1898-66-4Relevant articles and documents
Synthesis and spectral comparison of electronic and molecular properties of some hydrazines and hydrazyl free radicals
Ionita, Petre,Lete, Cecilia,Madalan, Augustin,Matache, Mihaela,Patrascu, Bianca,Paun, Anca,Popescu, Codruta
, (2020/08/28)
Continuing our work on hydrazyl free radicals, five triphenylhydrazine derivatives, one a new compound, were synthesized to compare the electronic and molecular properties of these compounds, study the influence of substituents on the phenyl rings, and compare their properties with the parent hydrazines and corresponding anions. These hydrazines demonstrate both acid-base and redox properties. The hydrazine proton can be removed by base, yielding the corresponding anion and both the hydrazines and their anions can be oxidized to the corresponding hydrazyl free radicals. ESR spectra confirmed their formation and X-ray crystallography of one compound confirmed their structures.
Manganese-porphyrins and -azaporphyrins as catalysts in alkene epoxidations with peracetic acid. Part 2. Kinetics and mechanism
Banfi, Stefano,Cavazzini, Marco,Coppa, Fausta,Barkanova, Svetlana V.,Kaliya, Oleg L.
, p. 1577 - 1583 (2007/10/03)
cis-Stilbene (cSt) and 1,1-diphenyl-2-picrylhydrazine (DPPH) were used as substrates for kinetic investigations of the catalytic system based on MnIII-porphyrins and peracetic acid in CH3CN. Catalysts employed were tetra-(2,6-dichlorophenyl)-porphyrinatomanganese chloride (TDCPPMnCl) 5, octanitrophthalocyaninatomanganese chloride (NO2PcMnCl) 6 and tetra(tert-butyl)-tetraazaporphyrinatomanganese chloride (TAPMnCl) 7. It was found that for all these catalysts the first step of the reaction mechanism is the formation of an adduct 'A' between the catalyst and AcOOH in a reversible way (k1/k-1), followed by an irreversible stage (k2) for the formation of Mnv-oxo species. The oxidative capability of the adduct 'A' was found to be dependent on the electronic structure of the catalyst, while the reactivity of Mn-oxo species is only slightly influenced by catalyst structure. The formation of the high-valent Mn-oxo species is the rate-determining step of alkene epoxidations as demonstrated by the same k2 value obtained with catalyst 6 in the epoxidation of cSt and trans-stilbene (tSt). Catalyst stability was found to be dependent on solvent polarity, CH3CN being the best reaction medium.
Influence of Nitrogen Base Ligation and Hydrogen Bonding on the Rate Constants for Oxygen Transfer from Percarboxylic Acids and Alkyl Hydroperoxides to (meso-Tetraphenylporphinato>manganese(III) Chloride
Yuan, Lung-Chi,Bruice, Thomas C.
, p. 1643 - 1650 (2007/10/02)
Equilibrium constants for axial ligation of imidazole (ImH), N-methylimidazole (N-MeIm), 4'-(imidazo-1-yl)-acetophenone (NAcPhIm), 2,6-lutidine (2,6-Py), and 3,4-lutidine (3,4-Py) with (meso-tetraphenylporphinato)manganese chloride ((TPP)MnIIICl) have been determined.The rates of oxygen atom transfer from percarboxylic acids and alkyl hydroperoxides (YOOH) to the manganese(III) porphyrin in the presence of varying concentrations of the nitrogen bases were determined.For this purpose, 2,2-diphenyl-1-picrylhydrazine (DPPH) was employed as a trap for the generated higher valent oxo-manganese porphyrin species.From the equilibrium and kinetic data, there was then calculated the second-order rate constants for oxygen atom transfer from YOOH compounds to the species (TPP)MnIIICl, TPP(Cl)MnIIIN, and TPP(Cl)MnIIIN2 (where N = ImH, N-MeIm, and 3,4-Py).Only the percarboxylic acids exhibit measurable rate constants for oxygen transfer to (TPP)MnIIICl, whereas alkyl hydroperoxides and percarboxylic acids transfer oxygen to the TPP(Cl)MnIIIN species.Of the species TPP(Cl)MnIIIN2, reaction with YOOH compounds is seen only when N is imidazole.This is attributed to an equilibrium of the unreactive bis axially ligated TPP(Cl)MnIII(ImH)2 with the reactive isomeric mono axial-ligated complex Cl(1-)...H-Im...H-Im...MnIIITPP.Nitrogen base ligation of (TPP)MnIIICl provides minimally a 1E3 increase in the rate constants for oxygen transfer in methylene chloride.Linear free-energy plots of the log of the second-order rate constants for oxygen transfer from YOOH vs. the pKa of YOH establish that β1g for oxygen transfer in which heterolytic O-O bond scission is rate-determining is large and negative.The value of β1g when oxygen transfer involves rate-determining homolytic O-O bond scission is small and negative.