Radical reactions involving esters of fumaric acid—I. Copolymerizations

¹⁴C-labelled samples of diethyl-, ethyl n-hexyl- and di-n-hexyl fumarates have been used in studies at 60° of their radical copolymerizations with styrene and with vinyl acetate. Changing the diluent from benzene to dimethylformamide in some of the copolymerizations had no effect on the compositions of the copolymers. Monomer reactivity ratios have been calculated for most of the systems; comparisons have been made of the reactivities of the fumarate esters towards the polyvinyl acetate radical.     

Radical transfer reactions in polymers

Free-radical transfer in polymers have been studied by pulse radiolysis and product analysis with the water-soluble polymers poly(vinyl alcohol), poly(acrylic acid), poly(methacrylic acid), polynucleotides and DNA. When OH radicals react with polymers the lifetime of the polymer radical thus created strongly depends on the number of radicals per polymer chain. Moreover, in negatively charged polymers the increased stiffness at high pH results in a remarkable increase of the lifetime of the radicals with respect to recombination. This allows a number of radical transfer reactions to occur (e.g. intramolecular H-transfer, β-fragmentation, depolymerization, reactions with additives).     

Radical reactions of epoxy esters induced by titanocene chloride

The reductive radical cyclizations of several epoxy esters have been achieved using titanocene chloride. The tether length from the initial radical to the carbonyl acceptor is the key of the reactions. We obtained products from radical cyclization onto carbonyl formate and products from formate and hydrogen elimination. The stereochemical outcome of the 5-exo radical cyclization of two diastereomers is reported. A radical cascade cyclization of an unsaturated epoxy formate is also described.     

Radical cascade reactions of unsaturated C–C bonds involving migration

During the past few years, with the rapid development of mild methods for the generation of radical species, great progress in radical cascade reactions of unsaturated C–C bonds has been made. Many radical cascade reactions involve functional groups migration, which leads structurally much more diverse, complex and valuable compounds not easily obtained through other methods. In this review, the recent achievements in unsaturated C–C bonds radical cascade reactions involving migration are summarized.     

Energy transfer processes involving ultraviolet stabilizers. Quenching of singlet oxygen

The role of electronically excited singlet (¹Δ_g) oxygen molecules in the photooxidation of polymers has received increased attention in recent years. Little information regarding the interaction of ultraviolet stabilizers with singlet oxygen is known, however. In this study, singlet oxygen was produced by a microwave discharge in a flow system and rate constants were obtained for quenching by ultraviolet stabilizers. It was found that some nickel chelate stabilizers are effective quenchers of singlet oxygen and their quenching behaviors can be correlated with ultraviolet stabilization effectiveness in thin polypropylene and polyethylene films. The best oxygen quenchers of those examined are nickel chelates with sulfur donor ligands.     

Catalytic transfer hydrogenation reactions of PEG-bound succinyl esters

Various substrates bound to polyethylene glycol (PEG) through succinyl ester linkages were cleaved under catalytic transfer hydrogenation conditions. The substrates with unsaturated functions also underwent hydrogenation. The protocol was found to be suitable for substrates having acid and base labile functional groups.     

Photochemistry of 1,3-cyclopentanediones. Oxetane formation involving both energy transfer and electron transfer processes

Photolysis of 2,2-dimethyl-1,3-cyclopentanedione in acetone resulted in oxetane formation in a two photon process involving energy transfer from triplet excited acetone and electron transfer from singlet excited acetone.     

Phosphate-phosphonate conversion: Nucleophilic displacement reactions involving phosphoric esters and methyllithium

The alkylation-metalation reaction of phosphoric esters depends on the way the lithium reagent has been prepared. With salt-containing methyllithium (LiBr or LiI), the alkylation is never complete. On the contrary, with salt-free methyllithium, the alkylation is completed at – 10°C. This reaction is performed independently of the substituents at the phosphoryl group.     

Activation of stable polymeric esters by using organo‐activated acyl transfer reactions

In this study, we succeeded in the in situ activation of nonactivated ester moieties embedded in polymer structures. Although poly(pentafluorophenyl methacrylate) (PPFPMA) can react with 2‐ethylhexylamine at 50 °C in the presence of proton scavenger such as NEt₃, such conditions were not suitable for poly(phenyl methacrylate) (PPhMA). Nevertheless, the combination of organo‐activating agents, namely 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and 1,2,4‐triazole (TZ) led to a facile conversion from ester to amide for PPhMA. The reaction between PPhMA and 2‐ethylhexylamine was conducted at 120 °C in the presence of one equivalent of TZ and three equivalents of DBU and yielded >99% ester conversion to afford corresponding polymethacrylamide derivatives as confirmed by FT‐IR and ¹H NMR measurements. In addition, poly(2,2,2‐trifluoroethyl methacrylate) (PTFEMA) and poly(methyl methacrylate) (PMMA) were also allowed to react with amines in the presence of the organo‐activating agents with dramatically increased conversions (>70%). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1353–1358     

Charge density analysis of some processes involving intramolecular hydrogen transfer

The variations in topology of the electron density along the reaction paths of the keto-enol tautomerism of acetaldehyde, the pinacol rearrangement of protonated 1,2-ethanediol, and the unimolecular decomposition of methanediol, were studied as examples of hydrogen transfer between, respectively, C?O, C?C, and O?O atoms. The evolution of atomic charges, determined using two different atomic partitionings (AIM and Hirshfeld), indicates that the main electronic charge transfer in keto-enol tautomerism takes place between the migrating hydrogen and the carbon of the carbonyl group. The topology of the electron density demonstrates that a hydrogen-bridge structure is never formed along the reaction path of the pinacol rearrangement. The methanediol decomposition follows a concerted mechanism with very small variations in the atomic charges.     

Redox reactions involving the indium(III) catecholate complexes

Indium catecholate complexes 3,6-CatInR (3,6-Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion (3,6-Q), R = Me (I) and Et (II)) are synthesized by the exchange reaction between RInI₂ and thallium catecholate 3,6-CatTl₂. Compounds I and II are trimeric in both the solution and crystalline state. The oxidation of compound I and earlier described complex [3,6-CatInI(THF)]₂ (THF is tetrahydrofuran) by various substrates (iodine, 3,6-Q, and tetramethylthiuram disulfide) is studied. Different indium(III) o-semiquinone complexes are the reaction products, depending on the reaction conditions.     

Autooscillation and autowave processes in belousov-zhabotinskii reactions involving α-ketoglutaric acid and iron(II,III) complexes

Concentration regions for the existence of temporal autooscillations and spacetime structures are determined, as well as dependences of the autooscillation parameters on initial concentrations of components for the reactions of sodium bromate, -ketoglutaric acid, and the complex of iron(II) with o-phenanthroline and of sodium bromate, -ketoglutaric acid, and the complex of iron(II) with 2,2-bipyridyl. The experimental results allow the conclusion that the relationships of the parameters of these systems to concentration are similar and that their mechanisms are probably similar. An advantage of these systems is the practically complete absence of gas formation and of the inhibiting effect of oxygen.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 179–185, March–April, 1988.     

Electron transfer. 123. Competitive redox reactions involving a Cobalt(I) intermediate

he hypophosphito derivative of Co^III, (NH₃)₅CoO₂PH₂ ²⁺, decomposes in basic media, yielding Co(II) quantitatively, along with a 1:1 mixture of hypophosphite and phosphite. Earlier studies point to a cobalt (I) intermediate, which rapidly reduces a second molecule of Co(III) reactant to Co(II). In the presence of an external cobalt (III) oxidant (Co³X), the latter competes with the hypophosphito complex for Co(I), lowering the yield of free hypophosphite. From the ratio of phosphorus products (P³/P¹), evaluated by proton decoupled ³¹P NMR, the relative reactivities (k_t/k_c) of the external Co(III) “traps” and the hypophosphito complex may be determined. A log-log plot comparing values of k_t/k_c with rates for reductions of the same series of Co(III) oxidants with Ru(NH₃)₆ ²⁺ (k_Ru values) is badly scattered with a slope of only 0.23, well below the value of unity stipulated by the Marcus model, indicating that an outer-sphere mechanism cannot operate for all of the Co(III)-Co(I) reactions and may not operate for any, except for that with Co(NH₃)₅(py)₃₊. Among the carboxylato-substituted oxidants, there are no rate enhancements by neighbouring pyridine, -SR,-OH, -CHO, or -SO₃H functions, in contrast to the accelerations previously observed for reductions by Cr(II), Eu(II) and Ti(III), which are attributed to intermediacy of chelate-stabilized precursor complexes. It is suggested that the Co(III)-Co(I) reactions, which determine the ratio of phosphorus products, are much more rapid than the ligand substitution at the Co(I) center which must precede chelate formation, and that the latter therefore does not intervene significantly in the redox processes.     

Electron transfer in nucleophilic vinyl substitution reactions involving bromovinyl sulfones

Conclusions It was shown that the reaction of phosphorous hexaalkyltriamides with-bromovinyl aryl sulfones proceeds via the step of electron transfer with the formation of ion-radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2785–2787, December, 1981.     

Chain transfer to aluminium in MAO-activated metallocene-catalyzed polymerization reactions

Chemical trapping of metal-bound oligomeric chains during the MAO-activated, metallocene-catalyzed polymerization of ethylene identify the two observed chain-bearing species to be alkylzirconocenium species and higher alkyl aluminiums, consistent with a proposed mechanism.     

Ion-ion proton transfer reactions of bio-ions involving noncovalent interactions: Holomyoglobin

Multiply protonated horse skeletal muscle holomyoglobin and apomyoglobin have been subjected to ion-ion proton transfer reactions with anions derived from perfluoro-1,3-dimethylcyclohexane in a quadrupole ion trap operated with helium as a bath gas at 1 mtorr. Neither the apomyoglobin nor holomyoglobin ions show any sign of fragmentation associated with charge state reduction to the 1 + charge state. This is particularly noteworthy for the holomyoglobin ions, which retain the noncovalently bound heme group. For example, no sign of heme loss is associated with charge state reduction from the 9 + charge state of holomyoglobin to the 1 + charge state despite the eight consecutive highly exothermic proton transfer reactions required to bring about this charge change. This result is consistent with calculations that show the combination of long ion lifetime and the high ion-helium collision rate relative to the ion-ion collision rate makes fragmentation unlikely for high mass ions in the ion trap environment even for noncovalently bound complexes of moderate binding strength. The ion-ion proton transfer rates for holo- and apomyoglobin ions of the same charge state also were observed to be indistinguishable, which supports the expectation that ion-ion proton transfer rates are insensitive to ion structure and are determined primarily by the attractive Coulomb field.     

Kinetics of outer-sphere electron transfer reactions involving synthetic models of copper “blue"” proteins

A model is constructed for a two-dimensional cellular automaton describing an autooscillatory chemical reaction in a spatially distributed medium on the basis of experimental data on the reentry map of the Belousovo-Zhabotinskii (BZ) reaction. It is shown that the behavior of such a cellular automaton is qualitatively similar to the temporal evolution of spatial structures in the BZ reaction.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 31–36, January, 1993.     

Chain transfer reactions in emulsion polymerization of butadiene/styrene

Calculation of regulating index r from M̄_W values determined by experiments is proposed. The calculation is based on the assumption that the M̄_W values only depend on the conversion and the regulating index in emulsion polymerization. On this basis the calculation of regulator concentration in the latex particles was also possible. M̄_W values calculated in this way and experimental M̄_W values show good agreement.