Stannous pyrophosphate and production method thereof

Abstract

Dental care compositions comprising tin pyrophosphate and methods of producing the same are provided. In one exemplary embodiment, a method of producing tin pyrophosphate includes mixing tin tetrafluoroborate with a pyrophosphate composition to produce a precipitate, where the precipitate includes tin pyrophosphate and tetrafluoroborate. The tetrafluoroborate is then removed from the precipitate.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 638,539, filed on November 4, 2022, which is incorporated herein by reference. Technical Field

[0003] The present disclosure generally relates to stannous pyrophosphate and methods of producing the same. More specifically, the present disclosure relates to producing stannous pyrophosphate by reacting stannous tetrafluoroborate with a pyrophosphate composition. Background Art

[0004] Stannous ion sources improve many oral care products and have favorable clinical benefits such as reducing gingivitis and reducing tooth demineralization due to erosion. Stannous fluoride is a well - known example of such a stannous ion source and has been used for many years. However, at least in part due to the reactivity of stannous ions, stannous fluoride is somewhat unstable in aqueous solution. Stannous salts hydrolyze at a pH above 4 and then precipitate from the solution. The precipitated form of the stannous salt can reduce the therapeutic properties.

[0005] Soluble stannous ions may also react unfavorably with certain rheology modifiers such as certain types of cellulose and gums. Such compounds are considered incompatible with soluble stannous ions, and these compounds are commonly used in dental health products.

[0006] Stannous pyrophosphate is known as a dentifrice polishing agent and can overcome the above - mentioned limitations. Stannous pyrophosphate having the chemical formula Sn 2 P 2 O 7 contains tetravalent pyrophosphate ions and divalent stannous cations (i.e., Sn(II)). Stannous pyrophosphate is substantially insoluble in water, especially under acidic conditions. However, the use of stannous pyrophosphate is limited by its high cost. In addition, for incorporating stannous pyrophosphate into dental care products, small particle sizes are required. Several methods of producing stannous pyrophosphate have been described, but a method for producing high - purity stannous pyrophosphate with small particle sizes is still desired.

[0007] Accordingly, it is desirable to find new stannous pyrophosphate production techniques that produce high - purity products. In addition, it is desirable to find production techniques for producing small - sized stannous pyrophosphate suitable for incorporation into dental care products. Additionally, in light of this background, other desirable features and characteristics of the present embodiments will become apparent from the following detailed description and the appended claims. Summary of the Invention

[0008] Provided are dental care compositions comprising tin pyrophosphate and methods for producing the same. In an exemplary embodiment, the method for producing tin pyrophosphate comprises mixing tin tetrafluoroborate with a pyrophosphate composition to produce a precipitate, wherein the precipitate comprises tin pyrophosphate and tetrafluoroborate. The tetrafluoroborate is then removed from the precipitate.

[0009] In another embodiment, a dental care composition is provided. The dental care composition includes tin pyrophosphate at a concentration of about 96 weight percent to about 99.999 weight percent based on the total weight of the dental care composition. The dental care composition also includes sodium tetrafluoroborate at a concentration of about 10 parts per million by weight to about 1,000 parts per million by weight based on the total weight of the dental care composition.

[0010] Another method of producing tin pyrophosphate is provided in another embodiment. A tin tetrafluoroborate solution comprising tin tetrafluoroborate and a tin tetrafluoroborate solvent is provided, wherein the tin tetrafluoroborate solvent comprises water. A pyrophosphate is provided, which comprises a pyrophosphate solvent and tetrasodium pyrophosphate, wherein the pyrophosphate solution comprises water. The pyrophosphate solution is adjusted to about 60 to about 85 degrees Celsius. The tin tetrafluoroborate solution and the pyrophosphate solution are mixed to produce a precipitate comprising tin pyrophosphate and sodium tetrafluoroborate. The precipitate is rinsed with a rinse solution to reduce the sodium tetrafluoroborate concentration to a level that makes the boron concentration less than about 100 parts by weight based on the gross weight of the precipitate. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present embodiment will be described hereinafter in conjunction with the following drawings, and wherein:

[0012] Figure 1 A technique for forming a tin tetrafluoroborate solution is shown;

[0013] Figure 2 A technique for forming a pyrophosphate solution is shown;

[0014] Figures 3 - 5 Various embodiments of techniques for forming a reaction product including tin pyrophosphate are shown;

[0015] Figure 6 An embodiment of washing the precipitate is shown; and

[0016] Figure 7 An embodiment of a dried precipitate is shown. DETAILED DESCRIPTION

[0017] The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or applications and uses of the embodiments described herein. Furthermore, it is not intended to be bound by any express or implied theory presented in the preceding technical field, background technology, summary of the invention, description of the drawings, or the following detailed description or drawings.

[0018] Stannous pyrophosphate has a very low solubility in water and is a relatively stable salt. Stannous pyrophosphate is sometimes called tin pyrophosphate and has the chemical formula Sn 2 P 2 O 7 . The Sn2+ cation is preferred over the Sn4+ cation and is the most prevalent in the reactions described below. Generally, stannous tetrafluoroborate having the chemical formula Sn(BF 4 ) 2 is mixed with a pyrophosphate compound to produce stannous pyrophosphate and a tetrafluoroborate by-product. In embodiments where the pyrophosphate is sodium pyrophosphate, it has the chemical formula NaBF 4 . When mixed, the reactants can be in solution, where the reactants are more soluble in polar solvents. Stannous pyrophosphate forms as a precipitate when formed in solution, and the size of the precipitate particles can be controlled as described below.

[0019] See Figure 1 . Stannous tetrafluoroborate 10 is available as a raw material and can be purchased from various suppliers in sufficient quantities, typically as an aqueous solution that is 50 / 50 weight % based on the total weight of the aqueous solution. Stannous tetrafluoroborate 10 is commonly used as an electroplating agent and / or a surface treatment agent. Stannous tetrafluoroborate 10 is a solid material with a melting point greater than 130 degrees Celsius (°C) and is miscible with water, forming a colorless and stable aqueous solution.

[0020] Stannous tetrafluoroborate solvent 12 can be mixed with stannous tetrafluoroborate 10 to form stannous tetrafluoroborate solution 14. Stannous tetrafluoroborate solvent 12 includes water and can include from about 50 weight % to about 100 weight % water based on the total weight of stannous tetrafluoroborate solvent 12. In some embodiments, stannous tetrafluoroborate solvent 12 is from about 95 weight % to about 100 weight % water, but in alternative embodiments can include other components. For example, an alcohol or other polar compound can be included in stannous tetrafluoroborate solvent 12. Exemplary alcohols have 1 to 6 carbon atoms, but other alcohols or other types of solvents can also be used. Generally, stannous tetrafluoroborate solvent 12 is capable of dissolving stannous tetrafluoroborate 10. In some embodiments, stannous tetrafluoroborate solution 14 is acidic, having a pH less than 7, and thus stannous tetrafluoroborate solvent can also have an acidic pH. In some embodiments, stannous tetrafluoroborate 10 is formed by adding a tin salt to a tetrafluoro boric acid solution, and stannous tetrafluoroborate 10 is separated by electrolysis. However, different production methods can be utilized in alternative embodiments.

[0021] See Figure 2 , a pyrophosphate compound 16 is mixed with a pyrophosphate solvent 18 to form a pyrophosphate solution 20. The pyrophosphate compound 16 can include having the chemical formula Na 4 P 2 O7 tetrasodium pyrophosphate, but the pyrophosphate compound 16 may also include those having the chemical formula Na 2 H 2 P 2 O 7 disodium pyrophosphate. In other embodiments, the pyrophosphate may include a metal other than sodium or a metal in combination with sodium as a cationic salt. As a non-limiting example, the cation may include one or more of potassium, rubidium, calcium, magnesium, iron, or others. In an exemplary embodiment, the pyrophosphate compound 16 contains about 50 wt% to 100 wt% of tetrasodium pyrophosphate based on the total weight of the pyrophosphate compound 16. Pyrophosphate compounds 16 of various grades and purities are readily commercially available.

[0022] The pyrophosphate compound 16 is slightly soluble in water, so the pyrophosphate solvent 18 may include about 50 wt% to 100 wt% of water based on the total weight of the pyrophosphate solvent 18. However, other solvents may also be included in the pyrophosphate solvent 18, such as alcohols or other solvents. Due to the limited solubility of the pyrophosphate compound 16 in the pyrophosphate solvent 18, the pyrophosphate solution 20 can be heated to facilitate dissolution. In an exemplary embodiment, the pyrophosphate solution 20 is heated to a pyrophosphate solution temperature 22 of about 60 °C to about 85 °C, but other temperature ranges are possible. The solubility of tetrasodium pyrophosphate in water is 6.7 grams per milliliter (g / ml) at 25 °C, but the solubility increases to 42.2 g / ml at 100 °C. In an exemplary embodiment, the pyrophosphate compound 16 is present in the pyrophosphate solution 20 in an amount of about 10 grams per liter to about 500 grams per liter or in an amount of about 100 grams per liter to about 300 grams per liter.

[0023] See Figure 3 and continue to refer to Figure 1 and Figure 2 , stannous tetrafluoroborate 10 is added to the pyrophosphate compound 16 to produce stannous pyrophosphate in the reaction product 38. As in Figure 3In the exemplary embodiment shown, stannous tetrafluoroborate solution 14 is added to pyrophosphate solution 20, where the two compositions react and form stannous pyrophosphate contained in precipitate 30. The reaction of stannous tetrafluoroborate 10 and pyrophosphate compound 16 can be controlled at a reaction temperature 32 of about 50 °C to about 100 °C, but other reaction temperature ranges are also possible. For example, reaction temperature ranges of about 50 °C to about 80 °C, or about 60 °C to about 70 °C can also be used. Stannous tetrafluoroborate 10 can be added to pyrophosphate solution 20 over an addition period of about 5 minutes to about 12 hours, but other addition periods are also possible. For example, the addition period can be about 20 minutes to about 2 hours, or in an alternative embodiment, about 30 minutes to about 60 minutes. The reaction of stannous tetrafluoroborate 10 and pyrophosphate compound 16 produces tetrafluoroborate as a by-product, such as sodium tetrafluoroborate when sodium pyrophosphate is in pyrophosphate compound 16. Thus, tetrafluoroborate is within reaction product 38.

[0024] Stannous tetrafluoroborate 10 and pyrophosphate compound 16 react to form stannous pyrophosphate and a tetrafluoroborate product. Viewing the chemical formula enables a chemist to determine the stoichiometry of stannous tetrafluoroborate 10 and pyrophosphate compound 16, where stoichiometry is the theoretical amount of all reactants (stannous tetrafluoroborate 10 and pyrophosphate compound 16) that react completely to produce the product. In an exemplary embodiment, stannous tetrafluoroborate 10 and pyrophosphate compound 16 are mixed in an amount of about 100% of the stoichiometry, where 100% of the stoichiometry is the stoichiometric amount. The term "about 100% of the stoichiometry" in this specification means within about 5% of the stoichiometry. In an alternative embodiment, stannous tetrafluoroborate 10 is added in an amount of about 100% to about 125% of the stoichiometry for reaction with pyrophosphate composition 16, so stannous tetrafluoroborate can be added in excess of the stoichiometry. In another embodiment, stannous tetrafluoroborate is added in an amount of about 75% to about 100% of the stoichiometry. Other embodiments are also possible.

[0025] Many different embodiments of the combination of stannous tetrafluoroborate 10 and pyrophosphate compound 16 are possible. For example, stannous tetrafluoroborate 10 can be added to pyrophosphate solution 20 in solid form, as Figure 4 shown. In another embodiment, stannous tetrafluoroborate solution 14 and pyrophosphate solution 20 are simultaneously injected into microfluidic reactor 34, as Figure 5As shown. In an exemplary embodiment, the reaction gas 36 is added together with the reactants, and the reaction product 38 is discharged, where the reaction product 38 includes a precipitate 30 having stannous pyrophosphate. Other alternative possible options include continuously and simultaneously adding stannous tetrafluoroborate 10 and a pyrophosphate compound 16 to a continuous reactor (not shown), where the stannous tetrafluoroborate 10 and / or the pyrophosphate compound 16 can be added as a solid or as a solution. Other possible reaction mechanisms are also possible.

[0026] The precipitate 30 can be removed from the reaction product 38 by filtration, sedimentation, centrifugation, or other separation techniques, as Figure 6 shown in the exemplary embodiment in and continue to refer to Figures 1 - 5 . The precipitate 30 can be washed to increase the purity of the stannous pyrophosphate and reduce the concentration of tetrafluoroborate. In an exemplary embodiment, the precipitate 30 is washed by rinsing with a rinse liquid 40, but other techniques for removing tetrafluoroborate are also possible. For example, the precipitate 30 can be slurried again and filtered again, the stannous pyrophosphate can be further purified by recrystallization, or other purification techniques can be used to remove tetrafluoroborate. In the exemplary embodiment in which the precipitate 30 is rinsed, the rinse liquid 40 contains water in an amount of about 50 wt% to about 100 wt% based on the total weight of the rinse liquid 40. Stannous pyrophosphate is much less soluble in water than the tetrafluoroborate by-product, so during rinsing or washing, the tetrafluoroborate dissolves earlier and is washed out from the stannous pyrophosphate in the precipitate 30. In an exemplary embodiment, the stannous pyrophosphate has a specification of 100 ppm boron, so the precipitate 30 can be washed until the tetrafluoroborate concentration is reduced to a point where the boron concentration is 100 ppm or less based on the total weight of the precipitate 30 after drying. Similarly, the precipitate 30 can be washed until the tetrafluoroborate concentration is about 10 ppm to about 1,000 ppm based on the total weight of the precipitate 30 after drying. In an exemplary embodiment, the amount of the rinse liquid 40 used is about 500 grams of water / 100 grams of stannous pyrophosphate in the precipitate 30 to reduce the tetrafluoroborate to about 1,000 ppm or less based on the total weight of the stannous pyrophosphate in the precipitate 30. In an alternative embodiment, about 300 grams or about 400 grams of water are used per 100 grams of stannous pyrophosphate. The rinsing can be repeated until the impurities are reduced to a level sufficient for dental products. In an exemplary embodiment, the rinsing can be repeated until the rinse liquid has a conductivity of about 500 microsiemens or less after passing through the precipitate 30. In alternative embodiments, other techniques can be utilized to verify the required purity.

[0027] The precipitate 30 can be dried after washing, for example, dried in a spray dryer, as Figure 7 shown and continue to refer to Figures 1 - 6The precipitate 30 can be slurried or otherwise fed into a spray dryer 50. A drying gas 52, such as hot air, is added to the spray dryer 50 together with the precipitate 30, wherein the drying gas 52 is discharged from the spray dryer 50 as exhaust gas 54, and stannous pyrophosphate 56 is discharged from the spray dryer 50 as a solid product. The precipitate 30 can be dried using many other techniques, such as fluidized beds, tray dryers, vacuum dryers, freeze dryers, and other drying techniques. The type of dryer used can affect the particle size of the product, which includes stannous pyrophosphate 56.

[0028] Based on the total weight of the product, stannous pyrophosphate 56 in the product can be present in the product at a concentration of about 96 wt% to about 99.99 wt%, wherein the product can be a dental care composition. Based on the weight of the product, the boron concentration can be from about 0.1 wt ppm to about 100 wt ppm. Sodium tetrafluoroborate (or other tetrafluoroborate) can be present in the product at a concentration of about 10 wt ppm to about 1,000 wt ppm based on the total weight of the product, wherein the tetrafluoroborate is generally retained in small amounts. In an exemplary embodiment, the presence of sodium tetrafluoroborate (or other tetrafluoroborate) in the product clearly indicates that stannous pyrophosphate 56 is produced using stannous tetrafluoroborate and a sodium pyrophosphate compound (or other pyrophosphate compound 16) as reactants. In various embodiments, the stannous pyrophosphate 56 product may contain a variety of other impurities, and these impurities may be generated from the raw materials used. Exemplary impurities that may be present include trace elements such as arsenic (As), cadmium (Cd), cobalt (Co), mercury (Hg), nickel (Ni), lead (Pb), antimony (Sb), vanadium (V), chlorine (Cl), chromium (Cr), potassium (K), etc. Generally speaking, these trace elements can optionally be present at a concentration of 0 ppm to about 500 ppm.

[0029] The stannous pyrophosphate 56 produced in the desired product has a small average particle size to facilitate incorporation into oral care products as a dental care composition. Various techniques can be incorporated into the production process to reduce the average particle size in the product. For example, a spray dryer 50 can be used to reduce the particle size. Incorporating an acid into the pyrophosphate solution 20 before the reaction can lower the pH, which slows down the reaction and can help reduce the average particle size. Phosphoric acid is an example of an acid that can be used, but other acids are possible, such as hydrochloric acid, sulfuric acid, citric acid, acetic acid, etc. In an exemplary embodiment, the acid can be incorporated into the pyrophosphate solution 20 in an amount of about 0.01 wt% to about 1.0 wt%, and in various embodiments, the pH of the pyrophosphate solution 20 can be reduced to a range of about 10 to about 6, or about 9.5 to about 7, or about 9.5 to about 9. In other embodiments, a scale inhibitor 24 can optionally be added to the pyrophosphate solution 20 in an amount of about 0.05 wt% to about 0.5 wt%, or 0.1 wt% to about 0.5 wt% based on the total weight of the pyrophosphate solution 20. The scale inhibitor 24 can be selected from citric acid, nitrilotris(methylene)triphosphonic acid (NTMP), nitrilotris(methylene)triphosphonic acid (NTMP), hydroxyethylidene diphosphonic acid (also known as hydroxyethylidene(1,1-diphosphonic acid)) (HEDP), phosphonobutane tricarboxylic acid, ethylenediaminetetra(methylene phosphonic acid), hexamethylenediaminetetra(methylene phosphonic acid), diethylenetriaminepenta(methylene phosphonic acid) (DTPMP), and combinations thereof. A microfluidic reactor 34 can also be used to produce small particle sizes.

[0030] Tests have shown that the stannous pyrophosphate 56 in the product can have an average particle size D95 of about 0.1 microns to about 100 microns, but higher particle sizes are possible based on the materials used and the production method. The D95 particle size refers to 95% of the particles being smaller than the stated particle size. In an exemplary embodiment, the particle size can be determined by laser diffraction through a suspension, but in alternative embodiments, other techniques can be used. In an exemplary embodiment, the use of phosphoric acid and / or the scale inhibitor 24 can reduce the particle size D95 of the stannous pyrophosphate 56 in the reaction product 38 to about 0.1 microns to about 100 microns. Using ultrasound on the slurried precipitate 30 also produces a particle size D95 of about 0.1 microns to about 100 microns. Additionally, an addition period of about 5 hours to about 12 hours has produced a particle size D95 of about 0.1 microns to about 100 microns.

[0031] Other techniques can also be used to reduce the particle size of the reaction product 38. For example, the precipitate 30 can be slurried and exposed to ultrasonic procedures, high-speed mixing, homogenization, and / or other rapid agitation techniques. Additionally, the reaction product 38 can be milled, ground, or otherwise processed to reduce the particle size, or the product can be screened and the smaller particles recovered. Extending the addition period slows down the reaction, and this can reduce the particle size. The various methods for reducing the particle size have advantages and disadvantages that need to be considered and balanced. For example, milling or grinding uses additional energy and may cause dust problems. The increased feed time slows down the production process, which increases labor costs, depreciation costs, and other related costs. The cost of the scale inhibitor 24 must be considered, as well as the cost of maintaining the additional product during the production process.

[0032] Experimental data

[0033] Several batches were prepared in the laboratory using the above techniques, and the results are provided below. In Table 1, all charge amounts are in grams unless otherwise indicated.

[0034] Table 1, Part 1

[0035]

[0036]

[0037] --------------------

[0038] 1 Weight of scale inhibitor, in grams.

[0039] 2 The feed time is the time for adding the stannous tetrafluoroborate solution to the pyrophosphate solution.

[0040] 3 The "ending temperature" is the temperature at which the precipitate is filtered out.

[0041] 4 All rinsing steps use 70 ml of deionized water.

[0042] 5 Particle size of the dried precipitate.

[0043] 6 Concentration of elemental boron in the dried precipitate, in weight PPM, based on the total weight of the dried precipitate.

[0044] Table 1, Part 2

[0045]

[0046]

[0047] --------------------

[0048] 7 The weight of the scale inhibitor, in grams.

[0049] 8 The feeding time is the time when the stannous tetrafluoroborate solution is added to the pyrophosphate solution.

[0050] 9 The "ending temperature" is the temperature when the precipitate is filtered out.

[0051] 10 All rinsing steps use 70 ml of deionized water.

[0052] 11 The particle size of the dried precipitate.

[0053] 12 The concentration of elemental boron in the dried precipitate, in weight PPM, based on the total weight of the dried precipitate.

[0054] Table 1, Part 3

[0055]

[0056]

[0057] --------------------

[0058] 13 DTPMP is diethylenetriamine penta(methylene phosphonic acid), NTMP is nitrilotri(methylene)triphosphonic acid, and HEDP is hydroxyethylidene diphosphonic acid.

[0059] 14 The weight of the scale inhibitor, in grams.

[0060] 15 The feeding time is the time when the stannous tetrafluoroborate solution is added to the pyrophosphate solution.

[0061] 16 The "ending temperature" is the temperature when the precipitate is filtered out.

[0062] 17 All rinsing steps use 70 ml of deionized water.

[0063] 18 The particle size of the dried precipitate.

[0064] 19 The concentration of elemental boron in the dried precipitate, in weight PPM, based on the total weight of the dried precipitate.

[0065] As shown by the results above, higher yields are produced by adding stannous tetrafluoroborate 10 and pyrophosphate compound 16 in approximately stoichiometric amounts. The use of scale inhibitor 24 can reduce the particle size, with some scale inhibitors 24 being more effective than others. Increasing the addition period (referred to as "feed time" in Table 1) reduces the particle size, but the results are not significant until the addition period is increased to several hours.

[0066] Although several embodiments have been presented in the foregoing detailed description, it should be understood that there are a large number of variations. It should also be understood that one or more embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. On the contrary, the foregoing detailed description will provide a convenient guide for those skilled in the art to implement various embodiments of the asphalt composition, and it should be understood that various changes can be made to the functions and arrangements of the described elements without departing from the scope as set forth in the appended claims and their legal equivalents.

Claims

1. A method for producing stannous pyrophosphate, the method comprising the following steps: mixing stannous tetrafluoroborate and a pyrophosphate composition to produce a precipitate, wherein the precipitate comprises the stannous pyrophosphate and tetrafluoroborate; and removing the tetrafluoroborate from the precipitate.

2. The method according to claim 1, the method further comprising: providing a stannous tetrafluoroborate solution comprising the stannous tetrafluoroborate and a stannous tetrafluoroborate solvent, wherein the stannous tetrafluoroborate solvent comprises water, and wherein the stannous tetrafluoroborate solution is produced before mixing the stannous tetrafluoroborate and the pyrophosphate composition.

3. The method according to claim 1, the method further comprising: producing a pyrophosphate solution comprising the pyrophosphate composition and a pyrophosphate solvent, wherein the pyrophosphate solvent comprises water, and wherein mixing the stannous tetrafluoroborate and the pyrophosphate composition comprises mixing the pyrophosphate solution and the stannous tetrafluoroborate.

4. The method according to claim 3, the method further comprising: before mixing the stannous tetrafluoroborate and the pyrophosphate solution, bringing the pyrophosphate solution to a pyrophosphate solution temperature of about 60 degrees Celsius (°C) to about 85 °C.

5. The method according to claim 3, wherein: mixing the stannous tetrafluoroborate and the pyrophosphate solution comprises adding the stannous tetrafluoroborate to the pyrophosphate solution.

6. The method according to claim 5, the method further comprising providing a stannous tetrafluoroborate solution comprising the stannous tetrafluoroborate and a stannous tetrafluoroborate solvent, wherein mixing the stannous tetrafluoroborate with the pyrophosphate solution comprises adding the stannous tetrafluoroborate solution to the pyrophosphate solution within an addition period of about 5 minutes to about 12 hours.

7. The method according to claim 3, wherein the pyrophosphate solution further comprises phosphoric acid to provide a pyrophosphate solution pH of about 9.5 to about 7.

8. The method according to claim 3, wherein the pyrophosphate solution further comprises phosphoric acid, and the amount of the phosphoric acid is sufficient to produce the precipitate with an average particle size of about 0.1 micrometer to about 100 micrometers.

9. The method according to claim 3, wherein the pyrophosphate solution further comprises a scale inhibitor in an amount of about 0.01 wt% to about 1 wt% based on the weight of the pyrophosphate solution, wherein the scale inhibitor is selected from citric acid, nitrilotri(methylene)triphosphonic acid, hydroxyethylidene diphosphonic acid, phosphonobutane tricarboxylic acid, ethylenediaminetetra(methylene phosphonic acid), hexamethylenediaminetetra(methylene phosphonic acid), diethylenetriamine penta(methylene phosphonic acid), and combinations thereof.

10. The method according to claim 3, wherein the pyrophosphate solution further comprises a scale inhibitor, and the amount of the scale inhibitor is sufficient to produce a precipitate with an average particle size of about 0.1 micrometer to about 100 micrometers, wherein the scale inhibitor is selected from citric acid, nitrilotri(methylene)triphosphonic acid, hydroxyethylidene diphosphonic acid, phosphonobutane tricarboxylic acid, ethylenediaminetetra(methylene phosphonic acid), hexamethylenediaminetetra(methylene phosphonic acid), diethylenetriamine penta(methylene phosphonic acid), and combinations thereof.

11. The method according to claim 1, wherein the pyrophosphate composition comprises sodium pyrophosphate.

12. The method according to claim 1, wherein: the stannous tetrafluoroborate is added in an amount of about 100% to about 125% of the stoichiometric amount that reacts with the pyrophosphate composition.

13. The method according to claim 1, wherein: the stannous tetrafluoroborate and the pyrophosphate composition are mixed in a microfluidic reactor.

14. The method according to claim 1, the method further comprises: spray-drying the precipitate.

15. The method according to claim 1, wherein removing the tetrafluoroborate comprises rinsing the precipitate with a rinsing liquid, wherein the rinsing liquid comprises about 50% to about 100% by weight of water based on the total weight of the rinsing liquid.

16. The method according to claim 1, wherein removing the tetrafluoroborate comprises washing the precipitate until the boron concentration in the precipitate is about 0.1 parts per million by weight to about 100 parts per million by weight based on the total weight of the precipitate.

17. The method according to claim 1, the method further comprises: drying the precipitate after removing the tetrafluoroborate.

18. A dental care composition, the dental care composition comprising: stannous pyrophosphate at a concentration of about 96% to about 99.999% by weight based on the total weight of the dental care composition; and sodium tetrafluoroborate at a concentration of about 10 parts per million to about 1,000 parts per million based on the total weight of the dental care composition.

19. The dental care composition according to claim 18, wherein the stannous pyrophosphate has an average particle size of about 0.1 micrometer to about 100 micrometers.

20. A method for producing stannous pyrophosphate, the method comprises the following steps: providing a stannous tetrafluoroborate solution comprising stannous tetrafluoroborate and a stannous tetrafluoroborate solvent, wherein the stannous tetrafluoroborate solvent comprises water; providing a pyrophosphate solution comprising sodium pyrophosphate and a pyrophosphate solvent, wherein the pyrophosphate solvent comprises water; adjusting the temperature of the pyrophosphate solution to about 60 degrees Celsius (°C) to about 85 °C, mixing the stannous tetrafluoroborate solution and the pyrophosphate solution to produce a precipitate comprising stannous pyrophosphate and sodium tetrafluoroborate; and rinsing the precipitate with a rinsing liquid to reduce the sodium tetrafluoroborate concentration to a level such that the boron concentration is less than about 100 parts per million by weight based on the total weight of the precipitate.

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