Radicals cumylperoxide

Figure 17.11 Thermo-kinetic relation for oxidation of various phenols of Table 17.3 by cumylperoxide radical (Cum ). Figure adapted from Ref. [75].

Abstract One of the most important yet complex chemistries is the spontaneous reaction of oxygen with organic matter, generally referred to as autoxidation. Suppressing this chemistry is important in many industries and critical when it comes to the performance of lubricants. The chapter summarizes kinetic parameters for reaction of the potent sulphur-containing antioxidants with both cumylperoxide radicals and cumene hydroperoxide. It also demonstrates that antioxidants can be formulated that have synergistic activity. One example of this phenomenon is the combination in one molecule of phenolsulphide and aminosulphide moieties, which results in an antioxidant with superior activity for the critical hydroperoxide decomposition process compared to molecules containing either moiety alone. 

The concentration of an initiator was 2 x 10 M and the concentration of antioxidants was varied in the range 0.5-10.0 x 10 M. All the antioxidants studied inhibit initiation of cumene oxidation by reacting with cumylperoxide radicals. Figure 9.1 presents the typical kinetic curves for cumene oxidation in the presence of sulphur-containing antioxidants. The rate constants for reaction of the antioxidants with cumylperoxide radicals (kj) was calculated by absorption kinetics of oxygen,... 

The rate constants for reaction of monophenolsulphides with cumylperoxide radicals kj) are in the range 2-6 x l(f M s that somewhat exceed the values... 

The kinetic parameters of reaction of bisphenolsulphides with cumylperoxide radicals are consistent with the termination of two oxidation chains (f 2). It is known that for bisphenolic antioxidants, / 4. This may be explained by an analogous mechanism of reaction with peroxide radicals proposed for monophenolsulphides that have the sulphur atom connected directly to the benzene ring, fc/ values for bisphenolsulphides are also in the range 2-6 x lO s. 

Aminosulphides terminate one oxidation chain (f=l), and from the rate constant for reaction with cumylperoxide radicals, are somewhat inferior to phenolsulphides (ky = 1-2 X 10 s.) The degree of inhibition of the transformation products of... 

Investigation of the reactions of these compounds with cumylperoxide radicals and cumyl hydroperoxide showed that the mechanism of antioxidant action of these compounds is similar to that of previously studied sulphur-containing phenol and amine derivatives, namely, they efficiently terminate oxidation chains by reacting with peroxide radicals (Fig. 9.10) and catalytically convert hydroperoxides into molecular products (Fig. 9.11). 

The reaction products of thiocarbamide derivatives with cumylperoxide radicals exhibit a secondary inhibiting effect. 

The kinetic parameters for reaction of the thiocarbamides with cumylperoxide radicals and cumyl hydroperoxide are also consistent with M-benzyl-A[ -(3-thiethanyl) thiocarbamide being faster in both oxidation chain termination (reacting with cumylperoxide radicals) and in catalytic decomposition of cumyl hydroperoxide. It was also shown that A -benzyl-V-(3-thiethanyl) thiocarbamide inhibits cumene autoxidation better than the other thiocarbamide derivatives when used in lower concentrations than the latter. 

Table 9.3 Kinetic parameters for the reaction of thiocarbamide derivatives with cumylperoxide radicals and cumyl hydroperoxide as well as the induction periods in cumyl autoxidation in presence of given antioxidants...

Fig. 9.12 Dependence of stoichiometric coefficient (f) of the reaction of cumylperoxide radicals with interaction products of W-benzyl-/V -thiethanylthiocarbamide (InH) with cumyl hydroperoxide (ROOH) on the ratio of InH ROOH and the incubation time of the InH - - ROOH mixture...

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