Inhibition of polymerization of methyl methacrylate by an ortho-benzoquinone-amine system

The kinetic features of the bulk polymerization of MMA in the presence of sterically hindered ortho-benzoquinones and the tertiary amines N,N-dimethylaniline and N,N-dimethylisopropanolamine have been studied. The irradiation of solutions of quinones and amines in MMA with visible light causes inhibition of the thermal polymerization of MMA, with the effects of quinones and amines being synergistic. The effect of inhibition is enhanced as the steric shielding of carbonyl groups of ortho-benzoquinone by substituents becomes weaker. The dependence of the induction period on the redox potentials of quinones passes through a maximum. It is shown that inhibition involves oxyphenoxyl radicals arising from the interaction of the original quinone with the product of its photoreduction in the presence of amines, pyrocatechol. The inhibiting effect depends on the concentration ratio of quinone and pyrocatechol and the nature of amine. When quinone is in excess with respect to pyrocatechol, additional inhibition of polymerization is observed and the rate of quinone consumption during the induction period is increased.     

Reactions of benzazole-2-thiones with 3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-hydroxybenzyl acetate

The benzylation of benzothiazole(oxazole, imidazole)-2-thiones with 3,5-di-tert-butyl-4-hydroxybenzyl acetate involves either the sulfur or nitrogen atom depending on the reaction conditions. The S- and N-benzylation products of benzazole-2-thiones are kinetically and thermodynamically controlled products, respectively. The use of 3,5-di-tert-butyl-4-hydroxy-benzyl acetate allows sterically hindered hydroxybenzyl derivatives of benzаzole-2-thiones to be generally synthesized under milder conditions than in known methods of their synthesis.     

Synthesis,structures, and properties of new sterically hindered hydrazine-based catecholaldimines

New sterically hindered catecholaldimines derived from hydrazine were synthesized in high yields. Two procedures for the synthesis of sterically hindered catecholaldimines were developed: by the reaction of 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde with hydrazines (hydrazine hydrate, phenyl-, 1,1-diphenyl-, and (diphenylmethylene)hydrazines, acetyl and benzoyl hydrazides) or by the reaction of 3,5-di-tert-butyl-6-(hydrazonomethyl)catechol with a carbonyl compound (the reaction with 4-N,N-dimethylaminobenzaldehyde). The X-ray diffraction analysis and IR, UV, and NMR spectroscopic studies showed that these compounds exist in the catecholic form both in solution and the crystalline state.     

Electrophilic Substitution of Hydrogen in Betulin and Diacetylbetulin

Betulin and diacetylbetulin, which can be regarded as sterically hindered alkenes, reacted with N-chloro-, N-bromo-, and N-iodosuccinimides to give products of allylic and vinylic substitution in quantitative overall yield. The contribution of allylic substitution increases in the series Cl < Br < I. Quantum chemical simulation of the reactions of diacetylbetulin with N-halosuccinimides showed that, regardless of the electrophile power, all reactions involve open-chain carbocationic intermediates. The direction of deprotonation of the latter with formation of allylic or vinylic substitution products is determined by preferential orientation of the vacant orbital and C–Hlg bond.     

Mannich Condensation of 3,3,5-Trimethylcyclohexanone and Its Oxime

Mannich condensation of 3,3,5-trimethylcyclohexanone with paraformaldehyde and dimethylamine or benzylamine hydrochloride involves both activated methylene group in the initial ketone to give compounds with equatorial aminomethyl substituent. The major isomer is that formed by addition at the less sterically hindered carbon atom. Likewise, Mannich condensation of the E and Z isomers of 3,3,5-trimethylcyclohexanone oxime react at both methylene groups, and the addition of aminomethyl fragment occurs preferentially at that methylene group which is located more closely to the oxime hydroxy group.     

Activated sterically strained C=N bond in <Emphasis Type="Italic">N</Emphasis>-substituted <Emphasis Type="Italic">p</Emphasis>-quinone mono- and diimines: XV. Synthesis,structure, and reactions with alcohols of <Emphasis Type="Italic">N</Emphasis>-carbamoyl-1,4-benzoquinone imines

The reaction of 4-aminophenols with N-nitrourea or with sodium cyanate in acetic acid gave the corresponding 4-ureidophenols which were oxidized to N-carbamoyl-1,4-benzoquinone imines, substituted N-(4-oxocyclohexa-2,5-dien-1-ylidene)ureas. N-(2,6-Dimethyl-4-oxocyclohexa-2,5-dien-1-ylidene)urea possessing activated sterically strained C=N bond reacted with alcohols to afford N-(1-alkoxy-2,6-dimethyl-4-oxocyclohexa-2,5-dienyl)ureas.     

3,5-Di-<Emphasis Type="Italic">tert</Emphasis>-butyl-1,2-benzoquinone in the synthesis of quinolino[4,5-<Emphasis Type="Italic">bc</Emphasis>][1,5]benzoxazepines,aminophenols, and phenoxazines

Reaction of 3,5-di-tert-butyl-1,2-benzoquinone with 5-amino-4-chloroquinolines gave derivatives of a new fused heterocyclic system, substituted quinolino[4,5-bc][1,5]benzoxazepines. The molecular structure of 9,11-di-tert-butyl-2,4,6-trimethyl-7H-quinolino[4,5-bc][1,5]benzoxazepine was determined by X-ray analysis. 3,5-Di-tert-butyl-1,2-benzoquinone reacted with o-nitro-, o-acyl-, and o-methoxycarbonylanilines and some amino-substituted nitrogen-containing heterocycles to form the corresponding sterically hindered N-aryl-(hetaryl)-o-aminophenols. Di-tert-butyl-substituted phenoxazines were obtained as a result of thermal cyclization of intermediately formed quinone imines.     

Template Assembling of the Pentadentate Redox-Active Ligand in the Coordination Sphere of Tin(IV)

Heptacoordinated tin complexes with pentadentate redox-active ligands containing the diiminopyridine fragment combined with two sterically hindered phenolate coordination centers, LSn-Cl₂ and L'SnCl₂ (L and L' are dianions of deprotonated 2,6-bis[2,4-di-tert-butyl-6-(methylidenylamino) phenol]pyridine and 2,6-bis[2,4-di-tert-butyl-6-(ethylidenylamino)phenol]pyridine, respectively), are synthesized. The molecular and electronic structures of the synthesized compounds were studied by X-ray diffraction analysis (for complex I, CIF file CCDC no. 1557838), a set of spectral methods, and quantum-chemical calculations. The redox properties of the obtained complexes are characterized by cyclic voltammetry.     

Polysubstituted Ionol Derivatives as Inhibitors of Lipid Peroxidation

Polysubstituted derivatives of sterically hindered phenol were found to reduce accumulation of hydroperoxides in the lipid extract from fish feed after 8-week incubation. Feeding of juvenile Russian sturgeon with fish food containing these compounds showed no negative effect on hydrobionts. Both in vivo and in vitro experiments revealed inhibition of hepatic lipid oxidation in juvenile Russian sturgeon in the presence of new bis-pyrrolidine derivatives of 2,6-di-tert-butylphenol. A reliable positive correlation was observed between the concentration of hydroperoxides in the lipid extract from fish feed and accumulation level of secondary enzymatic oxidation products of hepatic lipids in hydrobionts.     

Isatin Derivatives Containing Sterically Hindered Phenolic Fragment and Water-Soluble Acyl Hydrazones on Their Basis: Synthesis and Antimicrobial Activity

Condensation reactions of isatin derivatives with 3,5-di(tert-butyl)-4-hydroxybenzyl acetate and the Girard’s reagent T has afforded a series of novel water-soluble isatin-3-acyl hydrazones containing a sterically hindered phenolic fragment in position 1 of the heterocycle; antimicrobial activity of the products has been estimated. It has been shown that the isatin derivatives with bromine or methoxy substituent in the benzo fragment as well as the acyl hydrazones containing 5-methyl or 5-ethyl group are the most active against Staphylococcus aureus and Bacillus cereus.     

Photolysis of <Emphasis Type="Italic">meta</Emphasis>-azidophenol in solutions

The photolysis of meta-azidophenol in various organic solvents and aqueous solutions is studied by IR spectroscopy, electronic absorption spectroscopy, thin-layer chromatography (TLC), and analytical spot-test reactions. The polymeric derivatives of hydroxylamine are formed in organic solvents (benzene, chloroform, acetonitrile) via the interaction of nitrene with the phenol group of a neighboring m-azidophenol molecule. N-(meta-Hydroxyphenyl)hydroxylamine,—the product of the nitrene reaction with water, is formed in ethanol and aqueous solutions.     

α-Hydroxy- and (α-acyloxyimino)benzylphosphonates

N-Hydroxyfluorobenzimidoylphosphonates and their O-acyl derivatives are synthesized. Reaction of phosphorylated oximes with sulfinyl chloride proceeds with rearrangement and leads to synthetically prospective N-sulfonylimidoylphosphonates. By the method of ¹⁹F NMR are revealed values of σ-constants of N-hydroxy- and N-acyloxy substituted imidoylphosphonate groups.     

Alkylation of 2-(methylsulfanyl)-6-polyfluoroalkylpyrimidin-4(3<Emphasis Type="Italic">H</Emphasis>)-ones with haloalkanes

The alkylation of ambident anions of 2-(methylsulfanyl)-6-(polyfluoroalkyl)pyrimidin-4(3H)-ones with 4-bromobutyl acetate leads to concurrent formation of O- and N-(4-acetoxybutyl) derivatives. Polar aprotic solvents favor formation of the O-isomer, and weakly polar dioxane favors N-alkylation. The reaction of 2-(methylsulfanyl)-6-(trifluoromethyl)pyrimidin-4(3H)-one with an equimolar amount of 1,2-dibromoethane in polar acetonitrile gives a mixture of N,N-, O,O-, and N,O-bridged bis-pyrimidines, as well as N- and O-[2-(methylsulfanyl)ethyl] derivatives, whereas in the presence of 10 equiv of 1,2-dibromoethane the N,O-isomer is formed as the only product. The reaction in weakly polar tetrahydrofuran yields N,N- and N,O-bispyrimidines.     

Cycloaminomethylation of dihydric phenols catalyzed by <Emphasis Type="Italic">d</Emphasis>- and <Emphasis Type="Italic">f</Emphasis>-metal compounds

An efficient method has been developed for the synthesis of 7,16,25-triaryl-7,8,16,17,25,26-hexahydro-6H,15H,24H-tribenzo[f,m,t][1,5,8,12,15,19,3,10,17]hexaoxatriazacyclohenicosines, 3,8-diaryl-2,3,4,7,8,9-hexahydrobenzo[1,2-e:4,3-e′]bis[1,3]oxazines, 3,9-bis(chlorophenyl)-3,4,9,10-tetrahydro-2H,8H-benzo[1,2-e:3,4-e′]bis[1,3]oxazines, and 2,9-bis(chlorophenyl)-1,2,3,8,9,10-hexahydrobenzo[1,2-e:6,5-e′]bis-[1,3]oxazines via cycloaminomethylation of pyrocatechol, resorcinol, and hydroquinone with N,N-bis(methoxymethyl) anilines in the presence of samarium catalysts.     

Halocyclization of products of allyl isothiocyanate addition to acyclic methylene active compounds

Products of allyl isothiocyanate addition to methylene active compounds, salt-like N-allyl-N,S-ketenacetals or N-allylthioamides, react with iodine, bromine or N-bromosuccinimide with the formation of derivatives of 2-ylidene-5-halomethylthiazolidines. A dependence was found of isomeric composition of obtained thiazolidines on the solvent nature.     

Alternative synthesis of alverine

An efficient synthesis of alverine via iron-catalyzed double cross-coupling of (2E)-3-chloro-N-[(2E)-3-chloroprop-2-en-1-yl]-N-ethylprop-2-en-1-amine with phenylmagnesium bromide is described.     

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (k_H) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln k_H on the difference of the reciprocals of optical and static solvent permitivities (1/ε _∞–1/ε₀) is stepwise with a break point corresponding to CH₂Cl₂. A similar relationship lnk_H = f(1/ε _∞–1/ε₀) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH₂Cl₂, it has been found that the dependence of k_H on the free energy of electron transfer (ΔG_e) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔG_e = 0.11 eV.     

Reactions of dialkyl (3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-oxocyclohex-2,5-dienylidenemethyl)phosphonates with alcohols and some transformations of the adducts

Reactions of dialkyl [(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)methyl]phosphonates with butyl, benzyl and propargyl alcohols in the presence of catalytic amounts of trifluoromethanesulfonic acid resulted in the formation of nucleophilic 1,6-addition products. Azide-alkyne cycloaddition reaction of dimethyl (3,5-di-tert-butyl-4-hydroxyphenyl)(prop-2-ynyloxy)methylphosphonate with benzyl azide and 1,3-bis-(2-azidoethoxy)benzene in the presence of copper sulfate and sodium ascorbate afforded 1,2,3-triazoles with sterically hindered phenol fragments.     

Graphene oxide promoted synthesis of <Emphasis Type="Italic">p</Emphasis>-phenylenediamine antioxidants

Three p-phenylenediamine antioxidants (p-phenylenediamine-N,N,N′,N′-tetrapropionic acid tetramethyl ester, p-phenylenediamine-N,N,N′-tripropionic acid trimethyl ester, and p-phenylenediamine-N, N′-dipropionic acid dimethyl ester) were successfully synthesized via atom-economic aza-Michael addition of pphenylenediamine to methyl acrylate p-romoted by graphene oxide in water. The synthesized compounds were characterized by NMR, ESI-MS spectra, and elemental analyses. The effects of the solvent and graphene oxide on the reaction were investigated.     

Electrochemical transformations and anti/prooxidant activity of sterically hindered <Emphasis Type="Italic">o</Emphasis>-benzoquinones

The electrochemical properties of a series of sterically hindered o-benzoquinones in aprotic solvents were examined. The reaction of O₂ and KO₂ with o-benzoquinones and electrogenerated o-semiquinone radical anions was studied. The formation of o-semiquinone radical anions in the reactions of KO₂ with the studied o-quinones was detected using UV-visible and ESR spectroscopy. The influence of the test compounds on lipid peroxidation was considered at the molecular and tissue levels in vitro. In the most cases, o-quinones exhibit antioxidant activity, which varies depending on the type of lipid substrate.