Author Topic: Lithium Hydride synth u/ mild hydrogenation THF  (Read 533 times)

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Lithium Hydride synth u/ mild hydrogenation THF
« on: October 24, 2003, 05:12:00 PM »
synthesis of LiH via hydrogenation of butyl lithium in THF - also synth of l-selectride from tri-sec-butylborane. keeping in mind that LAH can be prepared from LiH, with etheral solution of AlCl3.

Method of synthesis of lithium substituted borohydride reagents and method of synthesis of reactive lithium hydride - Burkhardt ,   et al.    July 31, 2001

Patent US6268537

Preperation of LiH
Example 17
n-BuLi was added to the THF.THF (409 g) was placed in a glass low pressure reactor and cooled to approximately C. n-BuLi (60 ml of 10M) was placed in a Fisher-Porter bottle and chilled to approximately C. n-BuLi was added to the THF over about 15 minutes. The solvation reaction was exothermic, causing the mixture to rise in temperature up to approximately C. midway through the THF addition. Hydrogen was introduced to the vessel at approximately 35 psig. The reactor was kept at -15 to C. during the hydrogenation period of 8 hours. An IR spectrum of a filtered sample of the slurry showed a small peak at 1612 cm.sup.-1 for the lithium enolate of acetaldehyde; calculated amount of deprotonation was 0.7 mol %. The LiH slurry was quenched with methanol and discarded.

Preparation of l-selectride
Example 12
In a glovebox, tri-sec-butylborane (54.65 g) and tetrahydrofuran (250 ml) were charged to a Morton flask. The flask was closed and transferred to a hood. The flask was equipped with an addition funnel for solids and connected to a nitrogen manifold. The system was purged with nitrogen gas. Then lithium hydride (2.39 9) was charged over 55 min to the stirred reaction mixture at approximately C. The reaction mixture was stirred for 5.5 h, then allowed to sit overnight at ambient temperature. A sample of the reactor content was taken and analyzed by .sup.11 B-NMR. Integration of the .sup.11 B-NMR signals showed 42% lithium tri-sec-butylborohydride (.delta.=-7.16 ppm) and 58% tri-sec-butylborane (.delta.=85.9 ppm).