Inhibition of Autoxidation by Di-μ-thio-dithio-bis (dialkyldithiocarbamate) Dimolybdenum

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The effectiveness of molybdenum dialkyldithiocarbamates (I) and di-μ-thio-dithio-bis (dialkyldithiocarbamates) dimolybdenum (II) as antioxidants in the autoxidation of squalane was investigated and compared with zinc dialkyldithiocarbamate. Induction periods of doped squalane were measured using an automatic recording oxygen absorption apparatus.
These compounds show efficient inhibition action and give sharply defined induction periods, there being an abrupt change in O₂ uptake rate. It has been found that the potency as oxidation inhibitor of molybdenum compound (I) and (II) is the same irrespective of their degree of sulfurization. It seems, therefore, that the alkyl group play an important role in the activity of oxidation inhibition.
It has been experimentally found that zinc and molybdenum compounds (I, II) act as peroxide decomposer for tert-butyl hydroperoxide in chroloform solution and squalane hydroperoxide. Seemingly, capacity of molybdenum compounds (I, II) to decompose hydroperoxide is higher than that of zinc dialkyldithiocarbamate. For autoxidation of squalane initiated by azobisisobutyronitrile, the influence of zinc compound on the rate of oxidation is much more pronounced than the molybdenum compounds (I, II).
Therefore, it may be concluded that molybdenum compounds (I, II) suppress the autoxidation of squalane by acting as catalytic peroxide decomposer; on the other hand zinc dialkyldithiocarbamate by terminating the propagation of the oxidative chain reaction.