Sulfur compounds, hydroperoxide

Instead of either an acid-induced decomposition or acid-catalyzed sulfur compound—hydroperoxide decomposition reaction occurring— formation of alternative active species which catalytically decompose the hydroperoxide is possible, such as SCL, as suggested by Hawkins and Sautter (4). However, under conditions of this work where vigorous drying of solvents was not used, SOL could be converted into the acid which would then induce the acid-catalyzed decomposition of the peroxide. 

Sulfur compounds in combination with peroxyl radical acceptors are often used for the efficient break of hydroperoxide [14]. The mechanism of action of these inhibitory mixtures can, however, be more complex, as demonstrated with reference to a pair of 2,6-diphenylphenol and distearyl dithiopropionate [15]. The combined addition of these compounds with concentrations of 0.05% and 0.3%, respectively, results in an extended inhibitory period during the oxidation of PP (up to 3000 h at 413 K). Sulfide (for instance, (3,(3 -diphenylethyl sulfide) or its products not only break down ROOH, but also reduce the phenoxyl radical. Sulfoxide formed in the reaction of the sulfide with ROOH can react with ArO. Thus, the ability of sulfides and their products to reduce phenoxyl radicals can contribute to their synergistic effect. 

Bacillus subtilis defense mechanism, 610 bovine semm albumin y-radiation, 614 generation inhibition, 612 hydroperoxide synthesis, 315, 320 ludgenin oxidation, 645, 1250-1 luminol oxidation, 643, 644, 1242-4 organic sulfur compounds, 1032-9 ozone water disinfection, 606 peroxynitrite generation, 10, 611-12 Superoxide dismutase (SOD)... 

Although zinc dialkyl dithiophosphates, [(RO)2PS2]2Zn, have been used as antioxidants for many years, the detailed mechanism of their action is still not known. However, it is certain that they are efficient peroxide decomposers. The effect of a number of organic sulfur compounds, including a zinc dithiophosphate, on the rate of decomposition of cumene hydroperoxide in white mineral oil at 150°C. was investigated by Kennerly and Patterson (13). Each compound accelerated the hydroperoxide decomposition, the zinc salt being far superior in its activity to the others. Further, in each case the principal decomposition product... 

Kennerly and Patterson (13) studied the effect of several organic sulfur compounds, including thiols, sulfides, a disulfide, sulfonic acids, and a zinc dialkyl dithiophosphate, on the decomposition rate of cumene hydroperoxide in white mineral oil at 150 °C. In each case they found phenol as the major product. They suggested that the most attractive mechanism by which to explain these results involves ionic rearrangement catalyzed by acids or other electrophilic reagents (10) as... 

Scheme 2), which acts as a catalyst for the ionic decomposition of hydroperoxides (B-80MI11504, B-81MI11502). Other sulfur compounds known to be active peroxide decomposers are the nickel dialkyldithiocarbamates (3) (B-80MI11505) and the thiol (4) (B-81MI11502). 

Butyl hypochlorite, 55 of phenols to quinones Benzoyl /-butyl nitroxide, 28 2,3-Dichloro-5,6-dicyano-l, 4-benzoqui-none, 104 Periodic acid, 238 of phosphorus compounds Dimethyldioxirane, 120 of selenium compounds Potassium permanganate, 258 of sulfides to sulfoxides and sulfones /-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 ra-Chloroperbenzoic acid, 76, 112 Dimethyldioxirane, 120 of thiols to sulfur compounds Trimethylsilyl chlorochromate, 327... 

An antioxidant ties up the peroxy radicals so that they are incapable of propagating the reaction chain or to decompose the hydroperoxides in such a manner that carbonyl groups and additional free radicals are not formed. The former, which are called chain-breaking antioxidants, free-radical scavengers, or inhibitors. are usually hindered phenols or amines. The latter, called peroxide decomposers, are generally sulfur compounds or... 

Two types of antioxidants are used One type—amines and phenolics —reacts with the peroxy radicals to form more stable free radicals. The second type—sulfur compounds and phosphites—decomposes the hydroperoxides without formation of free radicals. The effect of sulfur compounds, such as dialkyl dithiocarbamates and alkyl thiols on the hydroperoxide decomposition has been investigated by Marshall. 

The object of this work was to gain some insight into the mechanism by which sulfur compounds function as stabilizers by studying the kinetics of the decomposition of hydroperoxides in the presence of dilauryl thio-dipropionate—one of the most widely used sulfur compounds in the stabilization of polyolefins. 

It is clear from these results that the reaction between Tetralin hydroperoxide and many sulfur compounds is not a simple one, inasmuch as at least 20 moles of hydroperoxide were decomposed by 1 mole of the... 

Kinetic Order of the Reaction. The decomposition of the hydroperoxide had an initial slow reaction or induction period followed by a faster main reaction. The induction period was unaffected by the addition of dilauryl sulfinyl dipropionate or by carrying out the reaction in an atmosphere of nitrogen but was eliminated by the addition of acetic acid. The length of the induction period decreased as the initial concentration of both hydroperoxide or sulfur compound increased. 

A first-order plot of logi0 [Hydroperoxide] vs. time (Figure 1) was linear, at least until the amount of hydroperoxide decomposed approached a value equal to the initial concentration of sulfur compound. After this point the rate of decomposition increased. Confirmation that the reaction was first order with respect to hydroperoxide was obtained by measuring the initial slopes of the rates of decomposition of varying amounts of... 

Considering the induction period and the initial stages of the main reaction only, it seems possible that during the induction period a complex is formed which involves the hydroperoxide and sulfur compound. 

The mechanism proposed so far takes account of the induction period and initial stages of the reaction only, and it is difficult to see how it can account for the large amount of hydroperoxide decomposed by the sulfur compound. However, Tetralin hydroperoxide is decomposed catalytically by acids (5). Although in the absence of dilauryl thiodipropionate the decomposition of Tetralin hydroperoxide in the presence of acetic acid at 70 °C. was very slow, if the acid species is a much stronger acid than acetic—e.g., a sulfonic acid as seems likely from the nature of the products of the reaction, the rate of acid-induced decomposition may be comparable with the rate of decomposition by the sulfur compound. Some evidence that acid-induced decomposition does occur at some stage in the over-all reaction is found in the presence of an ortho substituted aromatic compound in the solid product of the reaction. The acid catalyzed decomposition of Tetralin hydroperoxide follows the path of Reaction 14 (5) to give y-(o-hydroxyphenyl)butyraldehyde. This forms a brown resin which is mainly the aldol of this aldehyde (cfthe resin obtained in this work). 

Sulfoxides form complexes with hydroperoxides and can inhibit a partially oxidized substrate, but their inhibiting activity is destroyed by the simultaneous addition of an acidic substance such as stearic acid. The "activity of sulfur compounds cannot be wholly accounted for by their peroxide-decomposing action, and although they suppress peroxide-initiated autoxidation, they do not suppress oxidations initiated by free radical sources such as azobisisobutyronitrile (10). 

The detoxification of catalysts poisoned by Group V or VI compounds can be accomplished by reactions in which these inhibitors are converted to substances that do not have unshared electron pairs. For instance, bivalent sulfur compounds can be oxidized to sulfones or sulfonic acids by treatment with hypochlorite or hydroperoxides. "2,108 Thiophene, dimethyl sulfide and other sulfur and metal ion poisons as well as phosphorous"" and arsenic compounds " can be removed from platinum by washing the catalyst with acetic acid. This method for the reactivation of the catalyst is simpler than the oxidation techniques. Acidic or basic inhibitors are removed by the addition of an appropriate amount of base or acid, respectively. The effect of a small amount of inhibitor can frequently be overcome by the use of a larger amount of catalyst. 

Sulfur compounds are known as catalytic hydroperoxide decomposers (PD-C) one antioxidant molecule destroys several hydroperoxide molecules by the action of intermediate sulfur acid moieties.Thioethers and esters of thiodipropionic acid and metal dithiolates are examples of commercial significance (see Table 1, AOs 19-24). 

The efficient decomposition of hydroperoxides by a non-radical pathway can greatly increase the stabilizing efficiency of a chain-breaking antioxidant. This generally occurs by an ionic reaction mechanism. Typical additives are sulfur compounds and phosphite esters. These are able to compete with the decomposition reactions (either unimolecular or bimolecular) that produce the reactive alkoxy, hydroxy and peroxy radicals and reduce the peroxide to the alcohol. This is shown in the first reaction in Scheme 1.69 for the behaviour of a triaryl phosphite, P(OAr)3 in reducing ROOH to ROH while itself being oxidized to the phosphate. 

The strucmre of the aryl groups is designed to increase the hydrolytic stability of the compound. The sulfur compounds which are the most efficient hydroperoxide decomposers... 

The cumene feed must be free of oxidation propagation chain splitters, especially sulfur compounds, styrene, aniline and phenol. Since the reaction rate is extremely sensitive to these impurities, special care is taken to remove them. Phenol can be removed by treatment with caustic soda. However, its effect is less harmful than it appears, because it exerts an even more inhibitory action on side reactions, leading for instance to acetophenone or 2-phenyl 2-propanol, than on the main hydroperoxidation reaction, and because, in small amounts (10 to 1000 ppm), and combined with the sodium salt of cumyl hydroperoxide, its effect enhances tbe final yield ofthe operation. 

A.A. Oswald, F. Noel, and A.J. Stephenson, Organic sulfur compounds. V. Alkylammonium thiolate and peroxide salts possible intermediates in amine-catalyzed oxidation of mercaptans by hydroperoxides, J. Org. Chem. 1961, 26, 3969-3974. 

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