Oxidation of Selenium IV

The oxidation of selenium(IV) to selenium(VI) by Ce(IV) is suggested to involve the formation of a 1 1 complex and an Se(V) intermediate. The reaction is catalyzed by ruthenium compounds, via the formation of Ru(VIII) species/  

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Selenic acid is conveniently prepared by the oxidation of selenium(IV) oxide with 30 per cent hydrogen peroxide. Water and selenious acid are the only possible impurities. The former can be removed effectively by evaporation under reduced pressure the latter is present in small amount. 

Although gravimetric methods have been used traditionally for the determination of large amounts of tellurium, more accurate and convenient volumetric methods are favored. The oxidation of teUurium(IV) by ceric sulfate in hot sulfuric acid solution in the presence of chromic ion as catalyst affords a convenient volumetric method for the determination of tellurium (32). Selenium(IV) does not interfere if the sulfuric acid is less than 2 N in concentration. Excess ceric sulfate is added, the excess being titrated with ferrous ammonium sulfate using o-phenanthroline ferrous—sulfate as indicator. The ceric sulfate method is best appHed in tellurium-rich materials such as refined tellurium or tellurium compounds. 

The oxidation of teUurium(IV) by permanganate as an analytical method has been studied in some detail (26). The sample is dissolved in 1 1 nitric-sulfuric acid mixture addition of potassium bisulfate and repeated fuming with sulfuric acid volatilises the selenium. The tellurite is dissolved in 10 vol % sulfuric acid, followed by threefold dilution with water and titration with potassium permanganate ... 

Dibenzo[/),/]thiepin-10(l 1H)-one (1) is an important synthon for the transformation of thiepins into other heterocycles. Oxidation with selenium(IV) oxide gives dibenzo[7>,/]thiepin-10,l 1-dionc (2), in 45% yield,38 which can be condensed with a series of benzaldchydes in the presence of ammonium acetate to provide the substituted 2-aryldibenzo[2,3 6,7]thiepino[4,5-t/]imidazoles 3, known to have anti-inflammatory properties.38... 

Reaction of 1 with semicarbazide hydrochloride gives the semicarbazone 4, in 74 % yield, which can be oxidized by selenium(IV) oxide to provide dibenzo[2,3 6,7]thiepino[4,5-rf][l,2,3]selenadi-azole (5) in 80 % yield. Thermolysis of selenadiazole 5 leads, with subsequent release of nitrogen, to diradical 6, which can either dimerize to 7 or lose selenium to give the intermediate cycloalkyne. The latter can be trapped by dienes as cycloadducts.93 Thus, the thermolysis of 5 in the presence of 2,3,4,5-tetraphenylcyclopenta-2,4-dienone gives the cycloadduct 1,2,3,4-tetraphenyltribenzo-[/ ,<7,/]thiepin (8) in 14% yield. 

Properties of Selenium(IV) Oxide. 1. Test the reaction of sele-nium(IV) oxide with water, and also with solutions of acids and alkalies. Write the equations of the reactions. 

As copper dissolves in the nitric acid, add new portions of copper shavings to it. When the entire selenium is oxidized, disconnect the flask with nitric acid, and suck a stream of dry air through the apparatus. Extract the prepared selenium(lV) oxide from the tube, put it into a weighing bottle, and weigh it. Determine the yield ip per cent. Write the equations of the reactions. Test the properties of selenium(IV) oxide (see p. 116). Hand in the preparation to your instructor. 

W.-D. Woggon, Formation of C-0 Bonds by Allylic Oxidation with Selenium(IV) Oxide, in Stereoselective Synthesis (Houben-Weyl) 4th ed., 1996, (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schau-mann, Eds.), 1996, Vol. E21 (Workbench Edition), 8, 4947—4956, Georg Thieme Verlag, Stuttgart. 

Woggon, W. D. Formation of C-O Bonds by Allylic Oxidation with Selenium(iv) Oxide. In Houben-Weyl Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds. Thieme Stuttgart, 1996 Vol. E21, pp 4947-4956. 

The nature of the reactive species in selenium(IV) dioxide oxidations in ethanol and TBHP has been investigated. A solution of selenium(lV) dioxide/ethanol (1 2) in deuteriochloroform, obtained by ultrasonic treatment as described above, gave two resonances in the 77Sc-NMR spectrum, one consistent with the resonance obtained for pure 36 (S = 1344) the second signal (<5 = 1323) was not consistent with selenic(IV) acid. Thus, oxidations performed with solutions of selenium(IV) oxide in ethanol contain no selenium(IV) oxide but diethyl selenate(IV) (36) and ethyl hydrogenselenate(IV) (37), the former being the more reactive due to acid catalysis in the ene step, vide infra. 

Preparation and Properties of Selenium(IV) Oxide. Selenium compounds are very poisonous Hand in the prepared substances and residues of selenium preparations to the laboratory assistant. Run all experiments with selenium in a fume cupboard After work, thoroughly wash the ware and your hands. 

Valechha, N. D., Sewanee, J. P. Kinetics of oxidation of acetophenones by selenium dioxide. J. Indian Chem. Soc. 1986, 63, 970-973. Hassan, R. M. Kinetics and mechanism of selenium(IV) oxidation of ascorbic acid in aqueous perchlorate solutions. Croat. Chem. Acta 1991,64, 229-236. 

An improved synthesis of glutinosone (1) was also accomplished by Masamune and coworkers6 and this was based on procedure developed by Dastur7,8 for the synthesis of sesquiterpenes nootkatone. (Scheme 2) Diels-Alder reaction of 3,6-dihydro-3,5-dimethyl anisole with methyl acrylate in absence of Lewis acids afforded a 1 3 mixture of esters (17) and (18) which were converted to a,(3-unsaturated aldehydes (19) in 77% yield by oxidation with selenium (IV) oxide in dioxane. Wittig reaction of aldehydes under the usual condition yielded the dienes (20) in 63% yield which on being subjected to Grignard reaction with an excess of methyllithium produced tettiary alcohols (21) in quantitative yield. This on treatment with formic acid at room temperature gave bicyclic enone (22) and its formate (23) in 45% and 41% yield respectively. Formates (23) were hydrolyzed to enone (22) in 88% yield. 

Different distributions of selenium were observed between the crystals formed with selenite and the crystals formed with selenate. From Figure 4-1, almost uniformly distributed Se(IV) is recognized. Near the surface, Se(IV) is slightly higher than that near the center. Near the center, a small amount of Se(VI) was also detected. The partial oxidation of Se(IV) to Se(VI) was considered to be due to the following reaction with oxygen in air. 

From the results of the dissolution and leaching tests, the ferrite including selenate was more stable than that including selenite. This suggested that if the wastewater contained selenium in the form of Se(IV), the selenite should be oxidized to selenate before ferritization because a large amount of selenate is incorporated into the center of the ferrite particles. However, the complete oxidation of Se(IV) to Se(Vl) in the wastewater is not very easy, and requires the addition of concentrated HCl solutions and heating at nearly 100 C for one hour. 

Selenium(lV) oxide has been prepared by the oxidation of selenium using nitric acid, vapors of fuming nitric acid, oxygen, and oxygen admixed with nitrogen(IV) oxide. When selenium is burned in oxygen a product is obtained that contains appreciable quantities of what is presumed to be red selenium as an impurity. While the combustion of... 

Selenium(IV) oxychloride was syntheazed first by Weber in 1859 by heating together the vapors of selenium(IV) oxide and selenium (IV) chloride. It was later prepared by Michaelis by the interaction of selenium(IV) oxide and phosphorus(V) chloride. Cameron and Macallam allowed a mixture of selenium(IV) oxide and sodium chloride to interact and obtained sodium selenite and selenium(IV) oxychloride. 

The classical researches of Victor Lenher on selenium(IV) oxychloride (reviewed by Smith ) were begun about 1919 at the University of Wisconsin. Lenher suggested the following practical laboratory methods for the preparation of selenium(IV) oxychloride (1) union of selenium(IV) oxide and selenium(IV) chloride (2) partial hydrolysis of sele-nium(IV) chloride, and (3) dehydration of Se02 2HCl (dichloroselenious acid, H2Se02Cl2). ... 

Anhydrous Hydrogen Chloride. Since considerable quantities of hydrogen chloride are needed in the conversion of selenium(IV) oxide to dichloroselenious acid, the apparatus described by Maxson is modified as illustrated in Fig. 23. 

Ninhydrin (also named 1 2 3-triketoindane or 1 2 3-triketohydrindene hydrate) is prepared most simply from the inexpensive phthahc anhydride (I). The latter is condensed with acetic anhydride In the presence of potassium acetate to give phthalylacetlc acid (II) reaction of the latter with sodium methoxide in methanol yields 1 3-indanedionecarboxyhc acid, which is decomposed upon warming with dilute hydrochloric or sulphuric acid to indane-1 3-dione (or 1 3-diketohydrindene) (HI). Selenium dioxide oxidation of (III) afibrds indane-1 2 3-trione hydrate (ninhydrin) (IV). 

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