Lanthanum hydroxide

Lanthanum hydroxide is used to prepare other lanthanum salts. 

Lanthanum hydroxide is precipitated by adding excess of caustic soda, caustic potash or ammonia to an aqueous solution of a LaS+ salt, such as LaCls, LaCNOsls or La(S04)3 ... 

Reaction with strong alkahes at high temperature and pressure slowly forms crystals of lanthanum hydroxide, La(OH)3. 

A determination of the pH dependence of the lanthanum hydroxide gel-promoted hydrolysis of /3-glyceryl phosphate revealed that the two maxima exist in the pH-rate profile, one at pH 8.6 which presumably involves the species La (OH)+2 and another (smaller) maximum at pH 10.4 which involves the species La (OH) 2+ (4). Presumably the same kind of catalytic mechanism is operative in both cases. These reactions may serve as models for the metal ion-promoted alkaline phosphatases which have been shown to proceed with P—O cleavage (and with no oxygen exchange). 

E. Pena-Vazquez, A. Bermejo-Barrera and P. Bermejo-Barrera, Use of lanthanum hydroxide as a trapping agent to determine hydrides by HG-ICP-OES, J. Anal. At. Spectrom., 20(12), 2005, 1344-1349. 

Again, as in the method described by Azad et al. [ 186], lanthanum hydroxide coprecipitation is employed to remove interfering elements such as copper. Selenium in the soil extracts is converted to hydrogen selenide by reduction with sodium tetrahydroborate(III) and the hydrogen selenide introduced into the argon-hydrogen air-entrained flame. 

At the present time the technique of forming the volatile hydrides of certain elements (Ge, Sn, As, Sb, Bi, Se and Te), as a method of separation and rapid introduction of these elements into an atomiser (flame or hot tube), has had little impact in applied geochemistry. A few applications have been reported but are not yet widely used despite the very low detection limits which are obtainable. The main problems with the method are an abundance of interference effects, mainly from transition elements, and short linear calibration ranges. However Bedard and Kerbyson [4, 5] have shown that it is possible to separate in advance traces of As, Sb, Bi, Se and Te from pure copper, (the most serious interferer) by co-precipitating the elements on lanthanum hydroxide. It has further been shown that this precipitation method is applicable to the majority of interfering elements, and can be adapted to provide a rapid large batch method suitable for geochemical analysis of soil and sediment [6]. 

Natrajan, L., Pecaut, J., and Mazzanti, M. (2006) Fixation of atmospheric CO2 by a dimeric lanthanum hydroxide complex assembly of an unusual hexameric carbonate. Dalton Transactions, 1002—1005. 

To determine sonophoretic transport route(s) at the ultrastructural level, Bom-mannan and co-workers [72] visualized guinea pig skin with transmission electron microscopy (TEM) after the application of colloidal lanthanum hydroxide (an electron dense tracer) and treatment in vivo with 10- or 16-MHz ultrasound (0.2 W/cm ). In control samples, the tracer did not appear to penetrate into the stratum comeum. But in samples exposed to sonophoresis, the tracer was found in localized areas of the intercellular space, which may correspond to the lacunae (polar head-group domains) described by Hou and co-workers [73] as polar or head-group domains. In addition, sonophoresis for 5 minutes (at both 10 and 16 MHz) did not appear to alter the morphology of the epidermal cells, whereas damage to cells was observed after 20 minutes of treatment (16 MHz). Thus, sonophoresis appears to cause the permeation of the tracers via the intercellular route within the stratum comeum. 

In practice, a single crystal of europium-doped lanthanum fluoride (K,p = 2 X 10" ) responds in a matter of seconds according to (13-4) to fluoride ion activity in solutions containing fluoride from about 1 Af to 10" M. Europium doping increases fluoride mobility by introducing lattice disorder. Hydroxide ion, beginning at about 10" Af, is the principal interference, probably the result of competition due to the low solubility of lanthanum hydroxide. 

In a completely unrelated development, E. Bamann (7) showed that lanthanum hydroxide promotes the hydrolysis of glyceryl phosphate subsequently, BUTCHER and Westheimer (9) investigated the promotion of the hydrolysis of phosphate esters by lanthanum hydroxide gel, and found a more than thousandfold increase in the rate. Tliey also proposed a mechanism for the reaction which, however, involves water. 

Ternary systems have been prepared in this way as well. The sequential precipitation of aluminum hydroxide, lanthanum hydroxide and, finally, nickel hydroxide gave, after calcination and reduction, a lanthamun activated Ni/Al203 catalyst which had smaller metal crystallites and was somewhat more active than a catalyst prepared by the simultaneous coprecipitation of the three... 

Properties White, malleable ductile metal. Oxidizes rapidly in air. D 6.18-6.19, mp 920C, bp 3454C. Corrodes in moist air. Soluble in acids decomposes water to lanthanum hydroxide and hydrogen. Superconducting at approximately 6K. 

Finely divided particles in suspension can also interfere with colorimetric mea.surements if one of the indicator forms happens to be preferentially adsorbed. Lanthanum hydroxide is a very striking example of such interference. This compound is a strong base which is very slightly soluble in water. A saturated solution in water at 25° has a pH of 9.0. If the pH of a suspension (turbid solution) of the solid hydroxide is measured with thymol-phthalein, the result obtained is 10.5. The suspension is colored a dark blue, although thymolphthalein is colorless at pH 9.0. The precipitate settles after a time, leaving a colorless supernatant solution although the solid itself is dark blue. Because of the strong basic properties of solid lanthanum hydroxide, it forms on its surface a salt with the indicator acid. In other words, the adsorption of the colored indicator anion predominates, and the presence of the solid phase favors a displacement of the indicator equilibrium towards the alkaline form. Phenol-... 

In most cases the co-precipitation of traces consists in the formation of solid solutions. The separation by co-precipitation is not restricted by the very low concentration of the trace species. Smaller amounts can be separated by co-precipitation than by solvent extraction, which is limited by the stability of the complex extracted. The formation of a solid solution, e.g., in the separation of Pb traces with lanthanum hydroxide, consists in the replacement of some La atoms in the crystal lattice by Pb atoms. 

A simple experiment demonstrates the impermeability of certain tight junctions to many water-soluble substances. In this experiment, lanthanum hydroxide (an electron-dense colloid of high molecular weight) is injected into the pancreatic blood vessel of an experimental animal a few minutes later, the pancreatic acinar cells, which are specialized epithelial cells, are fixed and prepared for microscopy. As shown In Figure 6-10, the lanthanum hydroxide diffuses from the blood Into the space that separates the lateral surfaces of adjacent acinar cells, but cannot penetrate past the tight junction. 

A EXPERIMENTAL FIGURE 6-10 Tight junctions prevent passage of large molecules through extracellular space between epithelial cells. This experiment, described in the text, demonstrates the impermeability of tight junctions in the pancreas to the large water-soluble colloid lanthanum hydroxide. [Courtesy of D. Friend.]... 

The alkaline hydrolysis of l-methyl-2-propyl phosphate by lanthanum hydroxide gel proceeds in a similar manner with cleavage of the P—O bond and complete retention of configuration 12). 

Lanthanum hydroxide, though sparingly soluble, is a strong base and absorbs CO2, giving the carbonate. Base strength and solubility decrease on crossing the lanthanoid series, and Yb(OH)3 and Lu(OH)3 dissolve in hot concentrated NaOH (equation 24.14). 

Alkyl phosphates containing electronegative cyano groups at the -position of one of the alkyl groups readily undergo hydrolysis in alkaline media by P-elim-ination (Scheme 8.5.9). Another important neighboring effect concerns ribonucleotides. Ribonucleoside 3 - or 2 -phosphates are, for example, quantitatively hydrolyzed by lanthanum hydroxide at pH 6, whereas 2-deoxyribonucleotides are not dephosphorylated under these conditions. The role of the hydroxyl group is not known in this case. Heavy metal catalysis of phosphate ester hydrolysis is probably caused by complexation of the metal ions, which renders the phosphorus atom more electrophilic. 

Due to the low concentration of radioactive tracers in solution the solubility product for an "insoluble" salt is not always exceeded upon the addition of macro concentrations of a counter ion. Let us as example take the insoluble lanthanum hydroxides. The solubility product for the reaction La(OH)3 (s) La + 3 OH is K q 10 in 1 mM NaOH the... 

Normal azides are not known in group IIIB. Curtius and Darapsky [135] attempted to make them by dissolving, for example, lanthanum hydroxide in hydrazoic acid. The solution was assumed to contain the normal azide but only basic products were precipitated upon evaporation or by adding alcohol. The precipitate was insoluble in water, had the approximate composition La(OH)(N3)2 I.5H2O, and deflagrated upon heating. The same results were found with yttrium, cerium, dysprosium, thorium, and uranium azides. Based on the infrared spectra, Rosenwasser and Bryant [136] suggested two types of basic rare earth azides. The lanthanum type (a) was found for lanthanum, neodymium. 

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