DE1249231B - Process for the production of alanates of lithium, beryllium or magnesium - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

PATENT OFFICE

GERMAN

EDITORIAL

Int. Cl .:

German class

COIb

12 i-3,

IfO

Number: 1 249 231

File number: E 18703 IV a / 12 i

Filing date: December 30, 1959

Opened on: September 7, 1967

The invention is concerned with the improved production of lithium, beryllium or magnesium alanate.

These alanates have become quite important in recent times. For example, they are used as high-performance reducing agents and useful for numerous chemical intermediate product purposes and also as an additive to high-energy propellants for jet engines or rocket motors known.

The particularly interesting alanates include those of the alkali metals, especially lithium, and the alkaline earth metals. For example, lithium alanate is superior to sodium alanate in many ways, and alkaline earth alanates, such as beryllium and magnesium alanates, are also becoming increasingly important.

The previously used for the production of metal alanates Work styles and reactions were clumsy and underperforming. This is how it goes, for example the previously used reaction for the production of lithium alanate according to the scheme

4LiH + AlCl ₃ → LiAlH ₄ + 3LiCl

From this equation it can be clearly seen that this known reaction is due to various reasons must be very uneconomical. First, lithium hydride is practically only available through direct hydrogenation recoverable from metallic lithium. Second, only a quarter of the lithium hydride entered is in the desired end product is converted, while the main part, namely three quarters, to lithium chloride is degraded, which is only recovered and reprocessed in order to fully utilize all lithium must become. The inadequacy of the methods described above is also in their inertia at the start of the reaction and also in the extensive insolubility of the resultant Lithium chloride in ether, which therefore covers lithium hydride, which is also ether-insoluble and withdraws from further reaction, thus forcing the use of a large excess of lithium hydride.

Other manufacturing processes have also become known which have attempted to overcome these disadvantages to overcome.

Thus, in the journal for applied chemistry, 65, p. 20, a process is described that starts from lithium hydride and aluminum bromide. Here, however, it is extremely difficult to separate the lithium bromide formed as a by-product from the desired end product, since the solubility properties of these two products match in ether and amine solvents. Another disadvantage of this process is the cost of the process required for the preparation of alanates
Lithium, beryllium or magnesium

Applicant:

Ethyl Corporation,

New York, N.Y. (V. St. A.)

Representative:

Dr. phil. G. Henkel

and Dr. rer. nat. W.-D. Henkel, patent attorneys,

Munich 9, Eduard-Schmid-Str. 2

Named as inventor:
Gene Conrad Robinson,
Baton Rouge, La. (V. St. A.)

Claimed priority:
V. St. v. America February 24, 1959
(794 866)

Lithium hydrides. The process cannot easily be applied to other metals, e.g. B. Group II elements, transfer.

From the Zeitschrift für Naturforschung, 5b (1950), p. 397, a process for the production of magnesium alanate is known, in which lithium alanate is reacted with magnesium bromide. In the course of reworking it was found that the reaction, even if it is carried out under the most varied of conditions, leads at least in a significant proportion to a bromine-containing end product, ie to MgBr (AlH ₄ ). Therefore, this method is not satisfactory either. In addition, it is not used for the production of lithium alanate, but uses it as a starting material. The inadequacy of the previous production processes for the complex hydrides, with the production of which the invention is concerned, is therefore clear, and there was therefore a great need for a cheap and material-economical process for the production of lithium, magnesium and other metal alanates.

This requirement is met by the process according to the invention for the production of alanates of lithium, Beryllium or magnesium, the peculiarity of which is that sodium alanate under violent

709 640/514

Stirring with the chloride of the aforementioned metals in the presence of tetrahydrofuran or lower dialkyl ethers the polyethylene glycols or diethyl ether is implemented.

The liquid reaction media used according to the invention obviously consist of compounds those in the molecule only carbon, hydrogen and oxygen, but no active hydrogen substituents and are resistant to reduction. Furthermore, is for the success of the implementation according to the invention the fact that the solvents mentioned have at least a limited dissolving power for the reactants, namely sodium alanate and second metal chloride, have, however, for Part is not very strong. You solve z. B. per 100 g of tetrahydrofuran (THF), diethylene glycol dimethyl ether (DMG) or diethyl ether (A) the following number of grams of

Metal connection

DMG

Sodium alanate ...
Lithium chloride. ..
Magnesium chloride
Beryllium chloride.

" l ^ SSßf '29 essentially insoluble

4.2 1.36 0.00037

6.04 0.02 <0.00001

Complex formation see Everest, "The Chemistry of Beryllium", New York, 1964 - Elsevier Publishing Co.

In the case of imperfect solution, vigorous stirring according to the invention by means of a stirring device or the like. Ensured that the not yet dissolved portions of the reactants in slurried Remain state. The sodium chloride that forms during the reaction falls as a solid the end. After the sodium chloride has been separated off, the alanate solution can either be used as such for numerous used for different purposes or processed on pure metal alanate.

When carrying out the process, temperature and pressure are not particularly important, even if the rate of the reaction is somewhat temperature-dependent. The useful working temperatures are generally between 0 and about 100 ⁰ C, but must not be above the temperature normally begins with the decomposition of the resulting alanate or the solvent begins to enter into reaction with it. The amount of solvent or reaction medium used is also variable within wide limits, and between 7 or 8 up to 500 or even more parts of solvent to one part of sodium alanate are sufficient, but in all cases the amount should be sufficient to dissolve the alanate formed.

Particularly favorable procedures and embodiments of the invention are evident from the following Examples can be seen in which the details relate to weight.

example 1

On the one hand, a suspension of 38 parts of lithium chloride and, on the other hand, a solution of approximately 50 parts of sodium alanate in 1000 parts of dimethyl ether of diethylene glycol are prepared and the two batches are mixed with one another while stirring vigorously. The reaction mixture formed after stirring for a further half hour at room temperature was a milky solid slurry in the liquid phase, which was filtered through a fine glass frit filter. Analysis showed that there was no dissolved chloride in the clear filtrate, so it has been proven that almost all of the starting lithium has been converted into a hydride product. The solid substance contained practically all of the chlorine in the form of sodium chloride. About 71% of the lithium chloride originally introduced was converted to lithium alanate, LiAlH ₄ , which can easily be separated from the clear solution.

Example 2

First, a slurry of 35.4 parts of magnesium chloride in 2800 parts of tetrahydrofuran and a solution of 51 g of sodium alanate in 4200 parts of tetrahydrofuran were prepared separately from one another. The two batches were mixed with one another with vigorous stirring, the molar ratio of NaAlH ₄ to MgCl ₂ thus being approximately 2.5: 1, corresponding to an excess of approximately 25%. Stirring was continued for about 7 hours after which time the reaction mixture was partitioned into solids and clear filtrate by filtration. The analysis of the solid substance showed that about 85% of its metal content consisted of sodium, and thus proved a substantial conversion of the magnesium chloride into magnesium alanate Mg (AlH ₄ ) ₂ , which can easily be separated from the filtrate by vacuum distillation, crystallization or salting out. The analysis of a partial sample of the liquid phase showed an 85% conversion of the sodium alanate into magnesium alanate.

A further increase in the conversion up to about 90% can be achieved by using dimethyl ether of diethylene glycol in place of tetrahydrofuran and the reaction partially at elevated temperature, for. B. 50 ⁰ C, performs.

Example 3

Following the pattern of the previous experiment, a solution of approximately 110 parts of sodium alanate was made in 4000 parts of tetrahydrofuran with a slurry of about 80 parts of beryllium chloride in about 1000 parts of the same liquid mixed and for several hours at only moderate temperatures implemented. This produced beryllium alanate dissolved in the tetrahydrofuran in about 80% yield won.

g B e i s ρ i e 1 4

In a stirred autoclave marketed under the name "Magne-Dash-Reactor" electromagnetically driven stirrer

100 ecm of diethyl ether, 0.3 grams of sodium alanate, 0.30 grams of lithium chloride and also 50 mg or 0.4 mol percent of previously prepared sodium alanate, which was synthesized by pressure hydrogenation of finely divided aluminum and sodium in toluene as the reaction medium, and preferably for reasons of best activity had been left a little bit wet with toluene. Its purity was 97 ° / _0th The lithium chloride had a purity of more than 99% and had previously been dried ^{at about 100 ° C. in vacuo.}

After filling under a protective gas atmosphere, the autoclave was closed, ^{stirring was started while the temperature was kept constant at 25 °} C. and the reaction was continued for 3 hours. After this time, analysis of an aliquot of the liquid phase of the reaction mixture showed a yield of 95 ° / ₀ of lithium aluminum hydride LiAlH. ₄ Its deposition in highly pure crystal form was done in a simple manner by adding about the same volume of a higher-boiling liquid, miscible with the solvent used, to the reaction medium, e.g. B. toluene added, which had no solvent power for the lithium alanate formed, and then at z. B. 180 Torr evaporated to the original volume. A precipitate of needle-shaped crystals of lithium alanate formed in an amount of about 85 to 90% of the crude product.

The basic reaction according to the invention is self-evident not to the use of preformed sodium alanate other than that to be added to the reaction vessel Bound starting material, but can also be used in the same reaction vessel and in presence the solvent according to the invention prepared immediately beforehand in the usual way, Carry out fresh sodium alanate, the second metal chloride is then added. About that In addition, however, according to the invention it is also possible to use the sodium alanate required as a starting product even in the presence of the second metal chloride and the solvent according to the invention by the to produce known pressure hydrogenation from the elements or from aluminum and sodium hydride and so directly to get the alanate of the second metal.

Example 5

45

First, 10 parts of sodium metal and the alanate formation, namely about 11.7 parts of finely divided aluminum metal and 100 parts of diethylene glycol dimethyl ether, were placed in a stirred autoclave. Then, in the held to about 140 ⁰ C and vigorously stirred vice reaction system, hydrogen was injected with about 70 atmospheres gauge until he after about 8 hours, the equivalent amount was added. The raw alanate solution obtained in this way was mixed with 18.5 parts of dry, anhydrous, pure lithium chloride and processed according to Example 1 to give lithium alanate.

Obviously, this embodiment of the invention is also suitable for implementation in con- continuous operation by passing the aforementioned starting materials through an elongated, e.g. B. tubular reaction chamber sends through it and the hydrogen gas at the beginning of the chamber and the Second metal halide enters where the sodium alanate formation is practically complete.

Example 6

In a repetition of Example 5, the lithium chloride was added to the autoclave from the start and then injected hydrogen at about 141 atm for 7 hours. Also in this case were Degree of conversion and yield of lithium alanate high. This procedure also resulted in use the other solvents according to the invention to good in place of diethylene glycol dimethyl ether Exploit.

With regard to the proportions of reactants, it is expedient to use stoichiometric ratios worked. Sometimes and especially in those cases where there is a chloride content in the product is objectionable, however, a small excess of sodium alanate is desirable. In such cases it is desired metal alanate depending on the extent of the applied excess of a little more or accompanied by less sodium alanate.

For the separation of the alanate product from the reaction medium in a liquid-free form there are various possibilities. Vacuum distillation is often used. Other separation methods exist from crystallization with cooling or from cooling coupled with vacuum distillation. Man can also, as described in Example 4, add a liquid that is mixed with the solvent medium is completely or partially miscible, but has no dissolving power for the metal alanate. In in many cases and especially when a reaction medium with strong dissolving power for the alanate product is used, but no separation at all is required.

Claims (2)

Patent claims: 1. Process for the production of alanates of lithium, beryllium or magnesium, thereby characterized that sodium alanate with vigorous stirring with the chloride of the aforementioned metals in the presence of tetrahydrofuran or lower dialkyl ethers of polyethylene glycols or diethyl ether is implemented. 2. The method according to claim 1, characterized in that in the presence of the relevant Solvent and metal chloride, the sodium alanate to be reacted with the latter is known per se Way by pressure hydrogenation of a mixture of sodium or sodium hydride with finely divided Aluminum is formed in situ. Considered publications:
German Auslegeschriften Nos. 1 012 591, 1 045 375; French Patent No. 1,196,055;
British Patent No. 820,513;
Australian Patent No. 223,475;
Nature, 173: 126 (1954);
Bull. Soc. Chim. France, 1952, pp. 550/551;
Zeitschrift für Naturforschung, 5 b (1950), p. 397; Angewandte Chemie, 65 (1953), p. 20. 709 640/514 8 67 Bundesdruckerei Berlin