Mechanism of electrochemical oxidation of spatially hindered amines of 2,2,6,6-tetramethylpiperidine series

Electrooxidation of spatially hindered amines of the series of 2,2,6,6-tetramethylpiperidine in the medium of acetonitrile results in formation of radical cations, aminyl radicals, nitroxyl radicals, and oxoammonium salts identified using the methods of cyclic voltammetry and ESR spectroscopy.     

Mechanism of the oxidation of alcohols by 2,2,6,6-tetramethylpiperidine nitrosonium cation

Simple Hammett studies, hydrogen isotope effects, and attempted preparation of proposed transient intermediates are used to probe the mechanism of oxidation of alcohols by 2,2,6,6-tetramethylpiperidine nitrosonium ion.     

Electrochemical synthesis of 2,2,6,6-tetramethylpiperidine

A preparative method for the production of 2,2,6,6-tetramethylpiperidine based on the electrochemical reduction of 4-oxo-2,2,6,6-tetramethylpiperidine in 30% sulfuric acid on cadmium or lead electrodes was developed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 358–359, March, 1984.     

Hypervalent iodine oxidation. Synthesis of spin labeled, 1-oxyl-2,2,6,6-tetramethylpiperidine derivatives

Oxidation of 1-oxyl-2,2,6,6-tetramethyl-4-piperidone ( 1 ) with [I,I-bis(acetoxy)iodo]benzene in methanolic potassium hydroxide yields 1-oxyl-4,4-dimethoxy-3-hydroxy-2,2,6,6-tetramethylpiperidine ( 2 ). Treatment of 2,2,6,6-tetramethyl-4-piperidone ( 3 ) with [I,I-bis(acetoxy)iodo]benzene in methanolic potassium hydroxide gave 3-methoxy-2,2,6,6-tetramethyl-4-piperidone ( 4 ) which on oxidation with 30% hydrogen peroxide and catalytic amount of sodium tungstate gave 1-oxyl-3-methoxy-2,2,6,6-tetramethyl-4-piperidone ( 5 ). The esr spectra of 1-oxyl-4,4-dimethoxy-3-hydroxy-2,2,6,6-tetramethylpiperidine ( 2 ) as well as 1-oxyl-3-methoxy-2,2,6,6-tetramethyl-4-piperidone ( 5 ) show three lines.     

Influence of the nature of solvent and substituents on the oxidation potential of 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives

The influence of solvent (DMF, MeCN, and water) and R1, R2 substituent nature on the formal oxidation potential (E°´) of 4-R1,R2-2,2,6,6-tetramethylpiperidine 1-oxyls (1a—f) on a glass carbon electrode was studied by cyclic voltammetry. It was shown that for all the solvents the observed dependence had the form E°´ = ρ″σ″ + b, where σ″ is the substituent constant. The b values decreased with an increase of the solvent solvating ability, while the values ρ″ are similar for all the solvents, surpassing the corresponding values for nitroxyls of the imidazoline series with substituents at position 3, which can be interpreted as an abnormally strong influence of the substituent remote from the reaction center in 1a—f. The experimental values E°´ were linearly correlated with the reaction free energy values (ΔG) calculated by DFT B3LYP and MP2 for the gas phase contribution and by HF/PCM for the contribution of solvation effects. When applying the B3LYP and the HF/PCM approaches in combination, the dependence of ^E°´ on Δ^G for all the considered solvents was described by a linear correlation equation with a slope close to unity and a constant term which was close to the theoretical value of the absolute potential of the reference electrode used.     

Electrochemical halogenation of 4-hydroximino-2,2,6,6-tetramethylpiperidine

Electrochemical chlorination and bromination of 4-hydroximino-2,2,6,6-tetramethylpiperidine were studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1808–1810.Original Russian Text Copyright © 2004 by Kashparova, Kagan, Zhukova.     

Synthesis and polymerization of 4-o-vinylbenzyl-2,2,6,6-tetramethylpiperidine

Some hindered amine polymers containing 2,2,6,6-tetramethylpiperidine structure were synthesized. A new monomer, 4-O-vinylbenzyl-2,2,6,6-tetramethylpiperidine, was homopolymerized and copolymerized with some vinyl monomers in the presence of AIBN as an initiator. The obtained amine polymers were oxidized with hydrogen peroxide to obtain the polymers having nitroxyl radical moiety.     

Electrochemical modeling of the reaction of 1-Chloro- and 1-Bromo-2,2,6,6-tetramethylpiperidine photolysis

Electrolysis of 1-Chloro- and 1-Bromo-2,2,6,6-tetramethylpiperidines yields free nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl. The reaction mechanism is suggested, which is based on the intermediate formation of aminyl radical. Concurrently with the nitroxyl radical formation, electrochemical chlorination of 2,2,6,6-tetramethylpiperidine occurs. It is shown that the 2,2,6,6-tetramethylpiperidine can be used as a mediator in the electrochemical oxidation of alcohols.     

Synthesis of acetylenic carbinols of the 2,2,6,6-tetramethylpiperidine series

Conclusions A convenient method was proposed for the preparation of acetylenic carbinols of the 2,2,6,6-tetramethyl-piperidine series by the ethynylation of 2,2,6,6-tetramethyl-4-oxopiperidine in liquid ammonia in the presence of alcoholic alkali.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1680–1681, July, 1978.     

Synthesis and structure of diastereomeric trans-3,4-diamino-2,2,6,6-tetramethylpiperidine1-oxyl derivatives

The reaction of 3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl with (1S)-(+)-camphor-10-sulfonyl chloride gives a mixture of diastereomeric 4-monosulfonylamino derivatives. The products of their acylation have been obtained. The 3,4-bis-[(1S)-camphor-10-sulfonylamino] derivative was synthesized and resolved to individual diastereomers. For one of them thetrans relationship of the 3- and 4-substituents and the absolute (3S,4R)-configuration were established by X-ray structural analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 367–372, February, 1993.     

Diffusion of 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives of variable hydrophobicity in tropocollagen I solution

Electrochemical time-of-flight was used to measure the diffusion coefficients of 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives, C(n)TPA, (3 to 7 CH(2) groups), in tropocollagen I solution, as a function of the chain length and the cross-linking with glutaraldehyde. The values of the diffusion coefficient of C(n)TPA in pure aqueous electrolyte follow the Stokes-Einstein law, i.e. the diffusion coefficient is inversely proportional to the size of the redox probe. Different behavior is observed in 0.5% (w/v) tropocollagen solution where the molecules with longer alkyl chains show larger diffusion coefficients than the smaller molecules. This behavior is explained in terms of electrostatic interactions between tropocollagen chains and the C(n)TPA molecules. The measurements of the diffusion coefficients of C(n)TPA in 0.5% tropocollagen cross-linked with glutaraldehyde indicate that while the C(7)TPA and C(5)TPA probes exhibit lower diffusion coefficients upon addition of 0.05% GA and 0.1% (v/v) GA respectively, the other C(n)TPA molecules exhibit either unchanged or increased diffusion coefficients under the same conditions thus indicating the presence of hydrophobic pockets selectively interacting with C(n)TPAs. These results demonstrate the utility of electrochemical time-of-flight in measurements of diffusion coefficients in complex biopolymeric media.     

Intramolecular rearrangement with ring contraction of 1,4-dihydroxy-3-bromo-2,2,6,6-tetramethylpiperidine

Conclusions 1,4-Dihydroxy-3-bromo-2,2,6,6-tetramethylpiperidine on treatment with bases rearranged with ring contraction to 1,3-dihydroxy-2-(2-propenyl)-5,5-dimethylpyrrolidine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1582–1587, July, 1987.     

Some derivatives of 4-(4-aminophenylamino)-2,2,6,6-tetramethylpiperidine

4-(4-Aminophenylamino)-2,2,6,6-tetramethylpiperidine was synthesized by alkylation of 4-aminotriacetoneamine with 4-chloronitrobenzene, followed by hydrogenation of the nitro derivative. Its reactions with acrylic, methacrylic, and itaconic acids were carried out. Transformations of the N-substituted amino acids to derivatives of 2-pyrrolidinone and dihydropyrimidinedione were studied.Kaunas Technological University, Kaunas LT-3028. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 629–631, May, 1997.     

Structurally powered synergic 2,2,6,6-tetramethylpiperidine bimetallics: new reflections through lithium-mediated ortho aluminations

Recent times have witnessed many notable advances in metalation chemistry with halide salt supported strategies and alkali-metal mediated metalation being particularly prominent. This article begins with a brief account of both of these avant garde metalation methods focusing on selected recent examples not covered previously in a review. New results in the area of Alkali-Metal Mediated Alumination (AMMAl) are also presented. Thus, the putative lithium aluminate base THF·Li(μ-TMP)(2)Al((i)Bu)(2) (4) is shown to act via TMP basicity to efficiently ortho deprotonate a variety of functionalized aromatic molecules at room temperature, tolerating carboxamide and halide functionalities. These metalated species are electrophilically quenched with elemental iodine. Crystal structure determinations of the metalated intermediates confirm unequivocally that direct alumination of the substrates has occurred. Since the homometallic lithium or aluminum reagents are unable to effect such deprotonations these reactions are synergic in nature and can be considered examples of AMMAl. Drawing together previously published work in the field of AMMAl, together with other pertinent experimental observations and new density functional theory (DFT) computational studies, we propose a potential rationale for the "unusual" reactivity patterns witnessed in this branch of heterometallic synthetic chemistry with respect to other Alkali Metal Mediated Metalations which appear to behave in a more conventional manner.     

C-Nitroso compounds—XXXV : Reaction of organometallic compounds with 1-chloro-1-nitroso-2,2,6,6-tetramethylcyclohexane

Reaction of Grignard reagents and organolithium compounds (RM) with the congested 1-chloro-1-nitroso-2,2,6,6-tetramethylcyclohexane 1 leads to the formation of significant amounts of the reduction product 2,2,6,6-tetramethylcyclohexanone oxime 3 (61–90%) together with the corresponding oxime O-R ether 4 (0–11%). Attack on nitrogen is unimportant as shown by very low yields of nitrone. Formation of the products is rationalised with a pathway involving transfer of an electron from RM to 1. This leads—after separation of MCI—to a radical pair consisting of R and the relatively stable iminoxy radical 2 (Schemes 1 and 2). Combination of these radicals explains formation of oxime ether 4 and nitrone 5, while reaction of iminoxy radical 2 with excess of RM can give oxime 3. Reactive radicals R (i.e. Me, Ph, and to a minor extent n-Bu) are furthermore capable of abstracting hydrogen from the solvent (diethyl ether, toluene, or cumene), and the solvent derived radicals can also combine with 2 on oxygen, under formation of oxime ether (26% of 6a). The corresponding benzyl- and cumyl ethers 6b and 6c are only formed in trace amounts because dimerisation of benzyl radicals (7%) and cumyl radicals (22%) is favoured.     

Polymers having stable radicals. II. Synthesis of nitroxyl polymers from 4-methacryloyl derivatives of 1-hydroxy-2,2,6,6-tetramethylpiperidine

Polymers having stable pendant . radicals were synthesized through their precursor polymers by oxidizing them in air or by H₂O₂–Na₂WO₄. Hydrochlorides and sulfates of 4-methacryloylamino- and 4-methacryloyloxy-1-hydroxy-2,2,6,6-tetramethylpiperidines were synthesized as precursor monomers and polymerized by using α,α′-azobisisobutyronitrile under appropriate conditions to precursor polymers of high molecular weight: poly-4-methacryloylamino-/oxy-1-hydroxy-2,2,6,6-tetramethylpiperidinehydrochlorides and sulfates. The precursor polymers were converted to polymers having nitroxyl stable radicals, i.e., poly-4-methacryloylamino-/oxy-2,2,6,6-tetramethylpiperidine-1-oxyls, by oxidation in air or with H₂O₂–Na₂WO₄ without any main-chain scission. The structure of the resultant stable radical polymers was determined by infrared, ultraviolet, and ESR spectroscopy. Based on the results of spectroscopic analysis and Kjeldahl analysis, the transformation from precursors to nitroxyl stable radical polymers was found to be quantitative. Investigations on the applicability of polymeric nitroxyl radicals to oxidation-reduction reactions were attempted by means of polarography; the reduction half-wave potential was found to be ?1.16 V for the mercury pool.