Cobalt and manganese complexes with redox-active ligands in polymerization of acrylonitrile and methyl methacrylate

The influence of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinonato]cobalt(ii) and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzosemiquinonato]-[4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate]manganese(iii) on polymerization of methyl methacrylate and acrylonitrile in the presence of azobisisobutyronitrile (as a traditional radical initiator) and alkyl halides (used for initiation of controlled atom transfer radical polymerization process) was studied. The effect of the nature of the activating agents (amines) and the temperature conditions on the overall polymerization rate of the indicated monomers, as well as molecular weight characteristics of the synthesized polymers, were analyzed. The optimal conditions for the synthesis of polyacrylonitrile and poly(methyl methacrylate) with a relatively narrow molecular weight distribution were selected.     

Functionalization of sterically hindered catechol and <Emphasis Type="Italic">o</Emphasis>-benzoquinone with 2,2,6,6-tetramethylpiperidine 1-oxyl

Sterically hindered 4,6-di-tert-butyl-3-formylcatechol and 3,6-di-tert-butyl-o-benzoquinone react with 4-amino-2,2,6,6-tetramethylpiperidine 1-oxyl to give new chelate ligands of the o-quinone type bearing a 2,2,6,6-tetramethylpiperidine 1-oxyl neutral radical moiety. Structures of the synthesized compounds were established by ESR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray diffraction analysis.     

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.     

Polymerization of methyl methacrylate in the presence of <Emphasis Type="Italic">o</Emphasis>-iminoquinones: Reversible and irreversible inhibition

New regulators of radical polymerization of methyl methacrylate based on N-(aryl)-o-iminoquinones of various structures are proposed. It is shown that samples of polymethylmethacrylate with the participation of N-(aryl)-o-iminobenzoquinones could be used as macroinitiators of polymerization. Optimal conditions to synthesize polymers in the presence of o-iminobenzoquinones are determined, which make it possible to obtain polymethylmethacrylate with a polydispersity coefficient of no more than 1.5 on deep conversions during bulk polymerization.     

Syntheses,structures, and electrochemical properties of the tin(IV) complexes based on the 2-hydroxy-4-<Emphasis Type="Italic">N</Emphasis>-(phenyl)-3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">p</Emphasis>-iminobenzoquinone ligand

A series of the new tin(IV) complexes based on the 2-hydroxy-4-N-(phenyl)-3,6-di-tert-butyl-p-iminobenzoquinone ligand (LH) containing various hydrocarbon substituents R at the metal atom (R = Me, Et, ⁿ Bu, ^t Bu, and Ph) is synthesized. The structures of the synthesized compounds were determined by elemental analysis, IR spectroscopy, and ¹H and ¹¹⁹Sn NMR spectroscopy. The X-ray diffraction analyses are carried out for the LSnPh³ (I) and L²SnEt² (IV) complexes (CIF files CCDC no. 1557840 (I) and 1557839 (IV)). The main electrochemical characteristics in a solution are obtained for the whole series by cyclic voltammetry.     

New tin(<Emphasis Type="SmallCaps">iv</Emphasis>) <Emphasis Type="Italic">o</Emphasis>-iminosemiquinone complexes

New tin(iv) mono- and bis-o-iminosemiquinone complexes were obtained by the exchange reaction of radical anion lithium salt of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-imino-benzoquinone with tin(iv) organochlorides. The compounds synthesized were characterized by EPR spectroscopy and X-ray diffraction analysis. Substituents on the tin atom were found to affect stability of paramagnetic metal derivatives formed.     

Heterospin biradicals based on new piperidineoxyl-substituted 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

A nucleophilic addition reaction of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (OH-TEMPO) to 3,6-di-tert-butyl-o-benzoquinone was used to obtain a new sterically hindered o-benzoquinone (1) containing 2,2,6,6-tetramethylpiperidineoxyl functional group, which was characterized by IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction. A one-electron reduction of 1 with potassium and thallium is an efficient method for the generation of earlier unknown heterospin biradicals 5a and 5b, respectively, containing nitroxide and o-semiquinone radical centers. Analysis of the hyperfine structure of the ESR spectra of biradicals 5a and 5b in solution showed that they belong to the group of heterospin biradicals with strong (J >> a) and fast exchange interaction between the radical centers.     

Synthesis and membrane-protective activity of 2,6-diisobornylphenol derivatives with <Emphasis Type="Italic">N</Emphasis>- and <Emphasis Type="Italic">O</Emphasis>-containing fragments at position 4

Two series of new amide derivatives containing 2,6-diisobornylphenol moiety were synthesized based on 3,5-diisobornyl-4-hydroxybenzoic acid and 4-butylaminomethyl-2,6-diisobornylphenol. Toxicity, membrane-protective (MP) and antioxidant (AO) activity of the obtained compounds were evaluated using red blood cells of laboratory mice as the test object. The tests demonstrated the absence of hemolytic activity for all the synthesized derivatives and the presence of high MP and AO activity under conditions of acute H₂O₂-induced oxidative stress for (3,5-diisobornyl-4-hydroxyphenyl)(morpholino)methanone and N-n-butyl-N-(3,5-diisobornyl-4-hydroxybenzyl)acetamide. A comparison of the data of the newly obtained compounds and those of described earlier 2,6-diisobornylphenol derivatives with N- and O-containing fragments at position 4 (alkoxymethyl, carboxy, and aminomethyl derivatives) led to a conclusion that the most promising for further studies of pharmacological activity are compounds containing methoxycarbonyl, methoxymethyl, ethoxymethyl, morpholinomethyl, di-n-butylaminomethyl, (azepan-1-yl)methyl, or N-acetyl-N-alkylaminomethyl function, which provide low toxicity and high MP and AO activity.     

Transformations of 3(4)-amino-4(3)-(<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">NNO</Emphasis>-azoxy)furoxans in the annulation reactions into 1,2,3,4-tetrazine 1,3-dioxides

Reactions of 3(4)-amino-4(3)-(tert-butyl-NNO-azoxy)furoxans with excess (NO₂)₂S₂O₇ or with a HNO₃—H₂SO₄—Ac₂O mixture unexpectedly produce [1,2,5]oxadiazolo[3,4-e]?[1,2,3,4]tetrazine 4,6-di-N-oxide (furazanotetrazine dioxide) and products of amino group oxidation (mainly to the corresponding azofuroxans) instead of the expected furoxanotetrazine dioxides. In some cases, individual (Z)-3,3´-((E)-diazene-1,2-diyl)-bis-((Z)-2-tert-butyl-1-oxidodiazenyl)-1,2,5-oxadiazole 2-oxide) was isolated. Formation of furazanotetrazine dioxides was observed in the reaction of 3-nitramino-4-(tert-butyl-NNO-azoxy)furoxan sodium salt with H₂SO₄ in Ac₂O. Quantum chemical calculation at the DFT/B3LYP/6-31G(d) level of theory was used to estimate several aspects of the reactivity of 3(4)-nitramino-4(3)-(tert-butyl-NNO-azoxy)furoxans in a comparison with 3(4)-nitramino-4(3)-phenylfuroxans and the possible causes of the observed transformations were revealed.     

Reactions of 3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-1,2-benzoquinone with mercapto carboxylic acids

Heating of an equimolar mixture of 3,5-di-tert-butyl-1,2-benzoquinone with thiosalicylic acid led to 2-[(4,6-di-tert-butyl-2,3-dihydroxyphenyl)thio]benzoic acid. In the case of β-mercaptopropionic acid, 2-[(4,6-di-tert-butyl-2,3-dihydroxyphenyl)thio]propionic acid was formed, which upon reflux in Ac2O was converted to 6,8-di-tert-butyl-9-hydroxy-3,4-dihydro-2H-1,5benzoxathiepin-2-one.     

Photoreduction of <Emphasis Type="Italic">o</Emphasis>-benzoquinone moiety in mono- and poly(quinone methacrylate) and on the surface of polymer matrix pores

The kinetics of photoreduction under the action of visible light of the 3,6-di-tert-butyl-o-benzoquinone moiety in methacrylic monomer, polymer, and in the graft layer on the surface of pores in the presence of different N,N-dimethylanilines has been studied. The reaction is accelerated with the increasing electron-donating ability of the amine. In the presence of N,N-dimethylaniline at 50-fold molar excess of the amine, the photoreduction in the porous polymer occurs three and four times faster than in the monomer and the polymer, respectively.     

Reduction and diazotization of ethyl 7-amino-3-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-oxo-4,6-dihydropyrazolo[5,1-<Emphasis Type="Italic">c</Emphasis>][1,2,4]triazine-8-carboxylate

The ester group in ethyl 7-amino-3-tert-butyl-4-oxo-4,6-dihydropyrazolo[5,1-c][1,2,4]triazine-8-carboxylate was converted for the first time to methyl by the action of lithium tetrahydridoborate in the presence of boron trifluoride–diethyl ether complex. This reaction has almost no analogies among other classes of organic compounds. New difficultly accessible 7-chloro and 7-azido derivatives were synthesized via diazotization of the reduction product, and treatment of the latter with acetic anhydride afforded the exhaustively acetylated derivative. Diazotization of ethyl 7-amino-3-tert-butyl-4-oxo-4,6-dihydropyrazolo-[5,1-c][1,2,4]triazine-8-carboxylate, followed by reaction with sodium azide, gave the corresponding azide, and the product of azo coupling with ethyl acetoacetate failed to undergo intramolecular cyclization to tricyclic pyrazolo[3,2-c: 5,1-c′]bis[1,2,4]triazine system.     

Photochemistry of <Emphasis Type="Italic">N</Emphasis>-substituted salicylic acid amides

The products of photolysis of N-substituted salicylic acid amides, viz., 2-hydroxy-3-tert-butyl-5-ethylbenzoic acid N-(4-hydroxy-3,5-di-tert-butylphenyl)amide (1) and 2-hydroxybenzoic acid N-[3-(4-hydroxy-3,5-di-tert-butylphenyl)prop-1-yl]amide (2), in heptane were studied by optical spectroscopy and stationary and nanosecond laser photolysis (Nd: YAG laser, 355 nm). It was shown by the method of partial deuteration of amides 1 and 2 that they exist in both the unbound state and as complexes with intraand intermolecular hydrogen bond. Amides 1 and 2 are subjected to photolysis, which results in the formation of a triplet state and phenoxyl radicals RO? presumably due to the absorption of the second photon by the excited singlet state. The formation of radical products due to N–H bond ionization was not observed. The main channel of decay of the triplet state and radicals RO? is triplet–triplet annihilation and recombination (k _r ≈ 2.3?10⁸ L mol^–1 s^–1), respectively. The UV irradiation of compounds 1 and 2 leads to the excitation of the amide groups, and no formation of radical products due to N–H bond ionization was observed.     

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.     

Reactivity of double bonds of substituted <Emphasis Type="Italic">p</Emphasis>-(methacryloyloxy)-<Emphasis Type="Italic">N</Emphasis>-phenylmaleimides in free-radical polymerization

The thermoinduced free-radical polymerization of model systems, namely, methyl methacrylate and N-phenylmaleimide derivatives, has been studied. It has been shown that, in the polymerization of p-(methacryloyloxy)-N-phenylmaleimides, the yield of the polymer and its molecular-mass distribution (mono-or bimodal) and polydispersity depend on the degree of substitution and the nature of a substituent in a double bond of a maleimide fragment. The structure of the maleimide fragment, in turn, determines its capability to copolymerize with the methacryloyl group of a bifunctional monomer as well as the occurrence of chain-transfer and termination reactions.     

Interaction of 9-substituted anthracenes with oxidation systems <Emphasis Type="Italic">tert</Emphasis>-butylhydroperoxide-metal <Emphasis Type="Italic">tert</Emphasis>-butoxide

9-R-Anthracenes (R = Me, Ph) are effective acceptors of peroxyl and metalalkoxyl radicals in the systems tert-butylhydroperoxide-metal tert-butoxide (M = Al, V, Cr; C₆H₆, 20°C). Isolation of 9-R-9,10-dihydro-9,10-di-tert-butylperoxyanthracenes, 10-R-10-tert-butylperoxy-9-anthrones as major products reliably confirms the formation of tert-butylperoxy radicals and can be used for quantitative assessment of their content.     

Chromium(III) and indium(III) 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-semiquinolate complexes as redox mediators of hydrogen sulfide oxidation in reactions with cycloalkanes

The electrochemical oxidation of the chromium(III) and indium(III) complexes with 3,6-di-tert-butyl-o-semiquinolate leading to the formation of active monocationic species is studied by cyclic voltammetry. The reactions of the latter with hydrogen sulfide generate the radical cation of H₂S, whose fragmentation affords the proton and thiyl radical. These complexes are proposed for the first time as redox mediators for the one-pot thiolation of inert cycloalkanes C₆–C₈, which decreases the activation energy of hydrogen sulfide compared to that for direct electrochemical oxidation. The major products of cycloalkane functionalization involving H₂S are thiols and organic di- and trisulfides. The yield of the synthesized compounds depends on the type of the mediator: the chromium(III) complex exhibits the highest efficiency in the electrocatalytic transformations.     

Study of the mechanism of redox transformations of sterically hindered <Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminoquinones

The mechanisms of redox transformations of sterically hindered [¹IBQ]-[³IBQ], 9,10-iminophenanthraquinone [⁴IFQ], and o-aminophenol [⁵AP] have been studied by cyclic voltammetry. It has been shown that the reduction process in tetrahydrofuran consists of two consecutive reversible steps leading to the formation of a radical anion and a dianion. In the case of acetonitrile, only the first redox process is detected, which involves the steps of protonation and electron addition resulting in the formation of a monoanion. Quantum-chemical calculations indicate a lower degree of participation of the six-membered nonaromatic carbon ring in the spin density delocalization in the o-iminosemiquinonate radical anions as compared to o-benzosemiquinonate radical anions. The oxidation of iminoquinones results in the formation of an unstable radical cation, which undergoes further chemical transformations. An increase in the acidity of a medium leads to the formation of protonated forms with the reduction potential being shifted anodically. The introduction of screening groups makes it possible to suppress side reactions of hydrolysis and cyclization of oxidized o-aminophenol [⁵AP] forms. Therefore, the major product of complete electrolysis is o-iminobenzoquinone [²IBQ].     

Specific Features of <Emphasis Type="Italic">N</Emphasis>-Morpholinoethyl Methacrylate Synthesis

Methods for synthesis of N-morpholinoethyl methacrylate were compared. It was shown that the monomer produced by acylation of N-morpholinoethanol with methacrylic acid anhydride or methacryloyl chloride spontaneously polymerizes in storage. The possible reasons for the spontaneous polymerization of N-morpholinoethyl methacrylate produced by the acylation method were considered. The conditions in which a stable-in-storage monomer can be obtained in 86–88% yield by the method of re-esterification of methyl methacrylate with N-morpholinoethanol were determined.     

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.