Sulfoxyl radicals

Sevilla MD, Becker D, Yan M (1990a) The formation and structure of the sulfoxyl radicals RSO, RSOO, RSCV, and RS0200 from the reaction of cysteine, glutathione and penicillamine thiyl radicals with molecular oxygen. Int J Radiat Biol 57 65-81... 

This condensation with sulfur dioxide is rather peculiar. To the difference with carbonyl electrophiles, sulfur dioxide is more easily reduced than trifluoromethyl bromide. As already pointed out, initial consumption of zinc by this anhydride was obvious, producing the sulfoxylate radical anion which is known to be in equilibrium with the dithionite anion (Fig. 15). Incidentally, this salt mixed with sodium bicarbonate in aqueous acetonitrile was used for the transformation of liquid perhalogenoalkyl halides into their corresponding sulfmates (ref. 24). We have been able to transform the gaseous and poorly reactive trifluoromethyl bromide into sodium trifluoromethanesulfinate. However, the reaction conditions (Fig. 16) (ref. 25) were modified because no transformation occurred in the medium employed for the sulfinato-dehalogenation of the liquid halides. 

Experiments were performed with various sulfoxylate radical anion precursors sodium dithionite, sodium hydroxymethanesulfinate or a mixture of sulfur dioxide with a reductant, such as zinc or sodium formate (refs. 29, 30).In contradistinction with the trifluoromethylation of aromatic compounds (Figs. 19,20), a stoiechiometric amount of the sulfoxylate radical anion precursor was necessary. In the disulfide case, there is no intermediate able to reduce back the sulfur dioxide which is formed in the medium (Fig. 22). 

For many years now, the reactivity of trifluoromethyl bromide has been underestimated. During the past decade the major breakthrough in this area has been the realisation that trifluoromethylation of organic compounds with this halide can be induced by mild reductants such as thiolates, zinc or sulfoxylate radical anion. Nowadays, a great variety of fluorinated products are available by these new methods sodium triflinate and triflic acid, trifluoromethylated alcohols, trifluoromethyl-containing aromatic compounds, ethyl trifluoropyruvate, trifluoromethylsulfides. ... 

In this review the generic term sulfoxyl radical is used to define species with oxygens directly bonded to sulfur and carrying a substantial spin density in the sulfur-oxygen moiety. Species that fit this definition are sulfinyl, RSO sulfonyl, RSO2 thiyl peroxyl, RSOO sulfuranyl peroxyl, (RO) R 3 SOO sulfonyl peroxyl, RSO2OO and various kinds of sulfuranyl radicals, (RO) R3 S and SO species. Sulfuranyl and SO/ radicals will be mentioned only briefly in this chapter as they are reviewed separately in this book (see Chapter 9 by Margaretha and Chapter 3 by Huie and Sieck, respectively). 

The chemistry of sulfoxyl radicals has been reviewed several times. The latest and probably most complete reviews are those by Lunazzi and Pedulli in 1985 [1], Chatgilialoglu in 1988 [2], and Anklam and Margaretha in 1989 [3]. Our intention is to present an update of this rapidly developing area. 

Experimental techniques available to investigate sulfoxyl radicals have not changed significantly since the publication of the aforementioned reviews. ESR spectroscopy still remains the most informative and probably the most sensitive detection method. Unfortunately, a low time resolution of continuous wave (CW) ESR spectrometers with 100 kHz field modulation makes them incapable of providing significant kinetic information except for, perhaps, recombination rates. More advanced time resolved ESR techniques still have a limited application in kinetic studies and we are not aware of such techniques having been employed to study the reactions of sulfoxyl radicals. 

Flash photolysis/pulse radiolysis with optical detection are other techniques widely used in studies of sulfoxyl radicals. The major complication in the use of these techniques is the fairly weak absorptivity of sulfoxyl radicals combined with their low reactivity. Sulfonyl and thiyl peroxyl radicals are the only species... 

Sulfoxyl Radicals Formation, Structure, and Kinetics 4.3.3 Addition to double bonds... 

SULFOXYL RADICALS AND THEIR POSSIBLE BIOLOGICAL IMPACT... 

While the chief theory for the oxygen effect is considered to be the fixation model (oxygen reacts with the DNA damage site and fixes the damage before thiol repair), however, the oxygen effect may also involve the formation of sulfoxyl radicals [110]. In this model, repair proceeds by reactions such as reactions (36) and (37). With oxygen present then a series of reactions (38)-(41) take place ... 

Structural properties of several kinds of sulfur-centered radical have been discussed in excellent reviews [1-5]. The reader is referred to those references for studies up to 1993. The present article will concentrate on work appearing since those publications and on aspects not covered in them. The discussion includes S, S " and S2 ", alkyl thiyl and perthiyl radicals, alkyl sulfide and disulfide cation radicals, and disulfide anion radicals. The corresponding aryl thiyl species are also discussed where information is available. Attention is also paid to structures with two center-three electron 2(t/ (t bonds. Structures of alkyl sulfoxyl radicals are considered in Chapter 8. 

---