Hydrogen transfer, substituted phenols

Single-temperature equilibrium constant values may also yield quantitative information about reaction enthalpies, provided that the entropy term can be estimated. Take, for example, reaction 14.32, which involves hydrogen transfer between two substituted phenols (ArOH and Ar OH see examples in figure 14.4). Note that Kc = Km in this case. 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Quantitative kinetic studies of absolute rate constants for hydrogen atom transfer from substituted phenols to polystyrene peroxyl radicals by Howard and Ingold in the 1960s provided the first reliable data on substiment effects on antioxidant activities of phenols. Later, a very detailed report appeared providing data on substituent and structural effects on various classes of monohydroxy phenols. In addition, detailed reviews were given of substituent etfects ". These reports provide the basis for understanding how substituent and strucmral effects control the antioxidant activities of phenols and will be summarized in part below. 

HYDROGEN AND DEUTERIUM ATOM TRANSFER REACTIONS FROM SUBSTITUTED PHENOLS TO GALVINOXYL. 

---