# Patent

## Title
Method of making fluorosulfonylamine

## Abstract

The present invention is directed to methods comprising adding NH3 to a SO2F2 solution to directly form a FSO2NH2 and/or a salt of [FSO2NH]−, optionally quenching any unreacted NH3 present in the resulting mixture, and isolating the product from the resulting mixture.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of the filing date of U.S. Provisional Appl. No. 61/464,771, filed Mar. 8, 2011, which is incorporated by reference herein in its entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to methods of synthesizing fluorosulfonylamide, FSO2NH2, and salts of the fluorosulfonylamide anion, −[FSO2NH]−.
2. Background
It is known that slow addition of SO2F2 to NH3 (or vice versa) produces SO2(NH2)2 (sulfamide) and oligomers thereof. See, e.g., U.S. Pat. No. 3,411,889 (“Kopec”) and U.S. Patent Application Publication No. 2012/0020867 A1 (“Morinaka”). For example, in Comparative Example 1, Morinaka shows that SO2F2 added to a 3.2 molar excess of NH3 in acetonitrile at 5° C., followed by stirring at room temperature for 48 hours, filtration, and distillation of the solvent provided SO2(NH2)2 as a white powder. Analysis of the product showed that FSO2NH2 was produced as a minor (3%) impurity. In Comparative Example 2, Morinaka shows that slow addition of a 3.5 molar excess of NH3 to a solution of SO2Cl2 in acetonitrile provided SO2(NH2)2. Likewise, Kopec discloses that addition of SO2F2 to NH3 at −65° C. to −40° C. produces sulfamide (SO2(NH2)2) and oligomers thereof.
It has also been shown that FSO2NH2 is resistant to nucleophilic attack by ammonia at temperatures as high as −30° C. See R. Appel et al., “Uber die Umsetzung von Disulfurylfluorid, S2O5F2, mit Ammoniak und Diäthylamin,” Zeitschrift für anorganische und allgemeine Chemie 310 (1-2):90-93 (1961).
Conversely, a method of slowly adding NH3 to a stirred solution of SO2F2 to provide FSO2NH2 as the primary product has not been shown in the prior art.
BRIEF SUMMARY OF THE INVENTION
I have found that the addition of NH3 to a solution of SO2F2 in a suitable solvent initially reacts to produce FSO2NH2 and HF:

SO2F2+NH3→FSO2NH2+HF

Gaseous NH3 can be infused into the head space of a reactor containing SO2F2 in solution and/or slowly added as a solution of NH3 in a solvent. When the reaction is performed in a solvent at temperatures of −30° C. or less, NH3 does not readily attack the FSO2NH2 product, but instead forms a salt, per the following reaction:




Preferably, the complete consumption of SO2F2 is the endpoint of the reaction, which can be determined by a decrease in reactor pressure to a value approaching the vapor pressure of the solvent system. Additionally, the reaction can be halted at any time and the unreacted SO2F2 vented and recovered, if desired. Also, air or an inert gas can be introduced to the vessel after the addition of one or more reagents is complete, in order to maintain the reactor pressure close to atmospheric. The [FSO2NH]−[NH4]+salt does not appear to be very stable at room temperature, but can be treated with acid in situ at lower temperatures to give the product FSO2NH2. Generally, this sequence of reactions can be performed without the addition of an organic base. Optionally, an organic base more basic than ammonia (such as trimethylamine, triethylamine, and the like) may be introduced, and the complex FSO2NH−BH+ preferentially produced. This can enable ammonia to be used only as a reactant and not as a base, and can thereby help to inhibit the formation of byproduct sulfamide. Furthermore, as Morinaka has described, formation of the bis adduct [(FSO2)2N]−[B]+ is very slow at temperatures below about −10° C.

In embodiments in which excess NH3 is present in the solution after reaction of the SO2F2 starting material, the excess NH3 can be quenched by addition of a sufficiently strong acid, followed by warming of the reactor, filtration, and distillation, to provide pure FSO2NH2.


DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to methods for preparing FSO2NH2 and [FSO2NH]− without the use of fluorosulfonic acid or chloride metathesis reagents such as metal fluorides.
The present invention is directed to a method comprising adding NH3 to a SO2F2 solution to form a product, optionally quenching any unreacted NH3 present in the resulting mixture, and isolating the product from the resulting mixture.
As used herein, a “product” within the scope of the present invention includes, but is not limited to, FSO2NH2, [FSO2NH]−, and salts thereof.
The addition of NH3 to a solution of SO2F2 reacts instantly to initially produce fluorosulfonylamide (FSO2NH2) and HF. Typically, the two reactants, SO2F2 and NH3, are introduced as gases into a stirred reactor containing a solvent. In a preferred embodiment, SO2F2 is first added to the reactor in its entirety followed by the slow introduction of NH3. SO2F2 can be added in a single step at the beginning of the reaction, or added in portions (using, e.g., a gated valve). In some embodiments, SO2F2 is added in a single step when the starting reactor temperature is ≦−30 C. Generally, SO2F2 pressure during addition to the reactor can range from 100 psi to 300 psi, more preferably 120 to 250 psi. NH3 is typically added at a pressure of 50 psi to 200 psi, more preferably 70 psi to 120 psi. The gases can be added from any pressurized source, e.g., a cylinder, lecture bottle, and the like. Both SO2F2 and NH3 have large Joule-Thompson coefficients, and thus the SO2F2 and/or NH3 source can be heated to ensure at least a baseline pressure and/or substantially constant pressure is maintained during the adding.
Precise control of SO2F2 and/or NH3 introduction can be maintained using, e.g., mass flow controllers, caliper gauges, and the like. In some embodiments, the rate of NH3 addition (and/or SO2F2 addition) is controlled by internal reactor pressure, reactor temperature, or other variable conditions.
SO2F2 is highly toxic and completely odorless and colorless. Thus, significant precaution must be used when handling this substance. All reactions should be conducted in areas having sufficient ventilation. On the lab scale, this means all reactions must be conducted inside a fume hood, as well as post-reaction manipulations of the products. On the industrial scale, proper ventilation should be designed and proper safety measures followed.
The reaction of NH3 with a solution of SO2F2 is highly exothermic and can be extremely rapid, and the rate of NH3 addition should be carefully controlled. In preferred embodiments, the NH3 is slowly added over a course of at least 30 minutes, 1 hour or longer, or 2 hours or longer to a vigorously stirred SO2F2 solution. The rate of addition is typically regulated by the rise in temperature above a starting temperature. In some embodiments, the rise in temperature from the starting static temperature is maintained at ±5° C. or less, and more preferably ±2° C. or less during the addition of NH3. Effective cooling of the reactor is required.
Any solvent capable of dissolving SO2F2 can be used for the reaction. Exemplary solvents include tetrahydrofuran, ethyl acetate, ethyl ether, iso-propyl ether, 1,2-dimethoxyethane, acetonitrile, propionitrile, butyronitrile, dichloromethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrollidinone, and the like, and combinations thereof. In embodiments in which an acid is used to “quench” the reaction, the solvent should also be chemically inert to the acid under the conditions present in the reactor during quenching.
The molar ratio of NH3 to SO2F2 can be varied from about 1:1 to about 4:1. In some embodiments the molar ratio of NH3 to SO2F2 is about 1:1 to about 3:1, or about 3:1 to about 4:1. Generally, three mole equivalents of NH3 are sufficient to completely consume the SO2F2 present in the reactor. A mole ratio of less than 3:1 can be utilized to achieve improved SO2F2 conversion, or to eliminate the need for acidification, and any SO2F2 remaining after the reaction can be recovered and reused. Mole ratios greater than 3:1 (NH3/SO2F2) are generally not necessary, but can be utilized within the scope of the present invention. In some embodiments, a preferred molar ratio of NH3 to SO2F2 is about 3:1. In some embodiments, a preferred molar ratio of NH3 to SO2F2 is about 1:1.
The starting concentration of SO2F2 can be varied. Preferred concentrations of SO2F2 in solvent (expressed as molality, i.e., moles SO2F2 per kilogram of solvent) range from 0.1 to 3 molal, or 0.5 to 2 molal. In THF solvent at −70° C., SO2F2 concentrations greater than 2 molal can result in erratic pressure readings and reduced yield. Thus, while concentrations greater than 2 molal can nonetheless be employed at a starting temperature −70° C., preferred concentrations of SO2F2 for reactions performed at a starting temperature of −70° C. are 0.5 to 2 molal.
Dissolution of SO2F2 can be measured by comparison of the static vapor pressure in the reactor (of the SO2F2/solvent blend) with the static vapor pressure of pure SO2F2 under the same conditions.
The reactor pressure during reaction can range from well above atmospheric to the static vapor pressure of the reactor contents, obtained by evacuation of the reactor (containing solvent) at suitably low temperature. The preferred vapor pressure for the reaction is that of the solvent and reactants alone. Vapor pressures were observed as low as 3 torr to as high as four atmospheres above ambient pressure under a variety of reaction conditions.
Any NH3 remaining in the reaction mixture after addition should be quenched. Quenching is typically performed using a suitable acid. The main requirement for a quench acid is that it is a stronger acid than FSO2NH2—i.e., the pKa of the quench acid is less than the pKa of FSO2NH2. In some embodiments, the quench acid is capable of forming an insoluble ammonium salt. As noted herein, it is preferable that the solvent is inert to the quench acid under the quenching conditions. Exemplary suitable acids include HCl, HF, HBr, acetic acid, H3PO4, H2SO4, HSO3CH3, HSO3CF3, CF3COOH. In some embodiments, H2SO4 dissolved in tetrahydrofuran is preferred.
For a reaction of NH3 with SO2F2 in a 3:1 mole ratio, a ratio of quench acid to NH3 can range from 0.25 to 1.5 normal equivalents, more preferably from 0.5 to 1.0, most preferably 0.67 (2⁄3) normal equivalents. While within the scope of the present invention, ratios of quench acid to NH3 greater than 0.67 (2⁄3) can produce excess HF gas. While also within the scope of the present invention, ratios of quench acid to NH3 less than 0.67 (2⁄3) can result in reduced yield of FSO2NH2. Generally, a complete reaction between NH3 and FSO2NH2 can be assumed. Thus, the amount of NH3 required to completely react with the FSO2NH2 can be subtracted from the total amount of NH3 added, and an amount of acid sufficient to neutralize the remainder can be utilized.
The products formed in the resulting mixture can depend on the solvent, the partial pressure of free NH3 at the gas-liquid interface, the concentration of dissolved SO2F2, and the temperature.
Generally, maintaining a temperature of −30° C. or less during the addition provides conditions in which NH3 does not readily attack FSO2NH2 but instead acts as a base to form the [NH4]+[FSO2NH]− salt. Thus, in some embodiments, the present invention is directed to a method comprising adding NH3 to a SO2F2 solution to form a product, wherein SO2F2 solution is maintained at a temperature of −30° C. or less during the addition, optionally quenching any unreacted NH3 present in the resulting mixture, and isolating the product from the resulting mixture.
For example, at temperatures below −30° C., and in an aprotic solvent such as tetrahydrofuran, the initially formed FSO2NH2 forms [NH4]+[FSO2NH]−. This salt complex is insoluble and precipitates from solution along with the [NH4]+[F]− that is formed as a byproduct.
While temperatures below −30° C. are adequate for the formation of FSO2NH2, lower temperatures may be used. Thus, in some embodiments the temperature of the solution is maintained at −40° C. or less, −50° C. or less, −60° C. or less, or −70° C. or less during the addition. The low temperature limit is defined by the liquidus point of the SO2F2/solvent mixture. In some embodiments, the temperature of the solution is maintained at −80° C. to −30° C., −80° C. to −40° C., or −80° C. to −50° C. during the addition.
At temperatures below −30° C., fewer than three molar equivalents of NH3 can be used within the scope of the present invention, however, three molar equivalents of NH3 are required to fully complete the reaction at reduced temperature. Thus, in some embodiments, the present invention is directed to adding a threefold molar excess of NH3 to a vigorously stirred 1 molal solution of SO2F2 in tetrahydrofuran maintained at −70° C. (±5° C.) to produce FSO2NH2 as the product.
Lower temperatures result in a reduced pot pressure and the consumption of SO2F2 can be followed quantitatively by monitoring a drop in pressure as NH3 is added to the reactor. Furthermore, below −58° C. SO2F2 is a liquid and at −70° C. the vapor pressure in a sealed, evacuated reactor charged with SO2F2, is less than 100 torr. Thus, at this temperature range the SO2F2 is almost completely dissolved, or at least in liquid form, and maximally available for reaction with NH3. The reaction of dissolved NH3 with SO2F2 in THF is very fast, indeed almost instantaneous, at these low temperatures. I have found that −70° C. to −73° C. can be a convenient range of starting temperatures: It is readily achievable using a dry ice-acetone slush bath, and provides reactor pressures in a range of 100 torr to 3 torr during the course of reaction.
At −70° C. and about 1 molal SO2F2 in tetrahydrofuran, this vapor pressure is roughly 75 torr, the exact figure dependent on the SO2F2 concentration. The use of vacuum conditions allows for the partial pressure of NH3 to be estimated during the course of the reaction.
Observed NH3 partial pressures during addition are a dependent function of other reaction parameters such as the type of solvent, NH3 addition rate, cooling power, SO2F2 concentration, mixing speed, and the degree of completion of the reaction. In some embodiments, the NH3 partial pressure can range from 0 to 150 torr, more preferably less than 50 torr, most preferably less than 20 torr. In tetrahydrofuran solvent at −70° C., NH3 partial pressures of 2 torr to 20 torr are observed during the addition. However, under conditions of high SO2F2 concentration and toward the end of the NH3 addition, NH3 partial pressures of as much as 150 torr in THF have been observed without a corresponding rise in temperature. Other reaction conditions can require much higher NH3 partial pressures. Endpoint pressures for 3:1 NH3/SO2F2 are typically less than 5 torr at −72° C.
Although a reactor pressure greater than 760 torr can be employed within the scope of the present invention, reactor pressures at or below atmospheric are preferably maintained during the course of NH3 addition and especially at the endpoint. In some embodiments, the endpoint pressure (i.e., the reactor pressure after NH3 addition is complete) is within 1 to 2 torr of the solvent vapor pressure. Higher pressures at the endpoint can indicate a reactor leak or the presence of residual SO2F2.
In some embodiments, the reactor contents are allowed to warm to room temperature, or higher, under high SO2F2 partial pressure (up to 10 atmospheres). The following reactions ensue:

2[NH4]+[(FSO2)2NH]−→2FSO2NH2+NH3(slow)

and

2NH3+SO2F2→FSO2NH2+[NH4]+[F]−(fast)

Under these conditions, the product FSO2NH2 can be recovered without acidification of the pot contents.
In an alternate embodiment, temperatures between −80° C. and −30° C. are employed at substantially constant reactor pressure (i.e., ±5% change in pressure), by introduction of SO2F2 using a gated valve to maintain the desired pressure over the course of the addition. This can reduce the cost of cooling the reactor.
Following the addition of NH3, a sufficiently strong acid can be added to the resulting mixture to “quench” the reaction. In some embodiments, the same temperature that was maintained during the adding can be maintained during the quenching. However, temperatures above −30° C. can be maintained during the addition of a quench acid. For example, in some embodiments a temperature of 30° C. or less, or 0° C. or less can be maintained during the quenching.
In some embodiments, the solid, which comprises [NH4]+[F]− and [NH4]+[FSO2NH]−, is acidified in situ with an acid (e.g., H2SO4), warmed, and filtered. Acids capable of forming a precipitate with the ammonium ion when added in a stoichiometric amount are preferred. For example, sulfuric acid works well when the reaction is run in tetrahydrofuran because ammonium sulfate and ammonium bisulfate are insoluble in this solvent.
After acidification and isolation, further purification of the resulting FSO2NH2 can be performed. In some embodiments, after acidification, the resulting FSO2NH2 is further optionally purified by distillation. Prior to distillation, volatile solvent can be removed, for example, by rotary evaporation and other means. Upon removal of the volatile solvent, the liquid residue is subjected to an extensive pump down before the product FSO2NH2 begins to distill. In some embodiments, the crude product contains HF, presumably bound in a 1:1 complex with FSO2NH2. For example, the presence of HF can be indicated by the slow corrosion of glassware, which indicates the presence of HF in the vapor efflux.
Yields of 60% or greater (based on the mole amount of SO2F2 starting material) have been achieved.
Compositions Comprising the Products
The present invention is further directed to compositions comprising the products. In some embodiments, a composition comprises a product of the present invention (i.e., FSO2NH2, [FSO2NH]−, and salts thereof) having a purity of 95% or greater, 98% or greater, 99% or greater, 99.5% or greater, 99.9% or greater, 99.99% or greater.
In an embodiment, the present invention is directed to the salt [NH4]+[FSO2NH]−.
In some embodiments, the present invention is directed to a composition comprising FSO2NH2, [FSO2NH]−, and salts thereof, in a purity of 95% or greater, 98% or greater, 99% or greater, 99.5% or greater, 99.9% or greater, 99.99% or greater. In some embodiments, the composition comprising FSO2NH2 and/or [FSO2NH]− further comprises 5% or less, 2.5% or less, 1% or less, 0.5% or less, 0.1% or less, or 0.01% or less by weight of hydrofluoric acid, fluorosulfonic acid, or a combination thereof. In some embodiments, the composition comprising FSO2NH2 and/or [FSO2NH]− is essentially free from hydrofluoric acid. In some embodiments, the composition comprising FSO2NH2 or [FSO2NH]− is essentially free from fluorosulfonic acid.
EXAMPLES
Example 1
A 600 mL stainless steel pressure reactor (Parr Instrument Company) equipped with several inlets, an analog 100 psi pressure/vacuum gauge, a temperature probe, and a stir paddle, was charged with tetrahydrofuran (400 mL, distilled from CaH2), and cooled with stirring to a temperature probe reading of −73° C. using a dry ice-methanol bath, and evacuated with a high vacuum pump starting at about −50° C. After ten minutes the internal pressure of the reactor had reached approximately −1 bar. The pump was disconnected and SO2F2 from a lecture bottle was introduced into the reactor over about six seconds to create an approximate 1 molal solution, the bottle of SO2F2 being weighed before and after to obtain an exact weight (37.7 g, 0.37 mol). When the reactor temperature had again reached −70° C., the internal vacuum had reached about −0.85 bar. The stir rate was checked to make sure it was maximized and three mole equivalents of NH3 gas (18.8 g, 1.1 mol) were then metered at a constant rate into the evacuated volume at the top of the reactor over the course of fifty-three minutes. During this time the pressure and temperature within the vessel rose slightly and then dropped to −1 bar and −71° C. by the end of the addition. The reactor was stirred for six minutes at −72° C.
A chilled solution of H2SO4 (36.2 g, 0.37 mol) in tetrahydrofuran (55 mL) was then introduced into the reactor over 15 minutes at −72° C. to −66° C., followed by warming to +15° C. with a hot water bath over 13 minutes. The reactor was opened, the solids removed by filtration, and washed with tetrahydrofuran. The filtrate was concentrated on a rotary evaporator (“rotovapped”) in a 45° C. water bath at 10 torr to constant volume. The liquor so obtained was diluted with ethyl ether (25 mL) giving a precipitate (sulfamide) which was filtered off. The filtrate was again rotovapped to constant volume and placed under high vacuum in a 70° C. oil bath. After an hour, volatile solvent and HF were gone, and the product distilled off (52° C. to 46° C., 55 microns [remote gauge]); yield, 21.9 g (0.22 mol, 60%), as a dense colorless liquid.
Example 2
A reactor as described in Example 1 was charged with THF (400 mL), sealed, cooled to −30° C., and evacuated to a static pressure of 6 Torr. SO2F2 was added through a pressure-gated valve until the setpoint pressure of 700 Torr was achieved; approximately 50 grams SO2F2 was initially added. Ammonia (7.7 grams) was metered into the reactor at a constant rate over 110 minutes, maintaining a temperature range of −30 to −39° C. The absorption of ammonia was slow, compared to the reaction at −70° C.; low infusion rates of NH3 were required to keep the gated valve in operation (cycling on and off). Toward the end of the addition, cycling ceased and a pressure of 200 Torr over the setpoint (i.e., 900 Torr) was observed. The addition was halted and the SO2F2 cylinder was weighed; 99.7 g was introduced. The reactor contents were stirred for two hours while warming to room temperature (22° C.) and held at room temperature for an hour, reaching an internal pressure of 64 psi (0.44 MPa; 4.4 atm). The reactor was then vented, opened, and the contents filtered. The filtrate was concentrated to 13 grams and diluted with ethyl ether (20 mL), giving a precipitate of sulfamide (4.95 grams). The supernatant was decanted, the solid washed with ether, and the liquids combined and concentrated to constant weight at room temperature under dynamic vacuum, yielding 2.93 grams of FSO2NH2—HF complex as a clear acidic oil.
These examples illustrate possible embodiments of the present invention. While various embodiments of the present invention have been described above, it should be understood that these are presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.
All documents cited herein, including journal articles or abstracts, published or corresponding U.S. or foreign patent applications, issued or foreign patents, or any other documents, are each entirely incorporated by reference herein, including all data, tables, figures, and text presented in the cited documents.

## Claims

1. A method comprising:
adding NH3 to a SO2F2 solution to form FSO2NH2 or a salt thereof comprising [FSO2NH]− ion, wherein said solution is maintained at a temperature of −30° C. or less during the adding;
adding an acid to the resulting mixture; and
isolating the FSO2NH2 from the resulting mixture.

2. The method of claim 1, wherein the SO2F2 solution comprises SO2F2 in a concentration of 0.1 to 3 molal.

3. The method of claim 1, wherein the NH3 is added to the SO2F2 solution in a molar ratio of 0.5:1 to 4:1 relative to the SO2F2.

4. The method of claim 1, wherein the SO2F2 solution comprises a solvent selected from the group consisting of tetrahydrofuran, ethyl acetate, ethyl ether, iso-propyl ether, 1,2-dimethoxyethane, acetonitrile, propionitrile, butyronitrile, dichloromethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrollidinone, and a combination thereof.

5. The method of claim 1, wherein the SO2F2 solution is maintained at a temperature of −80° C. to 30° C. during the adding.

6. The method of claim 1, wherein the SO2F2 solution has an initial temperature of −30° C. or less and is maintained within ±5° C. of the initial temperature during the adding.

7. The method of claim 1, wherein the acid has a pKa less than that of FSO2NH2 and is added in an amount sufficient to provide a pH of 3 or less.

8. The method of claim 7, wherein the acid is selected from the group consisting of HCl, HF, HBr, acetic acid, H3PO4, H2SO4, HSO3CH3, HSO3CF3, CF3COOH, and a combination thereof.

9. The method of claim 7, wherein the isolating comprises distilling the FSO2NH2.

10. The method of claim 1, wherein the salt is [FSO2NH]31[NH4]30, and precipitates as a solid from solution as a result of the adding.

11. The method of claim 10, comprising acidifying the solid to provide FSO2NH2, and distilling the FSO2NH2.

12. A method comprising:
adding NH3 to a SO2F2 solution to form FSO2NH2, wherein the SO2F2 solution contains an organic base with pKb greater than the pKb of NH3, wherein said solution is agitated at a temperature of −30° C. or less during the adding;
acidifying and filtering the resulting mixture; and
distilling the FSO2NH2 from the resulting mixture.

13. The method of claim 12, wherein the NH3 is added to the SO2F2 solution in a molar ratio of 0.5:1 to 4:1 relative to the SO2F2.

14. The method of claim 12, wherein the SO2F2 solution is maintained at a temperature of −80° C. to −30 ° C. during the adding.

15. The method of claim 12, where the step of acidifying and filtering the resulting mixture comprises adding an acid in situ in the resulting mixture.