Subject selenium dioxide

An accidental spray of selenium dioxide into the eyes of a chemist caused superficial burns of the skin and immediate irritation of the eyes. Within 16 hours, the subject s vision was blurred and tbe lower portions of both corneas appeared dulled. Sixteen days after the accident, the corneas were normal. ... 

Selenium dioxide, Se02, is a widely used reagent for the allylic oxidation of alkenes and ketones. The subject has been extensively covered by recent review articles56,291 293 and only a short summary will be given in this chapter. 

Benzimidazole (but not 1-methylbenzimidazole) is oxidized by permanganate, dichromate or hydrogen peroxide to imidazole-4,5-dicarboxylic acid, while napth-[l,2-d]- and -[2,3-d]-imidazoles also form products in which the heterocyclic ring remains intact, hence demonstrating its stability to these conditions. With lead peroxide benzimidazole is subject to an unusual oxidation as it forms (101), also the reaction product of lead dioxide and 2,2 -bibenzimidazolyl. In dioxane, selenium dioxide oxidizes 2-methylbenzimidazole to o-hydroxyacetanilide (66RCR122). 

Cardiovascular Effects. Several workers experienced symptoms of shock, including lower blood pressure and elevated pulse rates, following an acute exposure (at most 20 minutes) to selenium dioxide fumes resulting from a fire (Wilson 1962). The subjects were treated with oxygen and inhalation of ammonia vapor, and pulse rates were normalized within 3 hours. 

Intermediate 20-5 is next subjected to the sequence used to incorporate a 9a-fluoro group (see Scheme 7.14) to afford 21-1 (Scheme 7.21). Hydrolysis of the acetal groups with mild acid restores the carbonyl groups at C3 and C20 (21-2). Dehydrogenation of this last intermediate by means of selenium dioxide introduces an additional double bond in ring A this product, dexamethasone (21-3), is yet another widely used corticoid. 

Enollactones. 2-Benzylidenecycloalkanones are subject to Baeyer-Villiger oxidation on reaction with SeOj-HjOj at room temperature. Selenium dioxide is present in a catalytic amount. 

The allylic alcohol was subjected to an Eschenmoser-Claisen rearrangement with dimethylacetamide dimethylacetal to introduce the C14 substituent in a stereoselective manner. Reduction of the amide to the corresponding aldehyde with phenyl silane in the presence of Ti(0/Pr)4 was followed by an acid-promoted closure of the C-ring of codeine. In order to prevent N-oxidation, the amine was converted to the corresponding tosylamide, via debenzylation and treatment with tosyl chloride, before the allylic alcohol was introduced by the reaction of the alkene with selenium dioxide (65). The stereochemistry of the C6 hydroxy functionality was corrected by applying the well-known oxidation/reduction protocol [46, 60] before the benzylic double bond was reductively removed under Birch conditions. Codeine (2) was obtained in 17 steps with an overall yield of approximately 0.6%. 

It could be found eight articles in the ISI Web of Science database, from the first year covered by the database (1945) using the keyword selenium. These articles covered subjects of Se toxicity (three articles), Se levels in soil, plants, or animals (two articles), or the photodynamic properties of Se, its spectral properties, or the oxidizing capacity of selenium dioxide (one article each). The subjects of those eight papers from 1945 that focused on physical, agricultural, or chemical properties of Se are in principle the very same subjects that have made selenium a much more studied topic in research than the more specific selenocysteine or selenoprotein topics (Am6r 2012). 

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