Chemistry of inorganic compounds – Phosphorus or compound thereof – Halogen containing
Patent
1993-10-07
1995-02-28
Langel, Wayne
Chemistry of inorganic compounds
Phosphorus or compound thereof
Halogen containing
C01B 2510
Patent
active
053935063
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for manufacturing alkali monofluorophosphate of the formula M.sub.2 PO.sub.3 F. Alkali monofluorophosphates, such as potassium fluorophosphate, are used as fluorine carriers in toothpastes or drinking water. Alkali monofluorophosphates also have a fungicidal and insecticidal effect and are therefore also used in wood preservatives. Furthermore, alkali monofluorophosphates are valuable intermediate products for the manufacturing of other monofluorophosphate compounds which, for their part, are used in wood preservativese such as monofluorophosphate compounds containing copper and zinc.
It is known that, for the manufacturing of alkali monofluorophosphates, anhydrous phosphates can be caused to react with fluorides at a very high temperature, usually above 600.degree. C. The resulting corrosive melt requires corresponding equipment expenditures for the reactors.
The German Published Patent Application DE- B 1 224 280 relates to the manufacture of different metal fluorophosphates. Based on aqueous or anhydrous mixtures which contain metal kations, phosphorus and fluorine at alternating ratios, by means of the reaction at temperatures of up to 800.degree. C., reaction products are produced which contain the above-mentioned elements. The DE-B 1 224 280 contains nothing concerning the type of chemical compounds contained in the reaction products. A targeted teaching for the synthesis of defined metal fluorophosphates is not found, only information that according to the type and quantity of the starting materials of the reaction conditions, such as temperature and time, many different products are obtained.
It is an object of the invention to provide a technically simple method for the manufacturing of defined metal fluorophosphates, specifically alkali mono-rubidium monofluorophosphate, and cesium monofluorophosphate. These objects are achieved by means of the method according to the invention. The method according to the invention for the manufacturing of alkali monofluorophosphate of the general formula M.sub.2 PO.sub.3 F(I) is characterized in that a reaction mixture which contains alkali metal cations M, phosphate, fluoride and water--the molar ratio of M:P:F being (2.+-.0.1):(1.+-.0.05):(1.+-.0.1), and the molar ratio of water:P being at least 1:1 is heated to a temperature of from 150.degree. C. to 400.degree. C., the alkali monofluorophosphate of the general formula (I) being formed as the reaction product, and the reaction product being isolated, if desired, after an aftertreatment.
When, for example, a reaction mixture is reacted in which M stands for sodium, according to the method of the invention, sodium monofluorophosphate can be produced which has a purity of approximately 80% in weight. The other alkali monofluorophosphates are obtained with an even higher purity.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates equipment which can be used to carry out the process of the present invention.
According to a preferred embodiment of the method according of the invention, pure alkali monofluorophosphates are manufactured. This preferred embodiment of the method according to the invention is characterized in that, for the manufacturing of a pure alkali monofluorophosphate of the general formula M.sub.2 PO.sub.3 F (I), wherein M stands for potassium, cesium or rubidium, a reaction mixture which contains alkali metal cations M, phosphate, fluoride and water -the molar ratio of M:P:F being (2.+-.0.05):(1.+-.0.05):(1.+-.0.1), and the molar ratio of water:P being at least 1:1--is heated to a temperature of from 150.degree. C. to 400.degree. C., the alkali monofluorophosphate of the general formula (I) being formed as the reaction product while water is evaporated, and the reaction product being isolated, if desired, after an aftertreatment.
In the present invention, it is particularly preferred that "alkali" or M stands for potassium. The method according to the invention is particularly well suited for the manufacturing of potassium monofluorophosphate--K.sub.2 PO.sub.3 F
REFERENCES:
patent: 3463605 (1969-08-01), White et al.
patent: 4374108 (1983-02-01), Nakaso et al.
Hartmann Ulrich
Meisel Manfred
Moewius Frank
Radonz Veronika
Rudolph Werner
Kali-Chemie Aktiengesellschaft
Langel Wayne
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