Lithium aluminum hydride manufacture and use

【China Aluminum Network】 1. Potassium aluminum hydride, also known as lithium tetrahydroaluminate and lithium tetrahydroaluminate, are white or off-white crystalline powders. Molecular formula: H4AlLi Molecular weight: 37.9543 Insoluble in hydrocarbons, soluble in ether, tetrahydrofuran, dimethylform Cellosolve, slightly soluble in n-butyl ether, insoluble or very slightly soluble in hydrocarbons and dioxane. The melting point is 140°C. Relative density (water = 1) 0.92 Stability Stable at room temperature Stable in dry air. Easily affected by moisture. Reaction to water and alcohol occurs violently.

Second, the lithium aluminum hydride preparation methods are Schlesinger method, high-pressure synthesis, sodium aluminum hydride and other preparations. Because the Schlesinger method is relatively simple, it is still the main method for producing lithium aluminum hydride.

1, Schlesinger method:

In 1947 Schlesinger, Bond, and Finholt first produced lithium aluminum hydride by reacting lithium hydride with anhydrous aluminum trichloride in diethyl ether: 4LiH + AlCl3 − Et2O → LiAlH4 + 3LiCl This reaction is generally called the Schlesinger reaction. The reaction yield was 86% calculated as aluminum trichloride. A small amount of lithium aluminum hydride was added as an initiator at the beginning of the reaction, otherwise the reaction would have to go through a period of induction before it could occur, and once it started, it would proceed at a fierce rate and be prone to accidents. The Schlesinger process has many disadvantages, such as the need for initiators, excessive amounts of lithium hydride, and high levels of fines, the need to use rare metal lithium as a raw material, the conversion of lithium hydride in 3/4 of the reaction to inexpensive lithium chloride, and the like.

2. High-pressure synthesis method: react with alkali metal or hydride, aluminum, and high-pressure hydrogen in a hydrocarbon or ether solvent.

LiH + Al + 2H2 → LiAlH4

3, made from sodium aluminum hydride. Industrial synthesis generally uses high temperature and high pressure synthesis of sodium aluminum hydride, and then undergoes metathesis reaction with lithium chloride. This preparation method can achieve high yields of lithium aluminum hydride:

Na + Al + 2H2 → NaAlH4

NaAlH4 + LiCl −Et2O→ LiAlH4 + NaCl

Among them, LiCl was filtered out with an ethereal solution of lithium aluminum hydride, followed by precipitation of lithium aluminum hydride to obtain a product containing about 1% (w/w) of LiCl. The sodium aluminum hydride mentioned above can also be reacted with potassium aluminum hydride and reacted with lithium chloride or diethyl ether or lithium hydride in tetrahydrofuran.

Lithium aluminum hydride is a white solid, but industrial products are usually gray powders due to impurities. Lithium aluminum hydride can be purified by recrystallization from ethyl ether, and a soxhlet extractor can be used if large-scale purification is performed. In general, impure gray powders are used for synthesis because impurities are harmless and can be easily separated from organic products. Pure lithium aluminium hydride powder is self-igniting in air, but large crystals do not ignite spontaneously. Some lithium aluminum hydride industrial products contain mineral oil to prevent the material from reacting with water in the air, but it is more common to seal it in a waterproof plastic bag.

Third, the use of lithium aluminum hydride:

1. It is used as reducing agent in medicine, spices, pesticides, dyes and other fine organic synthesis.

2, used as aldehydes, ketones, esters and other reducing agents, reactor control rods, battery materials.

3. Catalysts for the polymerization of diolefins such as butadiene and isoprene, additives for improving the mechanical properties of alloys, steelmaking and oxygen absorbers for the manufacture of copper alloys.

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