|Title of Invention||
A METHOD FOR THE PRODUCTION OF A SALT OF CARBOXYLIC ACID
|Abstract||A method for the production of a such of carboxylic acid by catalytic dehydrogenation effected by reacting the corresponding primary alcohol in aqueous solution with a alkaline hydroxide in the present of a copper catalyst, in which, before to catalyst dehydrograiation, the mass of the reagents comprising the said aqueous solution of primary alcohol is subjected to a deoxygenating stage in order to remove or reduce it level of dissolved molecular oxygen. The deoxygenating stage is preferably carried oi by bubbling an inert gas or by adding a reducing agent.|
The present invention relates to a method for the preparation of salts of carboxylic acids and, particularly, salts of amino carboxylic acids, by means of catalytic dehydrogenation effected by reacting the corresponding primary alcohol with an alkaline metal hydroxide in the presence of a copper catalyst.
The salts of the carboxylic acids have numerous applications in many fields; many salts, transformed into the corresponding acids, are used as primary materials in the preparation of pharmaceutical products, agrochemical products and pesticides.
The salts of amino carboxylic acids, such as glycine salts, iminodiacetic acid salts and nitriltriacetic acid salts, are of particular interest.
United States Patent Number 4,782,183 in the name Goto et al describes a method for preparing salts of amino carboxylic acids in which the corresponding amino alcohol is subjected to the action of alkaline metal hydroxides in the presence of a Raney copper catalyst.
Although the use of Raney copper as a catalyst has substantial economic advantages in comparison with the use of noble metal catalysts, an inherent problem with its use lies in the fact that it rapidly becomes poisoned; it has, in fact, been observed that the activity of the copper-based catalyst decreases with repeated use, rapidly increasing costs to economically unacceptable levels.
International patent application no. WO92/06069 describes a method for the production of salts of glycine, iminodiacetic
acid and nitriltriacetic acid in which monoethanolamine, diethanolamine or triethanolamine are brought into contact with an alkaline metal hydroxide in the presence of a Raney copper catalyst, and in which the catalyst is regenerated after each use by treatment with formic acid.
United States Patent Nos. 5,292,936 and 5,367,112, both in
the name of Frenzy, describe a method for catalytic
dehydrogenation using a Raney copper catalyst treated in an
addition reaction using particular metals, such as chrome,
titanium and molybdenum; in this way, it is possible to
prolong significantly the life of the catalyst,' thus making
its use in the industrial production of salts of carboxylic
acids economically advantageous. i
Other known processes utilize Raney copper as a catalyst in oxidative processes. In particular. United States Patent No. 5,225,592 describes a method for the production of salts of amino carboxylic acids by means of the oxidation of the corresponding alcohol in the presence of alkaline hydroxide and Raney copper with molecular oxygen, or a gas containing molecular oxygen, in which the oxygen partial pressure in the reactor is maintained between approximately 2 to 20 kg/cm2.
Similarly, EP-B-0 506 973 describes a method for the production of salts of amino carboxylic acids by means of the oxidative dehydrogenation of the amino alcohol with a copper catalyst with the addition to the reaction medium of aluminium or an aluminium- containing compound.
An object of the present invention is to provide a method that is simple from the operative point of view, and particularly advantageous from the economical point of view, which prolongs the life of the catalyst, maintaining the high activity thereof even after several teas of recycling.
Another object of the invention is to provide a method which enables the economical use of a commercial Raney copper oatatyst, which enables the advantageous conversion of amino alcohols of industrial interest into the corresponding carboxylic acids in salt forms.
Accordingly the present invention provides a method for the production of a salt of carboxylic acid such as herein described by catalytic dehydrogenation effected by reacting the corresponding primary alcohol such as herein described in aqueous solution with an alkaline hydroxide in the presence of a copper catalyst, to obtain salt of carboxylic acid characterised in that, before the catalytic dehydrogenation, the mass of reagents comprising the said aqueous solution of primary alcohol is subjected to deoxygenating to reduce the level of dissolved molecular oxygen to less than 0.3 ppm.
The primary alcohols that can be used as starting products in the process of the present invention can be aliphatic, cyclic or aromatic alcohols, and are those that are known to the experts in the field. The toddy requirement that the alcohol and the corresponding carboxylic acid must satisfy is for both to be stable under the severe conditions in which the process of the invention Is conducted.
In particular, the method is applicable to primary amino alcohols, represented by the formula (1):
in which n is between 2 and 10, and
R1and R2, independently of each other are preferably chosen from the group
comprising hydrogen, -CH2CH2OH, -CH2COOH,
alkyls having from 1 to 6 carbon atoms and phosphonomethyl.
If R1 is hydrogen and R2 is -CH2-CH2OH, the product resulting from the conversion of the amino alcohol is the salt of iminodiacetic acid.
Typically, the process is carried out by ^ introducing an
aqueous solution of the primary alcohol, an .alkaline
hydroxide and the appropriate quantity of Raney copper
catalyst into a nickel autoclave. .
The autoclave, which has a controllable discharge valve, is taken to the predetermined temperature, generally; between 100° and 220°C, at which the alcohol is converted to the salt of the corresponding carboxylic acid according to the reaction (2) which, by way of example, refers to the conversion of diethanolamine:
After sufficient time to enable the completion of the reaction, the reaction mass is filtered to recover ■ the catalyst which is then recycled in a subsequent reaction.
As is illustrated in the following comparative example 1, in
the absence of special precautions, the activity of the Raney
copper decreases fairly rapidly and, within six or seven
recyclings, in substantially the same time, the yield falls
from 98% to approximately 67%*.
According to the invention, it has been found that by eliminating or strongly reducing the presence of the
dissolved oxygen in the reagents, the activity of the
catalyst decreases surprisingly more slowly,; so that the same
catalyst can be reused many tens of times with a limited loss
The elimination of the oxygen, or its substantial reduction, can be achieved using physical or chemical means.
The physical elimination is effected by means of stripping, for example, by bubbling an inert gas or water' vapour, preferably helium or nitrogen, through the aqueous solution of the primary alcohol. This operation is preferably carried out immediately before loading the solution in the autoclave which is then preferably, immediately, cleansed with repeated vacuum/nitrogen cycles.
The bubbling time of the inert gas and the insufflation capacity necessary to reduce the level of dissolved oxygen to levels that will prolong the life of the catalyst depend on the efficiency of the bubbling system used, and can be determined by a technical expert in the field by prior testing.
A level of dissolved oxygen less than 0.2-0.3 ppm is particularly preferred.
The chemical removal is effected by means of the addition of appropriate quantities of reducing substances to the aqueous solution of the primary alcohols. The aforesaid reducing substances can be organic or inorganic, although they must be soluble in the reaction mass and such that they do not interfere with the progress of the reaction.
By way of non-limitative example, reducing substances such as sodium formiate can advantageously be used.
The quantity of reducing agent added to the reaction mass is preferably between 0.1 and 0.5% by weight, with reference to the total reaction mass.
The quantity of catalyst used to convert the alcohol can vary
from 1 to 70% by weight with respect to the alcohol, and
preferably from 10 to 40% by weight. These percentages are
calculated with respect to the dry content of Raney cbpper in
its aqueous formulation. j
The alkaline metallic hydroxides used in the method are those known to the experts in the field. The quantity of hydroxide is at least equal to one equivalent per equivalent of hydroxyl groups present in the alcohol utilised in the reaction. Sodium hydroxide and potassium hydroxide are preferred because of their availability and economy.
The temperature at which the process is conducted is preferably between 150° and 200°C; the pressure is generally between 5 and 50 kg/cm^ and preferably between 8 and 12 kg/cm^.
The pressure control valve is set depending on the vapour pressure of the water at the predetermined reaction temperature in order to enable the hydrogen that forms during the reaction to be easily discharged.
The invention will now be described in greater detail in the following examples, given purely by way of non-limitative example.
Example 1 (comparative)
This example illustrates the performance of the catalyst used
without special precautions for protecting its activity.
40 g of diethanolamine (0.38 moles), 85 g of water, 32 g of NaOH in drops (0.80 moles) and 16 g of commercially-available Raney copper containing 50% of water were introduced into a 500 ml nickel autoclave provided with a magnetically driven mechanical stirrer. The autoclave was closed/ cleansed three times with a vacuum/nitrogen, kept under agitation and heated to a temperature of 170°C. The pressure was allowed, to rise and was held at 9 kg/cm2 by adjusting the appropriate discharge valve of the autoclave.
Except for the first two cycles, the reaction was interrupted after a fixed time period of 4.5 hours and the mass analysed to determine the yield of disodium imminodiacetate. The catalyst, separated by filtration from the reaction mass, was reused in a subsequent reaction.
Table 1 shows the results of the tests.
TABLE 1 - Yield using unprotected catalyst
The example illustrates the use of the catalyst in the case of reduction of the presence of oxygen by physical means (degassing).
125 g of an aqueous solution of diethanalamine containing 40 g of diethanolaraine (0.38 moles) were added to a 500 ml nickel autoclave provided with a magnetically' driven mechanical stirrer. This solution was prepared by weighing the appropriate quantity of the two components ' of the solution into a flat-bottomed conical flask and then bubbling the solution with helium using a diffuser for five minutes. Then, 32 g of NaOH in drops (0.8 moles) and 16 g of commercially-available Raney copper containing 50% of water were added to the autoclave. The autoclave was closed, cleansed rapidly three times using a vacuum/nitrogen, kept under agitation and heated to 170°C.
The pressure was allowed to rise and was held at 9 kg/cm^, by controlling the appropriate discharge valve of the autoclave. When the production of hydrogen stopped, the reaction was stopped and the mass was analysed to determine the yield of disodium imminodiacetate. The catalyst, separated by filtration from the reaction mass, was kept in water degassed using helium awaiting its reutilisation in a subsequent reaction.
Table 2 shows the results of the tests.
The example illustrates the use of the catalyst in the case of reduction of the presence of oxygen by chemical means, by adding sodium formiate.
The procedure described in example 2 was followed except for the fact that instead of degassing the reagents using helium, 0.3 g of sodium formiate was added to the reaction mass for each cycle.
Table 3 shows the results of the tests.
TABLE 3 - Reaction with the addition of sodium formiate
1. A method for the production of a salt of carboxylic acid such as herein described by catalytic dehydrogenation effected by reacting the corresponding primary alcohol such as herein described in aqueous solution with an alkaline hydroxide in the presence of a copper catalyst to obtain salt of carboxylic add characterised in that before the catalytic dehydrogenation, the mass of reagents comprising the said aqueous solution of primary alcohol is subjected to deoxygenating to reduce the level of dissolved molecular oxygen to less than 0.3 ppm.
2. The method according to claim 1, wherein the said deoxygenating is effected by bubbling an inert gas or water vapor.
3. The method according to claim 2, wherein the inert gas is helium or nitrogen.
4. The method according to claim I, wherein the deoxygenating is effected by adding a reducing agent to the mass of reagents.
5. The method according to claim 4, wherein the reducing agent is sodium format.
6. The method according to any one of the preceding claims from I to 5, wheretn the said primary alcohol is a compound of the formula:
in which n is an integer between 2 and 10, and
R1 and R2, independently of each other are preferably chosen from the group comprising hydrogen, -CH2CH2OH, -CH2COOH, alkyls having from 1 to 6 carbon atoms and phosphomethyl.
7. The method according to any one of the preceding claims, wherein the catalytic dehydrogenation is carried out at a pressure of between 5 and 20 kg/cm2, and at a temperature of between 100 and 220°C.
8. The method according to any one of the preceding claim, wherein the alkaline hydroxide is chosen from sodium hydroxide and/or potassium hydroxide, the said hydroxide being utilized in a quantity equal to at least one equivalent per equivalent hydroxyl group print in the primary alcohol.
9. The method according to any one of the preceding claims, in which the catalyst is Raney copper and is utilized in a quantity of from 10 to 40% by weight with respect to the alcohol, the said percentage being calculated with respect to the dry content of Raney copper.
10. A method for the production of a salt of carboxylic acid, substantially as herein described and exemplified.
|Indian Patent Application Number||332/MAS/1999|
|PG Journal Number||36/2010|
|Date of Filing||22-Mar-1999|
|Name of Patentee||FINCHIMICA SPA,|
|Applicant Address||VIA LAZIO 13, I 25025 MANERBIO (BRESCIA)|
|PCT International Classification Number||C07C99/00|
|PCT International Application Number||N/A|
|PCT International Filing date|