WO2010032102A1

WO2010032102A1 - Method for producing alkali metal cyanoborate

Info

Publication number: WO2010032102A1
Application number: PCT/IB2009/006788
Authority: WO
Inventors: Roland Pawelke
Original assignee: Studiengeselischaft Kohle Mbh
Priority date: 2008-09-19
Filing date: 2009-09-08
Publication date: 2010-03-25
Also published as: DE102008048015A1

Abstract

A method is claimed for producing alkali metal cyanoborates of the general formula I, M⁺ [B(CN)₄]^- wherein M is selected from the group of Li, Na, K, Rb and Cs, in which BX₃t, an alkali metal tetrahalogen borate MBX₄ and or an adduct compound of the above, where M is defined as above and X stands for Cl, Br, or I, are caused to react under the effect of impact, friction and/or shear forces with an alkali metal cyanide MCN, where M is defined as above. With the claimed method, it is possible, for example, to produce KB(CN)₄ directly from BCl₃ and KCN in a mechanical-chemical reaction process with good yields.

Description

Process for the preparation of alkali metal covoborates

The present invention relates to a process for the preparation of alkali metal cyanoborates.

Ionic liquids or liquid salts are ionic species consisting of an organic cation and a generally inorganic anion. They contain no neutral molecules, and usually have melting points less than 373 K. The prior art discloses a large number of compounds which are used as ionic liquids. The properties of ionic liquids, eg. As melting point, thermal and electrochemical stability, viscosity, are strongly influenced by the nature of the anion. In contrast, the polarity and hydrophilicity or lipophilicity can be varied by the appropriate choice of the cation / anion pair. There is therefore a fundamental need for new ionic liquids with varied properties, which offer additional possibilities with regard to their use.

In W 02004/072089 a process for the preparation of alkali metal cyanoborates and their further conversion to salts of cyanoborate anions and organic cations, which can be used as ionic liquids disclosed. The alkali metal cyanoborates are prepared by reacting alkali metal tetrafluoroborate, such as K [BF ₄ ] or Na [BF ₄ ], with an alkali metal cyanide in the presence of lithium halide in a solid-state reaction. Alkalimetalltetrafluoroborat and alkali metal cyanide are preferably used in a molar ratio of 1: 9, the compounds are melted together at 300 ⁰ C. Yields between 40 and 70% are achieved. Particularly disadvantageous is the clearly superstoichiometric use of cyanide, which must be destroyed in the workup of the reaction product again, which means an additional process step in relation to the overall process.

The present invention was based on the object to provide a simplified process for the preparation of alkali metal cyanoborates available.

The present invention accordingly provides a process for the preparation of alkali metal cyanoborates of the general formula I. M ⁺ [B (CN) ₄ ] ^" I

wherein M is selected from the group Li, Na, K, Rb and Cs, which is characterized in that BX _3, an alkali metal tetrahalogeno borate MBX ₄ and / or an adduct compound of the preceding, wherein M is as defined above and X is Cl, Br, or I, with an alkali metal cyanide MCN, wherein M is as defined above, under the action of

Shock, friction and / or shear forces are reacted.

With the method according to the invention, it is possible, for example, to produce KB (CN) ₄ directly from BCI ₃ and KCN in good yields in a mechanochemical reaction procedure.

The process can be carried out without separate heat input. By the action of impact, friction and / or shear forces, the temperature of the reaction mixture may increase. A possible increase in temperature may depend, for example, on the energy input of the impact, friction and / or shear forces. External heaters are usually not required.

To carry out the process according to the invention, the reactants are reacted under the action of impact, friction and / or shear forces. The reaction is preferably carried out in a mechanochemical reaction apparatus. The forces mentioned occur, for example, in mills, which comminute the millbase using grinding media (grinding media mills), such as. As vibrating mills, stirred mills, stirred ball mills, ball mills, etc., but also in sintering presses in which pressure and friction are exerted simultaneously. Preferably, the process is carried out in a ball mill. Particularly suitable are, for example, planetary ball mills, such as the Pulverisette P7 from Fritsch, Schüttelkugel mills such as the Spex Mixer MiII 2000 but also the horizontal rotor ball mills, are particularly suitable for carrying out the method according to the invention. The mention of the mills is not exhaustive and only to be understood as an example. In the event that gaseous or volatile reactants, such as BCI ₃ , are used, the process is preferably carried out in a pressure reactor which is suitable as a grinding bowl for a high-energy mill.

In a further preferred embodiment, such grinding containers are used which can be operated under pressure and at the same time can be tempered. By the Milling of the solid heat is usually generated mechanically, which can lead to an increase in the temperature in the reaction space. This temperature rise generated by the grinding process is sufficient in most cases as the reaction temperature.

Particularly suitable grinding media (grinding bowls and / or grinding balls) are those made of sintered corundum (density> 3.8 g / cm ³ ), zirconium oxide (density 5.7 g / cm ³ ), stainless steel (density 7.8 g / cm ³ ), hardened steel (Density 7.93 g / cm ³ ), tungsten carbide (density 14.89 // 14.7 g / cm ³ ) and of materials which have sufficient hardness and / or density to achieve the desired effect in the process according to the invention, for example, be here Alloys, fiber-reinforced ceramics, or called aluminum. Particularly preferred media have high masses, preferably the high mass is achieved via high densities of the material and / or increased atomic weight. The mention of the grinding media and their materials is not to be understood as conclusive in this sense.

The ratio of the media (spheres or bodies) to the amount of solid reactants can be from 100: 1 to 10: 1. Preferably, the ratio of grinding media to powder is adjusted to 15: 1 to 30: 1. In the latter ratio, the space-time yield per method approach is particularly high.

The starting compounds are known, partially commercially available compounds or well-known in the art. Boron compounds which can be used are the boron trihalides and alkali metal tetrahalogen borates, with BCI ₃ and NaBCI ₄ or KBCl _{4 being} particularly preferred. As a suitable adduct compound BCI ₃ SMe _{2 can be} called. The adduct compounds allow the use of boron trihalides in solid form, so that can be dispensed with when using expensive pressure-resistant reaction devices. The cyanide is an alkali metal cyanide, preferably NaCN or KCN.

The reactants can be converted in quasi-stoichiometric amounts. To ensure the most quantitative conversion of the expensive boron compound, the cyanide compound can be used in a slight excess. Preferably, boron compound and the alkali metal cyanide are used in a stoichiometric ratio, the cyanide compound may be present in an excess of up to 15%, usually up to 10%. The use of higher amounts of cyanide, for example, a ratio of boron compound to alkali metal cyanide over 1: 2, however, did not lead to an increase in the yield. The stoichiometric or nearly stoichiometric use of the reactants eliminates the destruction of the cyanide. The reaction product can be easily dissolved out of the reaction mixture with an organic solvent such as acetone, acetonitrile or ethanol, etc., and further purified.

example

The reaction is usually carried out in a planetary ball mill Fritsch Pulverisette P7.

The grinding bowls were filled with the reactants in an argon-filled glove box (O ₂ <2 ppm, H ₂ O <1 ppm), to which was added 1.63 g (9 mmol) of boron trichloride-dimethyl sulfide adduct together with 2.39 g ( 36 mmol) of potassium cyanide in a 45 mL steel grinding bowl and 7 grinding balls (steel, 0 15 mm, ball to powder ratio of 24: 1). The grinding bowl was taped and ground at 800 rpm for 2 hours.

The ¹³ C-NMR analysis of the crude product (D ₂ O, 75.48 MHz) showed no excess cyanide at δc = 165.8 ppm, a work-up with alkaline H ₂ O ₂ was therefore omitted. The reaction mixture was extracted with 150 mL acetone, filtered and the solvent removed. There were obtained 900 mg of a crystalline brown mass (yield -65% of theory). The crude product was recrystallized from water / activated carbon to give 474 mg of slightly yellowish crystals. The product obtained was sparingly soluble in water (4.2 / 100 g of water at 25 ° C). The ¹³ C and ¹¹ B NMR data were in agreement with those of E. Bernhardt, G. Henkel, H. Willner, Z. Anorg. AIIg. Chem. 2000, 626, 560-568, published data.

Claims

claims

1. A process for the preparation of Alkalimetallcyanoboraten of the general formula I.

M ⁺ [B (CN) ₄ ] ^" I

wherein M is selected from the group Li, Na, K ₁ Rb and Cs, characterized in that BX _3, a complex alkali metal tetrahalogeno borate MBX ₄ and / or a

Adduct compound of the preceding, wherein M is as defined above and X is Cl ₁

Br, or I, is reacted with an alkali metal cyanide MCN, wherein M is as defined above, under the action of impact, friction and / or shear forces.

2. The method according to claim 1, characterized in that the reaction is carried out in a device with mechanochemical reaction.

3. The method according to claim 1 or 2, characterized in that the reaction is carried out in a grinding mill or a sintering press, preferably in a ball mill.

4. The method according to any one of claims 1 to 3, characterized in that it is carried out without separate heat input.

5. The method according to any one of claims 1 to 4, characterized in that the boron compound and the alkali metal cyanide in a stoichiometric ratio up to a ratio of 1: 1, 15 are used.

6. The method according to any one of claims 1 to 5, characterized in that as boron compound BCI ₃ , MBCI ₄ or an adduct compound such as BX ₃ SMe _{2 is} used.