Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus acids or salts thereof
Reexamination Certificate
1999-03-23
2001-02-27
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus acids or salts thereof
C562S008000
Reexamination Certificate
active
06194604
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the preparation of oxyacids of phosphorus and esters thereof, and more particularly to novel and improved processes for the preparation and recovery of oxyacids, especially phosphorous acid.
Phosphorus-containing compounds such as oxyacids of phosphorus, organophosphates and organophosphites are important precursors for the synthesis of other phosphorus species, which have various applications, for example, in herbicides, insecticides, fertilizers, flame retardants and plasticizers. The syntheses of such oxyacids of phosphorus, organophosphates and organophosphites have commonly used a halogen derivative of phosphorus, such as PCl
3
or POCl
3
, as a starting material. Nevertheless, since the halogen derivatives are themselves prepared from elemental phosphorus, an economic advantage could be gained by preparing oxyacids of phosphorus, organophosphates and organophosphites directly from elemental phosphorus. Such direct preparation could also provide environmental benefits by avoiding the use of halogen-containing phosphorus starting materials and production of halogen-containing byproducts.
White phosphorus, the elemental phosphorus allotrope also referred to as yellow phosphorus or tetraphosphorus (P
4
), is a potential starting point for the synthesis of a variety of phosphorus species. The tetrahedral structure of white phosphorus contains six phosphorus-phosphorus bonds and can provide a large number of reactive species having an intermediate existence in phosphorus reactions. The competition of these reactive species for the organic reactants, however, can give complex reaction mixtures with low yields of desired products.
Various references have disclosed processes for the aerobic oxidation of white phosphorus in the presence of alcohols, but the reported processes have not provided an economical procedure for obtaining desirable phosphorus-containing compounds with high yield and purity. For example, Ernsberger et al. (U.S. Pat. No. 2,661,364) describes a process for preparing dialkylphosphite wherein oxygen is introduced into a mixture of small cut-up pieces of white phosphorus and a monomeric, saturated alcohol exemplified by ethanol, n-butanol, n-propanol, isopropanol and n-hexanol. Ernsberger et al. indicates that the various reaction products are isolated from the reaction mixture by conventional techniques, e.g., removal of phosphorous acid by aqueous extraction and recovery of alcohol by distillation. Ernsberger et al. further state that some dialkylphosphites are too unstable to be separated by distillation and may be used without isolation from the reaction mixture.
Kellerman et al. (British Patent No. 1,112,976) describes a process for producing organophosphorus compounds by reaction of white phosphorus, oxygen and a hydrocarbon compound containing at least one phenolic hydroxy group, a hydrocarbon compound containing more than one alcoholic hydroxy group, or a hydrocarbon containing a thiol group, to produce a mixture of esters of oxyacids of phosphorus in which the overall oxidation state of phosphorus is substantially 4. The Kellerman et al. process may take place in an inert organic solvent. The product of the Kellerman et al. process is a viscous mixture of non-isolated esters of oxyacids of phosphorus.
Okamoto et al.,
Yukagaku
19(10):968-72 (1970) (translated) describes a process for preparing diethylphosphite by reacting white phosphorus, oxygen and ethanol, after which excess ethanol is removed by vacuum distillation to obtain a 43% yield of diethylphosphite. The reaction was also performed in water and carbon tetrachloride.
A need has remained in the art for improved processes for the preparation of oxyacids, and in particular for improved methods of separating mixtures that contain phosphorus oxyacids, organophosphites and/or organophosphates. There is a further need in the art for a process that directly converts phosphorus, most preferably white phosphorus, to oxyacids of phosphorus, organophosphates and/or organophosphites, wherein the various desired products are obtained in high yield and purity and with economical isolation techniques. There is also a need for such a process that is environmentally safe, preferably by using low levels of solvents and avoiding the use of halogen-containing starting materials.
SUMMARY OF THE INVENTION
Among the several objects of the present invention may be noted the provision of an improved process for the preparation of oxyacids of phosphorus; the provision of a process for separation of oxyacids from mixtures of oxyacids and esters thereof; the provision of a process for selectively converting esters of phosphorous acid to phosphorous acid; the provision of a process for separating, and/or for producing and separating, phosphorous acid from mixtures of phosphorous acid, phosphite esters, phosphoric acid, and phosphate esters; the provision of a process for isolating phosphorous acid from mixtures comprising phosphorous acid and phosphoric acid; the provision of a process in which phosphite esters and hypophosphorous acid are both converted to and recovered as phosphorous acid; and the provision of a process for separation of phosphorous acid from mixtures comprising phosphorous acid and hypophosphorous acid.
Briefly, therefore, the present invention is directed to a process for the preparation of phosphorous acid. The process comprises oxidizing a substrate selected from the group consisting of elemental phosphorus and a P(I) species to produce P(III) and P(V) oxidation products; esterifying the oxidation products by reaction with an alcohol; and selectively hydrolyzing phosphorous acid esters produced by the esterification, thereby producing a hydrolysis reaction mixture containing phosphorous acid and phosphate esters(s).
The invention is further directed to a process for the preparation of phosphorous acid comprising oxidizing a substrate selected from the group consisting of elemental phosphorus and a P(I) species in the presence of an alcohol in a condensed phase reaction medium containing not more than about 5% by weight water, to produce an oxidation reaction mixture comprising P(III) and P(V) oxidation products selected from the group consisting of alkyl esters of phosphorous acid, alkyl esters of phosphoric acid, phosphorous acid, phosphoric acid and mixtures thereof. The phosphorous acid esters produced in the oxidation reaction mixture are selectively hydrolyzed to produce a hydrolysis reaction product containing alkyl phosphates and phosphorous acid.
The invention is further directed to a process comprising oxidizing a substrate selected from the group consisting of elemental phosphorus and a P(I) species in the presence of an alcohol in a condensed phase reaction medium while removing water from the reaction medium to produce an oxidation reaction mixture comprising P(III) and P(V) oxidation products selected from the group consisting of alkyl esters of phosphorous acid, alkyl esters of phosphoric acid and mixtures thereof. The phosphorous acid esters produced in the oxidation reaction mixture are selectively hydrolyzed, thereby producing a hydrolysis reaction mixture containing alkyl phosphate esters and phosphorous acid.
The invention is further directed to a process for the preparation of phosphorous acid comprising oxidizing a substrate selected from the group consisting of phosphorus and a P(I) species in the presence of an alcohol to produce an oxidation reaction mixture comprising P(III) and P(V) oxidation products selected from the group consisting of phosphorous acid, alkyl esters of phosphorous acid, phosphoric acid, and alkyl esters of phosphoric acid. Water is removed from contact with the oxidation products to promote formation of alkyl esters of phosphorous acid and alkyl esters of phosphoric acid, inhibit hydrolysis thereof, and yield a mixture comprising said esters. Phosphorous acid esters of the ester mixture are selectively hydrolyzed to produce a hydrolysis reaction mixture containing alkyl phosphates and phosphorous ac
Heise Jerald D.
Ma Yinong
Monsanto Company
Senniger Powers Leavitt & Roedel
Vollano Jean F.
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