Oxoaminium Salt Research Articles

Elucidation of Acceleration Mechanisms by a Photosensitive Onium Salt for Nitroxide-Mediated Photocontrolled/Living Radical Polymerization

The acceleration mechanisms by a photosensitive onium salt for the nitroxide-mediated photocontrolled/living radical polymerization (photo-NMP) were determined. The photo-NMP of methyl methacrylate was performed by irradiation at room temperature using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator and (2RS, 2’RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator. The polymerization was accelerated in the presence of (4-tertbutylphenyl)diphenylsulfonium triflate (tBuS) to produce a polymer with a molecular weight distribution as narrow as the polymerization in its absence. (±)-Camphor-10-sulfonic acid or 2-fluoro-1-methylpyridinium p-toluenesulfonate had no effect on the polymerization speed, suggesting that tBuS did not serve as the photo-acid generator for the photo-NMP. It was found that the acceleration of the polymerization was based on the electron transfer from MTEMPO into tBuS in the excited state to temporarily generate a free radical propagating chain end and an oxoaminium salt (OAS), the one-electron oxidant of MTEMPO. This electron transfer mechanism was verified on the basis of the fact that the photo-NMP in the presence of tBuS was still accelerated by triphenylamine, the electron transfer inhibitor, to partly produce a polymer with an uncontrolled molecular weight. The formation of an uncontrolled molecular weight polymer indicated the generation of a free radical propagating chain end due to the deactivation of the OAS by the triphenylamine. It was deduced that tBuS served as the electron acceptor from MTEMPO in the excited state to temporarily produce a free radical propagating chain end along with OAS, resulting in the acceleration of the polymerization.

Control of micellization induced by disproportionation of 2,2,6,6-tetramethylpiperidine-1-oxyl supported on side chains of a block copolymer

The block copolymer micellization induced by the disproportionation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was performed using acids with different acid strengths. A poly(4-vinylbenzyloxy-TEMPO)-block-polystyrene diblock copolymer (PVTEMPO-b-PSt) produced micelles in 1,4-dioxane by the disproportionation of the TEMPO by HNO3, HCl, HClO4, and HSbF6. The acid strength affected the efficiency of the micellization. The acid/VTEMPO molar ratio required for the micellization decreased with an increase in the acid strength: \( {\text{HNO}}_{\text{3}} < {\text{HCl}} < {\text{HClO}}_{\text{4}} < {\text{HSbF}}_{\text{6}} \). The acid strength also made a difference in the hydrodyamic diameter of the micelles. The stronger acid provided larger micelles. This difference in the micellization was based on the difference in the solubility of the oxoaminium salt formed by the disproportionation of the TEMPO and on the steric hindrance of its counter anion.

Towards Controlled Graft Polymerization of Poly[styrene‐co‐(maleic anhydride)] on Functionalized Silica Mediated by Oxoaminium Bromide Salt. Facile Synthetic Pathway Using Nitroxide Chemistry

AbstractA TEMPO bromide salt is used to functionalize a silica surface with nitroxyl moieties. The functionalization reaction takes place in 48 h under mild conditions. In a second step, grafts of styrene‐maleic anhydride copolymer are grown from the functionalized silica surface by heating it in the presence of the monomers. FT‐IR and TGA analysis show that the silica was first functionalized with nitroxide moieties, and then that grafts of styrene‐maleic anhydride grew from the functionalized silica surface. A reaction mechanism is proposed in order to explain the findings. The results suggest that the oxoaminium salts are good candidates for the functionalization and grafting of surfaces that contain hydroxy groups and for the generation of hybrid materials with improved properties.magnified image

Electrochemical study of the nitroxyl radical derivatives built in the π‐conjugated poly(phenylenevinylene) skeleton

AbstractThe electrochemical oxidation and reduction of the stable neutral nitroxyl radical gave the oxoaminium salt and hydroxylamine or nitroxyl anion, respectively. The electrochemical behavior of the N‐butylnitroxyl radicals or N‐butylhydroxylamines built in to various phenylenevinylene species were discussed in connection with its developed π‐conjugated structure based on cyclic voltammetric measurements. The aromatic nitroxyl radical showed two pairs of oxidation–reduction waves, but the acidic proton (hydroxylamine) changed its cathodic peak to a broad one with a shift to the anodic side. The π‐conjugated poly(phenylenevinylene) backbone and mobile proton of the hydroxylamine unstabilized the nitroxyl radical by retaining the energy gap.

ChemInform Abstract: Convenient Synthesis of Bis‐1,3‐dithiolium Salts by One‐Electron Oxidation of Tetrathiafulvalene with Oxoaminium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Convenient Synthesis of Bis-1,3-dithiolium Salts by One-electron Oxidation of Tetrathiafulvalene with Oxoaminium Salts

Abstract Several bis-1,3-dithiolium salts, radical cation salts of tetrathiafulvalene were synthesized in quantitative yields by oxidation of tetrathiafulvalene with oxoaminium salts for 1min at room temperature.

Synthesis of Polystyrene Having an Aminoxy Terminal by the Reactions of Living Polystyrene with an Oxoaminium Salt and with the Corresponding Nitroxyl Radical

In order to introduce the C-O-N linkage at the polymer chain end, the reactions of poly(styryllithium) with 1-oxo-4-methoxy-2,2,6,6-tetrmaethylpiperidinium salt (OAS) and with the corresponding nitroxyl radical (MTEMPO) were investigated in THF at -18°C. The aminoxy terminal was found to be introduced in quantitative efficiency by the reactions of the living polymer with OAS in the presence of MTEMPO. It is considered that the reactions proceed via one-electron transfer from the polystyryl anion to OAS, resulting in the polymer radical, which is coupled with MTEMPO to yield the polystyrene with an aminoxy terminal

Convenient synthesis of polymers containing terminal aldehyde and ketone moieties by selective oxidation of polymeric terminal diols with an oxoaminium salt

AbstractSynthesis of polymers with aldehyde or ketone groups at both chain ends was carried out by oxidation of polymeric terminal diols with an oxoaminium salt (OAS), the oxidized form of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl. Terminal diols of polyethers, polyesters, polycarbonates, polybutadiene, and hydrogenated polybutadiene were oxidized with 2,0 equiv. of OAS in dichloromethane at room temperature in the dark. The corresponding aldehyde‐and/or ketoneterminated polymers were obtained in high yields with high conversion of OH group and little change in molecular weight. Poly(ethylene glycol) and poly(ethylene adipate) terminal diols were oxidized with low efficiency. Especially, in the case of poly(ethylene glycol), intermolecular reactions occurred to afford high molecular weight polymer. The ratio of aldehyde (CHO) to ketone (CO) groups in the oxidized polymer originating from the hydrogenated polybutadiene terminal diol was calculated to be 37/63.

Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

AbstractOxoaminium salt (1), derived from 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO, 2) by one‐electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3‐dihydrofuran, p‐methoxystyrene, N‐vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as 1H‐NMR and IR data suggested the formation of polymers containing NOC structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2‐benzylidene‐1,3‐dioxane) obtained by the polymerization of 2‐benzylidene‐1,3‐dioxane with oxoaminium hexafluoroantimonate (1, X = SbF6) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley &amp; Sons, Inc.

ChemInform Abstract: Oxidation of ω‐(Benzoyloxy)alkanols with an Oxoaminium Salt.

AbstractThe oxoaminium chloride (II), generated by oxidative chlorination of the tetramethylpiperidine‐1‐oxyl (I) either directly before the conversion or in situ, is employed in the oxidation of the hydroxyalkyl benzoates (III).

Oxidation of .omega.-(benzoyloxy)alkanols with an oxoaminium salt

Oxoaminium chloride, the oxidized derivative of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1) was found to display a novel selectivity in the oxidation of ester group containing alcohols

Oxidation of Cycloalkanols to the Corresponding Cycloalkanones with Chlorine in the Presence of Nitroxide Radical as a Mediator

Abstract A method for the oxidation of cyclic alcohols to the corresponding cyclic ketones with 2,2,6,6-tetramethyl-1-piperidinyloxyl (a mediator) and chlorine is described. This oxidation involves an oxoaminium salt, formed from the nitroxide radical and chlorine, which oxidizes cyclic alcohols to give the corresponding ketones in good yields.

Application of redox system based on nitroxides to organic synthesis

Abstract

ChemInform Abstract: New Selective Oxidation of Alcohols Containing Ester Groups with an Oxoaminium Salt.

AbstractThe oxidation of the ω‐(benzoyloxy)alkanols (I) with 1‐oxo‐4‐methoxy‐2,2,6,6‐tetramethylpiperidinium chloride depends on the length of the methylene chain: Satisfactory yields of the aldehydes (II) are only obtained from (Ic) ‐ (Ie).

Oxidation of benzyl alcohol with Cu(II) mediated by polymeric oxoaminium salt

The electrooxidation of alcohols in an aqueous disperse system with N-oxyl-immobilized poly(p-phenylene benzobisthiazole) network polymer particles (PBZTNT-N-Oxyl) as a disperse phase was performed successfully in a simple beaker-type undivided cell under a constant current condition to afford the corresponding ketones, aldehydes, and/or carboxylic acid in moderate to good yields. Recycle use of both the PBZTNT-N-Oxyl particles and the aqueous media could be achieved successfully by immobilization of additional N-oxyl moiety on the polymer particles in an appropriate interval. Notably, the shape and the particle size of PBZTNT-N-Oxyl were not appreciably changed even after 60 times recycle use.

Oxidation of poly(vinyl alcohol)s with an oxoaminium salt

Oxidation of poly(vinyl alcohol)s with an oxoaminium salt

New selective oxidation of alcohols containing ester group with an oxoaminium salt.

While 1-oxo-4-methoxy-2.2,6,6-tetramethylpiperidinium chloride 1 does not oxidize the hydroxy group of 2-hydroxyethyl benzoate and 3-hydroxypropyl benzoate, it oxidizes those of 4-hydroxybutyl benzoate, 5-hydroxypentyl benzoate and 6-hydroxyhexyl benzoate. Oxidation of 2-hydroxyethyl 4-hydroxybutyl phthalate with 1 selectively gives 2-hydroxyethyl 4-oxobutyl phthalate.

ChemInform Abstract: Application of Nitroxyl Radical Derivatives to Organic Synthesis

2, 2, 6, 6, -Tetramethylpiperidine-1-oxyl known as a stable radical is reduced to the hydroxylamine and is also oxidized to the oxoaminium salt. These redox reactions are reversible chemically. In this article we describe some application of nitroxyl radical to organic reactions based on its redox function.Hydroxylamine was demonstrated to work as a hydration reagent of nitriles to produce amides. Further, it was found that oxygen is reduced by an anion of hydroxylamine to give superoxide ion. Oxoaminium salt, an oxidized form of nitroxyl radical, oxidized hydroxide ion and alcohols to give selectively hydrogen peroxide and the corresponding carbonyl compounds, respectively. The redox systems using oxoaminium salt as a mediator were investigated. Further, we found that the polymeric mediator was superior to the monomeric mediator.

ChemInform Abstract: Oxidative Cleavage of Benzyl Ethers by Use of Oxoaminium Salt.

AbstractThe nitroxyl radical (I) is converted into the oxopiperidinium salts (II), which are used for the oxidative cleavage of the benzyl ethers (III) giving benzaldehyde (IV) and the corresponding halides (V).

ChemInform Abstract: Oxidation of Diols with Oxoaminium Salts.

AbstractDas aus (I) dargestellte Salz (II) oxidiert die Diole (III), (V) und (VIII) selektiv, wobei die Lactone (IV) und (VII), das Acetal (VI) und Acetoin (IX) erhalten werden.