Uncontrolled pseudoliving free-radical polymerization of methyl methacrylate in the presence of butyl-<Emphasis Type="Italic">p</Emphasis>-benzoquinones

Polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate in the presence of tri-n-butylboron and butyl-p-benzoquinone or 2,5-di-tert-butyl-p-benzoquinone occurred with no induction period. The yields and molecular masses of the polymers linearly increased with an increase in the conversion degree, which suggests the free-radical mechanism of “living” chain polymerization. The poly(methyl methacrylate) macrochains of the prepolymers contained sterically hindered aromatic structures with labile C-O bonds. The latter underwent reversible homolytic dissociation to give a growth-inducing radical and sterically hindered aryloxyls. Pseudoliving free-radical polymerization in the presence of the prepolymer (macroinitiator) was studied at 45, 60, and 80 °C. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1119–1122, June, 2007.     

Synthesis of magnesium catecholate and <Emphasis Type="Italic">o</Emphasis>-semiquinone complexes by oxidation of the metal with 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

Oxidation of amalgamated magnesium metal with 3,6-di-tert-butyl-o-benzoquinone (1) in different aprotic organic solvents afforded magnesium catecholate and bis-o-semiquinolate complexes. The catecholate derivatives of magnesium CatMgL₂ (Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, L = THF or Py) were synthesized in high yields in pyridine and tetrahydrofuran, respectively. The reactions in diethyl ether or dimethoxyethane produced hexacoordinated metal bis-o-semiquinolates SQ₂MgL_n (SQ is the 3,6-di-tert-butyl-o-benzoquinone radical anion, L = Et₂O, n = 2; L = DME, n = 1). The reaction with the use of toluene as the solvent gave a magnesium bis-o-semiquinolate complex containing the coordinated unreduced o-quinone molecule. The molecular structures of the [CatMgPy₂]₂ and SQ₂Mg·DME complexes were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–98, January, 2007.     

Polymerization of methyl methacrylate in the presence of 2,5-di-tert-butyl-p-benzoquinone

Polymerization of methyl methacrylate in the presence of 2,5-di-tert-butyl-p-benzoquinone is a combination of two processes: inhibited and controlled radical polymerization. The adduct of chain propagation radicals and p-quinone formed due to the inhibited polymerization is a macroinitiator of controlled radical polymerization. The fraction of the pseudo-living process is determined by the concentration of p-quinone in the starting polymerized composition. Post-polymerization proceeds via the reversible inhibition mechanism.

     

Alkylation of 2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylphenol with methyl acrylate catalyzed by potassium 2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylphenoxide

The kinetics of catalytic alkylation of 2,6-di-tert-butylphenol (ArOH) with methyl acrylate (MA) in the presence of potassium 2,6-di-tert-butylphenoxide (ArOK) depends on the method for the preparation of ArOK. The reaction of ArOH with KOH at temperatures > 180 °C affords monomeric ArOK, whose properties differ from those in the case of potassium 2,6-di-tert-butylphenoxide synthesized by the earlier methods. The regularities of ArOH alkylation depend on the ArOK concentration, the ArOH: MA ratio, and the effect of microadditives of polar solvents. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1971–1974, October, 2007.     

The reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide

Reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide in aprotic solvents leads to the generation of semiquinone (SQ^.H), alkylperoxy (ROO^.), and alkyloxy radicals. The reaction of SQ^.H and ROO^. produces 2,5-di-tert-butyl-6-hydroxy-1,4-benzoquinone, 3,6-di-tert-butyl-1-oxacyclohepta-3,5-diene-2,7-dione, and 2,5-di-tert-butyl-3,6-dihydroxy-1,4-benzoquinone. The radical generated from solvent attacks SQ^.H at position 4 with C−C bond formation. 4-Benzyl-2,5-di-tert-butyl-6-hydroxycyclohexa-2,5-diene-1-dione produced in this way is transformed into 4-benzyl-3,6-di-tert-butyl-1,2-benzoquinone under the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 943–946, May, 1999.     

<Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminobenzoquinones as novel regulators of radical polymerization

The effect of a number of quinoid compounds on methyl methacrylate polymerization initiated by azo-bis(isobutyronitrile) has been studied. It has been revealed that N-aryl-o-iminobenzoquinones, in contrast to o-benzoquinones, can provide radical polymerization of methyl methacrylate in controllable mode. The efficiency of the compounds as chain growth regulators has been found to depend on their composition and reaction conditions. It has been established that 4,6-di-tert-butyl-N-(2,6-diethylphenyl)-o-iminobenzoquinone and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone under radical initiation conditions provide the synthesis of poly(methyl methacrylate) with wide-range molecular weight, retaining polydispersity indices about ~1.4–1.8 up to deep conversions.     

Synthesis of new 1<Emphasis Type="Italic">H</Emphasis>-pyridazine derivatives <Emphasis Type="Italic">peri</Emphasis>-annelated with acenaphthene and acenaphthylene

The reaction of 6-acetyl-5-hydroxyacenaphthene with methylhydrazine afforded 1,3-dimethyl-1H-6,7-dihydroacenaphtho[5,6-de]pyridazine. Its dehydrogenation with chloranil gave 1,3-dimethyl-1H-acenaphtho[5,6-de]pyridazine, which is a heteroaromatic compound with an essentially new topology of the ρsystem. The reaction of 3-methyl-1H-6,7-dihydroacenaphtho[5,6-de]pyridazine with 3,5-di-tert-butyl-1,2-benzoquinone yielded a dimer containing the acenaphthene and acenaphthylene moieties of peri-annelated 1H-1,2-diazines connected in positions 1′ and 9.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 777–780, March, 2005.     

Photo-induced interfacial electron transfer from CdSe quantum dots to surface-bound <Emphasis Type="Italic">p</Emphasis>-benzoquinone and anthraquinone

Here we report transient spectral red-shift and transient absorption enhancement of p-benzoquinone radical in the presence of CdSe quantum dots after 355 nm pulse laser excitation. The spectral shift was caused by surface-bound p-benzoquinone molecules while the transient absorption increase was due to interfacial electron transfer from CdSe quantum dots to p-benzoquinone molecules. In contrast, spectral shift and absorption increase were much less significant for anthraquinone in the presence of CdSe quantum dots due to their weak adsorption abilities.     

5-{5-(bicyclo[2.2.1]hept-2-enyl)hydroxymethyl}-3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl<Emphasis Type="Italic">o</Emphasis>-benzoquinone and related polymers. Synthesis and some properties

A norbornene-containing ortho-quinone, 5-{5-(bicyclo[2.2.1]hept-2-enyl)hydroxymethyl)-3,6-ditert-butyl-o-benzoquinone, was synthesized by the nucleophilic addition of 5-(hydroxymethyl)bicyclo[2.2.1] hept-2-ene to 3,6-di-tert-butyl-o-benzoquinone. The structure of the compound was established by the X-ray analysis. The monomer obtained undergoes metathesis polymerization in the presence of Grubbs catalyst of the third generation with the formation of polynorbornene containing quinone fragments in the side chains.     

<Emphasis Type="Italic">o</Emphasis>-Semiquinone metal complexes as derivatives of sterically hindered di-<Emphasis Type="Italic">o</Emphasis>-quinone

ESR spectroscopy was used to study a series of mono- and binuclear o-semiquinone metal complexes, viz., derivatives of sterically hindered di-o-quinone 1,2-bis(2,5-di-tert-butylcyclohexadiene-1,5-dion-3,4-yl)ethane (1). Hindered rotation was found in the o-semiquinone moiety of the generated complexes. Magnetochemical measurements for polymeric bis(o-semiquinolate)copper(II) based on di-o-quinone 1 showed two antiferromagnetic channels of interaction between the paramagnetic centers. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1580–1584, July, 2005.     

Chlorination of 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-1,2-benzoquinone in two-phase catalytic system

Chlorination of 3,6-di-tert-butyl-1,2-benzoquinone in a two-phase catalytic system (CH₂Cl₂, HCl- H₂O, H₂O₂, Bu₄NCl) led to halogen addition at the C=C bond, and subsequent dehydrochlorination of the adduct gave 3,6-di-tert-butyl-4-chloro-1,2-benzoquinone. Chlorination of the latter afforded 3,6-di-tert-butyl-4,5-dichloro-1,2-benzoquinone.     

Photocrosslinking of polymers bearing epoxy or epithio groups by quinones in the solid state

Photocrosslinking of poly(glycidyl methacrylate) (PGMA) and a copolymer of 2,3-epithiopropyl methacrylate and methyl methacrylate [P(ETMA-co-MMA)] was studied in the solid state in the presence of various quinones. The efficiency of photocrosslinking was strongly dependent upon the structures of quinones and the kinds of polymers. For example, the alkyl-substituted quinones such as 2-ethyl-p-benzoquinone (EQ), 2-tert-butyl-p-benzoquinone (tBQ) and 2,5-di-tert-butyl-p-benzoquinone (2,5-dtBQ) did not induce photocrosslinking of poly(methyl methacrylate) (PMMA), whereas they acted as efficient photocrosslinking agents in PGMA and P(ETMA-co-MMA). The formation of charge transfer complexes did not play a principal role in this effective photocrosslinking, because the order of the photocrosslinking efficiency [EQ > tBQ > 2,5-dtBQ > p-benzoquinone (Q)] was not in agreement with that of the magnitude of the electron affinities of quinones, i.e., Q > EQ > tBQ > 2,5-dtBQ. Photopolymerization of propylene sulfide (PS) in the presence of tBQ or Q was also investigated. The presence of tBQ induced polymerization of PS upon UV irradiation. From these results, it was deduced that the photocrosslinking of P(ETMA-co-MMA) film containing tBQ proceeds via a cationic polymerization of epithio groups. A similar mechanism should be applicable to the photocrosslinking of PGMA film containing tBQ.     

Functionalization of sterically hindered <Emphasis Type="Italic">o</Emphasis>-benzoquinones: amino-substituted 3,6-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-<Emphasis Type="Italic">o</Emphasis>-benzoquinones

New sterically hindered functionalized o-quinones were synthesized by the 1,4-nucleophilic addition of secondary cyclic amines to 3,6-di(tert-butyl)-o-benzoquinone. The ability of these o-quinones to form o-semiquinone complexes with transition and main-group metals was studied by ESR spectroscopy in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1786–1793, September, 2007.     

Formation and structures of 2,5-di-<Emphasis Type="Italic">tert</Emphasis>-butylcyclopentadienone dimers

The structures of dimers formed from 2,5-di-tert-butylcyclopentadienone in the reaction with alkaline metals and in the Diels-Alder reaction were studied. A photochemical rearrangement with ring contraction was found for the second dimer. Spectral features of the dimers related to steric hindrance were studied by 1D and 2D NMR procedures.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2179–2183, October, 2004.     

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.     

Interaction of functionally-substituted 4-alkyl-2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylphenols with hydrohalic acids

Reactions of 4-alkyl-2,6-di-tert-butylphenols containing OH, SH, COOH, and COOMe groups in their para substituents with hydrogen chloride and hydrohalic acids were studied. One-step transformations of 2,6-di-tert-butyl-4-(ω-hydroxyalkyl)phenols to the corresponding 4-(ω-halogenoalkyl)phenols, as well as of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and its esters to phloretic acid were proposed. 4-(3-Mercaptopropyl)phenol upon heating with conc. HBr undergoes condensation to 3-(4-hydroxyphenyl)propyl 4-(3-mercaptopropyl)phenyl sulfide as the main product. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1078–1083, June, 2007.     

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.     

Oxidation of α-methylstyrene on an MCM-22 encapsulated (<Emphasis Type="Italic">R,R</Emphasis>)-(−)-<Emphasis Type="Italic">N,N′</Emphasis>-bis(3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) catalyst

(R, R)-(−)-N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) was encapsulated into MCM-22 using the zeolite synthesis method. The encapsulated catalyst proved to be active in the oxidation of α-methylstyrene with NaOCl with higher specific activity than the homogeneous catalyst. At the same time, this encapsulated catalyst was completely inactive in the hydrolytic kinetic resolution of racemic styrene oxide. This observation is in a good correlation with the assumption of the cooperative bimetallic mechanism proposed by Annis and Jacobsen.     

Kinetics of photolytic transformations of 4,4′-Bi(3-methyl-6-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone)

The quantum yields and apparant rate constants of the photolysis of 4,4′-bi(3-methyl-6-tert-butyl-o-benzoquinone) and of accumulation of its transformation products in hydrocarbon solutions under the action of light with λ 313 and 405 nm were determined. The probable scheme of photochemical reactions was suggested. Original Russian Text O.G. Mishchenko, S.V. Maslennikov, I.V. Spirina, N.O. Druzhkov, Yu.A. Kurskii, V.P. Maslennikov, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 12, pp. 1997–2001.     

Structure and intermolecular interactions of <Emphasis Type="Italic">N</Emphasis>-(3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-hydroxybenzyl)thioureas

The molecular and crystal structure and the hydrogen bonding in crystal and in solutions of N-phenyl-N-(3,5-di-tert-butyl-4-hydroxybenzyl)thiourea and N-(3,5-di-tert-butyl-4- hydroxybenzyl)thiourea were studied by single crystal X-ray diffraction and IR spectroscopy. The intermolecular interactions of these compounds are essentially different.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1864–1870.Original Russian Text Copyright © 2004 by Bukharov, Litvinov, Gubaidullin, Chernova, Shagidullin, Nugumanova, Mukmeneva.This revised version was published online in April 2005 with a corrected cover date.