JP2871107B2 - Method for producing lithium borohydride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing lithium borohydride.

[0002]

BACKGROUND OF THE INVENTION Lithium borohydride or lithium borohydride is an important reducing agent widely used in the field of organic synthesis.

[0003] Lithium borohydride is generally produced by reacting lithium chloride or lithium bromide with isopropylamine as a solvent (J, A, C, S, 75, 1).
99 (1953)).

[0004] As another method, it is also known to carry out a similar reaction using a mixed solvent comprising an alkylamine and an ether (GB Patent 1,104,200; Application 196).
5.9.15. Priority, US, Public Notice, 1968.2.21.).

Further, a method of reacting in a solvent of tetrahydrofuran or diethyl ether is also known, but it is also known that the reaction hardly proceeds with ordinary stirring (Japanese Patent Application Laid-Open No. 58-45112).

Among the alkylamines, isopropylamine, which is most commonly used for synthesis, is very expensive, has a low boiling point (33-34 ° C.), is difficult to handle, and has a low solubility of lithium borohydride (7.5-8.7 g). / 100g-S
olv) It had to be used in large quantities, which made the synthesized lithium borohydride very expensive.
On the other hand, tetrahydrofuran is relatively inexpensive, has a relatively high boiling point (66 ° C.), is easy to handle, and has a high solubility of lithium borohydride (22.2 g / 100 g-Sol).
v) Although the amount used was small, the reaction hardly proceeded by ordinary stirring as described above.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing lithium borohydride safely and economically.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and have completed the present invention.

That is, when sodium borohydride is reacted with lithium chloride or lithium bromide to produce lithium borohydride, liquid ammonia or a mixture of liquid ammonia and ethers is used as a solvent for the reaction. This is a method for producing a lithium borohydride.

According to this method, a high-purity lithium borohydride can be obtained in a high yield.

Hereinafter, the method of the present invention will be described in more detail.

As the sodium borohydride used in the present invention, a commercially available product may be used as it is. Lithium chloride or lithium bromide may also be a commercially available anhydride.

In the present invention, liquid ammonia is used as a reaction solvent. Liquid ammonia is very inexpensive and a good solvent for lithium borohydride (77g / 100g-Solv)
Not only is it a good solvent for the raw material sodium borohydride (104 g / 100 g-solv), lithium chloride, and sodium chloride.

Therefore, the reaction proceeds smoothly and the amount used is small. After the completion of the reaction, it can be easily separated from the reaction product by vaporization. Ammonia gas may be recovered, or may be released because it is inexpensive and may be subjected to waste gas treatment. It is used under pressure to maintain a liquid state at the reaction temperature, so that the reaction is carried out in a pressure-resistant autoclave. As this liquid ammonia, a commercially available cylinder filled with liquefied ammonia can be used as it is.

After separation of the ammonia gas and the reaction product, the lithium borohydride is removed using a good solvent for lithium borohydride and a poor solvent for sodium chloride, unreacted sodium borohydride, unreacted lithium chloride or lithium bromide. Is extracted. For example, tetrahydrofuran, diethyl ether and the like are preferable. If synthesis and extraction are not performed as separate operations but are desired to be performed at once, the reaction is performed using a solvent obtained by mixing a certain amount of ethers with liquid ammonia. By doing this,
Lithium borohydride is dissolved in the mixed solvent, and sodium chloride, lithium chloride, and sodium borohydride are insoluble.Therefore, a solution of lithium borohydride can be obtained by simply filtering after completion of the reaction. Lithium borohydride can be obtained. However, in this case, when recovering the used mixed solvent, an operation of separating ammonia and ethers is required. The amount of ethers added to liquid ammonia ranges from no addition to 200 times, and the reaction proceeds promptly within this range.

However, if lithium borohydride is expected to be separated from the by-product sodium chloride and the reaction residue, and if the reaction is expected to proceed smoothly, the range is preferably 1 to 100 times.

The ether used as the reaction solvent is a low-boiling aliphatic or cyclic ether. Preferred aliphatic ethers are lower alkyl ethers containing 1 to 4 carbon atoms wherein the alkyl group is straight-chain or branched;
Usual ethers and mixed ethers can be used. Examples of these ethers are dimethyl ether,
There are diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, diisopropyl ether and the like.
Tell can also be mentioned. Preferred cyclic ethers are 5- or 6-membered rings, such as tetrahydrofuran and dioxane. When these ethers are subjected to the reaction, it is necessary to perform a dehydration operation with sodium hydride or the like.

The reaction temperature for carrying out the reaction according to the present invention is as follows:
Temperatures between 0 ° C and 100 ° C, preferably between 20 ° C and 70 ° C, are suitable. The reaction pressure is preferably under normal pressure or under pressure (0 to 5 kg / cm ² -G as a gauge pressure).

When the proportion of ethers is small relative to liquid ammonia, a pressure-resistant reactor is required to keep the ammonia in a liquid state and to carry out the reaction under pressure. When the amount of ethers is overwhelmingly large with respect to ammonia, the reaction can be performed at normal pressure. When reacting at normal pressure, after mixing ammonia with ethers in advance, it may be used as a solvent, but as another method, while directly adding gaseous or liquid ammonia to a mixture of raw materials and ethers,
The reaction may be carried out while stirring the stirrer continuously for several minutes at several hundred revolutions. The reaction is conveniently carried out under an atmosphere of an inert gas from which water is excluded, for example, nitrogen or argon, and under an atmosphere of ammonia gas.

It is expedient to carry out the reaction with stoichiometric amounts of sodium borohydride and lithium chloride or lithium bromide. However, it is preferred to use an excess of sodium borohydride, up to about 10 mol%, especially about 1 mol%, based on the lithium chloride or lithium bromide used.
An excess of 55 mol% is particularly preferred.

The end point of the reaction can be determined by stopping the exotherm.

[0022]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereby.

Example 1 In a 500 ml small autoclave sufficiently purged with nitrogen, 32 g (0.757 mol) of anhydrous lithium chloride, 30 g (0.793 mol) of sodium borohydride and 220 g of tetrahydrofuran (4.2 times the mol based on ammonia) were added. And seal the container. While continuously rotating the stirrer at 500 revolutions / minute, 52 g of ammonia was allowed to react in a gaseous state for 4 hours while intermittently supplying the space in the reaction vessel for 4 hours. At this time, an exothermic reaction occurred simultaneously with the addition of the ammonia gas. The reaction temperature is from normal temperature to about 40 ° C,
The reaction was carried out at a pressure ranging from normal pressure to 4.5 kg / cm ² -G.

Thereafter, stirring was continued for one hour to complete the reaction, and then ammonia gas was released from the system.

The reaction solution thus obtained was taken out, the by-product sodium chloride precipitate was filtered off, and the filtrate was dried on a rotary evaporator to obtain 16 g of lithium borohydride (0.
735 mol).

The reaction yield was 97% and the purity was 99%.

Example 2 Anhydrous lithium chloride was placed in a 500 ml autoclave.
20 g (0.472 mol) was charged together with 50 g of ammonia, followed by purging with nitrogen. Then 18.4 g of sodium borohydride
(0.485 mol) was dissolved in 100 g of liquid ammonia, and charged over 3 hours with a pressure increasing pump while maintaining the reaction temperature at 35 ° C. Then, the mixture was stirred for 1 hour to complete the reaction. Thereafter, ammonia gas was released from the system. After sufficiently removing ammonia, the residue was washed with tetrahydrofuran to extract lithium borohydride.

Then, the product was dried on a rotary evaporator to obtain 10.1 g (0.463 mol) of lithium borohydride. The reaction yield was 98% and the purity was 98.5%.

[0029]

According to the method of the present invention, lithium borohydride can be produced at very low cost. or,
The reaction can be allowed to proceed in a solvent containing an ether, particularly tetrahydrofuran as a main component, which has heretofore been impossible.

These advantages are attributable to the use of a completely novel solvent, liquid ammonia, or a mixed solvent of liquid ammonia and ethers, which is a feature of the present invention, and greatly contributes to industry.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C01B 6/21

Claims (1)

(57) [Claims] 1. A method for producing lithium borohydride by reacting sodium borohydride with lithium chloride or lithium bromide, wherein liquid ammonia or a mixture of liquid ammonia and ethers is used as a solvent for the reaction. Of producing lithium borohydride.