METHOD FOR PRODUCING BORAZANE

Abstract

A process for obtaining borazane (NH.sub.3—BH.sub.3) includes introducing anhydrous liquid ammonia (NH.sub.3(l)) into a reactor thermostatically regulated to between a temperature θ.sub.1 and 40° C.; introducing, with stirring, into the reactor an amine borane complex (Am.BH.sub.3), the corresponding amine (Am) of which is soluble in anhydrous liquid ammonia only to a proportion of less than 10 g in 100 g of ammonia at 20° C., being introduced in an amount such that the mole ratio R=(NH.sub.3(l))/(Am.BH.sub.3) is greater than or equal to 5; stirring the mixture; stopping the stirring to obtain two demixed phases: a light phase constituted essentially of a solution of anhydrous liquid ammonia (NH.sub.3(l)) containing borazane; and a heavy phase constituted essentially of the amine corresponding to the amine borane complex introduced; isolating the borazane and drying under vacuum thereof; the temperature θ.sub.1 being greater than or equal to the melting point of the amine borane complex.

Claims

1. A process for obtaining borazane (NH.sub.3—BH.sub.3), comprising: providing a reactor, equipped with a stirring system and thermostatically regulated at a temperature between a temperature θ.sub.1 and 40° C.; introducing anhydrous liquid ammonia (NH.sub.3(l)) into said reactor; introducing, with stirring, into said reactor containing anhydrous liquid ammonia (NH.sub.3(l)), an amine borane complex (Am.BH.sub.3), said amine borane complex (Am.BH.sub.3), the corresponding amine (Am) of which is soluble in anhydrous liquid ammonia only to a proportion of less than 10 g in 100 g of anhydrous liquid ammonia at 20° C., being introduced in an amount such that the mole ratio R=anhydrous liquid ammonia (NH.sub.3(l))/amine borane complex (Am.BH.sub.3) is greater than or equal to 5; stirring the mixture to the point of depletion of said amine borane complex; stopping the stirring and obtaining, in said reactor, two demixed phases: a light phase constituted essentially of a solution of anhydrous liquid ammonia (NH.sub.3(l)) containing borazane; and a heavy phase constituted essentially of the amine (Am) corresponding to the amine borane complex (Am.BH.sub.3) introduced; isolating said borazane and drying under vacuum thereof; said temperature θ.sub.1 being greater than or equal to the melting point of said amine borane complex (Am.BH.sub.3).

2. The process as claimed in claim 1, wherein said anhydrous liquid ammonia (NH.sub.3(l)) is introduced at a pressure of between 5×10.sup.5 and 10.sup.6 Pa (5 and 10 bar).

3. The process as claimed in claim 1, wherein said reactor is, prior the introduction of the anhydrous liquid ammonia (NH.sub.3(l)), rendered inert.

4. The process as claimed in claim 1, wherein said amine borane complex (Am.BH.sub.3) is an alkylamine borane complex, the amine (Am) of which is a tertiary amine.

5. The process as claimed in claim 4, wherein said amine borane complex (Am.BH.sub.3) is chosen from the N,N,N-triisopropylamine borane complex, the N,N-diisopropyl-N-ethylamine borane complex, and mixtures thereof.

6. The process as claimed in claim 1, wherein said mole ratio R is between 5 and 20 (5≦R≦20).

7. The process as claimed in claim 1, wherein said reactor is thermostatically regulated between 18 and 30° C. and wherein said amine borane complex (Am.BH.sub.3) consists of the N,N-diisopropyl-N-ethylamine borane complex.

8. The process as claimed in claim 1, wherein isolating borazane comprises: discharging said heavy phase, constituted essentially of said amine (Am); removing by evaporation the anhydrous liquid ammonia (NH.sub.3(l)) of said light phase remaining in said reactor; and suction filtrating the solid obtained.

9. The process as claimed in claim 1, wherein said isolation of borazane comprises: removing, by evaporation, the anhydrous liquid ammonia (NH.sub.3(l)) of said light phase, lying on said heavy phase; and filtrating the mixture resulting from said removal.

10. The process as claimed in claim 8, comprising recompressing the ammonia removed by evaporation.

11. The process as claimed in claim 1, comprising, upstream, the synthesis of the amine borane complex (Am.BH.sub.3) from diborane (B.sub.2H.sub.6) and an amine (Am).

12. The process as claimed in claim 8, comprising, upstream, the synthesis of the amine borane complex (Am.BH.sub.3) from diborane (B.sub.2H.sub.6) and an amine (Am) and wherein the majority of the amine (Am) generated in said reactor, at least the amine (Am) present in said heavy phase, is recycled for performing said synthesis of the amine borane complex (Am.BH.sub.3).

13. The process as claimed in claim 5, wherein said amine borane complex (Am.BH.sub.3) consists of the N,N-diisopropyl-N-ethylamine borane complex.

14. The process as claimed in claim 6, wherein said mole ratio R is between 8 and 20 (8≦R≦20).

15. The process as claimed in claim 6, wherein said mole ratio R is between 8 and 12 (8≦R≦12).

16. The process as claimed in claim 7, wherein said reactor is thermostatically regulated between 18 and 25° C.

17. The process as claimed in claim 7, wherein said reactor is thermostatically regulated at 20° C.

18. The process as claimed in claim 9, comprising recompressing the ammonia removed by evaporation.

19. The process as claimed in claim 10, comprising recompressing the ammonia removed by evaporation and recycling thereof into said reactor.

20. The process as claimed in claim 18, comprising recompressing the ammonia removed by evaporation and recycling thereof into said reactor.

Description

[0083] Said figures illustrate two implementation variants of the process of the invention.

[0084] FIG. 1 is a flow chart of an implementation variant of the process of the Invention in which the borazane formed is recovered after discharge of the heavy phase (procedure A above);

[0085] FIG. 2 is a flow chart of an implementation variant of the process of the invention in which the borazane formed is recovered after being mixed into the heavy phase (procedure B above).

[0086] In FIGS. 1 and 2, the synthesis of the Am.BH.sub.3 complex is performed, upstream, from diborane (B.sub.2H.sub.6) and an amine (Am).

[0087] After introducing anhydrous liquid ammonia NH.sub.3(l) into reactor 1, the Am.BH.sub.3 complex synthesized upstream is introduced therein and reacted.

[0088] On conclusion of the reaction, the following are found, demixed, in said reactor 1: [0089] a light phase 1a, lying on a heavy phase 1b, said light phase 1a essentially containing the borazane formed (NH.sub.3BH.sub.3) dissolved in the anhydrous liquid ammonia NH.sub.3(l) but also amine (εAm) dissolved in said anhydrous liquid ammonia NH.sub.3(l); [0090] said heavy phase 1b essentially containing the amine (Am).

[0091] The presence, in small amounts, in said heavy phase 1b, of other products: εPi (essentially products of decomposition of said amine (Am)) has been indicated.

[0092] According to the procedure represented schematically in FIG. 1, the heavy phase 1b is discharged. The borazane formed is then isolated as follows: 1) reactor 1 is depressurized, for evaporation of the ammonia, and 2) the borazane obtained, contaminated with amine (εAm) is suction filtered by filtration under vacuum (it is thus, without impairment, virtually freed of the amine and the amine recovered is conveniently added to the heavy phase discharged). The borazane thus isolated is then contaminated only with traces of amine (εAm). It has been schematically shown that these traces are in very limited amounts (εAm<εAm). Said isolated borazane is finally dried under vacuum.

[0093] According to the procedure represented schematically in FIG. 2, reactor 1 is first depressurized. The ammonia is evaporated off and the borazane is found in solid form in the heavy phase 1b. It in fact is constituted by a solid/liquid mixture, which, besides said heavy phase 1b, thus contains said borazane and amine (εAm) originating from the light phase 1a. This mixture is referenced 1b′. For reasons of simplification, Am (=Am+εAm) has been indicated. Filtration (advantageously under an inert gas) is then performed for isolation of said borazane. The isolated borazane is dried under vacuum to be freed (without impairment) of the traces of amine (εAm) entrained on filtration. It has been schematically shown that these traces are in very limited amounts (εAm<εAm).

[0094] The heavy phase finally recovered (referenced 1B (=1b+(ε−ε)Am) in FIG. 1 and referenced 1b″ (=1b+(ε−ε)Am) in FIG. 2; said figures obviously being considered independently) is, according to the two procedures represented schematically, recycled for the upstream synthesis of the Am.BH.sub.3 complex. During this recycling, it is optionally (whence the dotted lines) purified. This optional purification may especially be performed by distillation. This purification is mainly directed toward removing the decomposition products of the amine Am (εPi, present, in more or less large amounts, depending on the operating temperature of the reaction).

[0095] The gaseous ammonia recovered is, according to the two procedures represented schematically, recompressed and used, in liquid form, to feed reactor 1.

EXAMPLE 1

[0096] A jacketed glass reactor, with a volume of 300 ml, withstanding a pressure of 10.sup.6 Pa (10 bar), equipped with a magnetic stirrer, was used.

[0097] It was rendered inert beforehand with nitrogen and thermostatically regulated at 20° C.

[0098] 0.59 mol of ammonia was transferred, from an ammonia bottle (under 7×10.sup.5 to 8×10.sup.5 Pa (7 to 8 bar of pressure)) into said inertized and thermostatically regulated reactor.

[0099] Stirring was then started. The amine-borane complex (N,N-diisopropyl-N-ethylamine borane (commercial product); 0.059 mol) was then added in less than 30 seconds. The ammonia (liquid)/amine borane complex mole ratio was thus equal to 10.

[0100] After 15 minutes, the stirring was stopped. To check that the reaction (N,N-diisopropyl-N-ethylamine borane+NH.sub.3 (liquid)) was complete, a sample of the reaction medium (liquid) was taken. The sampling (in a vial) was performed, hermetically, after placing the headspace of the internal volume of the reactor under nitrogen pressure. The sample withdrawn, diluted in tetrahydrofuran (THF), was analyzed by .sup.11B (boron) NMR. Absence of the amine-borane complex was confirmed. The reaction was thus complete (within the detection limits of the NMR analysis).

[0101] After stopping the stirring, the reaction medium was demixed and two phases were observed: a light phase, essentially containing the borazane (NH.sub.3BH.sub.3) formed in solution in the liquid ammonia, and a heavy phase essentially containing the amine (N,N-diisopropyl-N-ethylamine). Said two phases are liable to contain, in small amounts, side products (essentially dissolved amine for the light phase and essentially amine decomposition products for the heavy phase).

[0102] To isolate the borazane formed, present in the light phase, the process was performed as follows: [0103] discharging, via a withdrawal cannula located at the bottom of the reactor, of the heavy phase essentially containing the amine (N,N-diisopropyl-N-ethylamine); and then [0104] evaporating the (liquid) ammonia of the light phase by depressurization of the reactor (for 15 minutes at a temperature of 20° C.).

[0105] The (solid) borazane recovered contained (liquid) amine (about 9.5% by mass). It was first suction filtered by filtration (under nitrogen, at room temperature, under a vacuum of 10.sup.3 Pa (10 mbar)) and then dried under vacuum in an oven (at 20° C., for 12 hours, under a reduced pressure of 10.sup.3 Pa (10 mbar)).

[0106] Borazane was finally obtained in a yield of 93% (the sampling performed upstream was taken into account for the calculation of this yield).

[0107] Its purity was monitored by solid 11B NMR. It was pure to 97% by mass. The main impurity it contained was boron oxides. The borazane obtained was stored under argon.

[0108] The ammonia recovered was recompressed and recycled upstream of the synthesis (for reaction with the amine-borane complex).

EXAMPLE 2

[0109] A jacketed glass reactor, with a volume of 300 ml, withstanding a pressure of 10.sup.6 Pa (10 bar), equipped with a magnetic stirrer, was used.

[0110] It was rendered inert beforehand with nitrogen and thermostatically regulated at 20° C.

[0111] 0.665 mol of ammonia was transferred in, from an ammonia bottle (under 7×10.sup.5 to 8×10.sup.5 Pa (7 to 8 bar of pressure)), into said inertized and thermostatically regulated reactor.

[0112] Stirring was then started. The amine-borane complex (N,N-diisopropyl-N-ethylamine borane (commercial product); 0.013 mol) was then added in less than 30 seconds. The ammonia (liquid)/amine-borane complex mole ratio was thus greater than 51.

[0113] After 40 minutes, the stirring was stopped. To check that the reaction (N,N-diisopropyl-N-ethylamine borane+NH.sub.3 (liquid)) was complete, a sample of the reaction medium (liquid) was withdrawn. The sampling (in a vial) was performed, hermetically, after placing the headspace of the internal volume of the reactor under pressure of nitrogen. The sample withdrawn, diluted in tetrahydrofuran (THF), was analyzed by 1B (boron) NMR. Absence of the amine-borane complex was confirmed. The reaction was thus complete (within the limits of detection by NMR analysis).

[0114] After stopping the stirring, the reaction medium was demixed and two phases were observed: a light phase, essentially containing the borazane (NH.sub.3BH.sub.3) formed in solution in liquid ammonia and a heavy phase essentially containing the amine (N,N-diisopropyl-N-ethylamine). Said two phases are liable to contain, in small amounts, side products (essentially dissolved amine for the light phase and essentially amine decomposition products for the heavy phase).

[0115] To isolate the borazane formed, present in the light phase, the process was performed as follows: [0116] evaporating the (liquid) ammonia of said light phase by depressurization of the reactor (for 15 minutes at a temperature of 20° C.); [0117] recovering a solid/liquid mixture mainly containing borazane and amine ((solid) borazane/(liquid)amine); [0118] filtrating under inert gas (nitrogen) for recovery of said borazane.

[0119] The isolated borazane was then dried under vacuum, at 20° C., for 12 hours, under a reduced pressure of 10.sup.3 Pa (10 mbar) (for removal of the traces of amine contaminating it).

[0120] The borazane was thus obtained in a yield of 94% (the sampling performed upstream was taken into account for the calculation of this yield).

[0121] Its purity was monitored by solid .sup.11B NMR. It was pure to 97% by mass. The main impurity it contained consisted of boron oxides (despite the inertizing with nitrogen, it is in fact virtually impossible to avoid the formation of a very small amount of boron oxide(s), quite probably due to the presence of small amounts of oxygen in the inertizing gas and/or in the liquid ammonia). The borazane obtained was stored under argon.

[0122] The ammonia recovered was recompressed and recycled upstream of the synthesis (for reaction with the amine-borane complex).