Redox properties of novel pyrrolidine derivatives containing sterically hindered phenol fragment

The method of cyclic voltammetry on a platinum electrode in acetonitrile is used to study the redox properties of a number of novel pyrrolidine derivatives containing a sterically hindered phenol fragment. It is found that the obtained derivatives of (3,5-di-tert-butyl-4-hydroxyphenyl)pyrrolidine-2-carboxylic acid are irreversibly oxidized in two stages with formation of a phenoxy radical. The structural analogue containing no phenyl fragment is irreversibly oxidized under similar conditions in a single stage. Formation of a stable phenoxy radical from synthesized (3,5-di-tert-butyl-4-hydroxyphenyl)pyrrolidines under PbO₂ oxidation is confirmed by ESR spectroscopy. Application of the synthesized compounds as antioxidant agents has been suggested.     

Synthesis and study of electrochemical properties of the sterically hindered phenol derivatives and the corresponding radicals

1-(3,5-Di-tert-butyl-4-hydroxyphenyl)-2-arylbenzimidazoles were synthesized by the condensation of 2,6-di-tert-butyl-p-benzoquinone imine with aromatic aldehydes. 2-(3,5-Di-tert-butyl-4-hydroxybenzylidene) benzimidazoles were synthesized by the reaction of 2-aminobenzimidazole with 2,6-di-tert-butyl-4-hydroxybenzaldehyde. The substances were characterized by elemental analysis, IR and NMR spectra. The electrochemical reduction and oxidation of these compounds and phenoxy radicals derived from them was studied by cyclic voltammetry. The stability of the studied phenoxy radicals was confirmed by the electron spin resonance method.     

Influence of the redox state of the ligand on the dealkylation of substituted methylcobaloximes in the presence of heavy metal ions

The synthesis of cobaloxime and methylcobaloxime containing sterically hindered 2,6-di-tert-butylphenol fragments in the ligand is described. Spectral studies of the demethylation of methylbis(dimethylglyoximato)cobalt (1a), methylbis(diphenylglyoximato)cobalt (1b), methylbis[methyl-(3,5-di-tert-butyl-4-hydroxyphenyl)glyoximato]cobalt (1c) pyridinates were carried out in the presence of Cd²⁺, Hg²⁺, Sn⁴⁺, Pb²⁺, and Pb⁴⁺ ions, The free radical forms of the complexes containing a phenoxy radical W the ligand are formed during oxidation. The ESR spectra are given. The unpaired electron in the periphery of the methylcobaloxime ligand1c interacts with the Co-CH₃ fragment through the conjugated systems, enhancing the donating properties of the equatorial ligand of the complex, which leads to the rapid cleavage of the Co-C bond. Therefore the demethylation of methylcobaloxime in the presence of heavy metal ions occurs in a significantly shorter time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp, 1822–1827, July, 1996.     

Synthesis,properties, and catecholase-like activity of the [1,4-di(6′-methyl-2′-pyridyl)aminophthalazine]dimanganese(II) complex,Mn<Subscript>2</Subscript>(6′Me<Subscript>2</Subscript>PAP)<Subscript>2</Subscript>Cl<Subscript>4</Subscript>

The preparation, spectroscopic properties, and catecholase-like activity of the dimanganese(II) complex [Mn₂(6′Me₂PAP)₂Cl₄] [6′Me₂PAP: 1,4-di(6′-methyl-2′-pyridyl)aminophthalazine] are reported. The title compound was suitable catalyst for the oxidation of 3,5-di-t-butylcatechol (3,5-DTBCH₂) to 3,5-di-t-butyl-1,2-benzoquinone (3,5-DTBQ) with dioxygen under ambient conditions in good yields. The catalytic oxidation was found to obey Michaelis–Menten type kinetics.     

Oxygenation of 2,6-di-t-butylphenols bearing electron-withdrawing group at 4-position mediated by Co(II)-schiff base complex

4-Acyl-2,6-di-$\text{t}$-butylphenols except 3,5-di-$\text{t}$-butyl-4-hydroxybenzaldehyde were oxygenated in the presence of Co(Salpr) exclusively at the ortho position to give the corresponding 3,5-di-$\text{t}$-butyl-6-hydroperoxy-2,4-cyclohexadienone derivatives in quantitative yield.     

Synthesis,characterization and thermal study of some tetradentate Schiff base transition metal complexes

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR, UV–VIS) techniques, magnetic susceptibility measurements and thermogravimetric analyses (TG). The thermodynamic and thermal properties of complexes have been investigated. For further characterization Direct Insertion Probe-Mass Spectrometry (DIP-MS) was used and the fragmentation pattern and also stability of the ions were evaluated. The characterization of the end products of the decomposition was achieved by X-ray diffraction. The thermal stabilities of metal complexes of N,N′-bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine ligand (L) were found as Ni(II) > Cu(II) > Co(II) > Fe(II).     

π-Conjugated soluble and fluorescent poly(thiophene-2,5-diyl)s with phenolic,hindered phenolic and p-C6H4OCH3 substituents. Preparation,optical properties,and redox reaction

Dehalogenation polycondensation of 3-(4-methoxyphenyl)-2,5-dibromothiophene with Mg and a zerovalent nickel complex as well as chemical oxidative polymerization of 3-(4-methoxyphenyl)thiophene with FeCl₃ gives poly[3-(4-methoxyphenyl)thiophene-2,5-diyl] P3(4-MeOPh)Th. Treatment of soluble P3(4-MeOPh)Th with BBr₃ converts the OCH₃ group to an OH group and gives poly[3-(4-hydroxyphenyl)thiophene-2,5-diyl] P3(4-OHPh)Th. Oxidative polymerization of 3-[3,5-di-t-butyl-4-{(trimethylsilyl)oxy}phenyl]thiophene with FeCl₃ in an aqueous medium directly affords another kind of polythiophene with a sterically hindered phenolic group, poly[3-(3,5-di-t-butyl-4-hydroxyphenyl)thiophene-2,5-diyl] P3(4-OH-3,5-tBu₂Ph)Th. An organometallic dehalogenation polymerization using a nickel complex also affords P3(4-OH-3,5-tBu₂Ph)Th. All the polymers described above show strong photoluminescence in a region of 500–600 nm. Oxidation of P3(4-OH-3,5-tBu₂Ph)Th with PbO₂ gives stable radical species as confirmed by IR and ESR spectroscopy. Electrochemical redox behavior of the polymers is compared with that of other polythiophenes. © 1997 John Wiley & Sons, Inc.     

The reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide

Reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide in aprotic solvents leads to the generation of semiquinone (SQ^.H), alkylperoxy (ROO^.), and alkyloxy radicals. The reaction of SQ^.H and ROO^. produces 2,5-di-tert-butyl-6-hydroxy-1,4-benzoquinone, 3,6-di-tert-butyl-1-oxacyclohepta-3,5-diene-2,7-dione, and 2,5-di-tert-butyl-3,6-dihydroxy-1,4-benzoquinone. The radical generated from solvent attacks SQ^.H at position 4 with C−C bond formation. 4-Benzyl-2,5-di-tert-butyl-6-hydroxycyclohexa-2,5-diene-1-dione produced in this way is transformed into 4-benzyl-3,6-di-tert-butyl-1,2-benzoquinone under the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 943–946, May, 1999.     

Synthesis and X-ray single crystal structure of first aromatic ortho-di-tert-butyl azolo[1,2,4]triazine

Oxidation of 3,4-di-tert-butyl-8-methyl-1,4-dihydropyrazolo[5,1-c][1,2,4]triazine with NBS/K₂CO₃ furnished 3,4-di-tert-butyl-8-methylpyrazolo[5,1-c][1,2,4]triazine, a mildly strained heteroaromatic compound. X-Ray single crystal diffraction analysis indicated that the conjugated 1,2,4-triazine ring adopts a twist-boat configuration, while the two t-Bu substituents are located on the opposite sides of the azole plane. The related 3-tert-butyl-4-(o-C-carboranyl)-8-methyl-1,4-dihydropyrazolo[5,1-c][1,2,4]triazine was also synthesized, however, its oxidative aromatization was unsuccessful.     

Synthesis of new ordered aromatic polyester copolymers

Aromatic polyesters of 3,5-di-tert-butyl-4-hydroxybenzoic acid and 3,5-diisopropyl-4-hydroxybenzoic acid were prepared. The polymers were found to be high-melting but largely insoluble in organic solvents. The polymer based on 3,5-di-tert-butyl-4-hydroxy-benzoic acid was not degraded to monomer by sulfuric acid. A number of new aromatic polyesters were also prepared. Several new monomers for aromatic polyesters were synthesized, including bis(2,5-di-tert-butyl-4-carbophenoxyphenyl)terephthalate, m- and p-phenylene bis(3,5-di-tert-butyl-4-hydroxybenzoate), bis(2,6-di-tert-butyl-4-chlorocarboxyphenyl)terephthalate, and m-phenylene bis(3,5-diisopropyl-4-hydroxybenzoate). An aromatic polyester prepared from bis(2,6-di-tert-butyl-4-chlorocarboxyphenyl) terephthalate and resorcinol had a η_inh (trichloroethylene) of 1.05 (0.5%, 30°C) and a possible melting point of 330°C (DSC). Tough, creasable films could be cast from trichloroethylene solution of this polymer. Attempts to observe or to trap the keto-ketene that might result when 3,5-di-tert-butyl-4-hydroxybenzoyl chloride is treated with base were unsuccessful.     

Oxygenation of 4-(N-alkylimino)methyl-2,6-di-t-butylphenols mediated by Co(II)-Schiff base complex

4-(N-Alkylimino)methyl-2,6-di-$\text{t}$-butylphenols ($\text{1}$), Schiff bases of 3,5-di-$\text{t}$-butyl-4-hydroxybenzaldehyde can be oxygenated in the presence of Co(Salpr), a five coordinate Co(II)-Schiff base complex to give N-alkyl-3-$\text{t}$-butyl-5-formyl-2-hydroxy-2-pivaloyl-1,2-dihydropyridines ($\text{2}$ as the main product together with 3-formyl-2,5-di-$\text{t}$-butyl-2,4-cyclopentadienone ($\text{3}$) and 2,6-di-$\text{t}$-butyl-4-formyl-6-hydroxy-4,5-epoxy-2-cyclohexenone ($\text{4}$). These products result from dioxygen incorporation into the ortho position of $\text{1}$.     

Dynamic equilibrium between dissociation and regeneration of the C-C bond in trispiro-conjoined cyclopropane compound

-The oxidation of 2,2-di(3,5-di-t-butyl-4-hydroxyphenyl)indan-1,3-dione by potassium hexacyanoferrate(III) afforded a trispiro-conjoined cyclopropane compound due to the bond formation between the ipso-carbons. Its cyclopropane ring was found to exist in solution in dynamic equilibrium with biradical species by the dissociation of the C-C bond, which is as long as 1.595 Å as revealed by X-ray crystal analysis.     

Easy Large Scale Syntheses of 2,6-DI-t-Butyl- 7-Cyano-, 7-Carboxy-and 7-Methoxycarbonyl Quinone Methides

Easy large scale syntheses of 2,6-di-t-butyl-7-cyano-, 7-carboxy- and 7-methoxycarbonyl quinone methides 1-3 using cheap and readily available starting materials have been developed.     

Synthesis of 1,3-bis[(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)(dimethoxyphosphoryl)methyl]-4,6-dimethoxybenzene

A reaction of 1,3-dimethoxybenzene with dimethyl (3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidenemethyl)phosphonate gave rise to 1,3-bis[(3,5-di-tert-butyl-4-hydroxyphenyl)-(dimethoxyphosphoryl)methyl]-4,6-dimethoxybenzene, which was oxidized to 1,3-bis[(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)(dimethoxyphosphoryl)methyl]-4,6-dimethoxy-benzene.     

Complexes of the 14th group elements with tridentate redox-active ligand

New methods of synthesis of the 14th group metal (Si, Sn, Pb) complexes containing a redox-active ligand, 3,5-di-tert-butyl-1,2-quinone-1-(2-hydroxy-3,5-di-tert-butylphenyl)imine, in various redox states were developed. New compounds were studied by the ESR spectroscopy in solutions. The redox properties of the paramagnetic tin compounds are characterized by the cyclic voltammetry. The solvent and temperature effect on the ESR spectra parameters of paramagnetic complexes of Sn(IV)and Pb(IV) was revealed.     

Oxidation of Group II Metals with 3,5-Di-tert-butyl-1,2-benzoquinone

Kinetic regularities of zinc and cadmium oxidation in systems comprising 3,5-di-tert-butyl-1,2-benzoquinone and dimethylformamide or dimethyl sulfoxide are studied. Thermodynamic parameters of oxidant and ligand adsorption on metal surface are estimated. The oxidation of Group II metals (Be, Ca, Mg, Zn, Cd) with 3,5-di-tert-butyl-1,2-benzoquinone gives metal bis-o-semiquinolates. In the presence of excess metal in the medium of coordinating solvents, diradical products convert to the corresponding catecholate derivatives. It is shown that the dependence of the rates of metal reactions with 3,5-di-tert-butyl-1,2-benzoquinone on the donor number of solvent passes through a maximum. With less active metals, the maximum shifts to more basic ligands.     

Synthesis and properties of 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-5-nitroindazole

N-(2-Azido-5-nitrobenzylidene)-3,5-di-tert-butyl-4-hydroxyaniline (3a) and N-(2-azido-5-nitrobenzilidene) aniline (3b), when heated in dimethylformamide yielded 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-5-nitroindazole (4a) and 2-phenyl-5-nitroindazole (4b), respectively. The structure of4b was confirmed by X-ray analysis. A stable phenoxyl radical was shown to originate from the oxidation of4a with lead (IV) dioxide.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1095–1097, June, 1994.     

Synthesis,spectroscopic and redox properties of nickel(II) salicylaldimine complexes containing sterically hindered phenols

The preparation and spectroscopic characterization of a series of new bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylaldiminato]nickel(II) complexes, [Ni(L^X)₂], bearing one or two OH and MeO substituents on the salicylaldehyde moiety, as well as radical species generated from these compounds by the oxidation with PbO₂, are reported. The [Ni(L^X)₂] chelates, which appear to be tetrahedral in the solid state and in dioxane solution, are converted into a square-planar configuration in non-donor solvents. The OH-substituted complexes, unlike their MeO analogues, form six-coordinate adducts in pyridine, DMF and DMSO. These new compounds, unlike their analogues with electron-withdrawing substituents (Cl, Br, NO₂), are easily oxidized by PbO₂ to produce Ni^II-stabilized phenoxy radicals in which the unpaired electrons are delocalized over the ligand and do not couple with the second radical center. No e.s.r. signals were observed that could be attributed to a M = ±2 transition of the triplet state biradicals.     

Effects of Aminophenol Derivatives on Radiation-Induced Reactions Involving Various Organic Radicals

The effects of some aminophenol derivatives, diphenylamine, and ionol on the formation of ethanol and hexane radiolysis products in aerated and deaerated solutions were studied. The results allowed conclusions to be made about the effect of the structure of test compounds on their reactivity to oxygen- and carbon-centered radicals. It was found that 4,6-di-tert-butyl-2-(N-acetylamino)phenol, 4,6-di-tert-butyl-2-(N-benzoylamino)phenol, 2-hydroxydiphenylamine, and 4-hydroxydiphenylamine were highly competitive with commercial antioxidants in the efficiency of inhibition of radiation-induced processes of hexane oxidation. N-(2-Hydroxy-3,5-di-tert-butylphenyl)aniline, 4,6-di-tert-butyl-2-cyclohexylaminophenol, 2-hydroxydiphenylamine, 4-hydroxydiphenylamine, and N-phenyl-1,4-benzoquinonemonoimine were superior to ionol and diphenylamine in the inhibition of reactions of alkyl and -hydroxyalkyl radicals.     

Highly effective electrochemical anion sensing based on oxoporphyrinogen

The effect of anion binding on the oxidation potential of an anion receptor, N₂₁,N₂₃-dibenzyl-5,10,15,20-(3,5-di-t-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen, 1 in o-dichlorobenzene is reported. The anion binding site of 1, at its inner pyrrolic amine hydrogens, is an integral part of the highly conjugated macrocycle, thus predicting larger potential shifts upon anion binding. Accordingly, cathodic shifts up to 600 mV are observed upon anion binding and such potential shifts correlate well with the anion binding constants.