21 research outputs found
Oxidation of Sulfides with Pyridinium Tribromide in the Presence of Hydrated Silica Gel.
No full textA variety of sulfides have been oxidized to sulfoxides utilizing pyridinium tribromide in the presence of hydrated silica gel in a non-aqueous media. A combination of pyridinium tribromide and hydrated silica gel releases molecular bromine slowly in the reaction, affecting the oxidation. Hydrated silica gel also promotes decomposition of the bromosulfonium intermediate to the product. This procedure employs non-aqueous media for the first time in such a reaction. Copyright © Taylor & Francis Group, LLC
Chemistry of Phosphate Esters : Stereochemical Evidence for a Dissociative Mechanism
No full textMany attempts have been made to elucidate the various mechanism by which phosphates act in biological and other systems. There are many suggestions regarding mechanisms all of which fit into one of two broad categories. 1. Associative. 2. Dissociative. Of these two, interest to the associative type displacement has been of most investigators and this pathway has been established with certainty. On the other hand, less work has been done and there has been much controversy surrounding the dissociative mechanism. The dissociative mechanism is believed to be important because it has been thought that it represents the actual biological processes by which life utilizes phosphaphate esters. The schemes in fig. 5, represent the two types of displacement at the phosphorus atom. There has been a number of proposals which suggest a dissociative mechanism in displacements warrants an intermediate with a reduced coordination number. In the phosphorus esters this intermediate would be a phosphacylium ion analogous to a carboacylium ion generated from an acylhalide, fig. 6. Among several structural possibilities, a phosphacylium ion could retain the geometry of the starting material. This pathway then would produce a stereospecific product where the leaving group is replaced by the nucleophile while retaining the absolute configuration around the phosphorus atom, fig. 7. For the second possibility, the intermediate phosphacylium ion could attain planarity. If this is the case the nucleophilic substitution should give upon substitution a mixture of isomers. The phosphorus atom would be prone to be attacked by nucleophile from both sides, perpendicular to the plane of the ion, fig. 8. The ratio of isomers of the product may be equal or different depending on thermodynamic and kinetic parameters
Oxidation of thiols to disulfides with molecular bromine on hydrated silica gel support
No full textResults of oxidation of thiols to disulfides with molecular bromine on silica gel solid support are reported. The procedure utilizes organic media and does not require a base to neutralize HBr by-products to suppress acid promoted side reactions. Utilization of silica gel support simplifies work up and product isolation. © 2002 Elsevier Science Ltd. All rights reserved
Oxidation of Thiols to Disulfides with Molecular Bromine on Hydrated Silica Gel Support.
No full textChemInform Abstract: Ceric Ammonium Nitrate Catalyzed Oxidation of Sulfides to Sulfoxides.
No full textOxidation of sulfides to sulfoxides with a catalytic amount of ceric ammonium nitrate (CAN) reagent supported on silica gel has been achieved. Stoichiometric sodium bromate is utilized as the primary oxidant to continue the catalytic cycle involving CAN. Solid-supported CAN reagent allowed us to avoid using aqueous reaction media generally employed in CAN-promoted reactions. This heterogeneous CAN/NaBrO3 reagent has simplified the reaction work-up and product isolation, produced higher product yields, and shortened reaction times compared to reactions with homogeneous CAN reagents employing aqueous media. © Georg Thieme Verlag Stuttgart
A Simple and Efficient Heterogeneous Procedure for Thioacetalization of Aldehydes and Ketones.
No full textA new procedure for the protection of aldehydes and ketones as thioacetals promoted by catalytic amount of p-toluene-sulfonic acid and silica gel has been developed. This procedure offers versatility, short reaction time, excellent yield, good selectivity, and flexibility in terms of choice of solvent that can be utilized in this reaction. The procedure is easy to carry out and does not require aqueous work-up. A simple filtration followed by removal of solvent in most cases produces pure product. © Georg Thieme Verlag Stuttgart
ChemInform Abstract: A Facile and Selective Procedure for Oxidation of Hydroquinones Using Silica Gel Supported Catalytic Cerium(IV) Ammonium Nitrate.
No full textA facile and selective procedure for oxidation of sulfides to sulfoxides with molecular bromine on hydrated silica gel in dichloromethane
No full textA new method for oxidation of sulfides to sulfoxides with molecular bromine on a solid silica gel support has been developed. This procedure cleanly oxidizes sulfides to the corresponding sulfoxides in excellent yields. To our knowledge, this is the first example of oxidation of sulfides by molecular bromine in dichloromethane that does not require the presence of a base or another reagent to scavenge the byproduct hydrogen bromide in order to prevent side reactions. The reported procedure is simple, fast, product isolation is trivial, and it produces excellent yields
Chemoselective oxidation of sulfides to sulfones with magnesium monoperoxyphthalate (MMPP) on silica gel support in methylene chloride solvent
No full textA simple, efficient and chemoselective, non-aqueous procedure for oxidation of sulfides to the corresponding sulfones with magnesium monoperoxyphthalate on hydrated silica gel has been developed
A facile and selective procedure for oxidation of sulfides to sulfoxides on silica gel supported magnesium monoperoxyphthalate (MMPP) in dichloromethane
No full textThe scope of the magnesium monoperoxyphthalate (MMPP) oxidation of sulfides to sulfoxides has been extended by using hydrated silica gel as a solid support in dichloromethane media. This procedure works in the presence of a number of functional groups on the sulfides, including carbonyl and alkene groups that have been known to undergo Baeyer-Villiger oxidation and epoxidation with MMPP when using more conventional procedures. To our knowledge, this is the first example of oxidation of sulfides containing a carbonyl group with MMPP in non-aqueous media without any Baeyer-Villiger reaction. The reported procedure is easy to perform, product separation is trivial and it produces excellent yields
