Radical cation sulfur

Nowadays, ultramarine-type pigments are produced synthetically. Inside the zeolite structure the highly reactive sulfur radical anions are well protected which explains the stability of the blue color over thousands of years in air. However, the species responsible for the blue color should not be confused with the sulfur radical cations responsible for the blue color of sulfur solutions in fuming sulfuric acid (oleum) and similar oxidizing mixtures... 

Glasbeek M (2001) Excited State Spectroscopy and Excited State Dynamics of Rh(III) and Pd(II) Chelates as Studied by Optically Detected Magnetic Resonance Techniques. 213 95-142 Glass RS (1999) Sulfur Radical Cations. 205 1-87 Gobbi L, see Diederich F (1999) 201 43-129... 

In addition to silicon, sulfur groups have been used as auxiliaries for amide oxidation reactions (Scheme 31) [63], However, in these cases the mechanism of the reaction is different. The sulfur is oxidized to form a sulfur radical cation that is then eliminated from the molecule in order to... 

The unexpected formation of the blue crystalline radical cation (97) from the reaction of triazinium salt (98) with tetracyanoethylene has been reported and the product identified by its EPR spectrum and by X-ray crystallography (Scheme 42).199 Carboxylic acids react with the photochemically produced excited state of N-t-a-phenynitrone (PBN) to furnish acyloxy spin adducts RCOOPBN. The reaction was assumed to proceed via ET oxidation of PBN to give the PBN radical cation followed by reaction with RCO2H.200 The mechanism of the protodiazoniation of 4-nitrobenzenediazonium fluoroborate to nitrobenzene in DMF has been studied.201 Trapping experiments were consistent with kinetic isotope effects calculated for the DMF radical cation. The effect of the coupling of radicals with different sulfur radical cations in diazadithiafulvalenes has been investigated.202... 

Glass RS, Hojjatie M, Wilson GS, Mahling S, Gobi M, Asmus K-D (1984) Pulse radiolysis generation of sulfur radical cations stabilized by neighboring carboxylate and alcohol groups. J Am Chem Soc 106 5382-5383... 

A zero-order dependence on methionine concentration was observed in the Os(VIII)-catalyzed oxidation by HCF. A slow step consisting of reaction between a hydroxoos-mium derivative and HCF to form an intermediate has been suggested. The reaction of this intermediate with methionine in a fast step is postulated to yield a sulfur radical cation.94... 

Volume 2 begins with a thorough survey of sulfur radical cations, covering their synthesis, structure, stability, and reactivity, by Prof. Richard Glass. Prof. Naomichi Furukawa and Prof. Soichi Sato describe recent developments in the area of hypervalent organosulfur compounds, and the volume is completed by a discussion of the chemistry of thiophene 1,1 -dioxides by Prof. Juzo Nakayama and Prof. Yoshiaki Sugihara. 

Sulfonium salts have previously been formed by combination of carbon radicals with sulfur radical cations. The closest literature analogy to the proposed research was the extensive work of Shine et al. revealing that the sulfonium salts resulting from combination of carbon radicals with, for example, thianthrenium radical cations undergo facile substitution. 

The one-electron reduction potentials of the radical cations of thioanisole, benzyl methyl sulphide, and 2-hydroxyethyl benzyl sulfide in water and several organic solvents were investigated by cyclic voltammetry. For comparison, the one-electron oxidations in water were also measured using pulse radiolysis. ° The two methods are complementary and the reversible potentials determined by pulse radiolysis are fairly close to the peak potentials determined by cyclic voltammetry (Table 8) indicating that the peak potentials do correspond to the formation of sulfur radical cations for all three sulfides. 

Table 9. Kinetic parameters for the formation of sulfur radical cations in TiOj colloidal solutions containing MTPM and PTE at room temperature.

Sulfur-centered radical cations derived from aromatic thioethers (Ar-S-Ar) have been investigated much less extensively. An important feature of one-electron oxidation of aromatic thioethers is the lack of dimeric radical sulfur radical cations (ArS.. S-Ar) because of the spin delocalization onto the aromatic ring. Oxidation of thioanisole (Ar-S-CHj) by OH radicals was studied using pulse radiolysis. At neutral pH, OH addition led to the prompt formation of monomeric sulfur radical cations and hydroxycyclohexadienyl radicals (see Scheme 8). 

The latter radicals decay into products which do not include the corresponding radical cations with the delocalized positive charge on the aromatic ring. At low pH, OH addition, both to the thioether functionality and to the aromatic ring, led promptly only to the monomeric sulfur radical cations. These observations were rationalized in terms of the highly unstable nature of Ph -S-CHg radical... 

Monomeric sulfur radical cations derived from various carboxylic acids containing thioether functionality were generated in aqueous solutions using OH radicals. Three decay pathways (decarboxylation, deprotonation, and jS-fragmentation), similar to those presented for phenylthioacetic acid vide supm. Scheme 6), were identified and found to be dependent upon the structure of sulfur radical cations. 

The effect of N-acetyl substitution in methionine on the nature of transients formed after one-electron oxidation was studied as a function of pH and NAM concentration. The observed absorption bands with X = 290 nm, 360 nm, and 490 nm were respectively assigned to a-(alkylthio)alkyl, hydroxysulfuranyl and dimeric radical cations with intermolecular three-electron bond between sulfur atoms. N-acetylmethionine amide (NAMA) (Chart 7) represents a simple chemical model for the methionine residue incorporated in a peptide. Pulse radiolysis studies coupled to time-resolved UV-Vis spectroscopy and conductivity detection of N-acetyl methionine amide delivered the first experimental evidence that a sulfur radical cation can associate with the oxygen of an amide function vide infra). ... 

The latter radical is of particular note in that it supports recent observations of sulfur radical cations complexed with the oxygen... 

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