Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
1999-10-12
2001-01-23
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S063000, C556S148000, C534S016000
Reexamination Certificate
active
06177581
ABSTRACT:
The present invention relates to mixed-metal chelates and a process for the preparation thereof.
BACKGROUND OF THE INVENTION
Compositions containing two or more different metals have found use in several areas. Sometimes the compositions themselves can act as catalysts; more often, they behave as catalyst precursors, being transformed into active catalysts by reduction to give alloys or thin films or by oxidation (calcination) to give mixed-metal oxides. These oxides may behave as ceramics as well as catalysts. Often, these mixed-metal compositions are simple mixtures of single-metal compounds. Reduction or calcination of such mixtures can give non-homogeneous products because of incomplete mixing of the compounds, resulting in monometallic domains. When possible, it is advantageous to use as precursors unique compounds containing the desired metal ratio, because the metals will be intimately mixed, even at the molecular level.
Mixtures of metals have other uses, as well. For example, iron, zinc, and magnesium are found in agricultural nutrient formulations, whereas iron, zinc, chromium, cobalt, and calcium are found in animal and human dietary supplements. Routinely, these sorts of formulations contain mixtures of compounds, each compound containing one of the desired metals. To reduce the amount of ancillary organic material in these formulations, it can be advantageous to provide two or more metals in a single compound, thereby increasing the percentage of metals vis-{grave over (a)}-vis the organic ligands.
Iron chelates are a class of compounds that have found use in natural gas treating, photographic bleaching, fertilizers, and dietary supplements. Routinely, said iron chelates are used as ammonium or alkali metal salts. In such cases, the alkali metal or ammonium ion provides charge balance but otherwise imparts no useful properties to the iron chelate. For example, sodium ferric ethylenediaminetetraacetate (NaFeEDTA) has been used for iron fortification in foods. The iron provided is beneficial, but the sodium is possibly hazardous to those people requiring a low-sodium diet. On the other hand, iron chelate complexes with calcium can potentially be used to provide the dietary benefits of both metals.
Because of its tetravalent nature, ethylenediamine-tetraacetic acid (EDTA) can conceivably combine with a divalent and a trivalent metal to form complexes of the general formula M(II)M′(III)EDTA(OH).xH
2
O. To our knowledge no such mixed-metal complexes of EDTA have been reported in the literature.
The calcium salt of the ferric chelate of a similar ligand, hydroxyethylethylenediaminetriacetate (HEDTA), was reported as an amorphous, red solid (without analytical data) by Schugar, et al. in J. Amer. Chem. Soc., 89, 3712 (1967).
There is clearly a need for transition metal chelate, particularly iron chelate, complexes with calcium which can be used to provide the dietary benefits of both metals.
The present invention offers such transition metal chelate complexes with calcium and a process for their preparation.
SUMMARY OF THE INVENTION
In one aspect the present invention relates to mixed-metal chelates represented by the following general formula
CaM(III)EDTA(OH).xH
2
O
wherein M is a trivalent transition metal and x is 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8.
In another aspect the present invention relates to a process for preparing mixed-metal chelates of the general formula CaM(III)EDTA(OH).xH
2
O, wherein M is a transition metal and x is 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8, said process comprising the steps of a) reacting calcium hydroxide or calcium oxide, ethylenediaminetetraacetic acid, and a transition metal-containing material in an aqueous medium, optionally in the presence of an oxidant to convert any transition metal present in a divalent form to its trivalent form; and b) separating the formed mixed-metal chelate by filtration or evaporation.
DETAILED DESCRIPTION OF THE INVENTION
In the context of the present invention, the general formula CaM(III)EDTA(OH).xH
2
O is an empirical formula and is intended to include structures of higher nuclearity, such as, for example, Ca
2
[M(III)
2
(EDTA)
2
O].xH
2
O. The amount of water of hydration, “x”, is dependent both on M and the conditions of preparation.
For the purposes of this invention, the term transition metal includes the metals of the lanthanide series. The transition metal contemplated by the foregoing general formula may be any transition metal that can obtain a stable trivalent state, including, but not limited to, iron, manganese, cobalt, chromium, yttrium, and ruthenium. Iron is preferred.
The general reaction process comprehends the production of a mixed-metal chelate of the general formula CaM(III)EDTA(OH).xH
2
O, wherein M is a trivalent transition metal and x is as defined hereinbefore, by the steps of a) reacting calcium hydroxide or calcium oxide, ethylenediaminetetraacetic acid, and a transition metal-containing material in an aqueous medium, optionally in the presence of an oxidant to convert any transition metal present in a divalent form to its trivalent form; and b) removing water by evaporation.
In a straightforward reaction, a water-soluble salt of the trivalent transition metal is reacted with calcium hydroxide and EDTA according to the following equation:
2MX
3
+5Ca(OH)
2
+2H
4
EDTA→2CaMEDTA(OH)+3CaX
2
+8H
2
O (1)
wherein M is a transition metal, X is an inorganic or organic anion and H
4
EDTA is used to distinguish the free acid from the tetraanion. When the calcium salt of X
−
is soluble (e.g., X
−
is Cl
−
, NO
3
−
, CH
3
COO
−
), the bimetallic complex can, in principle, be separated by precipitation or crystallization. When the complex is crystallized from aqueous solution, water may be included in the crystals, either bound directly to one or both of the metals or held in by lattice forces. The amount of water of crystallization will be dependent on solution pH, temperature, and the metals, among other things. Sometimes water can be driven off at high temperature or under vacuum, providing other stoichiometric hydrates or anhydrous materials.
Many transition metals (e.g., Fe, Co, Mn, Ru, etc.) form stable divalent ions as well as trivalent ones. With the addition of an oxidant, the divalent salts of these metals can also be reacted with calcium hydroxide and EDTA to give the same type of bimetallic product:
MX
2
+2Ca(OH)
2
+H
4
EDTA+{fraction (
1
/
2
)}H
2
O
2
→CaMEDTA(OH)+CaX
2
+4H
2
O (2)
Because of its powerful chelating ability for many transition metal ions, aqueous slurries of EDTA are often able to dissolve metal oxides. For example, partially ammoniated slurries of EDTA are commonly reacted with Fe
3
O
4
to form ferric EDTA solutions used in the photographic industry. Metal oxides can likewise be used to prepare CaMEDTA(OH) solutions according to the following reactions:
MO+Ca(OH)
2
+H
4
EDTA+{fraction (
1
/
2
)}H
2
O
2
→CaMEDTA(OH)+3H
2
O (3)
M
2
O
3
+2Ca(OH)
2
+2H
4
EDTA→2CaMEDTA(OH)+5H
2
O (4)
M
3
O
4
+3Ca(OH)
2
+3H
4
EDTA+{fraction (
1
/
2
)}H
2
O
2
→3CaMEDTA(OH)+8H
2
O (5)
wherein M is a transition metal.
Oxidants other than hydrogen peroxide may be employed. A potential advantage to the metal-oxide route is that there is no concomitant formation of calcium salt by-products.
The elemental transition metal may also be used. EDTA will chelate the metal and oxidize it to the divalent state; another oxidant can complete the oxidation to the trivalent state:
M+Ca(OH)
2
+H
4
EDTA+{fraction (
1
/
2
)}H
2
O
2
→CaMEDTA(OH)+H
2
+2H
2
O (6)
Inasmuch as calcium oxide is converted to calcium hydroxide in aqueous medium, the oxide may replace the hydroxide as the calcium source. The transition metal may be any one that can obtain a stable trivalent state, includi
Nazario-Gonzalez Porfirio
The Dow Chemical Company
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