DFT study of the reaction sites of N, N′-substituted p-phenylenediamine antioxidants

Abstract

The geometry of N, N′-diphenyl- p-phenylenediamine (DPPD), N-phenyl- N′-(1′-methylbenzyl)- p-phenylenediamine (SPPD), N-phenyl- N′-(1,3-dimethyl-butyl)- p-phenylenediamine (6PPD), N-phenyl- N′-isopropyl- p-phenylenediamine (IPPD), and N-(1-methyl-1-phenylethyl)- N′-phenyl- p-phenylenediamine (CPPD) as well as of their dehydrogenation products has been optimized at B3LYP/6-31G ∗ level of theory. Our results support the idea of formation of stable ketimine Ph–N C structures (instead of quinonediimine structures) during consecutive dehydrogenation of SPPD, 6PPD, and IPPD antioxidants despite the formation of tertiary carbon-centered radicals in the first dehydrogenation step is energetically preferred for SPPD only.