Purification, general procedures halides

As a general procedure if the olefin is impure, the oxymercura-tion-reduction process may include an olefin purification step. Alternatively, this process may be used to purify the olefin for other purposes. - In such cases, acetone is substituted for ether and, after oxymercuration for the same length of time as suggested above, the solution is poured with stirring into two volumes of water containing one equivalent each of sodium bicarbonate and sodium chloride. The mercury derivative is filtered, recrystallized from ethanol-water, ether, dioxane, or ethyl acetate-heptane and then either reduced as described above (in 70-80% yield) to produce pure alcohol, or deoxy-mercurated with cold 6N HCl, with ethereal lithium aluminum hydride (added cautiously), or high concentrations of alkali halides - to produce the pure olefin. 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

The most common procedure for preparing bismuth alkoxides is the substitution reaction of bismuth halides with alkali metal alkoxides. The alternative is treatment of bismuth amides with alcohols. Bismuth alkoxides such as trimethoxide, triethoxide and triisopropoxide were first prepared in 80-93% yields by the reaction between BiCl3 and alkali metal alkoxides by Mehrotra et al. in 1966. Bismuth alkoxides are less soluble in organic solvents and the yields after purification by sublimation are generally very low (10-20%) [66IJC537]. Known aliphatic alkoxides include Bi(OEt)3... 

Alternative procedures for the preparation of N-carboxyanhydrides include reaction of the N -protected amino acids with PBrj. Generally, methods involving the use of phosphoro halides are hampered by the need for very long reaction times and extensive product purification, and often give only very poor yields. 

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