Unusual selectivities of radical reactions. Experimental studies on alkyl versus phenoxyl reaction systems

Rüegge, Daniel; Fischer, Hanns

doi:10.1002/kin.550210809

Cited by 38 publications

(19 citation statements)

References 27 publications

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“…Note that the steady state kinetics of the system just described has been studied theoretically by Hanns Fischer, 9 and the predictions of the theory were later tested by experiment. 28 The present study, on the other hand, addresses the question of transient kinetics.…”

Section: Introductionmentioning

confidence: 97%

“…Perhaps the best known types of such radicals are the nitroxide type radicals 20 ͑see the radical P in Scheme I͒ which appear in living free radical polymerization, [21][22][23][24][25] spin trapping reactions, 20 polymer stabilization ͑e.g., by hindered amine light stabilizers-HALS 26,27 ͒, radical scavenging reactions, etc. Some other radical types displaying similarly low self-reactivity are quinone type radicals which arise in the inhibition of free radical chain reactions by phenolic compounds, 28 some cobalt compounds, 29,30 and nitric oxide radicals 31 which have important biological roles.…”

Section: Introductionmentioning

confidence: 99%

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Kinetic isolation of persistent radicals and application to polymer–polymer reactions

Karatekin

O’Shaughnessy

Turro

1998

The Journal of Chemical Physics

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We analyze the transient kinetics of a mixture of two radicals (M and P), one of which (P) has very low, or zero self-reactivity ͑i.e., P is a ''persistent'' radical͒. For the case where the self-reactivity of the persistent radical is zero, we find a critical value for the initial concentration ratio rϵ P 0 /M 0 , above which the persistent radicals are isolated at long reaction times after all of the M 's react. If r is below its critical value the surviving fraction of P is zero. An experiment employing virtually zero self-reactivity nitroxide radicals is proposed to test the predicted critical behavior. If the self-reactivity of the M is stronger than the cross-coupling reactivity, then the critical value of the ratio r is negative, and a finite fraction of the persistent P radicals are always isolated, regardless of the initial concentration ratio r. For the case where the self-reactivity of the persistent radicals is finite but small, we find similar behavior, except now the P radicals react with one another on a much longer time scale following their isolation. The isolation process facilitates the measurement of P-P reaction kinetics in situations where it is difficult to generate the P radicals by themselves. An experiment to measure fundamental polymer-polymer reaction kinetics in concentrated solutions or melts is proposed based on these ideas.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Kinetic isolation of persistent radicals and application to polymer–polymer reactions

Karatekin

O’Shaughnessy

Turro

1998

The Journal of Chemical Physics

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“…Fischer et al [24][25][26][27][28][29] developed kinetic models that showed the change of radicals (both nitroxide and propagating) with time. These kinetic models (known as Persistent Radical Effect) proved that the concentration of radicals is not constant with time.…”

Section: Nitroxide Mediated Polymerization (Nmp)mentioning

confidence: 99%

Highlight on the Mathematical Modeling of Controlled Free Radical Polymerization

Al‐Harthi

2015

International Journal of Polymer Science

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Over the last quarter century, controlled free radical polymerization (CFRP) has received great attention by the researchers of polymer science and engineering. In addition to the experimental studies, many publications in the literature dealt with the modeling of CFRP processes. A review of acknowledged and well-received researches on mathematical modeling in the area of CFRP is presented in this work. Three main categories of CFRP (namely, ATRP, RAFT, and NMP) are taken into consideration in the review. The different techniques used in modeling CFRP processes are also enumerated with more emphasis on Monte Carlo simulation and the method of moments. The review provides a better understanding of the processes and the recent efforts to model CFRP.

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“…For example, α-tocopherol is the major lipidsoluble, chain-breaking antioxidant in human blood plasma and low-density lipoprotein. Phenolic antioxidants mechanism is believed to transfer its phenolic H-atom to chain-carrying radicals and then break the chain process of autoxidants [4][5][6][7][8][9][10][11][12][13][14] . The main reactions can be represented by the following reactions (1) and (2) [13][14][15][16] : ROO·+ ArOH → ROOH + ArO· (1) R· + ArOH → RH + ArO·…”

mentioning

confidence: 99%

A comparison of transition state of phenol in H-atom abstraction by methyl and methylperoxyl radicals

Sun

Liu

2007

CHINESE SCI BULL

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DFT method was employed to locate transition state for H-atom transfer from phenol by methyl radical and methylperoxyl radical. The reaction pathway energy profiles and the structure of transition state show that a common feature is the out-of-plane structure of the transition state: in contrast to the energetic minima of a hydrogen-bonded intermediate, the hydrogen bond in transition structures is considerably twisted out of the aromatic ring. From the values of enthalpy (ΔH) and activation energy (E a ) obtained, it is found that the rate of the reaction of peroxyl radical with phenolic antioxidant is higher than that of alkyl radical with antioxidant. Spin density distributions show that the electron transmission is between methyl (methylperoxyl) radical and phenol. density functional calculations, phenols, radical, activation energy, hydrogen atom abstraction Free radicals play a significant role in causing many diseases, deteriorating foods, and degrading chemical materials. In biologic system, alkyl radicals (R·) and peroxyl radcials (ROO·) are the main chain-carrying radicals. Phenolic antioxidants (ArOH) can efficiently scavenge these radicals and have attracted wide attention [1][2][3] . For example, α-tocopherol is the major lipidsoluble, chain-breaking antioxidant in human blood plasma and low-density lipoprotein. Phenolic antioxidants mechanism is believed to transfer its phenolic H-atom to chain-carrying radicals and then break the chain process of autoxidants [4][5][6][7][8][9][10][11][12][13][14] . The main reactions can be represented by the following reactions (1) and (2) [13][14][15][16] : ROO·+ ArOH → ROOH + ArO· (1) R· + ArOH → RH + ArO·(2) Understanding of the mechanism of H-atom abstraction from phenols needs the knowledge of the transition state and reaction pathway. Since experimental studies cannot obtain directly transition-state information, high level calculations are necessary. In this paper, we locate the transition state for hydrogen atom transfer from phenol by methyl radical and methylperoxyl radical and compare these transition-states structures. With the calculations of intrinsic reaction coordinate (IRC), we compare the energy, structure and electronic density changes along the reaction pathway. Calculation methodsThe geometries were optimized for the reaction molecules, transition state and the product molecules using density functional theory with B3LYP function on the basis set of 6-311+G(d,p) [17][18][19] . All stationary points were positively identified as minima or first-order saddle points by evaluation of the frequencies and normal modes. Single-point energy calculations at higher level with B3LYP/6-311++G(3df,2pd) were done to draw a reliable conclusion. Further, pathways between the transition states and their corresponding minima were char-

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Unusual selectivities of radical reactions. Experimental studies on alkyl versus phenoxyl reaction systems

Cited by 38 publications

References 27 publications

Kinetic isolation of persistent radicals and application to polymer–polymer reactions

Kinetic isolation of persistent radicals and application to polymer–polymer reactions

Highlight on the Mathematical Modeling of Controlled Free Radical Polymerization

A comparison of transition state of phenol in H-atom abstraction by methyl and methylperoxyl radicals

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