Selenium oxide oxidant

Selenious Anhydride Selenium Dioxide Selenium Oxide Selenium Oxide (fume)... 

At high temperatures oxygen reacts with the nitrogen in the air forming small amounts of nitrogen oxide (p. 210). Sulphur burns with a blue flame when heated in air to form sulphur dioxide SO2, and a little sulphur trioxide SO3. Selenium and tellurium also burn with a blue flame when heated in air, but form only their dioxides, Se02 and Te02. 

With concentrated nitric acid, selenium and tellurium form only their +4 oxoacids, H2Se03 and H2Te03 respectively, indicating a tendency for the higher oxidation states to become less stable as the atomic number of the element is increased (cf. Group V, Chapter 9). 

The elements, sulphur, selenium and tellurium form both di- and tri-oxides. The dioxides reflect the increasing metallic character of... 

A number of halide oxides are formed by sulphur and selenium but only one is considered here. 

Selenium dioxide, SeO, is ery poisonous (cf. p. I47), but is valuable particu larly for the oxidation of methylene ( CHs) groups to carbonyl ( CO) groups. 

The following oxidation of camphor to camphor-quinone illustrates the oxidising action of selenium dioxide, and readily gives a crystalline product. 

To meet the needs of the advanced students, preparations have now been included to illustrate, for example, reduction by lithium aluminium hydride and by the Meerwein-Ponndorf-Verley method, oxidation by selenium dioxide and by periodate, the Michael, Hoesch, Leuckart and Doebner-Miller Reactions, the Knorr pyrrole and the Hantzsch collidine syntheses, various Free Radical reactions, the Pinacol-Pinacolone, Beckmann and Arbusov Rearrangements, and the Bart and the Meyer Reactions, together with many others. 

Selenium dioxide. The compound is conveniently prepared by the oxidation of selenium with nitric acid, followed by dehydration of the selenious acid thus formed by cautious heating ... 

Oxidation of acetophenone with selenium dioxide iu the i)reseiice of dioxan or ethyl alcohol as solvent affords j.henylglyoxal ... 

CgHjCOCHj + SeOa —> CgHgCOCHO + Se + H O This is one example of the oxidation by selenium dioxide of compounds containing a methylene group adjacent to a carbonyl group to thecorresponding a-ketoaldehyde or a-diketone (see also Section VII,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). 

TTie reaction of 2.4-dimethylselenazole with an excess of benzaldehyde gives a monostyryl derivative exclusively (12). Oxidation of 2,4-dimethyl-selenazole with selenium dioxide yields 4-methylselenazole (Scheme 30) (4). 

Selenium dioxide oxidation of methyl derivatives (Scheme 30). 

Upon storage, the amount of ted phosphoms in soHd white or Hquid phosphoms may increase if the material is exposed to light or contains contaminants such as iodine, sulfur, selenium, or sodium that catalyze the conversion from white to ted. Also, because white phosphoms is generally stored under water, some surface oxidation to form viscous white or colored polymeric oxyacids also occurs, especially if the oxygen content of the water can be replenished by exposure to air. 

Furalazine, Acetylfuratrizine, Panfuran-S. Heating nitrovin in butanol or dimethylformamide at 100—130°C affords furalazine, 6-[2-(5-nitro-2-furanyl)ethenyl]-l,2,4-triazine-3-amine (34). An improved synthesis originates with 5-nitro-2-furancarboxaldehyde and acetone, proceeds through 4-(5-nitro-2-furanyl)-3-buten-2-one followed by a selenium dioxide oxidation to the pymvaldehyde hydrate, and subsequent reaction with aininoguariidine (35). Furalazine, acetylfuratrizine (36), and the A[-A/-bis(hydroxymethyl) derivative, Panfuran-S, formed from the parent compound and formaldehyde (37), are systemic antibacterial agents. 

Mocimycin was prepared from dihydromocimycin (3) by oxidation with selenium dioxide (14,56). 4-Amino-4-dehydroxyefrotomycins were obtained by aminolysis of efrotomycin-4-0-phenylchlorophosphate (57). 

Alkyl Isoquinolines. Coal tar contains small amounts of l-methylisoquinoline [1721-93-3] 3-methylisoquinoline [1125-80-0] and 1,3-dimetliylisoquinoline [1721-94-4J. The 1- and 3-methyl groups are more reactive than others in the isoquinoline nucleus and readily oxidize with selenium dioxide to form the corresponding isoquinoline aldehydes (174). These compounds can also be obtained by the hydrolysis of the dihalomethyl group. The 1- and 3-methyhsoquinolines condense with benzaldehyde in the presence of zinc chloride or acetic anhydride to produce 1- and 3-styryhsoquinolines. Radicals formed by decarboxylation of carboxyUc acids react to produce 1-aIkyhsoquinolines. 

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