Are natural-based isothiocyanate derivatives alternative antioxidant additives used in petrochemical products?

Synthetic additives used in petrochemical products, such as plastics, rubbers, resins and polymers, can enter the environment as contaminants and pollute the aquatic and soil environment. Thus, using natural-based alternative compounds has excellent potential to reduce the negative impact. In this study, the role of natural-based isothiocyanate derivatives Cp<b>1</b>-Cp<b>4</b>, i.e. allylisothiocyanate, 1-isothiocyanate-3-methylbutane, 4-methylphenyl isothiocyanate and 2-phenylethyl isothiocyanate in use as primary antioxidant additives was studied via their HO^•-radical scavenging activity. Formal hydrogen transfer, radical adduct formation and single electron transfer mechanisms were investigated in water and pentyl ethanoate (PEA) using density functional theory at M06-2X/6-311++G(3df,3pd)//M06-2X/6-311++G(d,p) level of theory. The results illustrated the high HO^•-scavenging activity of the isothiocyanate compounds with rate constants of about 10⁸-10⁹ M^-1 s^-1. Allylisothiocyanate Cp<b>1</b> represents the most efficient HO^•-scavenger with <i>k</i> _overall of 5.20 × 10⁹ M^-1 s^-1 in water and 1.85 × 10⁹ M^-1 s^-1 in PEA. These results allow us to enrich the data on effective antioxidant additives from natural sources to reduce HO^• radicals-induced oxidation processes in different environmental conditions.