Antioxidant efficiency and mechanism of antioxidant action of metal-containing dispersant additives

Enhancement of Diarylamine Antioxidant Activity by Molybdenum Dithiocarbamates

“…MDTCs are commonly employed in lubricants due to their excellent antiwear properties. These complexes have also been ascribed antioxidant activity, a property generally attributed to their ability to decompose peroxides. − More recently, it has been reported that MDTCs synergize with DPAsthat is, their antioxidant activity is more than the additive contributions of eacha result which we have corroborated above (Figure C). It has been suggested that this is due to coordination of the diarylamines and/or the nitroxides derived therefrom with the Mo-center of MDTCs. − Such a DPA-specific interaction would be in line with the fact that no such synergy exists between hindered phenols and MDTCswhich we have also corroborated above (Figure D).…”

“…Commonly employed sulfur-containing additives include molybdenum complexes, such as molybdenum dithocarbamates (MDTCs), which deposit a molybdenum disulfide (MoS 2 ) film upon continued exposure to elevated temperatures. − MDTCs and other organomolybdenum compounds have also been reported to have antioxidant activity. This is generally ascribed to their ability to decompose peroxides, − as has been shown for other metal dialkyldithiocarbamates. , MDTCs have been reported to lose their protective properties over time, which has been correlated to a decrease in their concentration throughout the course of oxidation. ,, As such, MDTCs rely on the action of hindered phenols and ADPAs with which they are typically blended in lubricants to prolong their antiwear ability over time. , Interestingly, MDTCs have been reported to extend the inhibition periods ascribed to ADPAs during the oxidation of lubricants. Guerret-Piécourt and co-workers, as well as Jianqiang et al, suggested that this synergism is due to the coordination of the N atom of the ADPA with molybdenum, stabilizing it to decomposition via sterics. , Later, Zhang and co-workers proposed that MDTCs increased the persistence of diarylaminyl and/or diarylnitroxide radicals formed in situ .…”