Patented Mar. 20, 1951 is 2,545,633 UNITED STAT ES PATENT office 2,545,633 PREPARATION OF LITHIUM BOROHYDRIDE Hermann I. Schlesinger, Chicago, Ill., and Herbert C. Brown, Detroit, Mich., assignors to the United States of America as represented by the United States Atomic Energy Commission ...... No Drawing. Application October 16, 1945, ------serial No. 622,686 Claims. (C. 23-14) 2

- This invention relates to the preparation of (s process is not completely known, the ether, in liq lithium borohydride. uid form, serves as a Solvent for the lithium boro “. It is an object of the invention to provide hydride and thereby facilitates the reaction by en lithium borohydride, LiBH4. It is a further ob Suring constant exposure of new lithium hydride ject of the invention to provide a convenient and surface when gaseous diborane is passed over the efficient method of preparing lithium borohy solid lithium hydride. The ether may also form dride. ... Further objects and advantages will ap an addition produced with diborane or borine pear from the following description. - (BH3) thus increasing the reactivity of the boron : In accordance with the present invention, it compound. In any case, it has been found that has been found that lithium borohydride may be the reaction proceeds unusually rapidly and effi obtained from the reaction of lithium hydride, ciently in the presence of sufficient ether to cover LiH, with diborane, B2H6. The reaction between the lithium hydride in the reactor. Other ethers, the lithium hydride and the diborane probably either simple or mixed, which are liquid at room proceeds according to the following equation: temperature may be used for this purpose. An amount of the ether Sufficient to permit effective stirring of the reaction mixture is used. It has also been found that the presence of a sol Air is removed Substantially completely from vent for lithium borohydride Such as, for ex the reactor and diborane is then pumped or drawn ample, diethyl ether facilitates the reaction. into the reactor by convenient methods. The Other ethers such as methyl ether, n-propyl 20 reaction proceeds to form the lithium borohy ether, n-butyl ether, dioxane or methyl Cello dride. During the reaction the corresponding Solve also may be used as well as other Solvents etherate of lithium borohydride frequently crys capable of coordinating with diborane or borine tallizes out of Solution. It may be redissolved by (BH3). warming the ether-solution. In forming the lithium borohydride by the re 2 The following example is illustrative. action of lithium hydride and diborane, the lith ium hydride is suspended in ether, placed in an Eacample I appropriate reaction vessel and diborane is in One gram of lithium hydride was placed in a troduced into the reaction vessel and into con tubular reactor having a narrow, elongated neck tact with the lithium hydride generally at or 30 extending upwardly from the tube and terminat about room temperature and the desired reac ing in a valved inlet. The reactor was evacuated tion takes place. The reaction readily proceeds to substantially completely remove air. The lith with evolution of heat at temperatures of 0 to ium hydride, having a particle size of approxi 50° C. mately 200 mesh, was introduced into the reactor In accordance with One manner of preparation 35 through the tubular neck. 50 cc. of anhydrous di of the lithium borohydride, the lithium hydride ethyl ether was added through the neck of the re and the diborane are reacted in a Suitably closed actor. One liter of gaseous diborane (at standard apparatus. The apparatus may comprise, in es conditions) was condensed in a gas bulb by means Sence, a closed reactor equipped with an agitator of liquid nitrogen, and the bas bulb was securely and provided with adequate evacuation and dis 40 closed and connected to the reactor. The gas tillation equipment. The reactor is also provided bulb containing the diborane was then opened to with conventional means for supplying the re the reactor and the diborane forced into the actants and inert gas thereto. reactor by warming the gas bulb. As the tem Preparatory to carrying out the reaction, a perature of the gas bulb was permitted to rise quantity of lithium hydride is placed in the re 45 to approximately that of room temperature, the actor. The lithium hydride is preferably in a temperature of the reactor was substantially finely divided form such as, for example, that lowered by means of liquid nitrogen, such cool having a particle size of from 100 mesh to 200 ing accelerating the passage of the diborane from mesh; generally, the more finely divided is the the gas bulb to the reactor. After the introduc lithium hydride, the more readily the reaction 50 tion of diborane was completed the reactor was proceeds. Sealed off and cooling of the reactor was discon As previously stated the reaction is carried out tinued. The temperature of the reactor was al using a lithium hydride-ether mixture and ac lowed to rise whereupon the reaction was ini cordingly an ether in anhydrous state is intro tiated and was complete after about three hours duced usually after the lithium hydride has been 55 standing at room temperature. added. While the function of the ether in the The lithium borohydride resulting from the re 2,545,633 4. action was isolated by heating the reactor to a The reaction vessel was removed from the line temperature of from 34° C. to 40° C., in the ab and its contents transferred to an extraction sence of air, to dissolve crystallized etherate of apparatus comprising a pair of Connected flasks lithium borohydride which is formed during the with a sintered glass filter connected between the reaction. The solution containing lithium boro flasks. The ether suspension and solution of hydride and/or its etherate was then filtered LiBH4 was warmed to 30° C., and forced by dry through a porous glass disk to remove unreacted N2 from the first flask through the sintered glass lithium hydride. The clear solution of lithium filter into the second flask. Thereafter a partial borohydride was then evaporated to remove the vacuum was applied to the first flask and the diethyl ether. The distillation was carried out O ether distilled back into it through the filter. in vacuum, the temperature being slowly raised The residue was extracted by forcing the distilled from room temperature to approximately 100° C. ether forced into the second flask through the The lithium borohydride remained in the distill filter as before. After three such extractions, all lation flask as a solid cake. A yield of lithium the ether in the filtrate was distilled off, first by borohydride of approximately 90% of the theo 5 heating to 100° C. and then by degassing in high retical yield was obtained. vacuum leaving white crystalline LiBH4 behind. Eacample II The yield of this product was 25 grams. 10 grams of LiH was placed in a reaction vessel The above detailed description is for purposes provided with an agitator and 400 cc. of anhy of illustration. Details of specific embodiments drous ethyl ether distilled in. The ether sus 20 thereof are not intended to limit the scope of the pension of LiH was stirred for a few minutes to invention except insofar as included in the fol allow any remaining water to react. An ice bath lowing claims. was then placed around the reaction vessel and What is claimed is: the air pumped out of the vessel. 13 liters of 1. A process of preparing lithium borohydride diborane in gaseous state (standard temperature 25 which conprises reacting diborane and lithium and pressure conditions) was condensed to liquid hydride. - - in a receiver by cooling to about ninus 190° C. 2. A process of prepairing lithium borohydride and the receiver was then connected to the re which comprises reacting diborane and lithium actor through a line having a stopcock. There hydride in the presence of an ether. upon the receiver which had been cooled to effect 30 3. A process of preparing lithium borohydride condensation of diborane was allowed to warm which coin prises reacting diborane and lithium up until a pressure of 700 mm. was developed hydride in the presence of diethyl ether. . ve in the receiver. The stopcock connecting the 4. A process of preparing lithium borohydride receiver with the reaction vessel was opened which comprises reacting diborane and lithium and temperature of the receiver maintained 35 hydride in the presence of dimethyl ether. such that the rate of evaporation of B2H6 just 5. A process of preparing lithium borohydride equalled its rate of adsorption in the reaction which comprises reacting diborane and lithium vessel and the diborane pressure in the reac hydride in the presence of dipropyl ether. tion vessel remained at t00 mm. After about 40 -6. The method of producing lithium borohy nine liters of diborane had been absorbed, a diride which comprises reacting lithium hydride heavy slurry of LiBH4 resulted, trapping some with diboraine out of contact with air. LiH. The reaction vessel, therefore, was warmed 7. The method of producing lithium borohy up to 15 to 20° C. at which point the LiBH4 re dride which comprises reacting lithium hydride dissolved. The absorption was continued until with fibofane in the presence of an ether and no more liquid phase was present in the receiver. out of contact with air. Next, the receiver was again cooled to about minus 195° C. in order to condense a "quantity of ether HERMANN I. SCHLESINGER. in the receiver together with residual diborane. HERBERT C. BROWN. This condensate was revolatilized by heating to 50 about 35-46° C. The condensed ether Served to No references cited. drive over the last traces of B2H6.