Hydrogen sulfide, titanium complex

Hydrogen, molybdenum complex, 27 3 tungsten complex. 27 6 Hydrogen sulfide, titanium complex, 27 66 tungsten complex. 27 67... 

Jimenez et al. have developed tridentate cyclopentadienyl-silesquioxanate titanium complexes for the epoxidation of cyclic and linear alkenes with aqueous hydrogen peroxide under mild reaction conditions with excellent reactivity and selectivity. The authors extended the studies of these complexes as catalysts for the oxidation of sulfides to sulfoxides or sulfones under mild reaction conditions. The catalysts showed high chemoselec-tivity and proved to be very stable as no loss of activity or selectivity was observed after 14 cycles. 

Friedel-Crafts reaction catalysts like anhydrous aluminum chloride are readily soluble in the nitroalkanes. Solutions containing up to 50% aluminum chloride are easily prepared in nitroalkane solvents. These catalytically active complexes, AICI3-RNO2, can be isolated and used in solvents other than the nitroalkane. The reactants in the Friedel-Crafts reaction are often soluble in the nitroalkane reaction medium. Other catalysts like boron trifluoride (BF3), titanium tetrachloride (TiCl4), and stannic tetrachloride (SnCl4) are also soluble in the nitroalkane solvents. Reaction types which use nitroparaffins as solvents include alkylation of aromatics, acetylation of aromatics, halogenations, nitrations, and the reaction of olefins and hydrogen sulfide to yield mercaptans. 

Recently, Katsuki and Saito reported that di-g-oxo titanium complexes of chiral salen ligands serve as efficient catalysts for asymmetric oxidation of various sulfides using H2O2 or the urea-hydrogen peroxide adduct as oxidants [108]. Enantioselectiv-... 

Jacobsen and Katsuki have both reported the use ofmanganese(III) (salen) catalysts for sulfide oxidation. These catalysts can be effective for the enantiose-lective oxidation of several aryhnethylsulfides using iodosylbenzene as the stoichiometric oxidant. Additionally, titanium(salen) complexes function as efficient catalysts in this procedure, providing up to 94% ee in the oxidation of methyl phenyl sulfide using the more economical urea hydrogen peroxide as oxidant. ... 

Bearing these considerations in mind, Reddy and Verkade prepared a titanium alkoxide complex, 72, with good stability toward moisture for the selective oxidation of sulfides to sulfones and sulfoxides with hydrogen peroxide in recyclable ionic liquid solvents at room temperature [56]. They optimized reaction conditions and recovering procedure for thioanisole 71, and used their obtained results for oxidation of different aliphatic, aromatic and xmsaturated sulfides. Their results proved the chemoselectivity... 

The most practical method that is used in the industrial synthesis of esomeprazole involves titanium-catalyzed oxidation with an alkyl hydroperoxide, and a dialkyltartrate as chiral ligand, in an organic solvent such as dichloromethane. A variety of oxidoreductases are known to catalyze the enantioselective oxidation of prochiral sulfides, usually as whole-cell biotransformations in aqueous media, but no simple metal complexes have been shown to be effective in water and the development of practical systems employing aqueous hydrogen peroxide as the primary oxidant is still an important challenge. In this context it is worth mentioning the enantioselective sulfoxidation of prochiral sulfoxides catalyzed by the semisynthetic peroxidase, vanadium-phytase, in an aqueous medium. 

---