Synthesis, spectroscopic characterization and redox reactivity of some new N-(2,6-di-tert-butyl-1-hydroxyphenyl) salicylaldimines

Abstract

New substituted N- (2,6-Di-tert-butyl-1-hydroxyphenyl) Salicylaldimines (LxH) were prepared by the condensation of various hydroxy and methoxy salicylaldehyde derivatives and 2,6-Di-tert-butyl-4-aminophenol and characterized by elemental analysis, IR, UV-Vis, H-1 NMR spectroscopy, as well as ESR studies of the oxidation products of LxH. It was found that LxH, unlike analogous electron-withdrawing Cl, Br, NO2 bearing derivatives, in the solid state exist both in associated and non-associated forms. UV-Vis and 1H NMR studies show that LxH in solutions exists both in phenolimine and ketoamine tautomer forms. In addition, alcohol solutions of LxH exhibited a new band in the region of 630-675 nm. The ESR studies of one electron oxidation of LxH, in the condition of THF, CHCl3 and toluene solutions at 300 K, indicate the formation of corresponding primary or secondary phenoxyl radicals. It was found that the stability and conversion pathway of the primary phenoxyl radicals are dependent upon both kind and position of the substituents in salicylaldehyde moiety of LxH. For some LxH without observation of primary phenoxyl radicals, the secondary Coppinger's type radical was detected. The ESR parameters of all radical intermediates have been determined.