US2749278A - Fluorinated dialkali-alkaline earth pyrophosphates and method of producing same - Google Patents

Description

United States Patent FLUORINATED DIALKALI-ALKALINE EARTH PYROPHOSPHATES AND METHOD OF PRO- DUCING SAME Henry V. Moss, Anniston, Ala., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application October 23, 1952, Serial No. 316,550

21 Claims. (Cl. 167-93) The present invention relates to a novel dentifrice base and to a method of preparing same.

An important object of the invention is to provide an improved fluorinated polishing and cleansing agent for dentifrices.

Another object is to provide a dentifrice base in the form of a slightly soluble complex fluorinated phosphate salt which provides an efiicient and reliable means for obtaining uniform distribution of the fluorine throughout the dentifrice.

An additional object is to provide a fluorinated dentifrice base having none of the objectionable properties of prior dentifrices which contain mechanical mixtures of alkaline earth salts and soluble or insoluble fluorides.

A further object is to provide a dentifrice including the improved fluorinated dentifrice base.

Other objects and advantages will be apparent to those skilled in the art as the description proceeds.

Most investigators of dental caries agree that this malady is caused by the local disintegration of the tooth structure by the action of bacteria upon food in the immediate environment of the tooth. As a result of considerable research which followed the discovery that people living in sections of the country where the drinking water contains fluorine in the proper concentrations suffer less from dental caries than those situated in localities where the drinking water is free or substantially free of fluorine, it is now generally accepted that this element is highly effective in the prevention and control of tooth decay.

It has been proposed to add soluble fluorides to the water supplies in caries susceptible areas, but this method of approach has a number of disadvantages.

One disadvantage of adding a soluble fluoride to drinking water is that in the process of drinking only the anterior teeth come into contact with the fluoride with the result that this compound has little, if any, beneficial effect on the other teeth. Another disadvantage is that in the naturally. Other disadvantages of this method of treating and controlling dental caries are set forth in detail by Dr. Basil G. Bibby in the Journal of the American Dental Association, vol. 31, No. 5, pages 317-321 (March 1944).

It is also known that the external application of water solutions of soluble fluorides reduces the development of caries by rendering the tooth structure more resistant to attack and by reducing the prevalence in the saliva of Lucio-bacillus acidophilus which is recognized to be one of the important factors in inducing caries. Thus, rinsing the mouth after meals with a dilute solution of sodium fluoride (5 parts per million F) has been shown by Dr. "A. Paul Atkins to be a relatively simple and effective way of applying this new knowledge (I. A. D. A., vol. 31,

2 No. 5,353-357-March 1944). However, in order to carry through this relatively simple treatment, a solution of suitable strength must be procured from a drugstore or other reliable source and a new habit must be formed of going through the additional chore of rinsing the mouth with a special solution.

The basic concept of incorporating a fluoride in a dentifrice is not novel as this is broadly disclosed in British Patent 3034/1914 to Lidgey and U. S. Patent 1,943,856 to Cross. However, it will be apparent from the considerations which immediately follow that the compositions described in these patents do not provide a satisfactory means for the treatment and prevention of dental caries.

First of all, the compounding of the dentifrices of the patents to Cross (1,943,856) and Lidgey (British 3034/ 1914) presents the difficulty of uniformly distributing, by the usualmechanical means, the small amount of fluoride salt required. Further, even if it is assumed that a homogeneous mixture could be obtained, there is danger of subsequent segregation of the physically added fluoride which would result in an undesirable concentration of the fluoride in portions of the compounded dentifrice while other portions would contain such a low concentration of soluble fluoride as to aiford no protection against dental caries.

Moreover, dentifrice compositions such as disclosed in Patent 1,943,856 to Cross, are excessively abrasive since bentonite'has a relative abrasive index of 17, whereas the acceptable upper limit for dentifrice bases should preferably not exceed 12. Therefore, such compositions would be unacceptable today in the dentifrice art.

Furthermore, when soluble fluorides are incorporated in tooth pastes similar to those disclosed by British Patent 3034/ 1914 to Lidgey and 1,943,856 to Cross, they tend to react with the colloidal silica of bentonite and/ or the alkaline earth compounds to form essentially insoluble products. This renders the fluorine unavailable and at the same time causes objectionable stiflening and caking of the tooth paste.

1 have discovered that the above disadvantages and difliculties can be overcome by providing acomposition of matter consisting essentially of a dialkali-alkaline earth pyrophosphate containing about 1% to about 5% by weight of fluorine as an intimately and substantially uniformly distributed component. This composition is prepared by reacting in an aqueous medium an alkaline earth salt such as an alkaline earth chloride, lactate, acetate and the like with a mixture of a soluble fluoride and a tetra-alkali pyrophosphate. This results in the production of a slurry, which is filtered to separate the precipitate from the mothor liquor. This precipitate is then washed to remove the alkali salts corresponding to the acid radical of the alkaline earth salt and dried. The product thus obtained is the dialkali-alkaline earth pyrophosphate containing various amounts of chemically combined fluorine depending upon the amount of soluble fluoride initially employed.

In the preparation of fluorinated disodium calcium pyrophosphate, a soluble calcium salt such as calcium chloride, calcium lactate, calcium acetate, etc. is reacted, in the presence of an aqueous medium, with a mixture of tetrasodium pyrophosphate and a soluble fluoride such as sodium fluoride, potassium fluoride, ammonium fluoride, etc. The reactants are employed in substantially the proportions required to produce disodium calcium pyrophosphate containing about 1% to about 5% and preferably about 2% to about 3.5% by weight of fluorine. The initial calcium salts are employed in the proportions ranging from theoretical to substantially in excess of the theoretical requirements. For example, these saltsare employed in proportions ranging from about 0% to about 3 200%, and preferably from about 10% to about 20% in excess of that required to form disodium calcium pyro phosphate.

In a similar manner, by selecting the appropriate salts, fluorinated disodium magnesium pyrophosphate, fluorinated dipotassium calcium pyrophosphate, fluorinated dipotassium magnesium pyrophosphate or the hydrates thereof may be prepared.

Production of fluorinated disodium calcium pyrophosphate tetraltydrate 3.2 pounds of tetrasodium pyrophosphate was dissolved in three gallons of water to form a solution containing between ten to fifteen percent tetrasodium pyrophosphate. To this solution 0.31 pound of sodium fluoride was added. The solution of tetrasodium pyrophosphate and sodium fluoride was heated with continuous stirring to 85 C., whereupon 1.34 pounds of a twenty-five percent calcium chloride solution was introduced. This was about 10% in excess of the theoretical amount of calcium chloride necessary to produce disodium calcium pyrophosphate. As the calcium chloride was added, the precipitating so dium calcium pyrophosphate caused the mix to become very thick and viscous at one point in the mixing cycle,

but as the stirring was continued, the batch again thinned out and good mixing resulted. The resulting slurry of fluorinated disodium calcium pyrophosphate tetrahydrate was heated at 85 C. to 95 C. for a period of an hour, cooled to 50 C., filtered, washed to remove excess sodium chloride and then dried at a temperature of 85 C.

The fluorinated disodium calcium pyrophosphate tetrahydrate produced by the above-described process contained about 2.9% by weight of fluorine. This product was used in the treatment of the teeth of Syrian hamsters, and it was found to reduce the number of caries teeth by about 40%. In contrast, thereto, samples of disodium calcium pyrophosphate tetrahydrate containing traces and about 0.4% of fluorine, respectively, had no effect in reducing the number of caries teeth.

The fluorinated dentifrice bases of the present invention may be used in tooth pastes and tooth powders.

In the compounding of tooth pastes, I preferably employ about 40%-60% by weight of the dry base, which base may be combined with varying percentages of glycerine, gums, water, flavoring material, massing agents, etc. In addition there may be incorporated various wetting. emulsifying or foaming agents such as the esters of the higher aliphatic alcohols, for example, the water soluble salts of sulfuric acid esters of lauryl or myristyl alcohol. Or I may advantageously use in place of the latter, alkali metal salts, such as the sodium or potassium salts of alkylated aromatic sulfonic acids, wherein the alkyl group contains from 8 to 18 or more carbon atoms.

In the preparation of tooth powders I preferably employ the fluorinated dentifrice base in amounts varying from 90%99% by weight of the final product, but a smaller proportion of the base may be used, if desired. I may also incorporate other salts with the finely divided dentifrice base. In patricular, I may make mixtures of the fluorinated base with magnesium pyrophosphate, dicalcium phosphate, tricalcium phosphate, calcium carbonate or insoluble sodium metaphosphate. I may also incorporate wetting, emulsifying or sudsing agents in dry form such as above-mentioned.

Other types of wetting, emulsifying or sudsing agents which may be advantageously added to tooth pastes and tooth powders containing my fluorinated dentifrice base are described in U. S. Patent No. 2,359,326 to Moss et 31. Of these agents, those of the tasteless and odorless variety are particularly suitable for use in tooth powders.

The compositions embodying my invention, when used as dentifrice per se or in combination with other normal constituents in paste or powdered form, are capable of cleaning and polishing the teeth and of restoring and maintaining their natural lustre without abrading or scratching the surface thereof. Moreover, they provide a novel and etlicient means for uniformly supplying controlled amounts of fluorine to the teeth.

Where the expression chemically combined fluorine" is used in the specification and claims, it is to be understood that the fluorine is chemically combined with one or more of the elements of the composition. The exact nature of the chemical combination is not definitely known, but it is thought that the soluble fluoride is combined in such a manner as to either provide a slightly soluble complex-, mixedor double salt with the dialkalialkaline earth pyrophosphate or an extremely intimate mixture of a fluoride with the dialkali-alkaline earth pyrophosphate. In any event, the soluble fluoride is so intimately and uniformly associated with the dialkali-alkaline earth pyrophosphate as to provide a unitary product which behaves essentially as a single compound.

The foregoing detailed description has been given for clearness of understanding, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible in view of the prior art.

What I claim is:

l. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of an alkali fluoride, an alkali metal pyrophosphate and a soluble alkaline earth metal salt to form a fluorinated alkali-alkaline earth metal pyorphospate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to yield a dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine.

2. As a new composition of matter, a dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 1.

3. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of an alkali fluoride, an alkali metal pyrophosphate and a soluble alkaline earth metal salt to form a fluorinated alkali-alkaline earth metal pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to yield a dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine, and said alkaline earth metal being selected from the group consisting of calcium and magnesium.

4. As a new composition of matter, a dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by Weight of chemically combined fluorine, said alkaline earth metal being selected from the group consisting of calcium and magnesium, said composition of matter being produced by the method defined in claim 3.

5. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of an alkali fluoride, an alkali metal pyrophosphate and a soluble alkaline earth metal salt to form a fluorinated alkali-alkaline earth metal pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to yield a dialkali-alkaline earth metal pyrophosphate containing about 2% to about 3.5% by weight of chemically combined fluorine, and said alkaline earth metal being selected from the group consisting of calcium and magnesium.

6. As a new composition of matter, an alkali-alkaline earth metal pyrophosphate containing from about 2% to about 3.5 by weight of chemically combined fluorine, said alkaline earth metal being selected from the group consisting of calcium and magnesium, said composition of matter being produced by the method defined in claim 5.

7. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of sodium fluoride, tetrasodium pyrophosphate and a water soluble calcium salt to form a fluorinated disodium calcium pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to form disodium calcium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine.

8. As a new composition of matter, disodium calcium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 7.

9. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of sodium fluoride, tetrasodium pyrophosphate, and a water-soluble magnesium salt to form a fluorinated disodium magnesium pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to form disodium magnesium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine.

10. As a new composition of matter, disodium magnesium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 9.

11. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of potassium fluoride, tetrapotassium pyrophosphate and a water-soluble calcium salt to form a fluorinated dipotassium calcium pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to form dipotassium calcium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine.

12. As a new composition of matter, dipotassium calcium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 11.

13. The method, which comprises reacting together,in a liquid aqueous medium, a mixture initially consisting essentially of potassium fluoride, tetrapotassium pyrophosphate and a water-soluble magnesium salt to form a fluorinated dipotassium magnesium pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to form dipotassium magnesium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluo- 14. As a new composition of matter, dipotassium magnesium pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 13.

15. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of sodium fluoride, tetrasodium pyrophosphate and a water soluble calcium salt to form a fluorinateddisodium calcium pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to form disodium calcium pyrophosphate containing about 2% to about 3.5% by weight of chemically combined fluorine.

16. As a new composition of matter, disodium calcium pyrophosphate containing about 2% to about 3.5% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 15.

17. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of sodium fluoride, tetrasodium pyrophosphate and a water-soluble calcium salt to form a fluorinated disodium calcium pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the proportions required to form disodium calcium pyrophosphate containing about 2.9% by weight of chemically combined fluorine.

18. As' a new composition of matter, disodium calcium pyrophosphate containing about 2.9% by weight of chemically combined fluorine, said composition of matter being produced by the method defined in claim 17.

19. The method, which comprises reacting together, in a liquid aqueous medium, a mixture initially consisting essentially of a water soluble alkali fluoride, an alkali tetrapyrophosphate and a water soluble alkaline earth metal salt to form a fluorinated alkali-alkaline earth metal pyrophosphate, and recovering said fluorinated pyrophosphate, said reactants being employed in the amount required to form a dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine and said initial calcium salt being employed in an amount varying from about 0% to about 200% in excess of that required to produce said dialkali-alkaline earth metal pyrophosphate.

20. A dentifrice containing about 40% to about 60% by weight of a fluorinated dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine.

21. A tooth powder containing about 90% to about 99% by weight of a fluorinated dialkali-alkaline earth metal pyrophosphate containing about 1% to about 5% by weight of chemically combined fluorine.

References Cited in the file of this patent UNITED STATES PATENTS 1,016,989 Galt Feb. 13, 1912 1,704,218 Rothe Mar. 5, 1929 1,799,882 Brenek Apr. 7, 1931 2,266,328 McCullough Dec. 16, 1941 OTHER REFERENCES Journal Amer. Dental Association, volume 38, February 1949, pages 204-212, page 210 pertinent.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, volume 3, page 892, volume 8, pages 975 and 976, Longman Green Co., New York, 1928.

Audrieth and Hill: Recent Developments in the Chemistry of Phosphorus, Journal of Chemical Education, February 1948, pages to 86, page 84 only cited.

Shourie et al.: Journal Dental Research, August 1950, volume 29, pages 529, 533.

Bibby: Journal American Dental Association, volume 34, January 1, 1947, pages 26, 31.

Claims (1)

1. 20. A DENTIFRICE CONTAINING ABOUT 40% TO ABOUT 60% BY WEIGHT OF A FLUORINATED DIALKALI-ALKALINE EARTH METAL PYROPHOSPHATE CONTAINING ABOUT 1% TO ABOUT 5% BY WEIGHT OF CHEMICALLY COMBINED FLUORINE.