Tellurium hydrides

Hydrogen selenide (selenium hydride), HjSe, and hydrogen telluride (tellurium hydride), HjTe... 

Andreae [564] coprecipitated tellurium (V) and tellurium (VI) from seawater and other natural waters with magnesium hydroxide. After dissolution of the precipitate with hydrochloric acid, the tellurium (IV) was reduced to tellurium hydride in 3 M hydrochloric acid. The hydride was trapped inside the graphite tube of a graphite furnace atomic absorption spectrometer, heated to 300 °C, and tellurium (IV) determined. Tellurium (VI) was reduced to tellurium (IV) by boiling with hydrochloric acid and total tellurium determined. Tellurium (VI) was then calculated. The limit of detection was 0.5 pmol per litre and precision 10-20%. 

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

Tellurium Hexafluoride, TeFe, appears to be more stable than tellurium tetrafluoride. It has been obtained by the action of fluorine on tellurium at —78° C. The resulting colourless crystalline solid vaporises on allowing the temperature to rise. The solidified substance melts at —36° C. and boils at —35-5° C., the critical temperature being 83° C. The vapour density is 119-5, agreeing with the formula TeFe. The gas has an unpleasant odour, recalling ozone and tellurium hydride. Water only slowly decomposes the gas, which does not attack glass. 

Water, therefore, if it conforms to the general rule, must have a molecular weight greater than that of tellurium hydride, viz. 129-5. This suggests very appreciable association. 

SYNONYMS Synonyms vary depending upon the specific tellurium compound, (tellurium) aurum paradoxum, metallum poblematum, tellurium, metallic, (hydrogen telluride) dihydrogen telluride, tellurium hydride, (potassium tellurite) potassium tellurate (IV). 

Inhalation of tellurium vapor and tellurium hydride causes irritation of the respiratory tract. Exposure of rats, rabbits, and mice to tellurium hexafluoride caused pulmonary edema [20]. In addition to this, elemental tellurium can cross the blood-brain and placental barriers in rats [21]. 

One hundred milliliters of a urine sample is digested with nitric and perchloric acids. After the sample solution has become colorless, it is evaporated to dryness. One milliliter of HCl is added to the residue and evaporated to dryness. The residue is dissolved with 6 M HCl. The sample solution is introduced into a hydride generator and then generated tellurium hydride is passed to a quartz cell heated by flame. The absorption signal is recorded at 214.3 nm. The tellurium content in the sample solution is determined by the method of standard addition. The lower detection limit is 0.04 p,g/liter [12]. 

Since the hydrogen-element bond energy decreases from sulphur to tellurium they are stronger acids than hydrogen sulphide in aqueous solution but are still classified as weak acids—similar change in acid strength is observed for Group Vll hydrides. 

These closely resemble the corresponding sulphides. The alkali metal selenides and tellurides are colourless solids, and are powerful reducing agents in aqueous solution, being oxidised by air to the elements selenium and tellurium respeetively (cf. the reducing power of the hydrides). 

Gases and vapors of volatile liquids can be introduced directly into a plasma flame for elemental analysis or for isotope ratio measurements. Some elements can be examined by first converting them chemically into volatile forms, as with the formation of hydrides of arsenic and tellurium. It is important that not too much analyte pass into the flame, as the extra material introduced into the plasma can cause it to become unstable or even to go out altogether, thereby compromising accuracy or continuity of measurement. 

Numerous methods have been pubUshed for the determination of trace amounts of tellurium (33—42). Instmmental analytical methods (qv) used to determine trace amounts of tellurium include atomic absorption spectrometry, flame, graphite furnace, and hydride generation inductively coupled argon plasma optical emission spectrometry inductively coupled plasma mass spectrometry neutron activation analysis and spectrophotometry (see Mass spectrometry Spectroscopy, optical). Other instmmental methods include polarography, potentiometry, emission spectroscopy, x-ray diffraction, and x-ray fluorescence. 

Reactions similar to these provide convenient syntheses of hydrides of such elements as phosphorus, arsenic, tellurium, and selenium, because these elements do not react directly with hydrogen and the hydrides are unstable. 

Petit [563] has described a method for the determination of tellurium in seawater at picomolar concentrations. Tellurium (VI) was reduced to tellurium (IV) by boiling in 3 M hydrochloric acid. After preconcentration by coprecipitation with magnesium hydroxide, tellurium was reduced to the hydride by sodium borohydrate at 300 °C for 120 seconds, then 257 °C for 12 seconds. The hydride was then measured by atomic absorption spectroscopy. Recovery was 90 - 95% and the detection limit was 0.5 pmol/1. 

Nakashima et al. [719] detail a procedure for preliminary concentration of 16 elements from coastal waters and deep seawater, based on their reductive precipitation by sodium tetrahydroborate, prior to determination by graphite-furnace AAS. Results obtained on two reference materials are tabulated. This was a simple, rapid, and accurate technique for determination of a wide range of trace elements, including hydride-forming elements such as arsenic, selenium, tin, bismuth, antimony, and tellurium. The advantages of this procedure over other methods are indicated. 

Lead(II,IV) oxide Lithium hydride Magnesium Same as for lead dioxide Nitrous oxide, oxygen Air, beryllium fluoride, ethylene oxide, halogens, halocarbons, HI, metal cyanides, metal oxides, metal oxosalts, methanol, oxidants, peroxides, sulfur, tellurium... 

Certain volatile elements must be analyzed by special analytical procedures as irreproducible losses may occur during sample preparation and atomization. Arsenic, antimony, selenium, and tellurium are determined via the generation of their covalent hydrides by reaction with sodium borohydride. The resulting volatile hydrides are trapped in a liquid nitrogen trap and then passed into an electrically heated silica tube. This tube thermally decomposes these compounds into atoms that can be quantified by AAS. Mercury is determined via the cold-vapor... 

The hydride generation technique is a technique in which volatile metal hydrides are formed by chemical reaction of the analyte solutions with sodium borohydride. The hydrides are guided to the path of the light, heated to relatively low temperatures, and atomized. It is useful because it provides an improved method for arsenic, bismuth, germanium, lead, antimony, selenium, tin, and tellurium. 

STANNIC BROMIDE STANNOUS CHLORIDE STANNIC CHLORIDE STANNIC HYDRIDE STANNIC IODIDE STRONTIUM STRONTIUM OXIDE TANTALUM TECNNETIUM TELLURIUM... 

Figure S.2 shows a schematic diagram of the automatic hydride/vapour-generator system designed by P.S. Analytical. This has been widely used to determine hydrideforming elements, notably arsenic, selenium, bismuth, tellurium and antimony, in a wide range of sample types. To provide a wide range of analyses on a number of matrices the chemistry must be very well defined and consistent. Goulden and Brooksbank s automated continuous-flow system for the determination of selenium in waste water was improved by Dennis and Porter to lower the detection levels and increase relative precision [10, 11]. The system described by Stockwell [9] has been specifically developed in a commercial environment using the experience outlined by Dennis and Porter.

A useful method for the reductive conversion of elemental tellurium into Te anions employs complex hydrides such as sodium or potassium borohydride and tetraalkyl ammonium borohydride as reducing agents. 

Better results are achieved with tellurium and sodinm hydride in DMF. ... 

Sodium telluride, obtained by heating elemental tellurium with sodium hydride in DMF, reacts similarly, leading to symmetrical divinylic tellurides (compare the similar reaction with aryl iodides, see Section 3.1.2.1). 

The reduction of acetylenic tellurides to the vinylic ones is achieved by treatment with NaBH4 in EtOH. The formal unusual reduction of the carbon triple bond by NaBH4 can be rationalized involving the attack of a hydride ion to the tellurium atom producing a tellurol and an acetylenic anion followed by the addition of the tellurolate anion to the acetylene, DIBAL-H has later been employed as a reducing agent. ... 

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