Thorium ions, reactions

It has also been argued10,40 that the second mechanism (rapid, reversible interconversion of II and IV) cannot be general. The basis for this contention is the fact that electrophilic catalysis is rare in nucleophilic aromatic substitution of non-heterocyclic substrates, an exception being the 2000-fold acceleration by thorium ion of the rate of reaction of 2,4-dinitrofluorobenzene with thiocyanate... 

Later work by Lin et al. overcame this problem by bubbling SC-C02 through a vessel containing TBP upstream of the extraction vessel43 Using this approach, super-saturation of the fluid phase by the extractant was avoided and a supercritical phase containing ca. 11% (on a molar basis)44 of TBP was consistently obtained (at 60°C and 120 atm pressure). This TBP-saturated C02 was then employed to extract uranyl and thorium ions from nitric acid solutions of various concentrations. The extraction of both ions increased with rising aqueous acidity, consistent with the extraction reactions observed in conventional systems (e.g., TBP-dodecane), such as that shown here for uranium ... 

The small steric size and propensity of cyanide groups to bridge metal centers have limited their use as ligands in molecular coordination chemistry of the actinides, where they are prone to form amorphous polymeric products. Limited metathesis studies have been conducted. Reaction of tetravalent halides with alkali metal cyanides in liquid ammonia is reported to give rise to a product of the formula UX3(CN)-4NH3, whereas use of the larger thorium ion yields unidentified products. 

The enthalpy of solution of ThCl4(cr) in ca. 16000 H2O was given at 288 K as -Till kJmol by Chauvenet [1911CHA]. As discussed in Appendix A, use of the constants for the hydrolysis of the thorium ion selected in this review (Table VIl-15) and of that for the formation of the first thorium chloride complex (Section Vlll.2.2) leads to a dissolution reaction that can be written as ... 

Sergeev, G. M., Almazova, V. D., Reaction of thorium(IV) with organic acids in aqueous solutions. I. Hydrolysis of thorium ions, Tr. Khim. Khim. TekhnoL, 1, (1970), 31-35. Cited on pages 135, 527. 

OKA/MOC] Okamoto, Y., Mochizuki, Y., Tsushima, S., Theoretical study of hydrolysis reactions of tetravalent thorium ion, Chem. Phys. Lett., 373, (2003), 213-217. Cited on pages 100, 679. 

Thermal equilibrium, 56 Thermite reaction, 122 Thermometers, 56 Thiosulfate ion, 362 Third-row elements, 101 compounds, 102 physical properties, 102 properties, table, 101 Third row of the periodic table, 364 Thomson, J. J., 244 Thomson model of atom, 244 Thorium... 

A calibration curve for the range 0.2-10 mg fluoride ion per 100 mL is constructed as follows. Add the appropriate amount of standard sodium fluoride solution, 25 mL of 2-methoxyethanol, and 10 mg of a buffer [0.1 Af in both sodium acetate and acetic (ethanoic) acid] to a 100 mL graduated flask. Dilute to volume with distilled water and add about 0.05 g of thorium chloranilate. Shake the flask intermittently for 30 minutes (the reaction in the presence of 2-methoxyethanol is about 90 per cent complete after 30 minutes and almost complete after 1 hour) and filter about 10 mL of the solution through a dry Whatman No. 42 filter paper. Measure the absorbance of the filtrate in a 1 cm cell at 540 nm (yellow-green filter) against a blank, prepared in the same manner, using a suitable spectrophotometer. Prepare a calibration curve for the concentration range 0.0-0.2 mg fluoride ion per 100 mL in the same way, but add only 10.0 mL of 2-methoxyethanol measure the absorbance of the filtrate in a 1 cm silica cell at 330 nm. 

The monazite sand is heated with sulfuric acid at about 120 to 170°C. An exothermic reaction ensues raising the temperature to above 200°C. Samarium and other rare earths are converted to their water-soluble sulfates. The residue is extracted with water and the solution is treated with sodium pyrophosphate to precipitate thorium. After removing thorium, the solution is treated with sodium sulfate to precipitate rare earths as their double sulfates, that is, rare earth sulfates-sodium sulfate. The double sulfates are heated with sodium hydroxide to convert them into rare earth hydroxides. The hydroxides are treated with hydrochloric or nitric acid to solubihze all rare earths except cerium. The insoluble cerium(IV) hydroxide is filtered. Lanthanum and other rare earths are then separated by fractional crystallization after converting them to double salts with ammonium or magnesium nitrate. The samarium—europium fraction is converted to acetates and reduced with sodium amalgam to low valence states. The reduced metals are extracted with dilute acid. As mentioned above, this fractional crystallization process is very tedious, time-consuming, and currently rare earths are separated by relatively easier methods based on ion exchange and solvent extraction. 

The heavy isotopes or francium can be formed by irradiation of uranium or thorium by protons of high energy the lighter isotopes can be obtained by nuclear reactions induced in gold, tellurium, or lead targets by heavy ions. 

For the trivalent lanthanides99-100 and actinides,99 as well as for yttrium and scandium,75 the equilibrium constant for the extraction reaction has been shown to vary inversely with the ionic radius of the metal ion. It has therefore been concluded that the extracted complexes are all of the M(HA2)3 type, involving predominantly ionic metal—ligand bonds.75 The similarity of the IR spectra of the scandium(III) and thorium(IV) complexes of D2EHPA to those of the alkali metals is also indicative of the importance of ionic bonding.102... 

The other metal ions that exhibited an appreciable reaction with Arsenazo(III) at 650nm under the separation and detection conditions used, were iron(III), zirconium(IV), thorium(IV) and the lanthanides. The lanthanides, iron(III) and zirconium(IV) were eluted at or near the solvent front before uranium(VI) and thorium(IV) was eluted after uranium(VI). 

Reactions of thorium(IV) ions To study these reactions use a 01m solution of thorium nitrate Th(N03)4.4H20 which contains a few per cent free nitric acid also. 

To check the mass balance of the reaction, the reaction products were analyzed after each run by a thorium nitrate method for fluoride and by a sodium hydroxide titration for hydrogen ions. 

Compounds of divalent samarium, europium, and ytterbium are well-known. In recent years, lower halides of other lanthanides, such as neodymium 48), praseodymium 45, 49, 90), and thulium 4) have been obtained by reducing the trihalide with the metal. The corresponding reaction of thorium tetraiodide with thorium metal has led to the identification of two crystalline forms of Thl2 41, 91) it is unlikely that the Th ", or even Th ", ion is present in Thl2, but like Prl2, which is formulated as Pr " (r)2( ) (2), the compound is probably of the type Th " (r)2(2 ) 41). Certainly one crystal form is diamagnetic 41), suggesting the latter formulation. 

With the exception of thorium and protactinium, all of the early actinides possess a stable +3 ion in aqueous solution, although higher oxidation states are more stable under aerobic conditions. Trivalent compounds of the early actinides are structurally similar to those of their trivalent lanthanide counterparts, but their reaction chemistry can differ significantly, due to the enhanced ability of the actinides to act as reductants. Examples of trivalent coordination compounds of thorium and protactinium are rare. The early actinides possess large ionic radii (effective ionic radii = 1.00-1.06 A in six-coordinate metal complexes),and can therefore support large coordination numbers in chemical compounds 12-coordinate metal centers are common, and coordination numbers as high as 14 have been observed. 

All early actinides from thorium to plutonium possess a stable +4 ion in aqueous solution this is the most stable oxidation state for thorium and generally for plutonium. The high charge on tetravalent actinide ions renders them susceptible to solvation, hydrolysis, and polymerization reactions. The ions are readily hydrolyzed, and therefore act as Bronsted acids in aqueous media, and as potent Lewis acids in much of their coordination chemistry (both aqueous and nonaqu-eous). Ionic radii are in general smaller than that for comparable trivalent metal cations (effective ionic radii = 0.96-1.06 A in eight-coordinate metal complexes), but are still sufficiently large to routinely support high coordination numbers. 

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