DE944546C - Process for the production of alkali borohydride - Google Patents

Description

Process for the preparation of alkali borohydride The subject of the invention is a process for the production of alkali borohydride. The new procedure works from, the usual raw materials for the production of hydrogen boride, namely. from BorhaJogeniden, preferably from the technically easily accessible boron trifluoride, respectively. their etherates and alkali hydride in the ethereal medium, and works according to the invention in a closed system at elevated temperature, inevitably overpressure adjusts. The increased reaction rate due to the increased temperature on the one hand and the increased concentration at the same time due to the increased pressure on the other hand, they cause the reaction to proceed as quickly and as completely as possible in the desired sense. That way you get. from technically accessible raw materials, such as boron trifluoride or boron trifluoride, rid-etherate and alkali hydrides, also on a large scale Scale not only Li - [B H4], but contrary to the previous view also all other alkali boron hydrides, such as. B. Na- [B H4] and K - [B H4], with great purity and excellent yield, with aas by-products only the indifferent and easily separable alkali halides occur.

In contrast, PF Winternitz (USA.-Patent Specification 2 532 217) works using the same raw materials, but in an open system, whereby the boiling temperature of the ether (35 °) must not be exceeded by carefully combining the two reactants and cooling, about the escape. to avoid unused diborane gas and uncontrollable reaction surges. Ultimately, the process is similar to the Grignard reaction and, like this, is therefore also subject to the technical difficulties associated with the Grignard reaction. Otherwise, the method is limited to the preparation of Li - [B H4].

The simultaneous application of pressure and elevated temperature will in U.S. Patent 2,534,533 on both the reaction of alkali metals described with HZ gas and alkyl borates, the pressure only generating alkali hydride is used, which is then at elevated temperature with alkyl borate too low, contaminated with AlkaJitrimethoxyborhydrid; Amounts of alkali borohydride converts, as well as in relation to the reaction between methyl borate and sodium hydride .. In both cases, it is against the present Process different raw materials.

In addition, more reactive by-products arise here, which are also more difficult to remove than alkali hylogenides.

In contrast, the new process brings significant progress in that it enables general applicability for the first time using easily accessible raw materials for the production of alkali-bo, r-hydrides in excellent quality and quantity, even on an industrial scale. Example i A suspension of 5 g (0.63 Mod) powdered lithium hydride in a little anhydrous ether is intimately mixed with 7.1 9 (0.05 mol) boron trifluoride etherate, which has been diluted with the same volume of anhydrous ether, and im Pressure vessel heated to 125 'for 24 hours. At the end of the reaction there is only a slight overpressure.

The contents of the pressure vessel are then mixed with anhydrous ether and the whole is freed from excess lithium hydride by filtration. The filtration residue is extracted several times with anhydrous ether. The ether extracts are united and for the most part freed from the ether. When the concentrated ether extract is cooled, it falls the lithium-bo, r-hydride in colorless needles with 1 mol of crystal ether.

Yield: About 49 = 85 bis. go ° / o of the theory (based on, Bo, rfiuo @ rid).

Example 2 A suspension of 49 (0.5 mol) powdered lithium hydride in a little anhydrous ether is with 14.2 g (0.1 mol) of Bo, rtrifluo, rid-ätherat that one dilutes liat with the same volume, anhydrous ether, and mixes intimately heated to 12a ° in a pressure vessel for 24 hours. At the end of the reaction, only prevails another slight overpressure. The temperature can, in, relatively wide limiters. vary. The same results were achieved at temperatures between 100 and i45 °. This is worked up according to example i.

Yield: about 8 g of Li - [B H4] - (C2 H5) 2 O = 85 to 10% of theory (based on boron fluoride). The crystal ether can be removed by drying in vacuo at 70 to 100 °. Example 3 14.2 g of boron fluoride etherate (0.1 mol), diluted with the same. Volume of anhydrous ether are also processed in one operation with an ethereal. Suspension of 15.6 = g of powdered sodium hydride (0.65 mol) implemented. - To do this, either the starting substances, cooled to -78 °, are mixed and then heated in the pressure vessel to 12o to 130 ° for 24 hours or the mixture is carried out in a closed vessel at normal temperature and then heated.

After the reaction has ended, the ether is evaporated and the residue extracted with isopropylamine or pyridine and the sodium borohydride from the extract precipitated by cooling or by adding ether.

Yield: about 3.3 g = 87% of theory. (related to boron fluoride). Example 4 In the same autoclave, 82 g (2.73 mol) of powdered NaH (8oo / oig), zoo cc of diethyl ether abs. and a solution of 34 g (0.5 mol) of ortrifluoride (B F3) in 14o ccm abs. Diethyl ether charged and made to react. The initial temperature of 20 ° rises to 38 '°' and then falls back to 3z ° '. There is only a slight overpressure and a gas sample taken shows a clear boron flame. Mars. now supplies heat,. so that after about 30 minutes an internal temperature of 80 '°' and a pressure of 5 atmospheres are established. It is heated further to 118 °, a pressure of ii atm occurs. This temperature is held for 8 hours, during which time the pressure falls to 8 atmospheres. A gas sample no longer shows any boron flames. After cooling the autoclave, the diethyl ether is removed by opening the valve and the dry, white residue with abs. iso, = propylamine or n-butylamine extracted. The extract is largely freed from amine by vacuum distillation, and the sodium o @ r-hydride is added from it. like of ether. It is then filtered and the remaining sodium boron hydride is washed with ether. and dried in a vacuum on a water bath.

Yield: ig g NaBH4, that is 100% of theory based on B F3. Example 5 The approach described under 4 is repeated, only take the place from 34 g of boron trifluoride 58 g (0.5 mol) of boron trichloride (B C13). The course of the reaction is practically the same, the yield is 15.2 g NaB H4, that is 80% of theory based on B C13.

Claims (1)

PATENT CLAIM: Process for the production of alkali borohydride from Boron halides, preferably boron tri $ uoride, or their etherates and. Alkali hydride in the presence of. Ethers., Characterized in that, ß the boron halides or their Etherate in a closed system with Alkalihydri.d, at elevated temperature below Pressure to be implemented. References: U.S. Patents No. 2,532 217, 2,534,533.