Organometallic peroxy radicals. Part 5. Trialkylsilylperoxy and trialkylstannylperoxy radicals

1979 ◽  
Vol 57 (20) ◽  
pp. 2761-2766 ◽  
Author(s):  
James Anthony Howard ◽  
John Charles Tait ◽  
Shiu Bor Tong
Keyword(s):  
Structural Difference ◽  
Bidentate Ligand ◽  
Resonance Spectroscopy ◽  
Peroxy Radicals ◽  
First Order ◽  
Radical Reactivity ◽  
Zero Order Kinetics ◽  
Spin Resonance ◽  
Alkylperoxy Radicals ◽  
Peroxy Group

A variety of organosilylperoxy and organostannylperoxy radicals, R3MO2•(R = Me, Et, n-Bu, t-Bu, and Ph and M = Si and Sn) have been prepared and studied by electron spin resonance spectroscopy. Trialkylsilylperoxy radicals exist in equilibrium with a tetroxide at temperatures below 233 K with ΔH0 = −11 ± 2 kcal mol−1 and ΔS0 < −30 cal deg−1 mol−1. Above 233 K these radicals decay either with first-order, one half-order, or zero-order kinetics depending on the radical and its concentration. Trialkylstannylperoxy radicals do not exist in reversible equilibrium with a dimer below ambient temperature and they undergo self-reaction with second-order kinetics. Tri-n-butylstannylperoxy radicals react with 2,6-di-tert-butyl-4-methylphenol and cobalt(II) acetylacetonate and Arrhenius parameters for these two reactions are reported. The structure of R3SiO2•resembles the structure of alkylperoxy radicals whereas the two oxygen nuclei of R3SnO2. are magnetically equivalent and the peroxy group becomes a bidentate ligand. This structural difference has a significant effect on radical reactivity.

Organometallic peroxy radicals. 4. Electron spin resonance spectra of the radicals produced by reaction of organophosphorus(IV) and organoarsenic(IV) radicals with 17O-enriched oxygen

1978 ◽  
Vol 56 (16) ◽  
pp. 2163-2166 ◽  
Author(s):  
J. A. Howard ◽  
J. C. Tait
Keyword(s):  
Electron Spin Resonance ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Peroxy Radicals ◽  
Factors Associated ◽  
Spin Resonance ◽  
Anisotropic Hyperfine ◽  
Unpaired Spin ◽  
Small Change ◽  
Alkylperoxy Radicals

It bas been shown that some tetra-coordinate phosphorus and arsenic radicals combine with oxygen to give peroxy radicals. The magnitude of the oxygen isotropic and anisotropic hyperfine coupling constants indicates that nearly all the unpaired spin is associated with the two oxygen nuclei with ca. 60% on the terminal oxygen. The large isotropic g-factors associated with Group VB peroxy radicals relative to alkylperoxy radicals is attributed to a small change in geometry of the peroxy function.The radicals with ap ∼ 9 G obtained during the reaction of photochemically generated tert-butoxy radicals with trialkylphosphites in the presence of oxygen are secondary species which appear to contain only one oxygen atom.

A kinetic electron spin resonance study of the reaction of some oxy radicals with vanadyl acetylacetonate

1981 ◽  
Vol 59 (14) ◽  
pp. 2184-2190 ◽  
Author(s):  
J. A. Howard ◽  
J. C. Tait ◽  
T. Yamada ◽  
J. H. B. Chenier
Keyword(s):  
Catalytic Reduction ◽  
Variable Temperature ◽  
Electron Spin Resonance Study ◽  
Reaction Products ◽  
Hydroxyl Proton ◽  
Vanadyl Acetylacetonate ◽  
First Order ◽  
Radical Reactivity ◽  
Spin Resonance ◽  
Spin Resonance Study

Reactions of phenoxyl, iminoxyl, nitroxyl, peroxyl, and alkoxyl radicals with VO(acac)2 in solution have been studied by kinetic esr spectroscopy. Rates of reaction are first-order with respect to each reactant and radical reactivity increases in the order galvinoxyl <2,4,6-tri-tert-butylphenoxyl <di(1-adamantyl)methylene-iminoxyl <tert-butylperoxyl. Rates of reaction are retarded by pyridine and accelerated by methanol and there is an isotope effect on the rate when the hydroxyl proton of CH3OH is replaced by deuterium. Vanadium-51 nmr spectroscopy has demonstrated that several vanadium(V) products are formed while conventional product studies have indicated that, in the case of phenoxyl and alkoxyl, the radical is reduced almost exclusively to the parent phenol and alcohol and that VO(acac)2 is eventually regenerated in substantial yields. The net reaction is, therefore, catalytic reduction of the radical. Variable temperature esr studies have shown that phenoxyl and iminoxyl radicals and VO(acac)2 exist in equilibrium with diamagnetic reaction products.

Metal complexes as antioxidants. 8. A kinetic and product study of the reaction of tertiary alkylperoxy radicals with cobalt(II) acetylacetonate

1980 ◽  
Vol 58 (18) ◽  
pp. 1962-1965 ◽  
Author(s):  
J. A. Howard ◽  
S. B. Tong
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Rate Constants ◽  
Arrhenius Equation ◽  
Electron Spin Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Polar Solvents ◽  
Spin Resonance ◽  
Alkylperoxy Radicals ◽  
Product Study

tert-Butylperoxy radicals react rapidly with Co(acac)2 in non-polar solvents and rate constants measured by kinetic electron spin resonance spectroscopy obey the Arrhenius equation log (nk/M−1 s−1) = (8.9 ± 0.7) − (4.7 ± 1.5)/θ, where θ = 2.303RT kcal mol−1 and n is ~ 0.1. Cumylperoxy radicals react with Co(acac)2 to give mainly α-cumyl alcohol and acetophenone. There is no evidence for the formation of "long-lived" alkylperoxy radicals co-ordinated to cobalt (III) or a stable alkylperoxo cobalt(III) complex in these systems.

Absolute rate constants for hydrocarbon autoxidation. XVI. Reactions of peroxy radicals at low temperatures

1969 ◽  
Vol 47 (20) ◽  
pp. 3803-3808 ◽  
Author(s):  
K. Adamic ◽  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constants ◽  
Low Temperatures ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Resonance Spectroscopy ◽  
Peroxy Radicals ◽  
Ambient Temperatures ◽  
Alkyl Groups ◽  
Bond Scission ◽  
Spin Resonance

The equilibrium constants for the formation of some t-alkyl tetroxides and the rate constants for irreversible decay of the tetroxides have been measured by electron spin resonance spectroscopy at low temperatures. The equilibrium constant appears to be virtually independent of the nature of the alkyl groups. It is concluded that differences in the rate of constants for chain termination by t-peroxy radicals at ambient temperatures are due chiefly to the differences in rate constants for irreversible tetroxide decomposition. The activation parameters for this reaction indicate that it occurs by one bond rather than two bond scission.

A New Dimeric Derivative of Ethoxyquin from Its Reaction with Alkylperoxy Radicals

1993 ◽  
Vol 58 (8) ◽  
pp. 1914-1918 ◽  
Author(s):  
Jaroslav Kříž ◽  
Luděk Taimr
Keyword(s):  
Mass Spectrometry ◽  
Nmr Spectroscopy ◽  
Peroxy Radicals ◽  
Methyl Group ◽  
Alkylperoxy Radicals ◽  
C Nmr

The structure of a new compound formed in the reaction of ethoxyquin with alkylperoxy radicals was resolved by 1H and 13C NMR spectroscopy (including COSY, NOESY, HHC RCT and SSLR INEPT techniques) and confirmed by mass spectrometry. The structure suggest participation of 4-methyl group of ethoxyquin in the deactivation of peroxy radicals. A mechanism of this reaction is proposed.

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