Chemistry of inorganic compounds – Phosphorus or compound thereof
Reexamination Certificate
1999-12-14
2002-08-27
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Phosphorus or compound thereof
C423S304000, C423S316000
Reexamination Certificate
active
06440380
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the preparation of phosphorus oxides and lower hydrides of phosphorus, and particularly to novel processes for the preparation of phosphorus (I) species and phosphorus (III) species.
BACKGROUND OF THE INVENTION
Phosphorus (I) oxides (P(I) oxides) and phosphorus (III) oxides (P(III) oxides), including oxyacids of phosphorus, are important precursors for the synthesis of other phosphorus species having various applications. Applications for such phosphorus oxides include use in herbicides, insecticides, fertilizers, flame retardants, and plasticizers.
Phosphorous acid (H
3
PO
3
), a P(III) oxide, is manufactured by hydrolyzing a halogen derivative of phosphorus, such as phosphorus trichloride (“Properties and Chemistry of Phosphorus and Its Compounds,”
Encyclopedia of Chemical Technology
, Vol. X, Interscience Encyclopedia, Inc., pp. 403-510, 1953, herein incorporated by reference). Hydrolysis of the phosphorus halogen derivatives produces undesired waste streams, such as sodium chloride, which are difficult and expensive to eliminate.
Hypophosphorous acid (H
3
PO
2
, a P(I) oxide) and hypophosphite salts are made by the oxidation of white phosphorus in the presence of base. For example, hypophosphites are prepared by contacting white phosphorus with a boiling lime slurry. Additionally, by-products of this reaction are calcium phosphite and calcium sulfate, which must be separated from the hypophosphite (
Kirk
-
Othmer Concise Encyclopedia of Chemical Technology
, John Wiley & Sons, New York, 1985, p. 874, herein incorporated by reference). A limitation to this method is that elemental phosphorus starting material is pyrophoric and poses a safety and handling hazard.
Phosphine (PH
3
) and other lower hydrides of phosphorus are strong electron pair donors and are frequently used in the manufacture of semiconductors. In other applications, they are often used as ligands in catalysts and to increase the solubility of metals in various liquid media. Phosphine is manufactured by hydrolyzing a metal phosphide such as Ca
3
P
2
or AlP. Alternatively, it may be made by reacting elemental phosphorus with water under acid- or base-catalyzed conditions (“Properties and Chemistry of Phosphorus and Its Compounds,”
Encyclopedia of Chemical Technology
, Vol. X, pp.403-510). These routes to phosphine are problematic because the starting materials can spontaneously combust and are toxic.
Phosphoric acid (H
3
PO
4
) is a potential starting point for the synthesis of a variety of phosphorus species. However, the phosphorus in phosphoric acid has a high oxidation state and high thermochemical stability. This stability has to this time made the large-scale conversion of phosphoric acid and other phosphorus (V) species (P(V) species) such as phosphorus pentoxide or phosphorus pentasulfide to phosphorus species of lower oxidation states generally unfeasible from an economic perspective. The hydrogen reduction of trace levels of calcium phosphate in iron ore at 600-1300° C. to elemental phosphorus and to phosphine gas is reported by Ezz and Shehata,
J. Chem. U.A.R
. (1967), 10(1), 97-107 (herein incorporated by reference). However, that reaction is limited by its inability to stop the reduction at P(I) or P(III) oxidation states. It is further limited by the low concentrations of starting material and products.
SUMMARY OF THE INVENTION
Among the several embodiments of the present invention is a process for the manufacture of lower oxyacids of phosphorus, especially phosphorous acid and hypophosphorous acid. One embodiment of the present invention is a process for the preparation of P(I) species, P(III) species, and lower hydrides of phosphorus, wherein the process comprises contacting a P(V) species with a reducing agent in the presence of a catalyst effective to promote reduction of the P(V) species by reaction with a reducing agent. Preferably the reducing agent comprises hydrogen.
In a preferred embodiment, the present invention is a process for the preparation of hypophosphorous acid, phosphorous acid, or mixtures thereof, wherein the process comprises contacting phosphoric acid, a phosphate salt, a polymeric phosphate, or a phosphoric acid anhydride with a reducing agent in the presence of a catalyst effective to promote reduction of the phosphoric acid, phosphate salt, polymeric phosphate, or phosphoric acid anhydride by reaction with a reducing agent. Preferably the reducing agent comprises hydrogen.
In another embodiment, the invention also includes a composition effective for use in the manufacture of lower oxyacids or lower hydrides of phosphorus. The composition comprises a mixture containing a P(V) species and a catalyst effective to promote reduction of the P(V) oxide or sulfide to a P(I) species, P(III) species, or lower hydrides of phosphorus by reaction with a reducing agent, preferably hydrogen.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. However, it should be understood that the following detailed description and examples, while indicating preferred embodiments of the invention, are given by way of illustration only since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An economic and environmental advantage could be realized by preparing phosphorous acid directly from phosphorus (V) oxides (P(V) oxides) such as phosphate, phosphoric acid, or phosphorus pentoxide (P
2
O
5
). Direct preparation from P(V) oxides could provide environmental benefits by avoiding the use of halogen-containing phosphorus starting materials and production of halogen-containing by-products.
Furthermore, it would be economically advantageous if hypophosphorous acid can be prepared directly from inexpensive and stable starting materials without the additional step of separation of hypophosphorous acid from phosphite by-products. It would also be advantageous to have an economically feasible method of preparing hypophosphorous acid which does not involve handling highly caustic materials such as boiling lime and does not use unstable pyrophoric starting materials such as white phosphorus.
A cost-effective route to phosphine which uses thermochemically stable starting materials having relatively low toxicity would be particularly advantageous.
P(V) species such as phosphoric acid, its salts, polymers, anhydrides, and sulfur derivatives are inviting starting materials for the preparation of other phosphorus species. The P(V) species are abundant and relatively inexpensive. Phosphoric acid and its salts are thermochemically very stable and have very low toxicity.
A need exists for a convenient, environmentally-compatible, safe, and cost-effective process for the reduction of P(V) species to P(I) species, P(III) species, or lower hydrides of phosphorus. A process which addresses these needs is now disclosed. Among the several embodiments of the present invention is a process for the manufacture of lower oxyacids of phosphorus, especially phosphorous acid and hypophosphorous acid.
The following detailed description is provided to aid those skilled in the art in practicing the present invention. Even so, this detailed description should not be construed to unduly limit the present invention as modifications and variations in the embodiments discussed herein can be made by those of ordinary skill in the art without departing from the spirit or scope of the present invention.
The contents of each of the references cited herein, including the contents of the references cited within these primary references, are herein incorporated by reference in their entirety.
a. Definitions
The following definitions are provided in order to aid the reader in understanding the detailed description of the present invention:
“P(V)” means a phosphorus atom which is in the +5 valence state.
“P(V) species” means a compound or ion which compris
Heise Jerald D.
Sall Erik D.
Bos Steven
Monsanto Technology LLC
Schaper Joseph A.
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