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Hydroperoxide decomposer, sulfur compounds

The final possible mode of action for an antioxidant is as a peroxide decomposer. In the sequences that lead to photodegradation of a polymer the ready fragmentation of the hydroperoxide groups to free radicals is the important step. If this step is interfered with because the peroxide has undergone an alternative decomposition this major source of initiation is removed. The additives which act by decomposing hydroperoxide groups include compounds containing either divalent sulfur or trivalent phosphorus. The mechanism involves... [Pg.124]

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... [Pg.332]

Some organosulfur compounds can function as fuel antioxidants by acting to decompose hydroperoxides. Organosulfides are believed to react with hydroperoxides to form sulfoxides. The sulfoxides then further react with hydroperoxides to form other more acidic compounds. These newly formed acids continue the process of decomposing and reaction with hydroperoxides. Thus, organosulfur compounds function in the process oxidation inhibition through hydroperoxide decomposition. However, in most fuel applications, sulfur-containing antioxidants are not utilized. [Pg.138]

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). [Pg.396]

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... [Pg.139]

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. [Pg.10]

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... [Pg.157]

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... [Pg.159]

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). [Pg.167]

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. [Pg.168]

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). [Pg.224]

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). [Pg.86]

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... [Pg.154]

There are two ways in which stabilizers can function to retard autoxidation and the resultant degradation of polymers. Preventive antioxidants reduce the rate of initiation, e.g., by converting hydroperoxide to nonradical products. Chain-breaking antioxidants terminate the kinetic chain by reacting with the chain-propagating free radicals. Both mechanisms are discussed and illustrated. Current studies on the role of certain organic sulfur compounds as preventive antioxidants are also described. Sulfenic acids, RSOH, from the decomposition of sulfoxides have been reported to exhibit both prooxidant effects and chain-breaking antioxidant activity in addition to their preventive antioxidant activity as peroxide decomposers. [Pg.220]

Recently we reported a study of the peroxide decomposing activity of sulfoxides, sulfenic acids, thiolsulfinates, and their oxidation or decomposition products (2,15). A benzene solution of the sulfenic acid reacted rapidly with both tert-butyl hydroperoxide and cumene hydroperoxide, consuming two moles of hydroperoxide per mole of sulfur compound. A slower catalytic process destroyed many additional moles of hydroperoxide per mole of sulfur compound. A similar solution of cumene hydroperoxide in benzene with thiolsulfinate present in a ratio of 10 moles of hydroperoxide per mole of sulfur compound showed no change for 22 hr at 25°C. At that time a catalytic decomposition started which destroyed many moles of hydroperoxide per mole of sulfur compound. [Pg.226]

These experiments were repeated in the presence of CaC03 to see if the base would affect the activity of the sulfur compounds as peroxide decomposers. The initial reaction of sulfenic acid with the hydroperoxide was slowed, as shown in Figure 2, but ultimately consumed two moles of ROOH per mole of RSOH. The subsequent catalytic decomposition was almost completely stopped with excess of base consistent with neutralization of an acid catalyst, presumed to be the sulfonic acid formed by oxidation of the sulfenic acid ... [Pg.226]

The polar nature of the catalytic decomposition of cumene hydroperoxide with added terf-butyl terf-butanethiolsulfinate has been clearly established (I). The thiolsulfinate is converted into an active peroxide decomposer capable of destroying many moles of hydroperoxide per mole of sulfur compound. The acidic character of the active species was demonstrated by its effective neutralization with the added base calcium carbonate. Formation of the active peroxide decomposer may be envisaged as involving one or more of the following three reaction types concerted process, ionic processes, and free-radical processes. [Pg.232]

Examples of widely used secondary antioxidants are phosphites, phosphonites, and sultides (Fig. 11.7). Usually, secondary antioxidants are used in combination with primary antioxidants to benetit from a synergistic effect. The main action of phosphites and phosphonites is the oxidation to the corresponding phosphates by reacting with hydroperoxides. These P compounds are mainly used as melt stabilizers during processing. Sulfur compounds act as well as hydroperoxide decomposers via sulfur oxide and sulfenic acid formation. Sulfur compounds are preferably used in combination with phenolic antioxidants to improve the long-term thermal stability of polymers at temperature ranges between 100 and 150 °C. [Pg.229]

Since hydroperoxides play a determining role in the photooxidative degradation of polymers, decomposition of hydroperoxides into more stable compounds, before the hydroperoxides undergo photolytic cleavage, would be expected to provide an effective means of UV protection. Metal complexes of sulfur-containing compounds such as dialkyldithiocarbamates (XIX), dialkyldithiophosphates (XX) and thiobisphenolates (XXI) are very efficient hydroperoxide decomposers even if used in almost... [Pg.118]

However, hydroperoxide decomposers may act by much more complicated mechanisms. Many sulfur compounds, like the thiodipropionate esters (DRTPs) or the metal dialkyldithiocarbamates (MRDCs) are oxidised to sulfur acids (sulfinic, sulfonic and SO3) which are ionic catalysts for the non-radical decomposition of hydroperoxides. The MRDCs are particularly important since, unlike the phosphites, they also contain complex transition metal ions and when M is a transition metal ion e.g. Ni) they are also UVAs. [Pg.56]

Since hydroperoxides are decomposed by heat and light to generate radicals which feed the degradation processes, it is essential that they be decomposed into nonradical products. Phosphites, such as di-stearyl pentaeiythritol diphosphite (Weston 618), and sulfur compounds, such as nickel dibutyl dithiocarbamate (Rylex NBC), provide this fimction and both provide UV-stabiUzing activity in polyolefin formulations. Phosphites usually are used in combination with other UV stabilizer types. [Pg.8731]

Undoubtedly more important than the rate of decomposition of hydroperoxides is the type of product obtained. Table 5 lists the major products obtained by completely decomposing TBHP with various sulfur compounds. With nickel and zinc dithiocarbamates... [Pg.124]

Hydroperoxide decomposers play an important role in hydroperoxide group decomposition. The most important are metal complexes of sulfur or phosphorous containing compounds. [Pg.523]

One of the reasons that sulfur-containing antioxidants are effective stabilizers lies in the fact that oxidation products of these stabilizers act as long-term heat stabilizers too [103-105], which can be even more effective hydroperoxide decomposers than the original compound [106]. [Pg.407]

Sulfur-based hydroperoxide decomposers, such as thioesters, suffer from the disadvantage that they may be malodorous or may yield compounds that are. This fact largely precludes their use in many products. For this reason, phosphorus-based compounds are the most widely used type of secondary antioxidants in polyethylene. [Pg.388]


See other pages where Hydroperoxide decomposer, sulfur compounds is mentioned: [Pg.241]    [Pg.594]    [Pg.353]    [Pg.595]    [Pg.155]    [Pg.156]    [Pg.158]    [Pg.164]    [Pg.169]    [Pg.58]    [Pg.231]    [Pg.404]    [Pg.148]    [Pg.65]    [Pg.333]    [Pg.7755]    [Pg.821]    [Pg.588]    [Pg.1313]    [Pg.1329]   
See also in sourсe #XX -- [ Pg.399 ]




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