Lithium aluminum hydride manufacture and use

A, potassium aluminum hydride, lithium aluminum hydride, also known as four, tetrahydro lithium aluminum hydride is a white or off-white crystalline powder molecular formula: H4AlLi Molecular Weight 37.9543 insoluble in hydrocarbon, was dissolved in diethyl ether, tetrahydrofuran, dimethyl cellosolve, micro- dissolved in n-butyl ether, insoluble or very slightly soluble in hydrocarbons and dioxane. A melting point of 140 ℃ Relative density (water = 1) 0.92 Stability stable in dry air at room temperature can be stable. Susceptible to tidal action. Water and alcohol react violently.

Second, the preparation of lithium aluminum hydride are Schlesinger, high pressure synthesis method, the preparation of sodium aluminum hydride and the like. Since Schlesinger method is more simple, it is still the main method of preparation of lithium aluminum hydride.

1, Schlesinger method:

1947 Schlesinger, Bond and Finholt first obtained lithium aluminum hydride, the method is to make lithium hydride and the reaction of anhydrous aluminum chloride in ether: 4LiH + AlCl3 -Et2O → LiAlH4 + 3LiCl This reaction is generally called Schlesinger reaction, The reaction yield calculated as aluminum trichloride to 86%. Beginning of the reaction to add a small amount of lithium aluminum hydride as the initiator, or else go through a period of induction period the reaction to take place, and once the rate will be after the start of a violent, prone to accidents. Schlesinger method has many drawbacks, for use initiator, lithium hydride and height requirements excess fine powder, need to use scarce raw material lithium, lithium hydride reaction 3/4 into inexpensive lithium chloride and the like.

2, high-pressure synthesis method: using an alkali metal or hydride, aluminum, high-pressure hydrogen reaction in a hydrocarbon or ether solvent.

LiH + Al + 2H2 → LiAlH4

3, taken from the system, sodium aluminum hydride. The industrial synthesis of high temperature and pressure synthesis generally use sodium aluminum hydride, lithium chloride and then carry out the metathesis reaction. This preparation method can be implemented in a high yield with lithium aluminum hydride:

Na + Al + 2H2 → NaAlH4

NaAlH4 + LiCl -Et2O → LiAlH4 + NaCl

LiCl wherein the ether solution of lithium aluminum hydride was filtered off, subsequently precipitated lithium aluminum hydride, obtained containing 1% (w / w) LiCl about products and services. If the aforementioned sodium aluminum hydride, potassium aluminum hydride can be replaced by the reaction, may be reacted with lithium chloride or lithium hydride in ether or tetrahydrofuran.

Lithium aluminum hydride as a white solid, but because it contains impurities of industrial products, typically gray powder. Lithium aluminum hydride can be re-crystallized from ether to be purified, if large-scale purification can use Soxhlet extractor. In general, impure gray powder used in the synthesis, since the impurities are harmless, can be easily separated from the organic product. Pure lithium aluminum hydride powder is spontaneous combustion in the air, but large crystals easily spontaneous combustion. Some industrial lithium aluminum hydride in mineral oil will contain, in order to prevent water reactive material in the air, but more generally the practice to put waterproof plastic bag sealed.

Three, the use of lithium aluminum hydride:

1, as a reducing agent in the pharmaceutical, perfume, pesticides, dyes and other fine organic synthesis.

The reducing agent 2, is used as aldehydes, ketones, esters and the like, the reactor control rods, battery materials.

3, butadiene, isoprene, pentadiene two olefin polymerization catalyst additive to improve the mechanical properties of the alloy, steel and copper alloy deoxidizer.

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