Chloride-selenites

While to date the pure transition metal containing rare earth selenites are restricted to copper as the transition metal, the chloride-selenites MRCl(Se03)2 allow greater variation of the transition metal M. They have been prepared with M = Mn, Co, Cu and for most of the larger rare earth metals (Wickleder and Ben Hamida, 2003 Ben Hamida, 2004). The synthesis can be done by the reaction of the transition metal oxides, MO, with rare earth trichlorides and Se02. Alternatively, the transition metal chlorides can serve as Cl somee, and R is added in form of the oxides. In aity case, the reactions are carried at 800 °C in evacuated silica ampoules, and excess of the chloride component is helpful if single crystals are desired. 

Discussion. This gravimetric determination depends upon the separation and weighing as elementary selenium or tellurium (or as tellurium dioxide). Alkali selenites and selenious acid are reduced in hydrochloric acid solution with sulphur dioxide, hydroxylammonium chloride, hydrazinium sulphate or hydrazine hydrate. Alkali selenates and selenic acid are not reduced by sulphur dioxide alone, but are readily reduced by a saturated solution of sulphur dioxide in concentrated hydrochloric acid. In working with selenium it must be remembered that appreciable amounts of the element may be lost on warming strong hydrochloric acid solutions of its compounds if dilute acid solutions (concentration <6M) are heated at temperatures below 100 °C the loss is negligible. 

Figure 3 Gradient separation of anions using suppressed conductivity detection. Column 0.4 x 15 cm AS5A, 5 p latex-coated resin (Dionex). Eluent 750 pM NaOH, 0-5 min., then to 85 mM NaOH in 30 min. Flow 1 ml/min. 1 fluoride, 2 a-hydrox-ybutyrate, 3 acetate, 4 glycolate, 5 butyrate, 6 gluconate, 7 a-hydroxyvalerate, 8 formate, 9 valerate, 10 pyruvate, 11 monochloroacetate, 12 bromate, 13 chloride, 14 galacturonate, 15 nitrite, 16 glucuronate, 17 dichloroacetate, 18 trifluoroacetate, 19 phosphite, 20 selenite, 21 bromide, 22 nitrate, 23 sulfate, 24 oxalate, 25 selenate, 26 a-ketoglutarate, 27 fumarate, 28 phthalate, 29 oxalacetate, 30 phosphate, 31 arsenate, 32 chromate, 33 citrate, 34 isocitrate, 35 ds-aconitate, 36 trans-aconitate. (Reproduced with permission of Elsevier Science from Rocklin, R. D., Pohl, C. A., and Schibler, J. A., /. Chromatogr., 411, 107, 1987.)...

In order to balance mineral intake, the following minerals were used in place of the usual mineral mix (% of diet) potassium chloride, 0.32 magnesium oxide, 0.084 manganous carbonate, 0.0123 ferric nitrate, 0.021 zinc carbonate, 0.0056 cupric carbonate, 0.0011 potassium iodate, 0.0004 sodium selenite, 0.00003 chromium potassium sulfate, 0.00193. 

The selenides may also be obtained by direct combination of the elements, either by passing selenium vapour over the heated metal in a vacuum or by heating the metal with selenium in a crucible, the reaction being started by means of a magnesium fuse.3 In the case of potassium the reaction is explosive. The compounds may also be obtained by the action of hydrogen selenide on the heated metal,4 on the heated metallic chloride or its vapour, preferably in the presence of nitrogen,5 or by reduction with hydrogen or carbon of an oxysalt such as a selenite.6 Selenides have also been prepared by electrolytic methods.7... 

If the oxychloride is applied in dilute benzene solution some nitrogen selenide or selenium nitride is also formed.3 With liquid ammonia in the presence of ether in open vessels, the primary product is the compound SeOCl2.4NH3, which is decomposed by water into selenium, selenium nitride, ammonium chloride, ammonium selenite and selenious acid in a sealed tube, selenium nitride is formed in comparatively good yield.4... 

By the action of hydrazine hydrate on a dilute solution of selenic acid, hydrazine hydrogen selenate may be obtained as a colourless compound which is not decomposed by boiling water, but which, when dry, explodes with great readiness when subjected to heat, to shock, or to fumes of hydrogen chloride. For this reason, before hydrazine hydrate is used in the analysis of selenium compounds (see p. 307), it is essential that selenic acid and selenates should be reduced to selenites by means of hydrochloric acid.3... 

With the exception of the calcium, strontium, barium and mercurous salts, the normal selenates are readily soluble in water. Barium chloride and mercurous nitrate are therefore convenient precipitation agents.6 Barium selenate is, however, more soluble than barium sulphate, and also differs from the latter salt in being slowly reduced to selenite by hydrochloric acid 7 for these reasons precipitation with barium chloride is not applicable to the quantitative determination of selenie acid. A concentrated solution of selenie acid which has been saturated with barium selenate deposits crystals of barium selenie acid, H2[Ba(Se04)2].8... 

Three parts of the dihydrochloride of 1 2-diaminonaphthalene-5 7-disulphonic acid in 50 parts of water are treated with a concentrated aqueous solution of two parts of acid sodium selenite. After a short time barium chloride is added, when the barium salt of the disulphonic acid separates. This crystallises from boiling water as long pale yellow needles or spears. The sodium salt is very soluble in water. 

Karlson and Frankenberger [60] have developed a simple column ion-chromatographic column method for the determination of selenite in soil extracts with the simultaneous determination of chloride, nitrite, nitrate and phosphate. Separation of the anions was conducted on a low-capacity ion-exchange column, and anions were quantified by conductiometric detection. The eluent stream consisted of 1.5 mmol/1 phthalic acid and adjusted to pH 2.7 with formic acid. 

The method requires minimal sample pretreatment, allowing for precise measurements of trace levels of selenite in the presence of high background levels of chloride, nitrites and phosphate. Interfering chloride ions were removed by reduction with a silver-saturated cation exchange resin. The detection limit for selenite was 3 xg/l of soil extract and the standard deviation was 6.7% with soil extracts of (0.5 mg/1). Between 0.5 and 99.6 xg/l of selenite were found in soil extracts. 

Selenium is a steel gray or purplish powder, also fabricated into pellets, sticks, or plates. Selenium dioxide, selenous acid, and the alkali-metal selenites and selenates are colorless powders or crystals. Selenium chloride (reddish yellow), selenyl chloride (colorless or yellow) (bp, 176°C), and selenic acid (colorless) are liquids, whereas selenium tetrachloride is a cream-colored crystalline solid.1... 

Wear nitrile rubber gloves, laboratory coat, and eye protection. Selenium powder may be mixed with sand and treated as normal refuse, as may the disulfide. Soluble selenites and selenates can be dissolved in water and run to waste, diluting with at least 50 times its volume of running water. Soda ash should be applied liberally to spills of selenium dioxide, selenic and selenous acids, and selenyl and selenium chlorides, which may then be mopped up cautiously with plenty of water wash down the drain, diluting greatly with at least 50 times its volume of water.16... 

An eluent composition of 2.0m mol L 1 sodium bicarbonate and 1.5m mol L 1 sodium carbonate was found to elute arsenate about midway between nitrate and sulphate. Selenite eluted between chloride and nitrate in an eluent that was 3.0m mol L 1 in sodium bicarbonate and 2.0m mol L 1 in sodium carbonate. 

Bromate, chloride, bromide, nitrite, nitrate, hypophosphite (HP022 ), selenite, selenate, sulphate, phosphate, pyrophosphate, arsenate, chromate, a-hydroxybutyrate, butyrate, formate, acetate, glycolate, gluconate, valerate, a-hydroxy valerate, pyruvate, monochloroacetate, dichloroacetate, trifluoroacetate, galactonurate, gluconurate, a-keto-glutarate, oxalate, fumarate, phthalate, oxalacetate, citrate, isocitrate, cis aconitate, trans aconitate, succinate, maleate, malonate, quinate, tartrate, hexane sulphonate, octane sulphonate, octane sulphate, decane sulphonate, dodecane sulphonate and dodecane sulphate... 

Fig. 2.14 Selenite in potable water, recycled twice sample size 10ml, lOOng of Se(IV) added—major peaks (1) fluoride (2) chloride (3) nitrate ...

Selenium and tellurium The elements are present as selenite and tellurite in dilute nitric acid solution. The mixture is spotted upon paper and dried thoroughly in the air. The solvent is dry n-butyl alcohol containing 4 per cent (v/v) of dry methanol. The atmosphere in the separation vessel is saturated with respect to the solvent vapour and the relative humidity is also maintained at 50 per cent by means of a saturated solution of calcium nitrate. The solvent is allowed to diffuse 8-10 cm down the strip (c. 2 hours). After evaporation of the solvent, the strip is sprayed with 0 5m tin(II) chloride in dilute hydrochloric acid. The tellurium is indicated by a black band (RF 0 1) and the selenium as an orange band (RF 0 5). It is possible to detect 1-5 pg of Se in the presence of 1 mg of Te by this method (see also Fig. VI.5g). 

Barium chloride solution white precipitate of barium selenite, BaSe03, in neutral solution, soluble in dilute mineral acids. 

Phosphate, silicate, borate, arsenate, selenite, chromate, and fluoride are anions for which ligand exchange is important. Nitrate, chloride, bromide, and perchlorate are not held, while sulfate and selenate may be weakly held. As a consequence, leaching of nitrate and sulfate from soil in drainage water can be significant, but very little phosphate is lost in solution. Of the trace metals, Co, Cu, Ni, and Pb are strongly held on oxide surfaces by chemisorption, but the process is much less important for Cd and Zn. 

Sodium selenite, Na2Se03.—The selenite is formed by heating a mixture of selenious acid and sodium chloride.11 At ordinary temperature the aqueous solution deposits the pentahydrate, above 60° C. the anhydrous salt.12 For the heat of formation from its elements in aqueous solution Thomsen gives 238-4 Cal. 

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