Lithium aluminum hydride, reaction properties

A facile method for the stereospecific labeling of carbon atoms adjacent to an oxygenated position is the reductive opening of oxides. The stereospecificity of this reaction is due to virtually exclusive diaxial opening of steroidal oxides when treated with lithium aluminum hydride or deuteride. The resulting /ra/w-diaxial labeled alcohols are of high stereochemical and isotopic purity, with the latter property depending almost solely on the quality of the metal deuteride used. (For the preparation of m-labeled alcohols, see section V-D.)... 

The lesser known four-membered cyclic ether, oxacyclobutane (oxe-tane), (CH2)30, also is cleaved readily, but less so than oxacyclopropane. Oxacyclopentane (oxolane, tetrahydrofuran) is a relatively unreactive water-miscible compound with desirable properties as an organic solvent. It often is used in place of diethyl ether in Grignard reactions and reductions with lithium aluminum hydride. 

A very extensive investigation of the reaction of pyridine and lithium aluminum hydride has been made by Lansbury and Peterson.60-82 These authors found that an aged solution of LAH in pyridine possessed unusual and selective reductive properties. Ketones and aldehydes were reduced while carboxylic acids were not, and diaryl ketones were reduced more readily than dialkyl ketones. These distinctive properties were found to result from a dihydropyridine-aluminum complex formed by the reaction of LAH and pyridine. 

Stearyl Alcohol Reduction of ethyl stearate in the presence of lithium aluminum hydride yields stearyl alcohol, which contains not less than 90% of 1-octadecanol. It is available as flakes or granules which are white in color and possesses a characteristic odor. It is insoluble in water and melts at 55-60 °C. Stearyl alcohol has stiffening, viscosity-enhancing, and emollient properties and hence is used in the preparation of hydrophobic ointments and creams. Its weak emulsifying properties help in improving the water-holding capacity of ointments. Hypersensitivity reactions are sometimes observed due to the presence of some minor impurities. Stearyl alcohol preparations are compatible with acids and alkalis and are preserved in well-closed containers in a cool and dry place [6]. 

Hydrides commonly used in laboratories are lithium aluminum hydride, potassium hydride, sodium hydride, sodium borohydride, and calcium hydride. The following methods for their disposal demonstrate that the reactivity of metal hydrides varies considerably. Most hydrides can be decomposed safely by one of the four methods, but the properties of a given hydride must be well understood in order to select the most appropriate method. (CAUTION Most of the methods described below produce hydrogen gas, which can present an explosion hazard. The reaction shouid be carried out in a hood, behind a shield, and with proper safeguards to avoid exposure of the effluent gas to spark or flame. Any stirring device must be spark-proof.)... 

Since topicity is a property of atoms in and spaces near a molecule, spaces around an achiral molecule can also be considered prochiral. For example, reduction of acetophenone (105) by lithium aluminum hydride gives eitiier (R)- or (S)-l-phenylethanol (106), depending on the pathway of the reaction (Figure 2.43). In talking about the reaction pathway, it is useful to differentiate... 

Unfortunately, none of the hyperbranched polymers smdied to date has demonstrated good mechanical properties. A hyperbranched PC is also expected to be a brittle material, but such a stmcture may prove interesting as a highly functionalized prepolymer for composites, coatings, and other applications. Hyperbranched PCs were synthesized and characterized by Bolton and Wooley. ° The products were prepared by the polymerization of an A2B monomer derived from l,Ll- nT(4 -hydroxyphenyl)-ethane. Silylation of the phenol terminated material with rert-butyldimethylsilyl chloride, followed by degradation of the carbonate hnkages by reaction with lithium aluminum hydride and analysis of the products by HPLC... 

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