Tetramethylpiperidine catalyst

In other cases, organic modification of the sol gel cages markedly protects the entrapped molecular dopant from degradation by external reactants, as shown for instance by the entrapment of the radical 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO). This is a highly active catalyst which in the NaOCl oxidation of alcohols to carbonyls in a CH2CI2-H20 biphasic system becomes highly stabilized upon sol gel entrapment in an ORMOSIL matrix it progressively loses it activity when entrapped at the external surface of commercial silica.25... 

Nitroxyl radicals can be oxidized to N-oxo ammonium salts that are themselves useful oxidants for primary and secondary alcohols. Recently, the behavior of different nitroxides as catalysts for alcohol oxidation has been studied by quantum chemical calculations [105]. Generally, 2,2,6,6-tetramethylpiperidine Ai-oxyl (TEMPO) (80) is used for the... 

A convenient procedure for the oxidation of primary and secondary alcohols was reported by Anelli and co-workers (8,9). The oxidation was carried out in CH2CI2 with an aqueous buffer at pH 8.5-9.5 utilizing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1) as the catalyst and KBr as a co-catalyst. The terminal oxidant in this system was NaOCl. The major disadvantage of using sodium hypochlorite or any other hypohalite as a stoichiometric oxidant is that for each mole of alcohol oxidized during the reaction one mole of halogenated salt is formed. Furthermore,... 

We wish to report here on a new and highly efficient catalyst composition for the aerobic oxidation of alcohols to carbonyl derivatives (Scheme 1). The catalyst system is based on 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), Mg(N03)2 (MNT) and N-Bromosuccinimide (NBS), utilizes ecologically friendly solvents and does not require any transition metal co-catalyst. It has been shown, that the described process represents a highly effective catalytic oxidation protocol that can easily and safely be scaled up and transferred to technical scale. 

Washing with hydrochloric acid and potassium iodide removes 2,2,6,6-tetramethylpiperidin-1-oxyl from the organic phase.6 Because of its volatility, the catalyst cannot be eliminated in the distillation of crude aldehyde. 

An alternative approach to the oxidation of alcohols to ketones was also reported by Shea et al., who incorporated a nitroxide catalyst into a polymeric matrix [56], A polymerisable 2,2,6,6-tetramethylpiperidine (90) was derivatised as /V-allyl-amine (91), which was removed after polymerisation, leaving a catalytically active nitroxide (92) able to form stable free radicals, thereby efficiently catalysing the reaction of oxidation with yields ranging from 55 to 88%. 

Stable organic nitroxyl radicals are of relatively recent use as catalysts in the oxidation of alcohols. Nitroxyl radicals are compounds that contain the A ,A -disubstituted NO-group with one unpaired electron, and their uses have been reviewed.124 The most simple radical of this class is 2,2,6,6-tetramethylpiperidin-l-oxyl (43, TEMPO). It is generally assumed that the active oxidizing species, the oxoammonium salt (44), is formed in a catalytic cycle by a one-electron oxidation of the nitroxyl radical by a primary oxidant [two-electron oxidation of the hydroxylamine (45) is also possible, depending on the primary oxidant] (Scheme 21). 

Our group have developed 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO)-functionalized PEG for biomimetic oxidation of alcohols together with CuCl in compressed C02, through a so-called mono-phase reaction, two-phase separation process to recover the catalyst, thus leading to conducting a homogeneous catalysis in a continuous mode [62]. 

The mechanism of the aerobic oxidation of alcohols depends on the particular catalyst used. Two general mechanisms can be considered (1) the direct oxygenation of alcohols by 02 through a free-radical chain process initiated by the catalyst, and (2) the direct oxidation of the alcohol by the catalyst, which is then regenerated by 02. Both mechanisms are well illustrated [6] by the aerobic oxidations catalyzed by the persistent tetramethylpiperidine-N-oxyl (TEMPO) radical 1 and the nonpersis-tent phthalimide-N-oxyl (PINO) radical 2. 

A comprehensive group of polyesters contains hindered piperidine or piperazine (HALS) moieties. Most of these stabilizers were prepared under transesterification conditions, using tetraalkyl titanates, lithium amide or sodium alkoxide as catalysts. Terminal HALS group was built in under these conditions into a polyether-polyester. Polyester 145 was prepared from a reactive diester derived from piperazinedione and fljco-alkylidenediol (n = 2-15) [188], A similar system contains 2,2,6,6-tetramethylpiperidine moiety [189]. 

A considerable number of papers describe the resulting molecules from the pyrolysis of polystyrene [2-26], etc. These studies include pyrolysis in inert conditions, in the presence of various catalysts [4], in the presence of carbon black [27], pyrolysis of H-T and H-H polymers, pyrolysis of polymers with different average molecular weights, pyrolysis of stereoregular polystyrene [28], pyrolysis of polystyrene obtained by controlled radical polymerization in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (stable nitroxide) [29], pyrolysis in the presence of water in subcritical conditions [30], pyrolytic studies for the understanding of large scale processes [31-36], etc. 

Conventionally, HAS are blended with PO during processing. 2-(Diethy-lamino)-4,6-bis[butyl(l,2,2,6,6-pentamethyl-4-piperidyl) amino]-l,3,5-triazine may be fed with an olefin directly into the low pressure polymerization process catalyzed with a modified MgCl2 supported Ziegler-Natta catalyst [142]. The catalytic activity was not impaired [143], Tetramethylpiperidine was reported to be a useful component in MgC -supported Ziegler-Natta catalysts as well. Very high stereospecificity of the synthesised PO was achieved. A complex of HAS with the alkyl aluminium activator was envisaged without interaction with the catalytically active alkyl titanium compound [144],... 

Hex-5-enyl)-2,2,6,6-tetramethylpiperidine was successfully copolymerized with propylene over supported Ziegler-Natta fourth-generation MgCk-supported catalyst [289]. 

Although Sc(OTf)3 has slightly different properties compared with other lanthanide triflates, the chiral Sc catalyst could be prepared from Sc(OTf)3, (7 )-binaphthol and a tertiary amine in dichloromethane (Kobayashi et al. 1994b). The catalyst was also found to be effective in the Diels-Alder reactions of acyl-l,3-oxazolidin-2-ones with dienes. The amines employed in the preparation of the catalyst influenced the enantioselectivities strongly. For example, in the Diels-Alder reaction of 3-(2-butenoyl)-l,3-oxazolidin-2-one with cyclopentadiene (CH2CI2, 0°C), the enantiomeric excesses of the endo adduct depended crucially on the amines employed aniline, 14% ee lutidine, 46% ee triethyl-amine, 51% ee 2,2,6,6-tetramethylpiperidine, 51% ee diisopropylethylamine, 69% ee 2,6-dimethylpiperidine, 69% ee 1,2,2,6,6-pentamethylpiperidine, 72% ee and cis-1,2,6-trimethylpiperidine, 84% ee. 

The stable, commercially available nitroxyl radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) 51 is an excellent catalyst, in conjunction with a co-oxidant, for the oxidation of alcohols. The most popular co-oxidant is buffered sodium hypochlorite (NaOCl). Oxidation of the nitroxyl radical gives the oxoammonium ion 52, which acts as the oxidant for the alcohol to form the carbonyl product. Primary alcohols are oxidized faster than secondary and it is often possible to obtain high chemoselectivity for the former. For example, oxidation of the triol 53 gave the aldehyde 54, with no oxidation of the secondary alcohols (6.44). The use of TEMPO is particularly convenient for the oxidation of primary alcohols in carbohydrates, avoiding the need for protection of the secondary alcohols. 

A good method for the direct conversion of alcohols to carboxylic acid uses 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) 51, in conjunction with the co-oxidant sodium chlorite (NaC102) and sodium hypochlorite (NaOCl) as a catalyst. See M. Zhao, J. Li, E. Mano, Z. Song, D. M. Tschaen, E. J. J. Grabowski and P. J. Reider, J. Org. Chem., 64 (1999), 2564. 

The Ru-catalyzed epoxidation of tran -stilbene in the presence of NaI04 was carried out using a bipyridyl ligand with a fluorous ponytail at the 4 and 4 positions. As illustrated by the first equation in Scheme 8, a triphasic system comprising water, dichloromethane and perfluorooctane was employed in the reaction. The reaction was complete in 15 min at 0°C and tran -stilbene oxide 5 was obtained from the dichloromethane layer in a 92% yield. The fluorous layer, containing the catalyst, could be recycled for four further runs without any addition of RuCls. The same perfluoroalkyl-substituted bipyridyl ligand was used successfully in the copper(i)-catalyzed TEMPO (2,2, 6,6 -tetramethylpiperidine (V-oxyl)-oxidation of primary and secondary alcohols under aerobic conditions (Scheme 8, second equation). ... 

The tetramethylpiperidine group is responsible for the stabilizing action. Different substituents on the nitrogen atom result in different pA b values, which are important in the area of use of the products. HALS I, bis(l,2,2,6,6-pentamethyl-4-piperidinyl) ester of decanedioic acid [415526-26-7], is used in systems that are not catalyzed by strong acids (interaction of the acid with the basic nitrogen atom). HALS II, bis(2,2,6,6-tetramethyl-l-isooctyloxy-4-piperidinyl) ester of decanedioic acid [122586-52-1], was developed for acid-catalyzed systems because it does not undergo undesirable interactions with acid catalysts. 

Li and coworkers developed an effective system for the oxidation of alcohols under an atmosphere of oxygen, without the need for any additional solvent or transition metal catalyst, by using catalytic amounts of (diacetoxyiodo)benzene, TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) and potassium nitrate (Scheme 4.56) [88]. A tentative mechanism for this catalytic oxidation involves the oxoammonium cation 109, which... 

Efficient recyclable bifunctional catalysts bearing ionic-liquid-supported TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) and iodoarene moieties have been developed and used for the environmentally benign catalytic oxidation of alcohols [115]. Ion-supported iodoarene-TEMPO bifunctional catalysts 147 and 148 were synthesized from ion-supported iodoarenes 144 and 145 by anionic exchange with TEMPO-sulfonate salt 146 (Scheme 5.45). 

Vinyl Compounds. Photorefractive polymers can be prepared by living radical polymerization. 4-Vinyltriphenylamine can be polymerized by a conventional radical catalyst or a 2,2,6,6-tetramethylpiperidine-V-oxyl (TEMPO) like catalyst, such as V-(a-methylbenzyloxy)-2,2,6,6-tetrameth-ylpiperidine. " ... 

While nitroxyl radicals, e.g., (2,2,6,6-tetramethylpiperidin-l-yl)oxyl (TEMPO) (2014COR459) and 2-aza-adamantane-Al-oxyl (AZADO) (2006JA8412), have been used extensively as catalysts in the oxidation of alcohols, there have been no reports of analogous uses for hydrazyls and... 

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