Peroxydisulfate initiators

In some cases, due to the highly polar character of the sulfate radicals, peroxydisulfate initiators can provide slow polymerization rates with some apolar monomers since the polar sulfate radicals cannot easily penetrate into the swollen micelle structures containing apolar monomers. The use of mercaptans together with the peroxydisulfate type initiators is another method to obtain higher polymerization rates [43]. The mercaptyl radicals are more apolar relative to the free sulfate radicals and can easily interact with the apolar monomers to provide higher polymerization rates. 

Recently, Smigol et al. [75] extensively studied emulsifier-free emulsion polymerization of different monomers including styrene, methyl methacrylate, and glycidyl methacrylate in an aqueous medium by using potassium peroxydisulfate as the initiator. In this study. 

Photolysis or thermolysis of persulfate ion (41) (also called peroxydisulfate) results in hoinolysis of the 0-0 bond and formation of two sulfate radical anions. The thermal reaction in aqueous media has been widely studied."51 232 The rate of decomposition is a complex function of pH, ionic strength, and concentration. Initiator efficiencies for persulfate in emulsion polymerization are low (0.1-0.3) and depend upon reaction conditions (Le. temperature, initiator concentration)."33... 

ESR experiments employing in situ photolytic decomposition of the peroxydisulfate anion (S20g ) have been carried out to study the reaction of S04 with aliphatic sulfoxides. In the case of dimethyl sulfoxide three radicals are detected ( CHj, CH3 S02, CH2 S(0)CH3), the proportion being pH-dependent. The reaction is assumed to proceed via an initially formed radical cation (not detected) which would be rapidly hydrated to give an intermediate identical with that generated by OH addition on the sulfoxide. Such a process parallels the rapid hydration of radical cations formed from thiophene in their reactions with SO/ and... 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

The per(poly)fluoroalkylation of olefins by per(poly)fluoroalkyl chlorides, initiated by ammonium peroxydisulfate and sodium formate, is also reported. The reaction proceeds smoothly in polar aprotic solvents. The presence of functional groups like sodium car-boxylate or sulfonate in the polyfluoroalkyl chloride appears to facilitate the reaction. This reaction represents the first example of the reactivity of per(poly)fluoroalkyl chlorides. 

ECL is obtained from these systems only when the potential of the working electrode is sufficiently negative that reduction of the transition metal complex occurs. In all cases peroxydisulfate will also be reduced at this potential. However, the S2O8 which reacts at the electrode does not participate in the ECL mechanism. Rather, it is the reaction of the reduced form of M with S2O8 - that initiates the luminescence process. The first two steps of this reductive oxidation ECL mechanism have therefore been proposed to be (6) ... 

Results with Silver Composition in Water with 10 ppm K2S2Os. For Salmonella, for the lower initial bacteria level (104), the following log reductions were recorded 0.26 at 0 minutes, 0.28 at 20 minutes, 0.35 at 60 minutes, and 0.58 at 240 minutes. For the higher initial bacteria level (106), the following log reductions were recorded 0.03 at 0 minutes, 0.16 at 20 minutes, 0.21 at 60 minutes and 0.36 at 240 minutes. The results indicate that the 10 ppm silver with 10 ppm potassium peroxydisulfate (K2S2Os) embodiment of this invention provides an effective bactericidal effect for Salmonella on beef steak. 

Related chemistry has been demonstrated for reactions involving initial reduction of one species and concomitant reduction of a second species that leads to production of a strong oxidizing agent. The peroxydisulfate dianion decomposes upon reduction, to produce SO4, which can annihilate with an anion radical to yield a luminescent species. White and Bard demonstrated this for reduction of solutions containing tris(2,2 -bipyridine) ruthenium(Il), [Ru(bpy)3] +, in the presence of S20g as shown below [22] ... 

Woods, Kolthoff, and Meehan found for the induced oxidation of As(III) by the Fe(II)-peroxydisulfate or Fe(II)-H202 reactions that the induction factor can approach infinity in the presence of Fe(III) or Cu(II). With peroxydisulfate the initiation reaction is given by (15-48) and by... 

Boyer and Ramsey found that the air oxidation of iodide is induced by the reaction of iodide with peroxydisulfate, Fe(III), ferricyanide, or V(V). The reaction with V(V) was investigated in detail and found to behave as a typical induced chain reaction. The proposed mechanism involves the formation of atomic iodine I or the ion I2" as an intermediate that reacts with oxygen. The chain is initiated by the reaction... 

In-line digestion of waters, as initially demonstrated in the amperometric determination of phosphate involving oxidation by peroxydisulfate [140]. 

The Effects of pH and of Time of Irradiation. In Figure 1 are given the results obtained in the radiolysis of a 10-4M K2S208 solution in water. It is seen that the initial rate of decomposition of peroxydisulfate is very high its value, inferred from the tangent to the curve at time zero, is about 6.0. The H202 yield is zero for the small doses but it increases as the peroxydisulfate concentration diminishes and, once the... 

On the other hand, the measured G(HSOr,") values are greater than those corresponding to peroxydisulfate (Figure 5 and Reference 1). It appears, therefore, that the initial yield of peroxymonosulfate formation in sulfuric solutions far exceeds that of peroxydisulfate. 

Large, colorless aggregates were observed by static and dynamic light-scattering measurements during the induction period of an oxidative polymerization of aniline with APS in dilute acidic aqueous solutions [177]. These aggregates are believed to be dianUinium peroxydisulfate ion clusters whose shape (rod-like) plays an important role in the initial formation of PANI-NFs. The formation of the interconnected, branched nanofiber networks by dilute polymerization was explained as follows [171]. Competition between a... 

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