Photochemical processes of 2,6-di-tert-butyl-4-methylphenol

The photosensitized oxidation of 2,6-di-t-butyl-4-methylphenol (BHT) by anthracene (A) in CCI₄, hexane and polystyrene films with light of wavelength 365 nm has been investigated. Interestingly, BHT was found to inhibit the consumption of A in the presence of oxygen. A possible kinetic scheme for the reaction of A + BHT + CCl₄ has been devised; the rate constants for the most important processes have been evaluated.     

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 of phosphorus derivatives of 2,6-Di-tert-butyl-4-methylphenol

Convenient procedures for the synthesis of 2,6-di-tert-butyl-4-methylphenol (ionol) mono-, di-and triphosphorus derivatives, starting from the readily accessible 3,5-di-tert-butyl-4-hydroxybenzaldehyde, are proposed, and some properties of the obtained compounds are presented.     

Dissociation energies of O–H bonds in alkylseleno- and alkyltelluro-substituted phenols

The O?H bond dissociation energy (D _O?H) has been determined for eight alkylseleno-substituted phenols, one alkyltelluro-substituted phenol, and one alkyltelluro-substituted pyridinol. D _O?H has been estimated by the intersecting-parabolas method from kinetic data using five reference compounds: α-tocopherol (D _O?H = 330.0 kJ/mol), 3,5-di-tert-butyl-4-methoxyphenol (D _O?H = 347.6 kJ/mol), 4-methylphenol (D _O?H = 361.6 kJ/mol), 2,6-di-tert-butyl-4-methylthiophenol (D _O?H = 336.3 kJ/mol), and 2,6-di-ter-tbutyl-4-methylphenol (D _O?H = 338.0 kJ/mol). The following D _O?H values (kJ/mol) have been obtained: 335.9 for 2,5,7,8-tetramethyl-2-phytyl-6-hydroxy-3,4-dihydro-2H-1-benzoselenopyran, 342.6 for 2-methyl-5-hydroxy-2,3-dihydrobenzoselenophene, 333.5 for 2,4,6,7-tetramethyl-5-hydroxy-2,3-dihydrobenzoselenophene, 339.4 for 2-tert-butyl-4-methoxy-6-octylselenophenol, 357.9 for dodecyl 3-(4-hydroxyphenyl) propyl selenide, 348.5 for dodecyl 3-(3,5-dimethyl-4-hydroxyphenyl)propyl selenide, 350.9 for dodecyl 3-(3-tert-butyl-4-hydroxyphenyl)propyl selenide, 338.0 for dodecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propyl selenide, 343.0 for 2,6-di-tert-butyl-4-(tellurobutyl-4′-phenoxy)phenol, and 338.8 for 6-octyltelluro-3-pyridinol. The stabilization energies of phenoxyl radicals containing R substituents (X = O, S, Se, Te) have been compared.     

Photolysis of 2,6 di-tert-butyl-4-tert-butylperoxy-4-methyl-2,5-cyclohexadienone

The photolysis of a heptane solution of 2,6-di-tert-butyl-4-tert-butylperoxy-4-methyl- 2,5-cyclohexadienone (1) with light of 360–480 nm in the presence of 2,6-di-tert-butyl-4-methylphenol or 2,4,6-tri-tert-butylphenol gives rise to their corresponding phenoxyls in a reaction with the tert-butoxyl arising in the photolysis. Direct evidence of the formation of t-BuO^. by the photolysis of 1 was provided by the ESR characterization of spin-adducts of this radical with nitrosobenzene and nitrosodurene. Evidence of the photolysis of the peroxide bond in 1 is important for the mechanism of reaction of phenolic chain-breaking antioxidants.     

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.     

Thermogravimetric Investigation of Antioxidant Activity of Selected Compounds in Lipid Oxidation

Uninhibited and inhibited autooxidation of ethyl linoleate(LnEt) in bulk phase initiated by 0.04 M azoisobutyronitrile (AIBN) was investigated by thermogravimetry in isothermal mode at 35, 40 and 50°C. LnEt oxidation was inhibited by:2,6-di-t-butyl-4-methylphenol (BHT), 2-t-butyl-6-methylphenol (BMP),2-hydroxyphenylacetic acid (PAA), 2-hydroxyacetophenone (HAP), α-tocopherol,2,2'-methylene-bis-(4-methyl-6-t-butylphenol) (BIS), caffeic acid andβ-carotene. All investigated compounds showed antioxidant activity measured by induction time, values of rate of oxidation during induction period (R _inh) and values of kinetic chain length ν. At lower temperatures the monohydroxyphenols are more efficient inhibitors than dihydroxyphenols while at 50°C dihydroxyphenols have better antioxidant efficiency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vapour—liquid equilibria in binary systems formed by N-Methylpyrrolidone with hydrocarbons and hydroxyl derivatives

The vapour—liquid equilibria (VLE) determined by an ebulliometric total pressure method under isothermal conditions for binary systems formed by N-methylpyrrolidone with hexane (333.25 and 343.15 K), dodecane (393.25 K), cyclohexane (333.25 and 354.15 K), methyl-cyclohexane (354.15 and 373.25 K), benzene (333.25 and 354.15 K), toluene (362.15 and 383.35 K), propylbenzene (352.15 and 373.75 K), butylbenzene (352.15 and 373.75 K), propanol-1 (354.15 K), hexanol-1 (351.75 and 393.35 K) and at 393.55 K for cyclohexanol, 4-methylphenol and 2,4-dimethylphenol are reported. The vapour pressures of the pure substances are given. The least squares analysis of VLE data by means of the Redlich-Kister equation is given.     

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 $\text{1}$.     

The production of artifacts during preparation of fatty acid methyl esters from fish oils,food products and pathological samples

Methyl esters were synthesized from lipid extracted by a modified Bligh and Dyer technique. The lipid was saponified and the free fatty acids methylated using boron trifluoride in methanol. Butylated hydroxytoluene (BHT; 2,6-di-tert-butyl-4-methylphenol) was added to the initial sample and to the extracted lipid prior to methyl ester synthesis. Under these conditions, the BHT was derivatized to a range of compounds, some of which can result in misinterpretation of the GC trace. Three components have been characterized by mass spectroscopy. Two of these, which eluted slightly before 16:0 on a polar column, were shown to be 2,6-di-tert-butyl-4-methoxyphenol and 2,6-di-tert-butyl-4-methoxy-methylphenol. The third component, which coeluted with 15:0 on the same column, is 2,6-di-tert-butyl-4-methoxy-5-hydroxyphenol.     

Synthesis of 3,3′,5,5′-Tetra-<Emphasis Type="Italic">tert</Emphasis>-butyl-4,4′-stilbenequinone and Its Catalytic Activity in the Liquid-Phase Oxidation of Inorganic Sulfides

The oxidation of 2,6-di-tert-butyl-4-methylphenol with hydrogen peroxide in the presence of potassium iodide gave 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone which catalyzed liquid-phase oxidation of sodium sulfide with oxygen more efficiently than did 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone.     

Apparent Molar Volume and Apparent Molar Adiabatic Compressibility Studies of 2,6-Di-tert-butyl-4-methylphenol and 2-tert-Butyl-4-methoxyphenol in Aqueous Micelle Solutions of Hexadecyltrimethylammonium Chloride as a Function of Surfactant Concentration and Temperature

Ultrasonic velocities and densities of aqueous solutions of cetyltrimethylammonium chloride have been measured at concentrations below 0.35 mol kg^-1 at 25, 35, and 45°C. Apparent molar volume and apparent molar adiabatic compressibility properties of the aqueous surfactant solutions were derived from these data. Apparent molar volumes and apparent molar adiabatic compressibilities of 2,6-di-tert-butyl-4-methylphenol and 2-tert-butyl-4-methoxyphenol dissolved in aqueous micellar solutions of cetyltrimethylammonium chloride were determined as a function of surfactant concentration and temperature. The results obtained for the binary and ternary systems are compared with those previously published for binary aqueous cetyltrimethylammonium bromide systems and for ternary systems of this surfactant containing the same additives. The degree of counterion dissociation from the micelles and the effect this has on the extent of hydration of the head group region of the micelle are shown to have an effect on the solubilization sites of hydrophobic-like additives in these micelles.     

Fused s-triazino heterocycles. XVI. 13H-1,3,7,8,12a, 13c-hexaazabenzo[de]naphthacene and 1,3,7,8,11b, 12,14,14d-octaazadibenzo[de,hi]naphthacene,two new ring systems

The reaction of 7,9-dibromo-5-tribromomethyl-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene ( 1a ) with 2-amino-5-picoline is shown to give 4,6-dibromo-2-t-butyl-13-imino-11-methyl-13H-1,3,7,8,12a,13c-hexaazabenzo[de]naphthacene ( 3 ) and the isomeric 7,9-dibromo-2-t-butyl-4-cyano-5N-(5-methyl-2-pyridyl)amino-1,3,-6,9b-tetraazaphenalene ( 2a ). A related annulation reaction of 7,9-dibromo-2-t-butyl-5-chloro-4-cyano-1,3,6,9b-tetraazaphenalene ( 1g ) with 2-amino-6-trimethylacetamidopyridine leads in two steps to 4,6-dibromo-2,13-di-t-butyl-1,3,7,8,11b,12,14,14d-octaazadibenzo[de,hi]naphthacene ( 4a ). The preparation of 1g , 5-azido-7,9-dibromo-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene ( 1c ) and the reaction of the latter with pyrrolidine leading to 7,9-dibromo-2-t-butyl-4-cyano-5-(1-pyrrolidino)-1,3,6,9b-tetraazaphenalene ( 1e ) are also reported. Attempted displacement of the azido-group on 1c by 2,6-diaminopyridine affords surprisingly 5-amino-7,9-dibromo-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene ( 1d ).     

p, T, x, y data of benzene + n-hexane and cyclohexane + n-heptane systems

The isothermal vapour—liquid equilibria of the benzene + n-hexane and cyclohexane + n-heptane systems have been studied using a dynamic method. The thermodynamic consistency of the data has been tested and the prediction from several empirical and semitheoretical models have been compared with the experimental values of different excess properties.     

Determination of antioxidants in new and used lubricant oils by headspace-programmed temperature vaporization–gas chromatography–mass spectrometry

A sensitive method is presented to determine antioxidants (2-, 3-, and 4-tert-butylphenol, 2,6-di-tert-butylphenol, 3-tert-butyl-4-hydroxyanisol, 2,6-di-tert-butyl-4-methylphenol, 1-naphthol, and diphenylamine) in new and used lubricant oil samples. Research was carried out on a GC device equipped with a headspace sampler, a programmed temperature vaporizer, and an MS detector unit. The proposed method does not require sample treatment prior to analyses, hence eliminating possible errors occurring in this step. Sample preparation is reduced when placing the oil sample (2.0 g) in the vial and adding propyl acetate (20 μL). Solvent vent injection mode permits a pre-concentration of the compounds of interest in the liner filled with Tenax-TA®, while venting other species present in the headspace. Thereby, both the life of the liner and the capillary column is prolonged, and unnecessary contamination of the detector unit is avoided. Calibration was performed by adding different concentrations of analytes to a new oil which did not contain any of the studied compounds. Limits of detection as low as 0.57 μg/L (2-tert-butylphenol) with a precision lower or equal to 5.3% were achieved. Prediction of the antioxidants in new oil samples of different viscosities (5W40, 10W40, and 15W40) was accomplished with the previous calibration, and the results were highly satisfactory. To determine antioxidants in used engine oils, standard addition method was used due to the matrix effect.     

A new route to 3-alkyl-2,5-di-t-butyl-2,4-cyclopentadienones from 4-alkyl-2,6-di-t-butylphenols

Base-catalyzed reaction of 5-acylmethyl-2,5-di-$\text{t}$-butyl-4-oxa-2-cyclopentenones selectively derived from 4-alkyl-2,6-di-$\text{t}$-butylphenols $\text{via}$ three steps involving oxygenation, acetylation, and acid-treatment gave 3-alkyl-2,5-di-$\text{t}$-butyl-2,4-cyclopentadienones in excellent yield.     

About selective methods of synthesis of 6-<Emphasis Type="Italic">tert</Emphasis>-butyl-2-methylphenol and 6-<Emphasis Type="Italic">tert</Emphasis>-butyl-2,4-dimethylphenol

Vapor phase catalytic methylation with methanol of 2-tert-butylphenol at the temperature 280–300°C proceeds selectively with formation of 6-tert-butyl-2-methylphenol. Elevating reaction temperature above 300°C leads to formation of 2,6-dimethylphenol. Reaction of 2-tert-butylphenol with methanol in alkaline medium in the presence of zinc oxide is shown to lead initially to formation of a mixture of calixarenes and methylenebisphenols that at elevated temperature exert splitting leading in future to 6-tert-butyl-2,4-dimethylphenol. Obtaining it in this reaction from 2,2′-methylenebis-(6-tert-butyl-4-methylphenol) proceeds selectively. Pathways of the reductive methylation of methylenebisphenols with methanol in alkaline medium is considered.     

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.     

Macromolecular antioxidants based on polysaccharides and 2,6-diisobornyl-4-methylphenol derivatives

New macromolecular antioxidants that were conjugates of dextran or hydroxyethylated starch with functionalized derivatives synthesized from 2,6-diisobornyl-4-methylphenol were prepared. Their antiradical activity compared with derivatives of 2,6-di-tert-butyl-4-methylphenol was studied in a model reaction with 2,2-diphenyl-1-picrylhydrazyl. The studied conjugates exhibited greater activity than sterically hindered phenols not bonded to a polymer chain. The synthesized isobornyl derivatives were more active than previously studied tert-butyl analogs.     

Hydrogen and electron transfer in the photoreduction reaction of quinones

The primary products of the photoreduction reaction of 3,6-dit-butyl-o-quinone in single crystals of 3,6-di-t-butyl-pyrocatechol are studied by EPR spectroscopy. Ion radical and neutral radical pairs are identified distinctly. In the case of the same o-quinone in single crystals of 2-6-dit-butyl-4-methylphenol the primary product is the radical pair composed of the two hydroxyphenoxyl radicals of phenol. This indicates the possibility of transfer of two hydrogen atoms in a single elementary photochemical event.