630. The rates of reaction of αα-diphenyl-β-picrylhydrazyl with certain amines and phenols

Abstract

The reactions of primary arylamines with aa-diphenyl-p-picrylhydrazyl in carbon tetrachloride have been found to obey the third-order law :Rate of disappearance of hydrazyl = k,[Hydra~yl]~[Aniline] A number of other amines and phenols gave a second-order reaction with the hydrazyl. Alcohols and t-butylamine did not, however, react a t an appreciable rate. The effects of substituents on the reaction with phenols are similar to their effects on reactions in which a carbonium ion is formed adjacent to a phenyl ring. Bulky groups ortho to the phenolic hydroxyl hinder the reaction. The reactions of 9-aminobenzonitrile, mand $-nitroaniline, $-aminobenzophenone, NN-dimethyl-pnitroaniline, and mand p-nitrophenol were greatly accelerated by light, and were then of first order with respect to aa-diphenyl-P-picrylhydrazyl and of zero order with respect to the amine or phenol. BRAUDE, BROOK, and LINSTEAD found that hydrogen transfer took place between the stable free radical aa-diphenyl-p-picrylhydrazyl and a number of quinols, catechols, hydroaromatic compounds, and aromatic amines. They measured the rates of reactions of the hydrazyl with some hydroaromatic compounds in dioxan, found that the reactions obeyed approximately the third-order law (rate = k,[Hydra~yl]~[Donor]), and showed that the energies of activation were between 20 and 35 kcal. per mole. Russell studied the reactions between aa-diphenyl-p-picrylhydrazyl and alkanethiols in benzene and found that the rates of disappearance of the hydrazyl could be expressed as 2k [Hydrazyl][Thiol]. At 6Q0, the values of k varied from 0-23 1. mole-1 min.-l for t-butanethiol to 4.56 for hexanel-thiol and the activation energy was in every case about 15 kcal. per mole. The products of the reactions of thiophenol, butanethiol, ammonia, hydrazine, hydroxylamine, methylamine, n-butylamine, isopropylamine, and diethylamine with aa-diphenyl-@-picrylhydrazyl were investigated and in every case high yields of aa-diphenyl-P-picrylhydrazine were obtained. The reactions between aa-diphenyl-P-picrylhydrazyl and some aromatic secondary amines have also been ~t u d i e d . ~. ~ Homolytic transfers of hydrogen atoms from donors to free radicals are of considerable interest in connexion with termination and transfer processes in chain reactions involving radicals. Autoxidations are important examples of such reactions. The propagation reactions are R* + 0, --t RO,.

The Inhibited Autoxidation of Styrene: Part Ii. The Relative Inhibiting Efficiencies of Meta- And Para-Substituted Phenols

“…Reaction [7] may possibly be an example of this phenomenon. Similarly, the fact that reaction [15] definitely follows u+ constants whereas reactions [13] and [14] tend more to favor a constants would also be in line with this suggestion.…”

Methods of measurement and evaluation of natural antioxidant capacity/activity (IUPAC Technical Report)

“…[25]. ANTIRADICAL ACTION DPPH • quenching reactions have been used to elucidate structural effects on chemical mechanisms and reactivity of simple phenols since the late 1950s [26][27][28][29]. Antioxidant activity assays for complex polyphenols were initiated in a 1985 pivotal study in which Wayner et al used the water-soluble azide azobis (2-amidinopropane hydrochloride) to generate radicals in plasma, then followed inhibition of oxygen consumption to investigate compounds contributing to antioxidant capacity [30].…”

“…Natural antioxidant capacity/activity 975 3.5 DPPH assays 3.5.1 Experimental approach DPPH is a stable radical with a deep purple colour whose reaction with other radicals, reducing agents, or compounds capable of HAT leads to loss of colour at 515 nm and loss of its electron paramagnetic resonance (EPR) free radical signal [26,29]. Like ABTS +• , DPPH • reacts with both electron and hydrogen donors [75,76], though more slowly, and steric accessibility to the radical site is a clear issue [27,28]. No antioxidant assay is simpler or less expensive to run than the DPPH assay, which accounts for its popularity and extensive use.…”

Kinetic, Electron Spin Resonance, and Product Studies of the Reaction Between 2,2-Diphenyl-1-picrylhydrazyl and 2,4,6- Tri-t-butylbenzenethiol

“…More recently it has been shown that DPPH can abstract hydrogen from aliphatic thiols (2), aromatic amines (3), and phenols (4,5). The rate constants for the overall disappearance of DPPH vary markedly with the type of X-H bond and, in the case of phenols, with the substituents in the ring.…”