Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-03-17
2001-05-29
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S539000, C562S553000, C562S571000, C562S572000
Reexamination Certificate
active
06239312
ABSTRACT:
The present invention relates to a method for the preparation of salts of carboxylic acids and, particularly, salts of aminocarboxylic 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 aminocarboxylic acids, such as glycine salts, iminodiacetic acid salts and nitriltriacetic acid salts, are of particular interest.
U.S. Pat. No. 4,782,183 in the name Goto et al describes a method for preparing salts of aminocarboxylic 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.
U.S. Pat. Nos. 5,292,936 and 5,367,112, both in the name of Franczyk, 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.
Other known processes utilise Raney copper as a catalyst in oxidative processes. In particular, U.S. Pat. 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/cm
2
.
Similarly, EP-B-0 506 973 describes a method for the production of salts of aminocarboxylic 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 tens of recyclings.
Another object of the invention is to provide a method which enables the economical use of a commercial Raney copper catalyst, which enables the advantageous conversion of amino alcohols of industrial interest into the corresponding carboxylic acids in salt form.
The invention provides a method for the production of a salt of carboxylic acid by catalytic dehydrogenation effected by reacting the corresponding primary alcohol in aqueous solution with an alkaline hydroxide in the presence of a copper catalyst, characterised in that, before the catalytic dehydrogenation, the reaction mass comprising the said aqueous primary alcohol solution is subjected to a deoxygenation stage for the removal or reduction of the level of dissolved molecular oxygen.
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 only 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
R
1
and R
2
, independently of each other, are preferably chosen from the group comprising hydrogen, —CH
2
—CH
2
OH, —CH
2
—COOH, alkyls having from 1 to 6 carbon atoms and phosphonomethyl.
If R
1
is hydrogen and R
2
is —CH
2
—CH
2
OH, 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 of activity.
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
itrogen 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 formate 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 copper in its aqueous formulation.
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 avai
Conti Gianna
Villanti Alberto
Deemie Robert W.
Finichimicia S.p.A.
Geist Gary
Kramer Levin Naftalis & Frankel LLP.
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