Synthesis and antioxidant activity of modified sterically hindered phenols

Salicylaldehyde derivatives containing sterically hindered phenol fragments were synthesized. The compounds obtained are capable to offer protection against UV radiation.     

Aggregation of dextran hydrophobically modified by sterically-hindered phenols in aqueous solutions: Aggregates vs. single molecules

The hydrodynamic properties of dextrans hydrophobically modified by sterically-hindered phenols in aqueous solution were characterized by a combination of Cryogenic Transmission Electron Microscopy (Cryo-TEM), fluorescent spectroscopy, and Dynamic Light Scattering (DLS). All solutions investigated contained aggregates the structure, shape, and critical aggregation concentration of which are influenced by the amount of the inserted phenol groups in the polymer matrix. We found that increasing of temperature enhances aggregation. It was established that the critical aggregation concentration could be well approximated by a logarithmic function of the substitution degree of the glycoside units. The results suggest that the proportion of aggregates is nevertheless negligible in comparison with the proportion of single molecules.     

Determination of sterically hindered phenols by gas-liquid chromatography

Conclusions The possibility has been shown and the optimum conditions have been found for the identification of various 4-alkyl-2,6-di-tert-butylphenols by gas-liquid chromatography on the stationary liquid phases poly(ethylene glycol adipate) and Apiezon-L deposited on Celite C22.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1618–1622, July, 1970.     

Molecular characteristics and antioxidant activity of polyethylene glycols modified by sterically hindered phenols

Chemical modification of polyethylene glycols by antioxidants belonging to the class of sterically hindered phenols is used to obtain water-soluble conjugates differing in the structure of the joined antioxidant and molecular weight. The inclusion of hydrophobic end groups in polyethylene glycol molecules leads to a decrease in the lower critical mixing point of the solution as compared to the original polymer. Dilute solution viscometry and light scattering are used to determine the molecular-mass characteristics of the polymers and the hydrodynamic radii of single conjugate molecules. The mass fraction of single molecules in aqueous solutions of the conjugates is greater than 95%. The aggregates are micellar-type particles whose core is formed by the hydrophobic moieties of sterically hindered phenols. It is shown that the antiradical activity of the antioxidants 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionic acid and 3- (3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid, which are used for the modification, differs only slightly, whereas the activity of the relevant conjugates increases significantly.     

New functional derivatives of sterically hindered phenols

Conclusions Dimethylaminoethyl (4-hydroxy-3, 5-ditert-butylphenyl) ketone, in contrast to certain other ketones of a series of sterically hindered phenols, reacts with phenylhydrazine, potassium hydroxide, sodium cyanide, and organic magnesium compounds as a normal -aminoketone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 920–922, April, 1968.The authors thank N.M. Emanuel for his interest in this work in the process of its fulfillment.     

Some heterocyclic derivatives of sterically hindered phenols

Five- and six-membered heterocyclic compounds containing sterically hindered phenols as structural fragments were obtained by dipolar 1,3-eycloaddition of substituted nitrile oxides to olefins, azomethines, and acetylenes.Translated fromIzvestiva Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 426–429, February, 1996.     

Aqueous biphase formation by mixtures of dextran and hydrophobically modified dextran

 A series of modified dextrans was prepared by condensation of straight chain saturated C3, C4 and C6 fatty acids and the phase behavior of aqueous solutions of these materials with unmodified dextran was measured as a function of temperature, concentration and degree of substitution. At a constant degree of substitution the tendency towards aqueous biphase formation increased with the length of the hydrophobic substituent, the temperature and the molecular weight. Fluorescence studies of the modified dextrans with pyrene as a probe indicated the presence of hydrophobic micro-domains. Rheological study showed that there was no large-scale association for C3 and C4 substituted dextran, mainly intramolecular association, however some intermolecular association existed for C6 substituted dextran. The results are compared with the behavior of the classical PEG/dextran biphase systems, and mechanisms driving phase separation are discussed. Received: 7 October 1997 Accepted: 20 January 1998     

Electrochemical oxidation and determination of high-molecular-weight sterically hindered phenols

The use of differential pulse voltammetry for the determination of Irganox 1010, a sterically hindered phenol used as an antioxidant, prompted an investigation of the electrochemical behavior of several other commercially available high-molecular-weight hindered phenols used as antioxidants and stabilizers. Although these compounds generally have at least two phenol groups per molecule, their electrochemical behavior is similar to that of simpler hindered phenols such as 2,4,6-tri-t-butylphenol. Detection limits ranging from 1.3 to 8.2 ppm were obtained in a methanol—0.07 M sulfuric acid medium. The oxidation of alkylphenols in neutral or acidic media is accompanied by follow-up chemical reactions, leading to formation of passivating films on the surface of the glassy carbon electrode. In alkaline media, the corresponding phenoxide is oxidized electrochemically to the corresponding stable phenoxy radical and filming can be avoided.     

Reactions of sterically hindered phenols with P2S5

The direction of the reaction of 2,6-disubstituted phenols with P₂S₅ leading to bis(hydroxyaryl)dithiophosphinic acids orO,O-bis(aryl) dithiophosphates is determined by the degree of shielding of the OH group. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1442–1444, July, 1998.     

Voltammetric determination of sterically hindered phenols in surfactant-based self-organized media

Tert-butylhydroquinone (TBHQ), butylhydroxyanisole (BHA), and butylhydroxytoluene (BHT) are irreversibly oxidized on a glassy-carbon electrode in a medium of acetonitrile-Britton-Robinson buffer solution (1: 9, pH 3.0) at 0.61, 0.79, and 1.1 V, respectively, to give quinones. Micellar media of Triton X100,Brij® 35, and sodium dodecyl sulfate affect their oxidation. The splitting and suppression of the oxidation steps for sterically hindered phenols (SHP) is observed in the presence of nonionic surfactants. Sodium dodecyl sulfate considerably enhances anodic currents and also shifts positive potentials to lower values. The conditions of the differential-pulse voltammetric determination of SHP in a 0.1 M sodium dodecyl sulfate supporting electrolyte are found. The calibration graphs are linear in the ranges 2.02–1010, 2.34–1170, and 6.15–615 μM and the detection limits (S/N = 3) are 0.23, 0.18, and 3.5 μM for TBHQ, BHA, and BHT, respectively. The possibility of determining SHP in TBHQ-BHT and BHA-BHT mixtures in wide ranges of component concentration is demonstrated. A method is developed for the extraction-voltammetric determination of BHT in vegetable oils.     

Indicator properties of oligoethylene glycol hybrids with sterically hindered phenols

Aqueous solutions of hybrid compounds (conjugates) formed by polyethylene glycols modified at the terminal hydroxy groups with sterically hindered phenol lose their phase stability at a certain temperature which depends on the molecular weight of polyethylene glycol, structure of sterically hindered phenol, conjugate concentration, and composition of the medium. This property may be used to estimate the effect of structural factors on the hydrophobic-hydrophilic balance in the conjugate-water system.     

Theoretical investigation of mechanism of antioxidant action of sterically hindered phenols

Heats of reaction describing the mechanism of antioxidant action of phenols in polyolefins have been calculated by the MNDO quantum-chemical method. It has been shown that reactions producing substituted quinones will proceed the most readily. The influence of substituents on the heat of reaction has been investigated.Vilnius University. Materials, Tambov. Translated from Teoreticheskaya i 8ksperimentaI'naya Khimiya, Vol. 27, No. 2, pp. 165–170, March–April, 1991. Original article submitted February 16, 1990.     

Gas-chromatographic separation of silicon-containing sterically hindered phenols and their oxidation products

Conclusions It was shown to be possible to separate and isolate in pure form 2,6-bis(trimethylsilyl)-4-terbutylphenol, 2,4-diterbutyl-6-trimethylsilylphenol, substituted bis(siloxy)diphenyls, and the compounds (obtained for the first time) 2,6-bis(trimethylsilyl)-1,4-benzoquinone and 2-terbutyl-6-trimethylsilyl-1,4-benzoquinone by gas-liquid chromatography.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 686–687, March, 1970.