Lonol

Enthalpies, Activation Energies, and Rate constants of Reactions of Phenoxyl Radicals (A O ) with 2,6-bis(1,1-dimethylethyl)-4-methylphenol (lonol) Calculated by IPM Method, Equations See in Chapter 6, for the Values of a, bre, and A, See Table 18.3... 

Two of the abstraction reactions listed in Table 6 will be discussed further viz. (a) the reaction of n-heptyl radicals with tetramethyl-ethylene which was studied specifically to help elucidate the conditions under which the reactions take place and (b) the reaction of peroxy-radicals with an oxidation inhibitor 2,6-di-t-butyl-4-methylphenol (lonol) which is of particular interest in that two distinct mechanisms have been proposed to account for its antioxidant properties. 

Experiments have been carried out with the rotating cryostat to study the reaction of 2,6-di-t-butyl-4-methyl phenol (lonol) with n-heptyl and n-heptylperoxy radicals. When lonol was deposited on n-heptyl radicals the e.s.r. spectrum showed that some reaction had occurred at 77°K. When the deposit was warmed slowly the spectrum of the residual n-heptyl radicals disappeared and was replaced by that of the substituted phenoxy-radical, (4), formed by loss of the hydroxyl hydrogen. 

It is concluded that (i) both n-heptyl and n-heptylperoxy radicals react with lonol by abstraction of the hydroxyl hydrogen in accord with the mechanism postulated by Bickel and Kooyman (1956) and (ii) the resultant phenoxy radical does not react readily with oxygen and mil therefore not continue an oxidation chain. 

Fiq. 16. Reaction of n-heptylperoxy-radieala withlonol. First derivative e.s.r. spectra of (a) n-heptyl, (b) n-heptylperoxy, and (c) mixture of n-heptylperoxy- and lonol phenoxy-radicals. 

A Waters GPC 150 CV, equipped with the DRI prototype 4 and a single capillary viscometer, was used for this study. A low-angle laser lightscattering (LALLS) detector (Chromatix CMX 100) was inserted between the column set and the GPC 150 CV detectors. Tetrahydrofuran (THF) was used at 40 °C and at a flow rate of 1 mL/mn. THF was filtered on a Millipore membrane-type FH and stabilized by lonol at a concentration of 0.04%. The columns used were a set of Waters Ultrastyragel (103—106 A). The narrow standards used for calibration were a set of polystyrene standards... 

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