Thiocyanate radical

The photoinitiated reactions of thiocyanogen (LXV) involve the thiocyanate radical and result in allylic substitution and addition.8 9 The relative proportions of the products vary with the structure of the olefin, e.g., cyclohexene gives a 1 1 mixture whereas octene-1 gives almost exclusively the addition product. 

Milligan JR, Aguilera J, Paglinawan RA, Ward JF (2000) Mechanism of DNA damage by thiocyanate radicals. Int J Radiat Biol 76 1305-1314... 

Gas phase kinetic studies of the reactions of hydroxyl radical are most conveniently carried out with direct monitoring of the OH radical with time using laser induced fluorescence (111. The low absorption coefficient of the aqueous hydroxyl radical ( 188nm 540 M 1 cm-1, (12)) precluded the direct measurement of this reactant species by its absorbance. Also, the absence of a readily observable product species for the reaction of OH + MSA at the wavelength range (275-575 nm) easily accessible in our experiments, has lead us to monitor the concentration of OH in solution indirectly by competition kinetics (13), measuring the absorption of the thiocyanate radical anion (ejsonm = 7600 M cm 1 (12)). 

In none of the experiments was there indication of absorbance by species other than the thiocyanate radical, which supports the assumption that any reactions between uncomplexed SCN radicals and other species present are unimportant. 

Figures 5a),b) show the diminution of the thiocyanate radical absorption at 480 nm (A) as increasing amounts of each added competitor substance were added for the substrates added. Using equation (1), plots of Aq/A vs [s]/[SCN ] were made, the slopes of which yielded k(OH + s)/k(OH + SCN), where s is...

Figure 5. Decreases of the thiocyanate radical anion absorption as a function of added competitor concentration. Absorbances monitored at 480 nm. a) DMSO b)MSAorDMS02.

Experiments generating sulfate radicals, SO/", by UV photolysis of S2O82 in aqueous suspensions of silica nanoparticles showed a fast disappearance of the aqueous sulfate radicals yielding two transient species with absorption maxima around 320 and 600 nm, respectively [20]. The results indicated that at pH 3-9 S04 radicals build up an adduct on the surface with maximum absorption at 320 nm. This adduct shows similar reactivity to that observed for the sulfate radical in aqueous solution. The transients with absorption maximum at 600 nm were identified as SiO surface defects formed from the reaction between the adduct and deprotonated geminal and single silanols. Other less oxidative radicals lead to different radical-silica interactions. For example, thiocyanate radicals react with deprotonated silanols, not involving silanol oxidation. 

It has been shown that the photocatalytic electron transfer processes at the semiconductor interface can be greatly enhanced by depositing a noble metal on the semiconductor particle [175-179]. The photogenerated holes are capable of oxidizing thiocyanate ions at the semiconductor interface [180]. The thiocyanate radicals ((SCN)2 ) generated in the photocatalytic oxidation can be conveniently monitored from its absorbance at 480 run [180-183]. 

A. Dawson P. V. Kamat, Com-plexation of Gold Nanopartides with Radiolytically Generated Thiocyanate Radicals ((SCN)2 )./. Phys. Chem. B 2000, 304, 11842-11846. 

Familiar examples of charge-transfer complexes include the phenolic complex of iron(III), the 1,10-phenanthroline complex of iron(II), the iodide complex of molecular iodine, and the ferro/ferricyanide complex responsible for the color of Prussian blue. The red color of the iron(III)/thiocyanate complex is a further example of charge-transfer absorption. Absorption of a photon results in the transfer of an electron from the thiocyanate ion to an orbital that is largely associated with the iron(III) ion. The product is an excited species involving predominantly iron(ll) and the thiocyanate radical SCN. As with other types of electronic excitation, the electron in this complex ordinarily returns to its original state after a brief period. Occasionally, however, an excited complex may dissociate and produce photochemical oxidation/reduction products. Three spectra of charge-transfer complexes are shown in Figure 26-4. 

The Thiocyanate Radiolysis Dosimeter. The thiocyanate dosimeter is a reliable, accurate, and convenient means of dose calibration in pulse radiolysis experiments, when coupled with a physical dosimeter of the type described earlier. An aqueous solution of KSCN (10 mmol dm" ) is saturated with N2O. The eaq are quantitatively converted to HO within about 3 ns, as described above (reaction 29). The hydroxyl radicals then oxidize SCN", transferring the radical center to the thiocyanate radical (SCN ) (reaction 30). The SCN radical rapidly couples with a thiocyanate ion, producing (SCN)2 ", a relatively stable radical with a high molar absorptivity (reaction 31) ... 

The cerium(IV)-mediated generation of heteroatom radicals by oxidation of anions such as azides was discovered many years ago [10], However, Nair et al. applied this strategy for a C-S bond-forming reaction by oxidation of ammonium thiocyanate le only recently [11], Addition of thiocyanate radical to indole 18 provides an intermediate radical, which is further oxidized to the cation by CAN. Loss of proton from the cationic intermediate provides the substituted arene 19 in excellent yield (Scheme 6). 

In agreement with the rate constants measured for amino-acids in solution, azide radicals attack primarily mostly tryptophan whereas halides like dibromide may also react with methionine. Thiocyanate radicals are also specific of tryptophan residues. However this process is a reversible equilibrium between lysozyme (119). 

It has been widely reported that electrooxidation of the thiocyanate ion at pH 4 yields hydrogen cyanide and (or) cyanide and sulfate ions as main products [134]. However, there is a huge gap in terms of the mechanism that takes place between the binding of thiocyanate to the catalyst and the products experimentally found. In order to get insight about the elemental reactions between these processes, it is proposed based on experimental evidence that the oxidation of thiocyanate particularly catalyzed by MPc and MPc like systems, leads to the production of thiocyanate radicals that dimerize to form the pseudohalogen molecule thio-cyanogen (SCN)2 [132, 135-139]. 

Sulfur atom, fluorosulfur, hydroxysulfur, and thiocyanate radicals... 

Sulfur atom, Fluowsulfur, Hydroxysulfur and Thiocyanate radicals ... 

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