Acidity lanthanide oxides

There are a number of minerals in which thorium is found. Thus a number of basic process flow sheets exist for the recovery of thorium from ores (10). The extraction of mona ite from sands is accompHshed via the digestion of sand using hot base, which converts the oxide to the hydroxide form. The hydroxide is then dissolved in hydrochloric acid and the pH adjusted to between 5 and 6, affording the separation of thorium from the less acidic lanthanides. Thorium hydroxide is dissolved in nitric acid and extracted using methyl isobutyl ketone or tributyl phosphate in kerosene to yield Th(N02)4,... 

Instead of Bronsted acids, lanthanide triflates can be used to catalyze the reaction of indole with benzaldehyde (Eq. 7.7). The use of an ethanol/water system was found to be the best in terms of both yield and product isolation. The use of organic solvent such as chloroform resulted in oxidized byproducts.17... 

Ranjit KT, Willner I, Bossmann SH, Braun AM (2001) Lanthanide oxide doped titanium dioxide photocatalysts Novel photocatalysts for the enhanced degradation of p-chlorophe-noxyacetic acid. Environ Sci Technol 35 1544—1549... 

Hydrated lanthanide salts may also be obtained by the addition of an excess of lanthanide oxide to a concentrated acid solution, heating at 80°C until the pH is between 5 and 6. The residual oxide is removed by filtration, and the filtrate is subjected to rotary evaporation. This procedure may lead to the presence of oxo and hydroxy species in solution. At present hydrated lanthanide salts of 99.9% purity are available commercially. Salts of the highest purity are generally used in spectroscopic and magnetic studies. The purity of lanthanide salts can be determined by complexometric titration with ethylenediamine tetraacetic acid [1]. 

Synthesis of lanthanide triflates is achieved by adding an excess of lanthanide oxide to a concentrated solution of triflic acid in water at 80°C. The reaction is complete when the solution has a pH of 6.0. The solution is filtered, and evaporated in a rotary evaporator. The resulting solid is dried in a vacuum at 100°C for 12 hours. 

Another method of synthesis involves the direct reaction of stoichiometric amounts of ligand in acid form and lanthanide oxide, hydroxide or carbonate in suspension in hot water. The mixture is heated under reflux until total dissolution is obtained. 

The sodium salt may be obtained by adding a dilute NaOH solution to attain pH 5.0. One of the main precautions is that the synthesis be done with dilute solutions. For example nitrilotriacetic acid (NTA) complexes have been synthesized using 0.02 M solutions and at higher dilutions in the case of heavy lanthanides [37]. Use of an excess of lanthanide oxide should be avoided since reactions of the following type may take place [38]... 

Braun AM (2001) Lanthanide Oxide-Doped Titanium Dioxide Photocatalysts Novel Photocatalysts for the Enhanced Degradation of p-Chlorophenoxyacetic Acid, Environ. Sci. Technol. 35 1544-1549. 

These are readily prepared by reaction of the lanthanide oxide or carbonate with the acid. Salts of noncoordinating anions most often crystallize as salts [Ln(OH2)9]X3 (X e.g. bromate, triflate, ethyl sulfate, tosylate). These contain the [Ln(OH2)9] + ion (Figure 4.1), even for the later lanthanides, where in aqueous solution the eight-coordinate species [Ln(OH2)8] predominates. 

Lanthanide oxides react with the acid to give (i) and (ii), formulated by Moeller, Moss and Marshall (1955) as... 

Various metals have been complexed to oligonucleotides to produce hydrolytic or oxidative cleavage of a target nucleic acid. Lanthanide complexes covalently attached to oligonucleotides are known to cleave single-stranded... 

All syntheses are carried out in an aqueous solution. Triflic acid, HSO3CF3 is distilled by the trap-to-trap method before use, and it is diluted with water (10 -10 M). Stoichiometric quantities of this diluted triflic acid is added to the lanthanide chloride or lanthanide oxide and heating at boiling for 30 min to 1 h. The unreacted lanthanide chloride or lanthanide oxide, if any, is removed by filtration, and the water is removed from the filtrate under reduced pressure. The resulting hydrate is then dried by heating under vacuum (1.33 Pa) at 180 °C to 200 °C for several days. 

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