Divalent state hydrogen peroxide

Organotellurium compounds are readily oxidized from the divalent to tetravalent state. Consequently, this property makes tellurides attractive as scavengers of reactive oxidizing agents such as hydrogen peroxide, hypochloride and peroxyl radicals. 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

Several medio are available for the intnxluction of sulfenyl groups a to carbonyl derivatives and these have been reviewed. - The most versatile procedure involves reaction of the enolate with an appropriate thiol derivative, but the preferred m od is largely dependent on the nature of the substrate employed (see below). In most instances, sulfur has been introduced in the divalent state and subsequently oxidized, although the oxidative step has been avoided by the direct introduction of sulfur at the S oxidation level. The oxidation of sulfides to sulfoxides is a trivial procedure that can be effected by a variety of reagents. Sodium metaperiodate, m-chloroperbenzoic acid and hydrogen peroxide are the most common oxidants, but r-butyl hydroperoxide, r-butyl hypochlorite, N-chlorobenzotriazole,... 

Many of the properties of sulfides stem from the fact that divalent sulfur is a reducing agent it is easily oxidized to two higher oxidation states. Treatment of a sulfide with one mole of 30% aqueous hydrogen peroxide at room temperature gives a sulfoxide. 

---