Aluminum trihydride

S. Orimo, Y. Nakamori, T. Kato, C. Brown, C.M. Jensen, Intrinsic and mechanically modified thermal stabiUties of a-, 3-and y-aluminum trihydrides AlH, Appl. Phys. A 83 (2006) 5-8. 

Methods for the preparation of aluminum trihydride-diethyl etherate, AlHa O.SffC Hs )20], t have been published,1,2 but the absence of complete experimental details makes duplication difficult. The following procedure is a modification of that reported by Finholt, Bond, and Schlesinger.1 Problems inherent in previous methods, such as premature precipitation, decomposition of the alane, and lithium chloride contamination, are avoided. 

Chloride is removed from the ether solution of aluminum trihydride by the addition of sodium tetrahydroborate. The LiBH4 remains in solution, while the sodium chloride precipitates and is removed by filtration. Best results are obtained when NaBH4t is dried under vacuum at 60°C. for 8 hours and ground to 1 /urn. or smaller. This last step is particularly important since both the reaction rate and efficiency of chloride removal are a function of NaBH4 particle size. 

The volume of clear aluminum trihydride solution is reduced to about 600 ml. by nitrogen-stream evaporation and then allowed to warm to room temperature. After 6 to 8 hours, the aluminum trihydride-diethyl etherate precipitates, which leaves the small amount of soluble LiBH4 and aluminum trihydride-diethyl etherate in the ether solution. The product is filtered, washed twice with 100 ml. of anhydrous ether, and dried under high vacuum for 10 to 12 hours. A yield of approximately 30 g. (58%) is obtained. A nal. Calcd. for A1H3 0.3[(C2HS )20] J Al, 50.78 C, 28.21 H, 11.61 Hydrolytic H2,5.69. Found Al, 50.60 C, 28.08 H, 11.62 Hydrolytic H2,5.68. 

Thc cold solution is necessary to prevent premature precipitation of the aluminum trihydride. 

The aluminum trihydride-diethyl etherate is a colorless solid which reacts violently with water or in a damp atmosphere. ( Caution. Sometimes this reaction is explosive ) The material is unstable to prolonged exposure to light at ambient temperatures, but can be stored at — 10°C. in a sealed container up to one year. The ratio of aluminum trihydride to ether (C2H2)20 in the solid varies between 0.29 and 0.33, depending upon the time under vacuum. The solubility of aluminum trihydride-diethyl etherate in diethyl ether is 0.2Af it is very soluble in tetrahydrofuran. Its infrared spectrum has broad bands in the... 

Caution. Solid aluminum trihydride tetrahydrofuran often decomposes explosively when exposed to a high vacuum. 

The solution of aluminum trihydride used in this synthesis is prepared by the reaction of 100% sulfuric acid with lithium tetrahydridoaluminate(l —) in dry tetrahydrofuran.3 Under nitrogen flow, a stoichiometric amount of the sulfuric acid is added dropwise by syringe at 0° to a solution of lithium tetrahydridoaluminate(l —) in dry tetrahydrofuran. The apparatus used is just like that shown in Fig. 2, except that an ice bath is used to cool the reaction flask and thus prevent ether cleavage. As the sulfuric acid is added to the lithium tetrahydridoaluminate(l —), a precipitate of lithium sulfate forms and hydrogen is evolved. For this reason, the reaction must be carried out in a hood. After all the sulfuric acid has been added, the resulting slurry is stirred for 2 hr, then filtered in a glove box.4,5 The filtrate, a clear solution of aluminum trihydride in tetrahydrofuran, is stored in the refrigerator at -20° until it is needed. 

SYNS ALANE ALUMINUM TRIHYDRIDE a-ALUMINUM TRIHYDRIDE... 

John specialized in fluorine, boron, sulfur, phosphorus, and metal carbonyl chemistry. With M. Frederick Hawthorne, he discovered a series of amine complexes of aluminum trihydride and showed that some of them give aluminum metal when heated this process later became useful for the formation of aluminum thin films by chemical vapor deposition. One of his notable achievements was the discovery that the PPN cation, bisftriphenylphosphoranyhdene) ammonium, forms air-stable salts with many air-sensitive anions such as [Co(CO)4] . He also discovered that cesium fluoride can serve as a catalyst for the synthesis of organic fluoroxy compounds (RpOF) by the fluorination of acyl halides. 

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