Lithium compounds organic media

Many organic syntheses requHe the use of stericaHy hindered and less nucleophilic bases than //-butyUithium. Lithium diisopropylamide (LDA) and lithium hexamethyldisilazide (LHS) are often used (140—142). Both compounds are soluble in a wide variety of aprotic solvents. Presence of a Lewis base, most commonly tetrahydrofuran, is requHed for LDA solubdity in hydrocarbons. A 30% solution of LHS can be prepared in hexane. Although these compounds may be prepared by reaction of the amine with //-butyUithium in the approprite medium just prior to use, they are also available commercially in hydrocarbon or mixed hydrocarbon—THF solvents as 1.0—2.0 M solutions. 

Dialkyl and diaryl ditellurium compounds are easily reduced to tellurols and tellurolates. Alkali metals in liquid ammonia or in an inert organic solvent, sodium borohydride in methanol, ethanol, alcohol/benzene, THF, DMF, or in a basic aqueous medium, lithium aluminum hydride in dioxane or THF/hexamethylphosphoric triamide, and thiourea dioxide in THF/50% aqueous sodium hydroxide have been used as reducing agents (p. 164). The tellurolates are easily oxidized in air. For this reason they are almost always used in situ. 

In a water-free medium chain growth polymerization can be initiated by numerous metal-organic or basic compounds, such as trityl sodium [81], butyl lithium [80,81], naphthyl sodium [80,81], benzophenone potassium [81], sodium methoxide [80,81], lithium organocuprates [85] and rhodium(I) complexes [86] or ammonia [87], er -phosphines [80,88], aliphatic amines [89], cyclic amines [90], and aromatic amines (pyridine [91,92],... 

The list of salty tasting substances contains numerous organic and inorganic salts including some toxic substances (e.g., lithium chloride), but also some nutritionally important cations and anions. Most abundant of all of these compounds is sodium chloride which, in addition to its physiological importance, was also part of the medium (sea water) in which many phyla evolved. For marine and terrestrial animals alike, the most common salty compound is sodium chloride with the toxic ones much less common. The distribution of NaCl is more patchy for terrestrial than for marine animals, however (21). Since NaCl is an absolute requirement for complex organisms, it is not surprising that nearly all species tested respond to it. 

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