3,207,570 United States Patent Office Patented Sept. 21, 1965 2 3,207,570 hydride, Metal Hydrides Inc., 1958), allowance must be PRODUCTION OF LITHIUM ALUMNUM made for soluble sodium borohydride, as follows: HYDREDE Gram molecules Heinrich Nöth, Munich, Germany, assignor to imperial per litre Chemical Industries Limited, London, England, a cor poration of Great Britain Total borohydride -------------------------- 0.06 No Drawing. Fied May 24, 1962, Ser. No. 197,255 Soluble sodium borohydride (1 gram per litre, mo Claims priority, application Great Britain, Dec. 2, 1956, lecular Weight 38) ------------------------- 0.026 38,975/56 8 Claims. (C. 23-14) Net LiBH4 -------------------------- 0.034 10 This concentration represents a yield of 2.4%; and This application is a continuation-in-part of my ap this value must be an overestimate since the analyses plication Serial No. 702,771, filed December 16, 1957, showed that lithium ion was present at a concentration now abandoned. of 1.07 gram molecules per litre, which is just less than This invention relates to the production of lithium equivalent to the concentration of chloride ion. If aluminium hydride. lithium borohydride were present, its concentration should it is known to produce lithium aluminium hydride by be equal to the excess of lithium ion concentration over reacting lithium hydride with aluminium chloride ac chloride ion concentration, since the only soluble chlo cording to the following equation: ride in the system is lithium chloride. The rest of the filtrate was evaporated to dryness in 4LiH-AICI->LiAlH4-3LiCl 20 vacuo in an atmosphere of nitrogen and the resulting This process is unsatisfactory in that only 25% of the white solid was dried at 100° C. for 1/2 hours, giving expensive lithium hydride starting material is converted 9.1 grams of product. A sample of this was analysed into lithium aluminium hydride. It would be valuable to be able to convert sodium by titration with N/10 hydrochloric acid and found to 25 contain 1.21% boron. A sample was titrated with N/10 aluminium hydride to lithium aluminium hydride by a silver nitrate and was found to contain 75.1% of chlo simple metathetical reaction with a lithium salt, but this rine. A sample analysed by flame photometer was found has hitherto been considered impossible, because the anal to contain 15.7% of lithium. A sample reacted with ogous reaction of sodium borohydride (which is, more acid gave a volume of hydrogen corresponding to a hy over, more salt-like than sodium aluminium hydride) 30 dride ion content of 0.12%. Hence the product con takes place very inefficiently if it takes place at all. This tained 90.5% of lithium chloride and 2.62% of boro is known from the publications of two groups of work hydride calculated as lithium borohydride. For the rea ers, Paul and Joseph (Bulletin de la Société Chimique de sons mentioned above it is believed that at least part France, 1954, 550) and Kollonitsch, Fuchs and Gabor of the borohydride was present as sodium borohydride. (Nature, 1954, 173, 125-6), and has since been con 3 5 I have now surprisingly found that sodium aluminium firmed by the following experiment: hydride can be caused to undergo a metathetical reaction ATTEMPTEED REACTION OF SODIUM BOROHY with a lithium halide, if a liquid reaction medium chosen from a limited range of ether-like solvents is used. DRIDE WITH LITHIUM CHLORIDE It is an object of the present invention to provide an Fourteen grams of sodium borohydride (98.2% pure 40 inexpensive and safe process for producing lithium alu as determined by hydride activity measurement) were minium hydride from sodium aluminium hydride. placed in a 500 ml. three-necked flask fitted with a con According to the invention therefore there is pro denser, an agitator and a thermometer as a suspension vided a process for the production of lithium aluminium in 200 mls. of tetrahydrofuran which had been free from hydride which comprises reacting sodium aluminium hy peroxide by passing it through a column of activated 45 dride with a lithium halide in the presence of at least alumina and then distilling it over sodium. There were one liquid selected from the class of ethers consisting of then added 20 grams of lithium chloride (ca. 95% pure tetrahydrofuran, tetrahydropyran, 4-methyl-tetrahydro after dehydration by the method described in Inorganic pyran and diethylene glycol dimethyl ether. Synthesis, volume 5, page 154). The flask was immersed Any lithium halide may be used in the process. It is, in a bath of running water to keep the temperature of 50 however, preferred to use lithium chloride or lithium the mixture at 20-1° C. and agitation was maintained bromide, especially lithium chloride. for 8 hours. The mixture was filtered: the residue was The above-mentioned liquids are substantially inert washed twice with 25 mls. of fresh tetrahydrofuran and under the conditions of the process and in them the re the washings were added to the filtrate. The total vol actants, Sodium aluminium hydride and a lithium halide, ume of the filtrate was 254 mls. A sample was analysed 5 5 are appreciably soluble and the reaction products, lithium by titration with N/10 hydrochloric acid and followed aluminium hydride and a sodium halide, are respectively by back-titration with N/10 sodium hydroxide. A fur appreciably soluble and relatively insoluble. In this way ther sample was analysed by titration with N/10 silver the progress of the reaction and the separation of the nitrate solution. A further sample was analysed for reaction products by, for example, filtration, are facili lithium by means of a flame photometer. From the re 60 tated. Preferred from among those liquids are tetra Sults of these analyses it was calculated that the filtrate hydrofuran, tetrahydropyran and diethylene glycol di contained methyl ether. Tetrahydrofuran is especially valuable. Gram molecules The reaction takes place at a practicable rate at tem per litre peratures of 0° C. upwards, but it is preferred to operate Total borohydride --------------------------- 0.06 65 it at higher temperatures, not exceeding of course the de Chloride ----------------------------------- 1.08 composition temperature of lithium aluminium hydride, and preferably up to about 135° C. The pressure is suit The total borohydride concentration represents a yield ably atmospheric though pressures above and below at of 4.25% on the weight of the sodium borohydride start mospheric may be employed. ing material, but since sodium borohydride is soluble in 70 The reaction mixture should be well stirred; and hence tetrahydrofuran to the extent of 0.1% (Manual of Tech it is advantageous to maintain the liquid boiling under niques using Sodium Borohydride and Potassium Boro reflux conditions. This is possible at acceptable tem 3,207,570 3. 4 peratures and atmospheric pressure when any of the above content was 7.95% and its lithium to active hydrogen liquids other than diethylene glycol dimethyl ether is used ratio was 1 to 3.9. The yield was 60.6% calculated as pure as the reaction medium. pure lithium aluminium hydride. It is very desirable that the process should be carried Example 3 out in the absence of water, oxygen and carbon dioxide. Air is suitably displaced from the apparatus by an inert A solution of 0.21 g. of sodium aluminium hydride atmosphere of for example, nitrogen, hydrogen or an inert (90% pure) and 0.175 g. (16% excess) of lithium gas from Group O of the Periodic Table, for example chloride in 25 mls. of tetrahydrofuran was stirred at room argon. Any liquid used is preferably thoroughly dried emperature (about 22 C.) in an argon-filled flask for before use. 10 22 hours, whereafter 70 mls. of dry diethyl ether were The reaction product comprises a solution of lithium stirred in. The resulting mixture was filtered in an argon aluminium hydride and a precipitate of a sodium halide. atmosphere. The filtrate was evaporated to dryness, leav The sodium halide may be separated by for example, ing a white powder which after drying for 1% hours at decantation, filtration or centrifuging or a combination 110° C. in vacuo gave 0.073 g. of a white powder. This of these processes. The solvent may then be distilled from 5 was shown by analysis to contain 0.0403 g. of lithium the solution of lithium aluminium hydride, and this leaves 1 aluminium hydride, representing a yield of 30.3%. a residue containing lithium aluminium hydride and any Example 4 excess lithium halide or any unreacted sodium aluminium hydride. If desired, excess lithium halide and unreacted A solution of 0.4 g. of sodium aluminium hydride sodium aluminium hydride may be removed by mixing 20 (70% pure) and 0.5 g. (11% excess) of lithium bromide the reaction product with a liquid which is inert under the in 30 mls. of tetrahydrofuran was stirred and refluxed in conditions of the process and in which lithium aluminium argon atmosphere for 2 hours. The mixture was cooled hydride is soluble but lithium halides and sodium alumin and filtered; and to the filtrate were added 60 mls, of ium hydride are substantially insoluble. Diethyl ether is dry diethyl ether. Excess lithium bromide and unre highly suitable. The precipitated sodium halide and so 25 acted sodium aluminium hydride separated and were fil dium aluminium hydride or lithium halide are then sep tered off. The filtrate was evaporated to dryness to give arated and the resulting clear liquor is evaporated to give a white Solid which after drying in vacuo for 2 hours at lithium aluminium hydride. As an alternative, lithium 110° C. weighed 0.131 g.