Powder selenium

Digestion. 20-25 mg. of the substance whose nitrogen content is to be estimated are weighed out in a stoppered weighing-tube and then transferred to the flask L that has been previously dried in an oven at izo C. With care, the substance may be transferred directly into the bulb of the flask without any adhering to the sides. If any material sticks on the way down, the flask should be tapped gently to cause the substance to fall to the bottom. 2 G. of the catalyst mixture (32 g. of potassium sulphate, 5 g. of mercury sulphate and ig. of selenium powder, well mixed) are added and 3 ml. of A.R. cone, sulphuric acid are measured out carefully and poured into the digestion... 

Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

Selenium precursor stock solution was prepared by adding 0.32 mmol of selenium powder to 20 mL deionised water in a three-necked flask. Sodium borohydride (0.81 mmol) was carefully added to this mixture and the flask was immediately purged with nitrogen gas to create an inert environment. The mixture was then stirred for 2 h, at room temperature. The entire selenium dissolves in water giving rise to a colourless selenium solution. The cadmium solution was prepared by adding 0.32 mmol of CdCb powder in 20 mL of deionised water. The zinc solution was prepared by dissolving 0.32 mmol ZnCb in 20 mL of... 

A simple, rapid and efficient method has been reported for the synthesis of dibenzyl diselenides under the action of MW irradiation. Benzyl halides are reacted with selenium powder in the presence of a base and phase-transfer agent (Eq. 57 and Tab. 5.29) [80]. The reactions were performed either in THF or in C6H6-H20. 

One of the first series of reports on ultrasonically-enhanced electrosynthesis was by Gautheron, Tainturier and Degrand [69] who used the technique to explore routes to organoselenium and tellurium derivatives. Instead of employing a sacrificial cathode of elemental selenium, their procedure allowed the direct use of selenium powder with carbon cloth as cathode to produce Se and Se. A further benefit was that this method also allowed production of the corresponding tellurium anions. These species could be employed in situ in aprotic solvents such as DMF, THF and MeCN for the synthesis of selenides and tellurides by nucleophilic displacement from haloalkanes. 

Sulphuric acid-selenium reagent, approx 98% m/m H SO - Safety note wear PPE because this is highly corrosive. Add 4 g selenium powder to 400 ml sulphuric acid (approx. 98% m/m H SO ), and heat until just fuming. Stir occasionally with a glass rod until all the selenium has dissolved to give a dark green solution. Carefully remove from the hotplate and allow to cool. Make up to approximately 1 I with sulphuric acid. 

Production. Cadmium red pigments are produced in a similar way to the cadmium yellow pigments. The cadmium salt solution is prepared by dissolving the metal in mineral acid and then sodium sulfide is added. A certain amount of selenium powder is dissolved in the sodium sulfide solution to obtain the desired color shade. In an alternative procedure, the cadmium solution is mixed with sodium carbonate solution to precipitate cadmium carbonate which is reacted with the selenium-containing sodium sulfide solution. 

Because selenium powder and sodium selenite are extremely toxic, they can only be used under a fume hood with local exhaust ventilation. In addition, goggles, rubber gloves, an apron, and a dust mask should be worn. If the toner is heated, local exhaust ventilation should be provided. 

Oxidation of fused 1,2,3-selenadiazole 223 with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) at room temperature gave naphtho[l,2-<7][l,2,3]selenadiazole 88 in 55% yield (Equation 26) <2000JHC1325>. Reaction of compound 224 with selenium powder in an equimolar ratio in an inert atmosphere gave aromatized product 225 (Equation 27) <1998JCM784>. 

Selenium powder is insoluble in water the dioxide, selenous acid, and the alkali metal selenites are water soluble. Highly poisonous hydrogen selenide (offensive smell) is generated when an acid solution of a selenium compound is reduced by metals such as tin and zinc. Selenic acid reacts vigorously with water.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... 

For those who wish to mix their own selenium toner, I have included Dassonville T-55 Direct Selenium Toner, Dassonville T-56 Bleach and Redevelop Selenium Toner, and Flemish Toner (Formulas Toners Selenium Toners). The latter two are both bleach-and-redevelop selenium toners. The advantage to mixing your own is that it is possible to obtain colors not possible with the commercial products. The disadvantage is that selenium in powder form is highly toxic and all three formulas require heating to dissolve the selenium powder which poses the further risk of inhaling fumes. Only mix selenium toner in a well-ventilated area or outdoors and wear a face mask rated for hazardous chemicals. 

Dissolve the sodium sulfite in 100.0ml of warm water. Add the selenium powder and slowly heat until dissolved. Allow to cool. 

Sodium sulfide, 40.0g Selenium powder, 1.0 g Water to make 1.0 liter... 

Thermolysis of para-substituted diphenylzirconocene 70a in the presence of gray selenium powder gives, in addition to the expected complex 71a, the rearranged product 72a in a ratio of 60 40 55 whereas 70b gives only the rearranged product 72b [Eq. (15)]. Formation of the rearranged product was rationalized by proposing an equilibrium between two isomeric benzyne complexes [Eq. (16)] prior to reaction with selenium. 

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