Acids selenium dioxide

The pyrazine ring is stable toward permanganate oxidation, and this explains a variety of pyrazinecarboxylic acids that have been prepared from quinoxalines or benzo-fused quinoxalines. In contrast, alkyl side chains on pyrazines are effectively oxidized by permanganate, selenious acid, selenium dioxide, or dichromate to afford the corresponding carboxylic acids (Section 8.03.7.1). Oxidation of pyrazines with hydrogen peroxide or percarboxylic acids gives pyrazine A -oxides and/or A, A -dioxides (Section 8.03.5.2). 

Ni(OH)2-electrode 48) % Phenylselenic acid Selenium dioxide > Manganese dioxide... 

Sodium methoxide Perchloric acid Selenium dioxide... 

NITRILES Chlorosulfonylisocyanate. Dimethylaluminum amide. Hydroxyl-amine. Hydroxylamine-O-sulfonic acid. Selenium dioxide. Triethoxydiiodophos-phorane. Trifluoroacetic anhydride-Pyridine. Trimethylamine-Sulfur dioxide. 

Preparation of Allyl Carbonates of Unsaturated Fatty Acids Selenium Dioxide Oxidation... 

Under the influence of selenous acid (selenium dioxide) arylhydrazines are oxidized (80) to diazonium salts, which can be detected by coupling them with 1-naphthylamine (81)... 

When camphor (I) is heated with selenium dioxide in acetic acid, the methylene group next to the carbonyl group is oxidised also to a carbonyl group, to form camphorquinone (II). Note that the compound (II) is not a true quinone but a 1,2-diketone ... 

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 ... 

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). 

Both pyrrole and indole react with selenium dioxide in the presence of nitric acid to give a deep violet solution. Very small quantities (ca 4 of pyrrole can be detected by this method. 

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. 

It is generally unacceptable to emit sulfur dioxide, thus the scmbber effluent must be treated for sulfur dioxide removal. If the plant aheady possesses faciUties for the production of sulfuric acid, this rather concentrated sulfur dioxide stream can be easily fed into the wet gas cleaning circuit and disposed of in the sulfuric acid plant. The quantity is so small that it does not put any additional burden on the sulfuric acid plant. Because no tellurium is carried over with the selenium dioxide during roasting, it is possible to produce a selenium product which can be purified to commercial grade (99.5-99.7%). 

Selenium trioxide, SeO, is white, crystalline, and hygroscopic. It can be prepared by the action of sulfur trioxide on potassium selenate or of phosphorous pentoxide on selenic acid. It forms selenic acid when dissolved in water. The pure trioxide is soluble in a number of organic solvents. A solution in Hquid sulfur dioxide is a selenonating agent. It is stable in very dry atmospheres at room temperature and on heating it decomposes first to selenium pentoxide [12293-89-9] and then to selenium dioxide. 

Contact with elemental selenium does not injure the skin. Selenium dioxide, however, upon contact with water, sweat, or tears, forms selenous acid, a severe skin irritant. Selenium oxyhaHdes are extremely vesicant and cause bums when in contact with human skin (91,92). Hydrogen selenide affects the mucous membranes of the upper respiratory tract and the eyes (93). 

A number of esters of arsonic and arsinic acids have been prepared. One method involves the oxidation of dialkyl alkylarsonites with selenium dioxide ... 

A constant problem in the use of selenium dioxide is the removal of selenium-containing contaminants in the above example it was found necessary to treat the product with chromic acid to remove materials which otherwise poisoned subsequent hydrogenation steps. 

Reactions with selenium dioxide appear to be sensitive to the medium employed. Refluxing t-butanol is the usual solvent, often with small amounts of acid present, although pyridine has been introduced with acid labile substrates. 

Estr-5(10)-en-3-ones also react with methanol to give dimethyl ketals. Weak acid catalysts such as malonic and oxalic acid or selenium dioxide, which are unable to promote conjugation of the double bond, are conveniently used. ... 

Selective ketalization at C-3 in the presence of a 20-ketone is achieved by the selenium dioxide procedure, at room temperature with " or without an additional acid catalyst. 

Aldehydes are also obtained from thenylalcohols by oxidation with selenium dioxide,A"-bromosuccinimide, persulfate,lead dioxide, and nitric acid. ... 

---