NTA).

Description: The invention concerns a process for obtaining derivatives of acetic acid, specifically glycine and iminodiacetic and nitrilotriacetic acids by oxidizing monoethanolamine, diethanolamine and triethanolamine, respectively, with the use of oxygen or a gas that contains oxgygen and a Copper-Raney catalyst. BACKGROUND TO THE INVENTION The glycine, the iminodiacetic acid (I.D.A.) and the nitrilotriacetic acid (N.T.A.), described in numerous patents, are widely used in different sectors. For example, glycine can be used as a nutrient and both I.D.A. and N.T.A. are used in the process of synthesizing herbicides, among other applications. Since these products have appeared on the market, a variety of ways of obtaining them have been described and patented. The Japanese patent 53077009 held by the Mitsui Toatsu Chemical Co. Ltd, describes a procedure for obtaining I.D.A. and N.T.A. through the oxidation of diethanolamine and triethanolamine respectively, with oxygen gas in a base aqueous solution, using a noble metal (Pt and Pd) as catalyst for the reaction. Although the acids mentioned can be obtained through this procedure, the yield obtained for both I.D.A. (69%) and N.T.A. (60%), is rather low, and there is the added drawback that the possible losses of the noble metal used as a catalyst make this process unprofitable from an economic point of view. On the other hand, it is a fact, recognised by experts in catalysis, that noble metal losses occur in catalytic processes both for acids and bases, through the solution of the metal in the reaction water, a complex process being required for their recovery, and that there are also losses when the above-mentioned catalysts are being handled. As a result, it is difficult to make this type of process profitable considering that the end-products are of little economic value. So, it would be useful if a process existed through which glycine and the acids I.D.A. and N.T.A. could be obtained in such a state of purity and with sufficiently high yields resulting from oxidation of mono-, di- and triethanolamine, respectively, using a catalyst that was not a noble metal (e.g. Copper-Raney), that the aforementioned economic shortcomings would be reduced to a minimum. Therefore, one of the aims of the invention is to provide a process for oxidizing mono-, di- and triethanolamine, in the presence of a Copper-Raney catalyst, which gives good yields in the reaction performance as well as minimizing cost of the catalyst when obtaining the end-product. On the other hand, other Japanese patents held by Nippon Catalytic Chem. Ind., 60078948, 60/78949, 60/97945, 60/100545 and 61/65840, provide a process for obtaining glycine, I.D.A. and N.T.A. by dehydrogenation of the mono-, di- and triethanolamine in a base aqueous solution using Copper-Raney as a catalyst, but with oxygen or gas that contains oxygen, obtained using a water decomposition reaction according to the following reaction diagrams, respectively: C₂H₇ON+H₂O → C₂H₅O₂N+2H₂ (Glycine) C₄H₁₁O₂N+2H₂O → C₄H₇O₄N+4H₂ (I.D.A.) C₆H₁₅O₃N+3H₂O → C₆H₉O₆N+6H₂ (N.T.A.) In this process calculating, for example theoretically, the heat of the combustion and reaction required to obtain the iminodiacetic acid, this would be 2.053 Kcal/Kg of I.D.A. and the amount of hydrogen produced would be around 0.061 Kg H₂/Kg of I.D.A. So, for a load of 13.5 Kg of I.D.A. produced in 4 hours using the above-mentioned Japanese patent nº 69/78948, the amount of hydrogen released would be 0.81 Kg that, at 25ºC. and 1 atmosphere, would be equivalent to 41 litres of hydrogen per minute, and this would have to be allowed to leave the reaction so that it could be carried out at the pressure of 9 Kg/cm² which is referred to in the patent. So, in order to adopt this process, it would be necessary to have fireproof installations, and to work in greater safety conditions due to the presence of the hydrogen, and furthermore, the amount of heat to be delivered would have a considerable effect on the final manufacturing cost of the end-products. As a result of the aforementioned, a second aim of this invention is to provide a mono-, di- and triethanolamine oxidation process in the presence of a Copper-Raney catalyst, this type being the same as in the two previous processes, but with the advantage of it not being necessary to carry out the procedure in fireproof installations, plus the additional advantages of notably reducing the safety conditions for the process and reducing to a minimum the heat expenses required to manufacture the desired compounds. The two aims of the process adopted for this invention arise from the new technology for the manufacture of glycine, I.D.A. and N.T.A., which are carried out according to the following reaction diagrams: which are slightly exothermic reactions, without releasing hydrogen and carried out without the use of noble metals but with Copper-Raney as the catalyst. BRIEF DESCRIPTION OF THE INVENTION The invention deals with a process for obtaining acetic acid derivatives, specifically glycine, iminodiacetic acid and nitrilotriacetic acid by oxidation with O₂ or a gas which contains it, of mono-, di- and triethanolamine respectively, in reactions carried out with hardly any hydrogen and in the presence of a Copper-Raney catalyst. To bring about this reaction, it is suggested that the process should start without any sweeping taking place with nitrogen or hydrogen, once the components of the reaction have been added and the heating begun for the obtaining of the temperatures and pressures mentioned below. In addition, the catalyst to be used is Copper-Raney, wetted for safety reasons. DETAILED DESCRIPTION OF THE INVENTION The invention provides a process for obtaining the acetic acid derivatives of general formula (I) where R₁ and R₂ can either be H or -CH₂ -COOH groups independently. The process of the invention can be represented by the following reaction diagram in which Copper-Raney figures as the catalyst. where R and R' can be H or -CH₂ -CH₂ OH groups independently. As can be seen, when R = R' = H, the aminoalcohol (II) is the monoethanolamine and compound (I) obtained is the glycine (R₁ = R₂ = H). Likewise, when one of either R or R' is H and the other is -CH₂ -CH₂ OH, compound (II) is the diethanolamine and the compound (I) obtained is the iminodiacetic acid (one of either R₁ or R₂ is H and the other is -CH₂-COOH), and when R = R' = -CH₂ -CH₂OH, the compound (II) is triethanolamine and compound (I) obtained is nitrilotriacetic acid. The above reaction diagram n, can have the values 1, 2 or 3, respectively. Thus the invention process includes the oxidation of an aminoalcohol in formula (II) where R and R' can either be H or -CH₂-CH₂OH groups independently with O₂ or with a gas that contains O₂. The reaction can be carried out at temperatures ranging from 25ºC to 200ºC, preferably between 150ºC and 195ºC. It can take place at a partial O₂ pressure inside the reactor, at 20 Kg/cm², preferably between 2 and 13 Kg/cm². Water is used as a solvent, and an alkali metal hydroxide in a molar relation with respect to the hydroxide groups of the initial aminoalcohol (II) has been added, situated between 5% and 20% in stoichiometric excess, preferably between 5% and 10%. This means that from 1.05 to 1.10 moles of alkali metal hydroxide are used per mol of monoethanolamine, from 2.10 to 2.20 moles of the hydroxide per mol of diethanolamine and from 3.15 to 3.30 moles of alkali metal hydroxide per mol of triethanolamine. An alkali metal hydroxide can be used as long as the salts formed with the acids obtained are soluble in the reaction environment. It is preferable that these salts are soluble in water at a temperature of 80 - 95ºC. Sodium hydroxide and potassium hydroxide are examples of suitable alkali metal hydroxides. The initial concentration of the aminoalcohols (II) ranges between 20% and 35% in weight, with reference to the total initial weight of the components of the reaction mass, preferably between 30% and 35% in weight. Larger concentrations can cause yield losses as a result of diffusion of the oxidant gas, and lower concentrations reduce the productivity without improving the results. The catalyst used in the invention process is Copper-Raney, although it is also possible to use a Nickel-Raney catalyst if small modifications are made in the process. The Copper-Raney catalyst can be easily manufactured through leaching with sodium hydroxide in a reducing atmosphere of the alloy Al₂Cu, following the processes that have already been mentioned. The catalyst is added in amounts less than the 30% weight of the initial aminoalcohol (II) content, preferably between 15% and 30% in weight, although with an average percentage of 25%, it is possible to obtain excellent results. The oxidizing agent is oxygen or a gas containing oxygen such as air or synthetic air, no more than the minimum amount necessary being used to maintain the reaction of the above-mentioned partial pressure of O₂ (less than 20 Kg/cm²), and no more than the gas necessary should be used as a replacement. The time the reaction takes, operating in these conditions, ranges from 3.5 to 5.0 hours depending on the number of times the catalyst is used. The reaction is monitored by measuring the conversion of the initial aminoalcohol (II) and the appearance of the acetic acid derivative (I). Once the reaction is completed, the reaction environment is subjected to a filtration process under heat, at a temperature of between 80ºC and 95ºC, preferably between 85ºC and 90ºC, with a view to recovering the catalyst used, so that it can be regenerated and reused in successive reaction cycles. After this, the base solution in the reaction environment, that which contains the soluble alkali metal salts of the derivatives of the acetic acid, is subjected to an isolation and purification process so that the corresponding acids of formula (I) can be obtained. This treatment can be carried out either by chemical means, through crystalization of the reaction solution at temperatures ranging from 75ºC to 85ºC, preferably between 80ºC and 85ºC, of the reaction solution after it has been treated with hydrochloric acid, so as to obtain a pH of between 0.5 and 2.5, depending on the acid obtained, or by electrochemical means, applying the electrodialysis procedure referred to in the Spanish patent nº 9000130 (held by person who is applying for a patent for this invention). The present invention is clearly illustrated by the following examples, which should not be regarded as restrictive but simply serving as references, and which make it easier to understand the nature of the invention process. EXAMPLE 1 183 g of 97% sodium hydroxide; 300 g of demineralized water; 163.2 g of 98% diethanolamine; 64 g of Copper-Raney with a humidity level of 30%, which really means using 44.8 g of net-weight catalyst in the test, and finally 40 further g of demineralized water, to break down all the previous reagents, are all stirred into a stainless steel autoclave reactor (AISI 316) with a 1 litre capacity, and in the above-mentioned order. Then, and while still stirring, the heating process is started until 170ºC is reached and the pressure inside the reactor is 18 kg/cm². At this stage, the reactor is brought into contact with a shot of oxygen previously set at 18 kg/cm² so as to have the same pressure and making sure that the pressure is kept constant during the course of the process, the oxygen consumed being continually replaced. The suspension is continuously stirred for 3.5 hours. When this time has elapsed, the reaction is concluded, and it is cooled to 90ºC and filtered with suction with Buchner and Kitasato, regaining the humidity weight of 71.0 g of the copper catalyst, this being kept for successive reuse after regeneration. The reaction solution, once analyzed by chromotography, provides a 95% yield of free iminodiacetic acid in the form of disodium salt, and this can be easily isolated and purified either by crystalization at 85ºC and at pH≃2, or electrochemically using one of the electrodialysis processes mentioned before. The purification yield is quantitative (100%) using the isolation process and purification by electrodialysis. EXAMPLE 2 An experiment carried out with the same methodology as in Example 1, but using 201.25 g of 98.5% monoethanolamine; 144.3 g of 97% sodium hydroxide 338.15 g of demineralized water and 66.2 g of Copper-Raney with an approximate humidity of 25%, which amounts to 49.6 g in net weight. The temperature of the reaction was 155ºC and the duration 4.25 hours. The final yield of the reaction was 85.8% glycine. The isolation and purification in this case, was carried out by electrodialysis and a substantial purification yield was obtained.

Claims: Process for preparing acetic acid derivatives of general formula (I) where R₁ and R₂ are independently selected from H or -CH₂-COOH groups, or alkali metal salts thereof, characterized in that it comprises the following stages: a) oxidation of an aminoalcohol of formula (II) where R and R' are independently selected from H or -CH₂-CH₂OH groups; with oxygen or a gas that contains oxygen, and in the presence of an alkali metal hydroxide capable of forming salts which are soluble in water at a temperature of 80ºC - 95ºC with the desired derivatives of the acetic acid (1), demineralized water and a Copper-Raney catalyst, and thereafter, if appropriate, b) isolation and purification of the free acid (I) either by chemical or electrochemical means. Process of claim 1, characterized in that the amount of catalyst is between 15% and 30% by weight, based on the weight of the initial aminoalcohol (II) present in the reaction environment. Process of claim 1, characterized in that the alkali metal hydroxide is sodium hydroxide or potassium hydroxide. Process of claim 1, characterized in that the temperature of the oxidation reaction is between 25°C and 200°C. Process of claim 4, characterized in that the oxidation reaction is carried out at a temperature of between 150ºC and 195ºC. Process of claim 1, characterized in that the partial pressure of oxygen is between 2 and 20 kg/cm². Process of claim 6, characterized in that the partial pressure of oxygen is between 2 and 13 kg/cm². Process of claim 1, characterized in that the initial aminoalcohol (II) is monoethanolamine and the end-product obtained is the glycine or a salt thereof. Process of claim 1, characterized in that the initial aminoalcohol (II) is diethanolamine and the end-product obtained is iminodiacetic acid or a salt thereof. Process of claim 1, characterized in that the initial aminoalcohol (II) is triethanolamine and the end-product obtained is nitriloacetic acid or a salt thereof.

Inventors: DE DIEGO ZORI ASUNCION, MARTIN RAMON JUAN LUIS, OCHOA GOMEZ JOSE RAMON, SANCHEZ SANCHEZ JOSE MIGUEL, DE DIEGO ZORI, ASUNCION, MARTIN RAMON, JUAN, LUIS, OCHOA GOMEZ, JOSE, RAMON, SANCHEZ SANCHEZ, JOSE, MIGUEL, de Diego Zori, Asunción, OCHOA GOMEZ, José, Ramón, SANCHEZ SANCHEZ, José, Miguel
Applicants: MONSANTO CO, MONSANTO COMPANY
Application year: 1991
Main classification: C07C227
IPC codes: C07C229, C07C227