Abstract
The catalytic properties of bulky water-soluble salen complexes in the oxidation of isoeugenol (2-methoxy-4-(1-propenyl) phenol) have been investigated in aqueous ethanol solutions in order to obtain a mixture of polymeric compounds through dehydrogenative polymerization. The average molecular weight of dehydrogenated polymers (DHPs) was monitored by GPC and correlated to reaction conditions such as time, concentration of substrate, concentration of catalyst, type of oxidation agent, etc. The DHP synthesized by adopting the best reaction conditions was characterized by different analytical techniques (GPC, 13C-NMR, 31P-NMR and LC-MS) to elucidate its structure. The lignin-like polymer resulting from isoeugenol radical coupling possesses valuable biological activity and finds applications in a variety of fields, such as packaging industry and cultural heritage conservation.
Highlights
Plant polyphenols constitute an important source of renewable carbon in the biosphere
In order to investigate the catalytic properties of salen complexes a new set of water-soluble salen were synthetized following Schemes 1 and 2
Afterwards, the effect of pH on the polymerization reaction catalyzed by Cu(SS) was taken into account monitoring the Mn and molecular weight (Mw) values of dehydrogenated polymers (DHPs) synthesized into different buffer solution
Summary
Plant polyphenols constitute an important source of renewable carbon in the biosphere. The most valuable property of salen complexes lies in their modulatory nature: the ligand structure, as well as the coordinated metal ion, can be varied to modify their hydrophilicity to match the end-use application [6]. Another important reaction of salen complexes is the single electron oxidation of phenols to produce phenoxy radicals, and by radical coupling, dehydrogenative polymerization products (DHPs) [7,8,9]. The antioxidant properties of the obtained isoeugenol polymer were investigated
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