Cumenes, autoxidation inhibition

Emulsion oxidation of alkylaromatic compounds appeared to be more efficient for the production of hydroperoxides. The first paper devoted to emulsion oxidation of cumene appeared in 1950 [1], The kinetics of emulsion oxidation of cumene was intensely studied by Kucher et al. [2-16], Autoxidation of cumene in the bulk and emulsion occurs with an induction period and autoacceleration. The simple addition of water inhibits the reaction [6], However, the addition of an aqueous solution of Na2C03 or NaOH in combination with vigorous agitation of this system accelerates the oxidation process [1-17]. The addition of an aqueous phase accelerates the oxidation and withdrawal of water retards it [6]. The addition of surfactants such as salts of fatty acids accelerates the oxidation of cumene in emulsion [3], The higher the surfactant concentration the faster the cumene autoxidation in emulsion [17]. The rates of cumene emulsion oxidation after an induction period are given below (T = 353 K, [RH] [H20] = 2 3 (v/v), p02 = 98 kPa [17]). 

As discussed in the introduction, chlorine substituents may be expected to influence the autoxidation of organic substrates as a result of their electron-directing properties, but these effects may be complex. Thus, for example, Kulicki [161] has reported that halogen and nitrate substituents, particularly in the ortho position, have an effect on the autoxidation of cumene by inhibiting the primary oxidation, but they also accelerate the homolysis of any hydroperoxide that is formed the net result is an overall acceleration of oxidation. Similar effects were noted by Kovalev and... 

The role of aromatic moieties in the polymerization of vinyl acetate is interesting since benzene, for example, may be considered a natural solvent for the solution of polymerization of vinyl esters. Yet, in the presence of oxygen, cumene (isopropylbenze) inhibits the autoxidation process which may use up oxygen. Thus, the onset of polymerization may be delayed. On the other hand. 

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. 

Aryl phosphites inhibit the initiated oxidation of hydrocarbons and polymers by breaking chains on the reaction with peroxyl radicals (see Table 17.3). The low values of the inhibition coefficient / for aryl phosphites are explained by their capacity for chain autoxidation [14]. Quantitative investigations of the inhibited oxidation of tetralin and cumene at 338 K showed that with increasing concentration of phosphite /rises tending to 1 [27]. 

The present paper reports the results of a kinetic study of the inhibition of the azobisisobutyronitrile-initiated autoxidation of cumene at 60 °C. and of Tetralin at 70 °C. by zinc diisopropyl dithiophosphate, undertaken to test the validity of the chain-breaking inhibition mechanism proposed above. In addition, the effectiveness of several metal dialkyl dithiophosphates as antioxidants in the autoxidation of squalane... 

From these results, it is clear that neither Equation A nor B represents the kinetics of the zinc diisopropyl dithiophosphate-inhibited autoxi-dation of cumene or Tetralin. This does not immediately indicate that the mechanism in Scheme 1 is wrong since it is highly idealized and takes no account of possible side reactions. A similar situation occurs in the inhibition of hydrocarbon autoxidation by phenols (AH), for which a basic mechanism similar to that in Scheme 1 is accepted. Termination occurs via Reactions 7 and 8 instead of Reactions 5 and 6. 

Emulsion oxidation of alkylaromatic compounds appeared to be more efficient for the production of hydroperoxides. The first paper devoted to emulsion oxidation of cumene appeared in 1950 [1]. The kinetics of emulsion oxidation of cumene was intensely studied by Kucher et al. [2-16]. Autoxidation of cumene in the bulk and emulsion occurs with an induction period and autoacceleration. The simple addition of water inhibits the reaction... 

With oxidizing agents, phenol readily forms a free radical which can dimerize to form diphenols or can be oxidized to form dihydroxybenzenes and quinones. Since phenol radicals are relatively stable, phenol is a suitable radical scavenger and can also be used as an oxidation inhibitor. Such a property can also be undesirable, e.g. the autoxidation of cumene can be inhibited by small quantities of phenol. 

The reactions of phosphites with peroxy radicals continue to attract attention because of the use of phosphites as anti-oxidants. The autoxidation of a variety of hydrocarbons, e.g. tetralin, cumene, styrene, and cyclohexane, is inhibited by zinc dialkyldithiophosphates (60). In order to assess the reactivity... 

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