A Comparison of the Activity of Polymer Immobilised TEMPO (PIPO) with MCM-41 and Silica Supported TEMPO as Heterogeneous Catalysts for the Oxidation of Alcohols

Dijksman, A.; Arends, Isabel W. C. E.; Sheldon, Roger A.

doi:10.1055/s-2001-9708

Cited by 72 publications

(40 citation statements)

References 9 publications

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“…[74] PIPO was compared with the silica-and MCM-41-supported TEMPO catalysts in the bleach oxidation of octan-2-ol, under the chlorinated solvent-and bromide-free conditions. [73] As shown in Figure 18, PIPO is the most active catalyst. Surprisingly, all of the immobilized catalysts exhibited a higher activity than homogeneous TEMPO.…”

Section: Reviewsmentioning

confidence: 94%

“…[73,74] Similarly, Minisci and coworkers [101] have recently described the use of the oxidized form of another hindered amine precursor, chimassorb 966, analogous to PIPO, as a co-catalyst (see Figure 28) for the aerobic oxidation of a range of alcohols. Good results were obtained in combination with Mn(II) and Co(II) or Cu(II) nitrates (see above) in acetic acid solution, in the presence of a strong acid such as p-toluenesulfonic acid, at room temperature and atmospheric pressure.…”

Section: ð16þmentioning

confidence: 99%

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Organocatalytic Oxidations Mediated by Nitroxyl Radicals

2004

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The use of nitroxyl radicals, alone or in combination with transition metals, as catalysts in oxidation processes is reviewed from both a synthetic and a mechanistic viewpoint. Two extremes of reactivity can be distinguished: stable (persistent) dialkylnitroxyls, such as the archetypal TEMPO, and reactive diacylnitroxyls, derived from N-hydroxy imides, such as N-hydroxyphthalimide (NHPI). The different types of reactivity observed are rationalized by considering the bond dissociation energies (BDEs) of the respective N-hydroxy precursors, substrates and reaction intermediates. Reactive diacylnitroxyl radicals are generated in situ from the corresponding N-hydroxy compound. The protagonist, NHPI, catalyzes a wide variety of free radical autoxidations, improving both activities and selectivities by increasing the rate of chain propagation and/or decreasing the rate of chain termination. In the absence of metal co-catalysts improved conversions and selectivities are obtained in the autoxidation of hydrocarbons to the corresponding alkyl hydroperoxides. For example, cyclohexylbenzene afforded the 1-hydroperoxide in 97.6% selectivity at 32% conversion when the autoxidation was performed in the presence of 0.5 mol % NHPI, and the product hydroperoxide as initiator, at 100 8C. This forms the basis for a potential coproduct-free route from benzene to phenol. In combination with transition metal co-catalysts, notably cobalt, NHPI and related compounds, such as N-hydroxysaccharin NHS, afford effective catalytic systems for the effective autoxidation of hydrocarbons, e.g., toluenes to carboxylic acids, under mild conditions. In the case of the less reactive cycloalkanes, NHS proved to be a more active catalyst than NHPI which is attributed to the higher reactivity of the intermediate nitroxyl radical, resulting from the replacement of a carbonyl group in NHPI by the more strongly electron-attracting sulfonyl group. Stable dialkylnitroxyl radicals, exemplified by TEMPO, catalyze oxidations of, e.g., alcohols, with single oxygen donors such as hypochlorite and organic peracids. The reactions involve the intermediate formation of the corresponding oxoammonium cation as the active oxidant. Alternatively, in conjunction with transition metals, notably ruthenium and copper, they catalyze aerobic oxidations of alcohols. These reactions involve metal-centered dehydrogenations and the role of the TEMPO is to facilitate regeneration of the catalyst (Ru and Cu) and oxidation of the alcohol (Cu) via hydrogen abstraction or one-electron oxidation processes. Detailed mechanistic investigations, including kinetic isotope effects, revealed that oxoammonium cations are not involved as intermediates in these reactions. In contrast, oxoammonium cations are involved in the aerobic oxidation of alcohols catalyzed by the copper-dependent oxidase, laccase, in combination with TEMPO. This different mechanistic pathway is attributed to the much higher redox potential of the copper(II) in the enzyme. Similarly, N-hydroxy compounds such as ...

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Section: Reviewsmentioning

confidence: 94%

Section: ð16þmentioning

confidence: 99%

Organocatalytic Oxidations Mediated by Nitroxyl Radicals

2004

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“…In fact, higher catalytic efficiency was reported for the polymeric TEMPO derivative 26 compared to a silicasupported catalyst. [107] Electrochemistry can be used to regenerate the polymeric oxoammonium salts.…”

Section: Immobilized Nitroxides As Reusable Catalysts In Oxidationsmentioning

confidence: 99%

Nitroxides: Applications in Synthesis and in Polymer Chemistry

2011

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This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.

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“…240 Furthermore, polymeric nitroxides can also be used in the nitroxidecatalyzed oxidation of benzylic and allylic alcohols with copper(I) chloride and air in dimethylformamide. 241 Nitroxide-catalyzed oxidations of aliphatic alcohols are very slow, whether mediated by catalytic or stoichiometric quantities of Cu(II). 244 Copper chelates of 37 245 and 38, a compound containing an ionic liquid function, have been used.…”

Section: Copper Complexes In Combination With Air As Secondary Oxidantsmentioning

confidence: 99%

Oxoammonium‐ and Nitroxide‐Catalyzed Oxidations of Alcohols

2009

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The discovery in 1959 of stable nitroxide‐based free radicals such as the prototypical 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) led to their use as electron spin resonance (ESR) spin labels in chemistry, biomedicine, and materials science. These nitroxides are prepared by the oxidation of secondary amines that contain no hydrogen atoms on the alpha‐carbons. The unique redox properties of nitroxides enable their use as oxidants in organic synthesis. The varied preparation and uses of oxoammonium salts as stoichiometric oxidants for alcohols are one subject of this review. Oxoammonium ions as oxidants for alcohols have a number of advantages, for example, the method is heavy‐metal free and some of the reactions can be performed in water or aqueous mixtures. A few side reactions are associated with these oxidations. The most serious is the fast reaction of the oxoammonium ion with free amines The several ways these oxidation reactions can be carried out are discussed in detail. They are: Oxidations using stoichimetric quantities of preformed oxoammonium salts carried out in either acidic, neutral, or basic conditions; reactions in which stoichiometric quantities of oxoammonium salts are generated in situ by disproportionation of a nitroxide in the presence of a strong acid; nitroxide‐catalyzed oxidations using a secondary oxidant; efficient nitroxide‐catalyzed oxidations of primary alcohols to carboxylic acids; and oxidations of primary alcohols or hemiacetals that can lead to lactones.

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A Comparison of the Activity of Polymer Immobilised TEMPO (PIPO) with MCM-41 and Silica Supported TEMPO as Heterogeneous Catalysts for the Oxidation of Alcohols

Cited by 72 publications

References 9 publications

Organocatalytic Oxidations Mediated by Nitroxyl Radicals

Organocatalytic Oxidations Mediated by Nitroxyl Radicals

Nitroxides: Applications in Synthesis and in Polymer Chemistry

Oxoammonium‐ and Nitroxide‐Catalyzed Oxidations of Alcohols

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