Aerobic oxidation of substituted phenols catalysed by metal acetylacetonates in the presence of 3-methylbutanal

The aerobic oxidation of substituted phenols with the catalytic system M(acac)_n/3-methylbutanal/O₂ has been investigated. Co(acac)₂ and Mn(acac)₃ promoted the transformation of 2,6-dimethylphenol and 2,6-di-t-butylphenol into their corresponding diphenoquinones and benzoquinones. In the oxidation of 2,3,6-trimethylphenol, the same catalysts yielded 32–34% of the relevant biphenol. Cu(acac)₂ converted 2-naphthol into 1,1′-bi-2-naphthol with 84% yield. Supported Co(II) and Cu(II) complexes have also been used as heterogeneous catalysts for the oxidation of 2,6-di-t-butylphenol and 2-naphthol, respectively.     

β-Hydroxyalkylation of sterically hindered phenols with epoxides in acid medium

Reactions of 2,6-dialkylphenols with ethylene oxide, propylene oxide and epichlorohydrin in the presence of SnCl₄ at the temperature from ?5 to +5°C leads to the formation of respective phenols containing a hydroxy group in the β-position of the aliphatic chain of the para-substituent. The conditions for maximum selectivity of the reaction of 2,6-di-tert-butylphenol with ethylene oxide were determined. By HPLC-MS method the directions of the side reactions were explored. The method has been successfully tested in a pilot installation. With 2,6-dimethylphenol instead of 2,6-di-tert-butylphenol a sharp increase occurs in the content of ethers in the reaction product. With epichlorohydrin, 2,6-di-tert-butylphenol affords a product, which is easily converted into an epoxide containing a sterically hindered phenol in its structure.     

Potassium and sodium 2,6-di-tert-butylphenoxides and their properties

The crucial factor of the reaction of 2,6-di-tert-butylphenol with alkali hydroxides is temperature, depending on which two types of potassium or sodium 2,6-di-tert-butylphenoxides are formed. These types exhibit different catalytic activity in the alkylation of 2,6-di-tert-butylphenol with methyl acrylate. More active forms of 2,6-Bu^t ₂C₆H₃OK or 2,6-Bu^t ₂C₆H₃ONa are synthesized at temperatures higher than 160 °C and are predominantly the monomers, which dimerize on cooling. The data of ¹H NMR, electronic, and IR spectra for the corresponding forms of 2,6-Bu^t ₂C₆H₃OK and 2,6-Bu^t ₂C₆H₃ONa isolated in the individual state are in agreement with cyclohexadienone structure. In DMSO or DMF, the dimeric forms of 2,6-di-tert-butylphenoxides react with methyl acrylate to form methyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate in 64–92% yield. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2138–2143, December, 2006.     

Polyfluoroalkylation of 2,6-di-tert-butylphenol by 1,2-dibromotetrafluoroethane activated by sulfur dioxide

It was shown that it was possible to perform fluoroalkylation of both sterically-hindered phenolates and phenols with the use of 2,6-di-tert-butylphenol as an example. The role of sulfur dioxide as an activator of the interaction process was established.     

Template synthesis of polyaniline/Pd nanoparticle and its catalytic application

Pre-organization of Pd(II) species on polyaniline to form the corresponding d,π-conjugated complex provided a versatile route to a small and well-dispersed nanoparticle, which worked as an efficient redox catalyst for oxidative coupling reaction of 2,6-di-t-butylphenol.     

Gas-phase thermochemical properties of some tri-substituted phenols: A density functional theory study

The study of the energetics of phenolic compounds has a considerable practical interest since this family of compounds includes numerous synthetic and naturally occurring antioxidants. In this work, density functional theory (DFT) has been used to investigate gas-phase thermochemical properties of the following tri-substituted phenols: 2,4,6-trimethylphenol, 2,6-dimethyl-4-tert-butylphenol, 2,6-dimethyl-4-methoxyphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxyphenol, 2,4,6-trimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-tert-butylphenol. Molecular structures were computed with the B3LYP and the ωB97X-D functionals and the 6-31G(d) basis set. More accurate energies were obtained from single-point energy calculations with both functionals and the 6-311++G(2df,2pd) basis set. Standard enthalpies of formation of the phenolic molecules and phenoxyl radicals were derived using an appropriate homodesmotic reaction. The OH homolytic bond dissociation enthalpies, gas-phase acidities and adiabatic ionization enthalpies were also calculated. The general good agreement found between the calculated and the few existent experimental gas-phase thermochemical parameters gives confidence to the estimates concerning the phenolic compounds which were not yet experimentally studied.     

Synthesis and coordination properties of the zinc complex of dimeric porphyrin in reactions with imidazole, 2-methylimidazole, and the pyridine in benzene

Dimeric porphyrin(2,6-bis[15′-(3″,5″-di-tert-butylphenol)-3′,7′,13′,17′-tetramethyl-2′,8′,12′,18-tetraethylporphin-5′-yl]-4-tert-buthylphenol) and its binuclear zinc complex were obtained from 4,4′-dimethyl-3,3′-diethyldipyrrolylmethane, 2,6-diformyl-4-tert-butylphenol and 3,5-di-tert-buthylbenzaldehyde. Coordina-tion properties of dimeric zincporphyrin in the intermolecular reaction with nitrogen-containing bases (imidazole, 2-methylimidazole, and pyridine) in benzene were studied. Geometry and electronic structure of the zincporphyrin and its molecular complexes were calculated by a quantum-chemical method. Energy characteristics of the intermolecular reaction of the dimeric zincporphyrin with bases were determined. The calculated energies of the central metal atom interaction with the nitrogen atom of an extra-ligand agree well with the stability of the Zn-porphyrin molecular complexes. The influence of the deformation distortions of the porphyrin ligand on the strength of the metal-extra-ligand σ-bond was established.     

Vapour pressure of binary,three-phase (S-L-V) systems and solubility

Solubilities and vapour pressures along the solid-liquid equilibrium line for systems 2-t-butyl-4-methylphenol+benzene, 2-t-butyl-4-methylphenol+cyclohexane, 2,6-di-t-butyl-4-methylphenol+benzene, 2,6-di-t-butyl-4-methylphenol+cyclohexane and enthalpies of fusion for six phenols have been measured.The effect of specific interactions, leading to association, on solubilities and vapour pressures of 13 binary three-phase systems (S—L—V) has been discussed. Results of solubility prediction from vapour pressure measurements and vice versa are presented.     

Effect of Donor and Acceptor on the Mechanism of a Photochemical Reaction in Doped Single Crystals for Radical Pairs in 4-Bromo-2,6-Di-tert-Butylphenol Single Crystal Doped with 2,6-Di-tert-Butyl-p-Quinone

Radical pairs produced by the photolysis of 4-bromo-2,6-di-tert-butylphenol single crystals doped with 2,6-di-tert-butyl-p-quinone are studied by EPR spectroscopy. The mechanism of radical pair generation changes from hydrogen-atom transfer to electron transfer (without proton transfer). The reasons for this change are discussed.     

Reactions of perfluoro(2-methylpent-2-ene) and perfluoro(5-azanon-4-ene) with primary amines containing a 2,6-di-tert-butylphenol fragment

Reactions of perfluoro(2-methylpent-2-ene) and perfluoro(5-azanon-4-ene) with 4-(2-aminoethyl)-2,6-di-tert-butylphenol and 4-(3-aminopropyl)-2,6-di-tert-butylphenol in acetonitrile in the presence of triethylamine gave the corresponding azetidine, 1,2-dihydroazete, and 1,2-dihydro-1,3-diazete derivatives, respectively. The reaction mechanisms, role of triethylamine, and factors affecting the intramolecular nucleophilic cyclization process are discussed.     

Oxidation of substituted phenols with chlorine dioxide

Chlorine dioxide was used to oxidize sterically hindered phenols and their derivatives (2,6-di-tertbutylphenol, 2,6-diisobornylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-diisobornyl-4-methylphenol, and 3,5-diisobornyl-4-hydroxybenzaldehyde) in organic solvent.     

Inhibitory effect of 2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylphenol groups in iron and manganese porphyrins on the catalytic activity in the oxidation of hydrocarbons by hydrogen peroxide

Iron and manganese porphyrins containing 2,6-di-tert-butylphenyl groups (R₄PFeCl and R₄PMnCl) have been synthesized to be further immobilized on silica gels via various spacers. The activity of these porphyrins in the oxidation of alkanes and alkenes by hydrogen peroxide has been studied. 2,6-Di-tert-butylphenol groups decrease the catalytic activity of porphyrins in oxidation processes.     

The complexes of multiimidazole with copper（Ⅰ） display tyrosinase activity

The six multiimidazole copper(Ⅰ)complexes are utilized to mimic tyrosinase.The main product is 3,5-di-t-butylcatechol from o-hydroxylation of the substrate 2,4-di-t-butylphenol.The highest yield of catechol is up to 82.2% and selectivity 94.8% by [Cu(I)_(3b)(MeCN)_2](ClO_4)_2 and O_2 under mild conditions,which are found to be more efficient than that already reported.     

Synthesis, structure, and antioxidant activity of hybrid N-substituted salicylic acid amides

Sterically hindered phenols, 3-tert-butyl-N-(3,5-di-tert-butyl-4-hydroxyphenyl)-5-ethyl-2-hydroxybenzamide and N-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl]-2-hydroxybenzamide, were synthesized as potential antioxidants, and the formation of hydrogen bonds by their molecules was shown by UV and IR spectroscopy.     

Amino-derivatives of usninic acid

Products from the reaction of usninic acid and 4-(3-aminopropyl)-2,6-di-t-butylphenol, 4-(2-aminoethyl)-2,6-di-t-butylphenol, antipyrine, N,N-diethylaminoethylamine, p-chloroaniline, and p-bromoaniline in addition to the quaternary ammonium salt (E)-2-(1-(6-acetyl-7,9-dihydroxy-8,9b-dimethyl-1,3-dioxo-1,9b-dihydrodibenzo[b,d]furan-2(3H)-ylidene)ethylamino)-N,N-diethyl-N-methylethaneammonium iodide were obtained.     

Urotropin synthesis of 3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butylsalicylic acid derivatives

The stability of 3,5-di-tert-butylsalicylic aldehyde against oxidation is due to autoinhibiting of the chain process. However its oxidation into 3,5-di-tert-butylsalicylic acid was performed at the use of acetyl protection of the hydroxy group. In reaction of 6-bromo-2,4-di-tert-butylphenol with urotropin the formation was discovered of 3,5-di-tert-butylsalicylic acid, its nitrile and amide.     

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.     

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.     

Hydroxylation of substituted diatomic phenols and their derivatives

Oxidation of 3,6-di-tert-butylpyrocatechol in protic media is accompanied by the formation of 3,6-di-tert-butyl-2-hydroxy-para-benzoquinone. Hydroxylation of the 3,5-isomer results in dealkylation and isomerization with the formation of 6-tert-butyl-2-hydroxy-para-benzoquinone and the quinone mentioned above, respectively. Their ratio depends on the nature of the solvent. Analogous processes accompany redox transformations of 2,6-di-tert-butylhydroquinone, 2,6-diphenyl-para-benzoquinone, and 2,4,6-tri-tert-butylphenol adsorbed on silica gel. Derivatives of 3,5-substituted pyrocatechols formed under conditions of heterophase oxidation in air are capable of transformations to form nitrogen-containing compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2007–2010, October, 1998.     

Development of a one-stage synthesis of 2,6-di-<Emphasis Type="Italic">tert</Emphasis>-4-ethylbutylphenol from 2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylphenol

Investigation of the catalyzed reaction of 2,6-di-tert-butylphenol with ethanol, ethylene glycol, oligomeric glycols, and paraldehyde in a strongly basic medium permitted to develop a technologically suitable procedure for manufacture of 2,6-di-tert-4-ethyl-butylphenol, used in the synthesis of Antioxidant-425.