WO2014029834A1

WO2014029834A1 - Method for the preparation of tetraalkylammonium tetracyanidoborates

Info

Publication number: WO2014029834A1
Application number: PCT/EP2013/067436
Authority: WO
Inventors: Lothar Ott; Christiaan RIJKSEN; Stefan Ellinger; Katharina SIEVERT; Jörg HARLOFF; Axel Schulz
Original assignee: Lonza Ltd
Priority date: 2012-08-24
Filing date: 2013-08-22
Publication date: 2014-02-27

Abstract

The invention discloses a method for the preparation of tetra alkylammonium tetracyanidoborate starting from tetraalkylammonium tetrafluoroborate and trimethylsilylcyanide.

Description

METHOD FOR THE PREPARATION OF TETRAALKYLAMMONIUM

TETRACYANIDOBORATES

The invention discloses a method for the preparation of tetra alkylammonium

tetracyanidoborate starting from tetraalkylammonium tetrafluoroborate and

trimethylsilylcyanide.

BACKGROUND OF THE INVENTION

The term "ionic liquid" (IL) is usually used to refer to a salt which is liquid at temperatures below 100°C, in particular at room temperature. Such liquid salts typically comprise organic cations and organic or inorganic anions, and are described inter alia in P. Wasserscheid et al., Angew. Chem., 2000, 112, 3926-3945.

Ionic liquids have a series of interesting properties: Usually, they are thermally stable, relatively non-flammable and have a low vapour pressure. In addition, they have good solvent properties for numerous organic and inorganic substances. Owing to their ionic structure, ionic liquids also have interesting electrochemical properties, for example electrical conductivity which is often accompanied by a high electrochemical stability. Therefore, there is a fundamental need for ionic liquids having a variety of properties which open up additional opportunities for their use.

An interesting family of ionic liquids contains tetra valent boron anions. Tetrafluoroborate containing ionic liquids were among the first of this new generation of compounds and 1- ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF₄]) was prepared via metathesis of [EMIm]I with Ag[BF₄] in methanol as disclosed by J. S. Wilkes et al., J. Chem. Soc. Chem. Commun. 1990, 965.

E. Bernhardt, Z. Anorg. AUg. Chem. 2003, 629, 677-685, discloses the reaction of M[BF₄] (M = Li, K) with (CH₃)₃SiCN (TMSCN). The preparation of Li[BF(CN)₃] is disclosed to take 7 days, that of K[BF(CN)₃] takes one month. The yield of K[BF(CN)₃] was 60%, the product contained 5% K[BF₂(CN)₂]. The molar ratio of [BF₄]^~ : TMSCN was 1 : 7.8. EP 2 327 707 A claims in claim 7 a method for producing an ionic compound represented by the general formula (I), comprising a step of reacting starting materials containing a cyanide and a boron compound. General formula (I) is a salt of a cation Kt^m+ with [B(CN)4] .

The examples disclose various methods for preparing tetrabutylammonium tetracyanoborate, for example:

1) Example 1-1 of EP 2 327 707 A discloses a reaction of tetrabutylammonium bromide, zinc (II) cyanide and boron tribromide in toluene at 130°C for 2 days, with a yield of 35%. The molar ratio of boron compound : TMSCN was 1 : 5.5.

2) Example 2-1 of EP 2 327 707 A discloses a reaction of tetrabutylammonium bromide, tetrabutylammonium cyanide and boron tribromide in toluene at 130°C for 2 days, with a yield of 77%. The molar ratio of boron compound : tetrabutylammonium cyanide was 1 : 7.1.

3) Example 3-3 of EP 2 327 707 A discloses a reaction of tetrabutylammonium bromide, trimethylsilyl cyanide and boron trichloride in p-xylene at 150°C for 30 hours, with a yield of 98%. The molar ratio of boron compound : TMSCN was 1 : 5.5.

4) Example 3-11 of EP 2 327 707 A discloses a reaction of boron trifluoride diethyl ether, tetrabutylammonium bromide and trimethylsilylcyanide at 170°C for 30 hours, with a yield of 75%.

But not all embodiments which fall under claim 7 actually work well: Example 3 of the instant invention shows one embodiment also starting with boron trifluoride diethyl ether, which falls under claim 7, but produces the desired [B(CN)₄] salt only as a by-product in negligible amounts, the main product is a [BF(CN)_B] salt.

There was a need for a process for the preparation of tetracyanidoborates, which provides economic access to this class of substances, which for example can be used as ionic liquids or as precursors for the preparation of ionic liquids. The process should have satisfactory yield and purity, and the reaction time should be short. The boron source should be a readily available compound with low costs. The cyanide source should not be a metal cyanide to avoid its negative impact on the environment. The number of reactants should be small and the method should allow the conversion without the presence of a solvent. Furthermore the content of CI and Br in the final product should be low, and preferably no reaction solvent should be required. Also the content of Si and cyanide in the final product should be low.

Unexpectedly a process can be provided by a reaction of tetraalkylammonium

tetrafluoroborate and trimethylsilylcyanide. Irrespective of various work up procedures comprising a treatment with H₂0₂, the yields of the instant reaction are higher than reported in EP 2 327 707 A, which is demonstrated in examples 1, 5, 6, 7 and 12 in comparison e.g. to the yield of example 6-2 of EP 2 327 707 A. Example 12 employs a work up procedure similar to the one disclosed in example 5-1 of the EP 2 327 707 A.

By the selection of the substrates the process is free of CI and Br.

The method of the invention provides the desired products in high yield and high purity, the reaction time is shorter compared with the prior art. No metal compound is necessary as cyanide source, and only the two reactants boron source and cyanide source are needed. The method does not necessitate the presence of a solvent, whereas all examples of EP 2 327 707 A use a reaction solvent such as toluene, dimethylsulfoxide or p-xylene. The repetition of the only example 3-11 of EP 2 327 707 A using a boron fluoride compound as starting material already proved to be unsuccessful when the ammonium component was exchanged (tetraethylammonium fluoride in example 3 of instant invention instead of

tetrabutylammonium bromide in example 3-11 of EP 2 327 707 A). This result would not encourage the skilled person to avoid the use of ammonium bromides or chlorides as disclosed and suggested in the EP 2 327 707 A, in order to minimize the Br and CI content in the final product.

The content of Si and cyanide in the final product is low, and this low content is obtained irrespective of the work up procedure as exemplified in instant examples 1, 5 and 12. The values for the content of Si and of cyanide in instant examples 1, 5 and 12 demonstrate, that the instant method allows to obtain a content of Si and of cyanide, which is even lower than the values given in EP 2 327 707 A in Table 3 for Synthesis Example 6-2, which in comparison to instant examples 1, 5 and 12 is an example that uses similar substrates and similar work up procedure to obtain the same product tetrabutylammonium tetracyanoborate. The yield of the instant method is high, and is actually higher in comparison to e.g. Synthesis Example 6-2 of EP 2 327 707 A.

In this text,

alkyl means linear, branched, cyclic or cyclo alkyl;

cyclic alkyl or cyclo alkyl are intended to include cyclo and polycyclo, such as bicyclo or tricyclo, aliphatic residues;

IL ionic liquid;

RT room temperature, it is used synonymously with the expression ambient temperature; TMSCN (CH₃)₃SiCN, trimethylsilylcyanide; "wt%", "% by weight" and "weight-%" are used synonymously and mean percent by weight; if not otherwise stated.

SUMMARY OF THE INVENTION

Subject of the invention is a method for the preparation of compound of formula (I);

R4 by a reaction between compound of formula (II) and trimethylsilylcyanide;

R4

Rl , R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of hydrogen and Ci_io alkyl.

DETAILED DESCRIPTION OF THE INVENTION

Preferably, Rl is hydrogen or Ci_io alkyl; and

R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of Ci_io alkyl;

more preferably, Rl , R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of Ci_io alkyl;

even more preferably, Rl , R2, R3 and R4 are identical and selected from the group consisting of C i-io alkyl;

especially, Rl , R2, R3 and R4 are identical and selected from the group consisting of Ci_s alkyl;

more especially, Rl , R2, R3 and R4 are identical and selected from the group consisting of methyl, ethyl, propyl, butyl or octyl; even more especially, Rl, R2, R3 and R4 are identical and selected from the group consisting of methyl, ethyl, n-butyl or n-octyl;

in particular, Rl, R2, R3 and R4 are n-butyl. Preferably, from 4 to 10 mol equivalents, more preferably from 4.1 to 8 mol equivalents, even more preferably from 4.1 to 7 mol equivalents, especially from 4.1 to 5 mol equivalents, of trimethylsilylcyanide are used, the mol equivalents being based on the mol of compound of formula (II). Preferably, the reaction is done in the absence of a solvent, i.e. no solvent is used.

Preferably, the reaction temperature is from 180 to 220 °C, more preferably from 190 to 220°C.

Preferably, the reaction time is from 30 min to 48 h, more preferably from 30 min to 36 h, even more preferably from 30 min to 24 h, especially from 2 h to 18 h; more especially from 5 h to 18 h, even more especially from 10 h to 18 h.

Preferably, the reaction is done in a closed system and at the pressure caused by the chosen temperature.

Preferably, the reaction is done under inert atmosphere. Preferably, the inert atmosphere is achieved by the use if an inert gas preferably selected from the group consisting of argon, another noble gas, lower boiling alkane, nitrogen and mixtures thereof.

The lower boiling alkane is preferably a Ci_₃ alkane, i.e. methane, ethane or propane.

After the reaction, compound of formula (I) can be isolated by standard methods such as evaporation of volatile components, extraction, washing, drying, concentration,

crystallization, chromatography and any combination thereof, which are known per se to the person skilled in the art.

Preferably, after the reaction the reaction product is treated with hydrogen peroxide, preferably with aqueous hydrogen peroxide. More preferably for isolation, the reaction product is mixed with aqueous hydrogen peroxide to provide a mixture (M).

Preferably, the concentration of the hydrogen peroxide is from 10 to 40 wt% hydrogen peroxide, the wt% based on the total weight of the aqueous hydrogen peroxide.

Preferably, from 1 to 10 mol equivalents, more preferably from 1 to 5 mol equivalents, of hydrogen peroxide are used, the mol equivalents being based on the mol of compound of formula (II). Preferably mixture (M) is stirred for 5 min to 12 h, more preferably for 10 min to 6 h, even more preferably for 15 min to 2 h.

Preferably mixture (M) is stirred at a temperature (M), temperature (M) is preferably from ambient temperature to 100°C, more preferably from 40°C to 80°C.

After treatment with hydrogen peroxide, mixture (M) is preferably filtrated. The residue of the filtration is preferably washed with a solvent (WASH), solvent (WASH) is preferably water. The residue is preferably dissolved with a solvent (DISSOLV) to provide a solution

(DISSOLV), solvent (DISSOLV) is preferably CH₃CN, CH₂C1₂, ethyl acetate, CHC1₃, MeOH or EtOH, more preferably CH3CN.

The amount of solvent (DISSOLV) is preferably from 2 to 40 fold, more preferably from 3 to 20 fold, even more preferably from 5 to 15 fold, of the weight of compound of formula (II).

Preferably, solution (DISSOLV) is treated with charcoal, preferably 1 to 10 times.

The amount of charcoal is preferably 0.1 to 1 fold of the weight of compound of formula (II). In another preferred embodiment, mixture (M) is extracted with a solvent (EXTRACT). Solvent (EXTRACT) is preferably selected from the group consisting of dichloromethane, diethyl ether and chloroform. Any drying of an organic phase, e.g. the organic phase obtained after extraction with solvent (EXTRACT), is preferably done with Na₂S0₄, K₂C0₃, CaCl₂ or MgS0₄.

Any isolation from a solution, e.g. from solution (DISSOLV), is preferably done by evaporation of the solvent.

Compounds of formula (II) are known compounds and can be prepared according to known methods, e.g. by metathesis reaction starting from HBF₄, from KBF₄ or from LiBF₄.

Examples

Methods

1H and ¹³C NMR spectra were recorded on a Bruker AVANCE 300 (300 MHz) (300 MHz for 1H and 250 MHz for ¹³C) instruments in CD₃CN or d6-DMSO. Chemical shifts are expressed in parts per million referred to TMS and coupling constants (J) in Hertz.

IR-spectra were recorded on a Nicolet 380 FT-IR spectrometer. Measurements were done at room temperature.

RAMAN-spectra were recorded on a Kaiser Optical Systems RXN 1-785. The intensity was normalized on 10 for the most intensive peak.

The C/H/N-analyses were measured on a C/H/N/S-Analysator (Thermoquest Flash EA 1112).

Melting points were measured on a DSC 823e from Mettler-Toledo. The calibration was carried out with the melting points of In (156.6 ± 0.3°C) and Zn (419.6 ± 0.7°C) with an heating rate of 5 K per min. Cyanid content was determined by polarography using a Metrohm 795 VA Computrace.

Settings were according to Application Bulletin Nr. 110/2 d of Metrohm for the determination of free cyanide.

Sample preparation: 0.1 to 0.4 g of sample was suspended in aqueous KOH (25 ml, 0.01 mol/L).

Si content was determined by Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) using a Thermo ICP/OES Spektrometer Intrepid II XDL.

Samples preparation was the same as for the determination of cyanide content. Example 1 : Synthesis of [(n-Bu)₄N] [B(CN)₄]

[(n-Bu)₄N][BF₄] (1.03 g, 3.13 mmol), prepared according to example 2, and (CH₃)₃SiCN (1.87 g, 18.85 mmol) were filled under argon atmosphere with a residual oxygen content of below 5 ppm and with a residual water content of below 1 ppm into a teflon tube of an autoclave. The autoclave was placed inside a muffle furnace and heated to 200°C within 30 minutes. The temperature was held for 15 hours.

After cooling to ambient temperatures the black oily reaction mixture was mixed with water (10 ml) and aqueous H₂0₂ (1 ml, 10 mmol, 30 wt%). After stirring at 60°C for an hour and cooling to ambient temperature the suspension was filtered. The brown solid was washed two times with water. The crude product was dissolved in 10 ml of CH₃CN and 0.5 g activated charcoal was added. After stirring for 15 minutes at 50°C the suspension was filtered and new activated charcoal was added. This procedure was repeated four times. The orange solution were evaporated on a rotary evaporator to obtain the product with a yield of 836 mg (75%, 2.34 mmol).

Only one boron species, the one of the desired product, and no fluorine species is visible in ⁿB NMR and in the ¹⁹F NMR respectively.

Analytics

Mp: 79°C

C/H/N Analysis calc. % (found): C 67.22 (66.18), H 10.15 (9.85), N 19.60 (19.99)

1H NMR (25°C, CD₃CN, 300.13 MHz, delta in ppm): 0.96 (t, 12H, CH_3, ³J(1H-1H) = 7.3 Hz), 1.35 (m, 8H, CH₃-CH_2, ³J(1H-1H) = 7.5 Hz), 1.59 (m, 8H, CH₂-CH₂N), 3.07 (m, 8H, NCH₂) ¹³C NMR (25 °C, CD₃CN, 250.13 MHz, delta in ppm): 14.40 (s, 4C, CH₃), 20.94 (m, 4C, CH₃-CH₂), 24.93 (m, 4C, CH₂-CH₂N), 59.98 (m, 4C, NCH₂), 123.85 (q, 4C, CN, ^("B-^C) = 71.0 Hz)

^UB NMR (25°C, CD₃CN, 96.29 MHz, delta in ppm): -38.63 (s, IB, B(CN)₄, ^("C^B = 71.0 Hz)

IR (ATR, 32 scans, v in cm^"1): 2963 (s), 2935 (m), 2876 (m), 2221 (w), 1705 (w), 1591 (w), 1474 (m), 1456 (w), 1409 (w), 1381 (w), 1360 (w), 1324 (w), 1244 (w), 1169 (w), 1110 (w), 1060 (w), 1035 (w), 991 (w), 967 (w), 931 (s), 885 (m), 842 (w), 824 (w), 802 (w), 736 (m), 534 (w)

Cyanid content was 81 ppm.

Si content was 163 ppm.

Example 2: Synthesis of [(n-Bu₄)N] [BF₄]

K[BF₄] (3.12 g, 24.78 mmol) was dissolved in 15 ml of H₂0. [(n-Bu)₄N]Br (8.05 g, 24.98 mmol) was dissolved in 25 ml of CH₂C1₂ and added to the aqueous solution of K[BF₄]. After stirring for 24 hours at ambient temperature the phases were separated. The organic phase was washed three times with 10 ml of water dried over anhydrous Mg₂S0₄ and filtered. The filtrate was concentrated on a rotary evaporator to obtain a white solid. The obtained solid was dried at 90°C in vacuo for 15 hours. The yield of [(n-Bu₄)N][BF₄] was 7.83 g (96 %, 23.8 mmol).

Analytics

Mp: 153°C

C/H/N Analysis calc. % (found): C 58.36 (58.48), H 11.02 (10.84), N 4.25 (4.13)

1H NMR (25°C, CD₃CN, 300.13 MHz, delta in ppm): 0.96 (t, 12H, CH₃, ³J(1H-1H) = 7.3 Hz), 1.35 (m, 8H, CH₃-CH₂, 1.61 (m, 8H, CH₂-CH₂N), 3.11 (m, 8H, NCH₂)

¹³C NMR (25 °C, CD₃CN, 250.13 MHz, delta in ppm): 14.42 (s, 4C, CH₃), 20.94 (m, 4C,

CH₃-CH₂), 24.95 (m, 4C, CH₂-CH₂N), 59.93 (m, 4C, NCH₂)

UB NMR (25°C, CD₃CN, 96.29 MHz, delta in ppm): -1.18 (s, IB, BF₄)

1⁹F NMR (25°C, CD₃CN, 300.13 MHz, delta in ppm): -151.61 (4F, BF₄)

IR (ATR, 32 scans, v in cm^"1): 2960 (m), 2935 (w), 2875 (w), 1486 (m), 1468 (w), 1382 (w), 1285 (w), 1152 (w), 1093 (m), 1047 (s), 1034 (s), 881 (w), 800 (w), 739 (w)

RAMAN (460 mW, 150 scans cm^"1): 2964 (7), 2933 (10), 2876 (10), 2746 (1), 1453 (4), 1327(2), 1153(1), 1137 (2), 911 (2), 880 (1), 766 (1), 256 (2), 79 (1) Example 3: Conversion of BF₃ OEt₂ with Et₄NF and TMSCN in analogy to example 3-11 of EP 2 327 707 Al

A 100 ml three-necked-flask equipped with a magnetic stirrer and a reflux condenser was loaded with tetraethylammonium fluoride

(4.112 g, 27.6 mmol). Then (CH₃)₃SiCN (19.8 g, 200 mmol) was added at room temperature and stirred and mixed. Next 3.98 g (28.00 mmol) of boron trifluoride diethyl ether complex were added dropwise through a spraying device.

Then the reaction container was heated to 170°C. The temperature was held for 30 hours. The formed (CH₃)₃SiF volatilized through a bubble counter (bp: 16°C).

After cooling to ambient temperature the excess (CH₃)₃SiCN was removed under reduced pressure. Next the black crude product was dissolved in ethyl acetate to obtain a 10 wt% solution in ethyl acetate,

and 8 g of activated carbon were added. The suspension was heated to 50°C and stirred at 50°C for 10 minutes. The suspension was filtered to yield a filtrate. The activated carbon residue on the filter was 5 times extracted, each time with 10 ml ethyl acetate, by suspending the activated carbon in the ethyl acetate, stirring for 10 min at 50°C and filtering.

The obtained filtrate and the five ethyl acetate extracts were combined and the ethyl acetate was removed under reduced pressure. The obtained product was heat-dried at 50°C in vacuo to yield 0.72 g (5.53 mmol, 20%).

Hydrogen peroxide (aqueous 30 wt% H₂0₂ solution, 1.6 g) was added to the obtained product. The solution was stirred for 60 minutes at 50°C. After cooling to ambient temperature 6.5 g butyl acetate was added to the H₂0₂ solution. After mixing the solution was transferred into centrifuge tubes. After centrifugation (1700 rpm, 10 minutes) the supernatant layer was separated. The butyl acetate was removed on a rotary evaporator. In accordance with ⁿB NMR the main product was [Et₄N][BF(CN)₃] with a yield of 0.384 g (2.95 mmol, 11 %). [Et₄N][B(CN)₄] was detected as a minor by-product with the ratio [BF(CN)₃] : [B(CN)₄] of the peak areas of the boron peaks being 99: 1. Example 4: Synthesis of [(n-Bu)₄N] [B(CN)₄]

Example 1 was repeated with the following differences:

1. [(n-Bu)4N][BF₄] (2.14 g, 6.50 mmol), prepared according to example 2, and (CF£₃)₃SiCN (3.87 g, 39.00 mmol) were used.

2. After the 15 hours at 200°C the reaction mixture was cooled to ambient temperature and the excess (CF£₃)₃SiCN was removed in vacuo. The brown solid was dissolved in 20 ml of ethyl acetate and 4 g activated carbon was added. The suspension was stirred at 50°C for 10 minutes. The suspension was filtered off to obtain an orange solution. The activated carbon residue on the filter was 5 times extracted, each time with 10 ml ethyl acetate, by suspending the activated carbon in the ethyl acetate, stirring for 10 minutes at 50°C and filtering.

The orange solution and the five ethyl acetate extracts were combined and the ethyl acetate was removed under reduced pressure. The obtained solid was dried in vacuo to yield 2.20 g (95%, 6.16 mmol) of [(n-Bu₄)N][B(CN)₄]. Only one boron species, the one of the desired product tetracyanidoborate, and no fluorine species, is visible in ⁿB NMR and in ¹⁹F NMR respectively.

Example 5: Synthesis of [(n-Bu)₄N] [B(CN)₄] [(n-Bu₄)N][B(CN)4] (2.20 g, 6.16 mmol), prepared according to example 4, was suspended in aqueous H₂0₂ (5 ml, 30 wt%). After stirring at 60°C for an hour the suspension was filtered and washed two times with 10 ml of water. The obtained white solid was dissolved in 20 ml CH₂C1₂. The CH₂C1₂ solution was also washed with 10 ml of water. After separation the organic layer was dried with Na₂S0₄ and filtered. The dichloromethane was removed under reduced pressure. The obtained white solid was heat-dried in vacuo to yield 1.81 g (78%, 5.07 mmol) of [(n-Bu₄)N][B(CN)₄].

Analytics

Mp: 83°C

C/H/N Analysis calc. % (found): C 67.22 (67.21), H 10.15 (10.02), N 19.60 (19.37)

The IR and NMR data are the same as in Example 1.

Cyanid content was 34 ppm.

Si content was 71 ppm.

Example 6: Synthesis of [(n-Bu)₄N] [B(CN)₄]

Example 1 was repeated with the differences:

1. [(n-Bu)₄N][BF₄] (0.532 g, 1.62 mmol), prepared according to example 2, and

(CH₃)₃SiCN (0.98 g, 9.91 mmol) were used.

2. The temperature was 190°C instead of 200°C, which was held for 18 h instead of 15 h. A white crystalline product [(n-Bu)₄N][B(CN)₄] was obtained (0.44 g, 76%, 1.23 mmol).

Analytics

C/H/N Analysis calc. % (found): C 67.22 (66.83), H 10.15 (10.11), N 19.60 (20.16)

The NMR and IR data are the same as in example 1.

Example 7: Synthesis of [(n-Bu)₄N] [B(CN)₄]

Example 1 was repeated with the differences:

1. [(n-Bu)₄N][BF₄] (0.355 g, 1.08 mmol), prepared according to example 2, and

(CH₃)₃SiCN (0.65 g, 6.57 mmol) were used.

2. The temperature was 180°C instead of 200°C, which was held for 30 h instead of 15 h. A white crystalline product was obtained (0.28 g, 73%, 0.79 mmol). Analytics

C/H/N Analysis calc. % (found): C 67.22 (67.07), H 10.15 (9.98), N 19.60 (19.65)

The NMR and IR data are the same as in example 1.

Example 8: Synthesis of [Me₄N] [B(CN)₄]

Example 1 was repeated with the differences:

1. [Me₄N[BF₄] (0.367 g, 2.28 mmol), prepared according to example 10, and

(CH₃)₃SiCN (1.29 g, 13 mmol) were used.

2. After addition of water and aqueous hydrogen peroxide, stirring at 60°C for an hour and cooling to ambient temperature a solution was obtained and not a suspension as in example 1. This solution was filtered. The filtrate was concentrated on a rotary evaporator. The product was dried at 90°C and 0.001 mbar for 10 h. The yield of the white crystalline product [Me₄N][B(CN)₄] was 0.32 g (74%, 1.69 mol).

Analytics

C/H/N Analysis calc. % (found): C 50.83 (50.64), H 6.40 (6.37), N 37.05 (37.12)

1H NMR (25°C, CD₃CN, 300.13 MHz, delta in ppm): 3.06 (s, 12H, CH₃ )

1³C NMR (25 °C, CD₃CN, 250.13 MHz, delta in ppm): 54.41 (t, 4C, CH₃), 123.65 (q, 3C, CN 1J(¹¹B-¹³C) = 71.1 Hz)

nB NMR (25°C, CD₃CN, 96.29 MHz, delta in ppm): -38.63 (s, IB, B(CN , ^("C^B = 71.0 Hz)

Example 9: Synthesis of [(n-Oct)₄N] [B(CN)₄]

Example 1 was repeated with the differences:

1. [(n-Oct)₄N][BF₄] (0.038 g, 0.07 mmol), prepared according to example 11, and

(CH₃)₃SiCN (0.12 g, 1.21 mmol) were used.

2. After evaporation on the rotary evaporator the product was dried at 90°C and ca. 0.001 mbar for 10 h. The yield of the oily orange product [(n-Oct)₄N][B(CN)₄] was 0.028 g (70%, 0.05 mmol).

Analytics

C/H/N Analysis calc. % (found): C 74.32 (73.66), H 11.78 (11.54), N 12.02 (11.82)

1H NMR (25°C, CD₃CN, 300.13 MHz, delta in ppm): 0.89 (t, 12H, CH₃), 1.30 (m, 40H, CH (CH2)s), 1.58 (m, 8H, N-CH2-CH2), 3.04 (m, 8H, N-CH2)

¹³C NMR (25 °C, CDsCN, 250.13 MHz, delta in ppm): 14.35 (s, 4C, CHs), 22.29 (s, 4C, CH3-CH2), 23.32 (s, 4C, N-(CH₂)2-CH₂), 26.82 (t, 4C, N-CH2-CH2), 29.56 (s, 4C, N- (CH₂)3-CH₂), 29.67 (s, 4C, CH3-(CH₂)2-CH₂), 32.43 (s, 4C, CH3-CH2-CH2), 59.72 (t, 4C, N-CH2), 123.62 (q, 4C, CN, ^("B-^C) = 71.1 Hz)

^UB NMR (25°C, CD3CN, 96.29 MHz, delta in ppm): -38.62 (s, IB, B(CN , ^("C^B = 71.0 Hz)

Example 10: Synthesis of [Me₄N] [BF₄]

[Me₄N]OH (2.03 g, 22.27 mmol) was dissolved in 10 ml of water. Aqueous HBF₄ (1.96 g, 22.53 mmol, 50 wt%) was added dropwise. Immediately a white precipitate occurred. The suspension was filtered. The obtained white solid was washed with 10 ml of water and dried at 90°C in vacuo for 15 hour. The yield of [Me₄N][BF₄] was 3.22 g (90%, 20.03 mmol). C/H/N Analysis calc. % (found): C 29.85 (29.73), H 7.51 (7.48), N 8.70 (8.54)

1H NMR (25°C, d6-DMSO, 300.13 MHz, delta in ppm): 3.08 (s, 12H, CH₃)

1³C NMR (25 °C, d6-DMSO, 300.13 MHz, delta in ppm): 54.3 (t, 4C, CH₃)

UB NMR (25°C, d6-DMSO, 96.29 MHz, delta in ppm): -1.24 (s, IB, BF₄)

1⁹F NMR (25°C, d6-DMSO, 300.13 MHz, delta in ppm): -151.53 (q, 4F, BF₄)

Example 11: Synthesis of [(n-Oct) N] [BF ]

K[BF₄] (0.136 g, 1.08 mmol) was dissolved in 5 ml of H₂0. [(n-Oct)₄N]Br (0.334 g, 0.61 mmol) was dissolved in 5 ml of CH₂C1₂ and added to the aqueous solution of K[BF₄]. After stirring for 24 hours at ambient temperature the phases were separated. The organic phase was washed three times with 5 ml of water dried over anhydrous Mg₂S0₄ and filtered. The filtrate was concentrated on a rotary evaporator to obtain a white solid. The obtained solid was dried at 90°C in vacuo for 15 hours. The yield of [(n-Oct)₄N][BF₄] as a white crystalline product was 0.321 g (95%, 0.58 mmol). Analytics

1H NMR (25°C, CD₃CN, 300.13 MHz, delta in ppm): 0.89 (t, 12H, CH₃), 1.30 (m, 40H,

CH₃-(CH₂)₅), 1.78 (m, 8H, N-CH₂-CH₂), 3.05 (m, 8H, N-CH₂)

1³C NMR (25 °C, CD₃CN, 250.13 MHz, delta in ppm): 14.34 (s, 4C, CH₃), 22.26 (s, 4C,

CH₃-CH₂), 23.32 (s, 4C, N-(CH₂)₂-CH₂), 26.80 (t, 4C, N-CH₂-CH₂), 29.56 (s, 4C, N- (CH₂)₃-CH₂), 29.66 (s, 4C, CH₃-(CH₂)₂-CH₂), 32.40 (s, 4C, CH₃-CH₂-CH₂), 59.38 (t, 4C, N-CH₂)

^UB NMR (25°C, CD₃CN, 96.29 MHz, delta in ppm): -1.19 (s, IB, BF₄)

Example 12: Synthesis of [(n-Bu)₄N] [B(CN)₄]

Example 1 was repeated with the following differences:

1. [(n-Bu)4N][BF₄] (1.4464 g, 4.39 mmol), prepared according to example 2, and

(CH₃)₃SiCN (2.48 g, 25.00 mmol) were used.

2. After the 15 hours at 200°C the reaction mixture was cooled to ambient temperature and the excess (CH₃)₃SiCN was removed in vacuo. The brown solid was dissolved in ethyl acetate to obtain a 10 wt% solution in ethyl acetate. 2 g of activated carbon was added to the solution. The suspension was stirred at 50°C for 10 minutes. The suspension was filtered off to obtain an orange solution. The activated carbon residue on the filter was 5 times extracted, each time with 10 ml ethyl acetate, by suspending the activated carbon in the ethyl acetate, stirring for 10 minutes at 50°C and filtering.

The orange solution and the five ethyl acetate extracts were combined and the ethyl acetate was removed in reduced pressure. The obtained beige solid was dried in vacuo to yield 1.401 g (95%, 4.00 mmol) of [(n-Bu₄)N][B(CN)₄].

[(n-Bu₄)N][B(CN)₄] was suspended in aqueous H₂0₂ (3 ml, 30 wt%). After stirring at 50°C for 1 h butyl acetate (13 g) was added. The suspension was mixed and transferred into centrifuge tubes. After centrifugation (1700 rpm, 10 minutes) the supernatant layer was separated. The butyl acetate was removed on a rotary evaporator to obtain to solid. The light yellow solid was heat-dried in vacuo to yield 76% (1.170 g, 3.34 mmol) [(n-Bu₄)N][B(CN)₄]. The NMR and IR data are the same as in example 1.

Cyanid content was 109 ppm.

Si content was 217 ppm.

Claims

1. Method for the preparation of compound of formula (I);

R4 by a reaction between compound of formula (II) and trimethylsilylcyanide;

R2

Rl I R3

(Π)

R4

2. Method according to claim 1 , wherein

Rl is hydrogen or Ci_io alkyl; and

R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of Ci_io alkyl.

3. Method according to claim 1 or 2, wherein

Rl , R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of Ci_io alkyl;

4. Method according to one or more of claims 1 to 3, wherein

from 4 to 10 mol equivalents of trimethylsilylcyanide are used, the mol equivalents being based on the mol of compound of formula (II).

5. Method according to one or more of claims 1 to 4, wherein

the reaction is done in the absence of a solvent.

6. Method according to one or more of claims 1 to 5, wherein the reaction temperature is from 180 to 220 °C.

7. Method according to one or more of claims 1 to 6, wherein the reaction time is from 30 min to 48 h.

8. Method according to one or more of claims 1 to 7, wherein after the reaction the reaction product is treated with hydrogen peroxide.