REACTIONS WITH ORGANOSULFUR COMPOUNDS

Figure 7 Emission spectra obtained in the reaction of DMS with F2. (A) 155 mtorr CH3SCH3, 30 mtorr F2, 570 mtorr He (B) 30 mtorr CH3SCH3, 20 mtorr F2, 350 mtorr He (C) 30 mtorr CH3SCH3, 50 mtorr F2, 900 mtorr He. (Reprinted from RJ Glinski, EA Mishalanie, JW Birks, Molecular emission spectra in the visible and near IR produced in the chemiluminescent reactions of molecular fluorine with organosulfur compounds, Journal of Photochemistry 37 223, 1987, with permission from Elsevier Science.)...

Under excess F2 conditions, the reaction with DMS and other organosulfur compounds may produce CH as well, and at the low pressures ( 1 torr) of the FCLD, a more favorable reaction may be,... 

Organosulfur chemistry is presently a particularly dynamic subject area. The stereochemical aspects of this field are surveyed by M. Mikojajczyk and J. Drabowicz. in the fifth chapter, entitled Qural Organosulfur Compounds. The synthesis, resolution, and application of a wide range of chiral sulfur compounds are described as are the determination of absolute configuration and of enantiomeric purity of these substances. A discussion of the dynamic stereochemistry of chiral sulfur compounds including racemization processes follows. Finally, nucleophilic substitution on and reaction of such compounds with electrophiles, their use in asymmetric synthesis, and asymmetric induction in the transfer of chirality from sulfur to other centers is discussed in a chapter that should be of interest to chemists in several disciplines, in particular synthetic and natural product chemistry. 

With each of the C, P and S centers, compounds with several oxidation states are possible, thus multiplying the types of nucleophilic reactions extant. Importantly, the types of compounds cover a variety of classes each with its characteristic behaviors and reactivities, each defining a specific area in chemistry. Since the C, P and S reactive centers are incorporated in the majority of molecules in living systems it follows that the chemistry to be considered in this chapter is closely tied with the chemistry of life, i.e. bioorganic reaction mechanisms. It is known in fact that many organophosphorus and organosulfur compounds are toxic toward mammalian organisms which renders their destruction under mild conditions of critical importance. 

Unusual fragmentation reactions for thietanium salts have been observed. Their analysis may reveal more information about the influence of d-orbitals in the reaction mechanisms of organosulfur compounds. Alkylation of certain thietanes leads to 5-methylthietanonium salts. The thietanium salt 193, which is formed from 2,4-dimethylthietane and (CH3)30" BF4, breaks up when treated with n-butyllithium into a reactive biradical and its resulting cyclopropane and a thioether. 

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. 

By careful control of the conditions of the reaction one can obtain preferentially oxidation of sulfur to its four coordinate oxidation state and by using a second set of conditions one can obtain the oxidation to the six-coordinate sulfur species. The dynamic NMR study of SF3CF2SF3 is currently in progress in collaboration with A. H. Cowley (60). This differentiation of oxidation states is extremely promising, and work in progress shows that this is not at all an isolated situation. Mercaptans and other organosulfur compounds definitely exhibit this capacity in fluorine reactions. 

In sharp contrast to the thioketenes, carbon disulfide S=C=S, carbon oxysulfide 0=C=S and the isothiocyanates R-N=C=S are stable compounds although highly reactive, and are widely used in organosulfur chemistry. Some of their reactions with organometallics have been mentioned previously (see Section 2.8.3). 

Sigmatropic, electrocyclic, cycloaddition and cycloelimination, and cheletropic reactions have all been carried out with organosulfur compounds and often used for synthetic puiposes. A chapter of Block s monograph (203] is devoted to this topic, and most of the pericyclic processes include examples with sulfur compounds. The treatises by Barton and Ollis [482], Trost and Fleming [483] and Klamann [484] are guides to the more specialized literature. Some reviews deal with specific cases thiocarbonyl compounds [120] or cycloaddition reactions [485],... 

In addition, several metal-coordinated thials have been described in studies pertaining to hydrodesulfurization (HDS) reactions. This catalytic process is used to remove sulfur from organosulfur compounds present in fossil fuel feedstocks by reaction with hydrogen and a transition metal (Rh, Ir) and possesses both commercial and environmental importance393,394. 

Organosulfur compounds are especially useful for C-fluorine bond forming reactions with (difluoroiodo)arenes. For example, dithioketal derivatives of benzophenones are readily converted to diaryldifluoromethanes with two equivalents of DFIT in dichloromethane [105]. This transformation has also been effected with electro chemically prepared p-(difluoroiodo)anisole/Et3N 3HF, and by anodic oxidations of p-iodoanisole in acetonitrile solutions containing Et3N 3HF and dithioketal substrates (Scheme 35) [96]. Under the latter conditions, p-(difluoroiodo)anisole is continuously regenerated, and the iodoarene was employed at catalytic levels for high yield conversions of the dithioketals to diaryldifluoromethanes. 

Methanesulfonic acid, dimethyl sulfoxide and dimethyl sulfone are potential intermediates in the gas phase oxidation of dimethylsulfide in the atmosphere. We nave measured the rate of reaction of MSA with OH in aqueous solution using laser flash photolysis of dilute hydrogen peroxide solutions as a source of hydroxyl radicals, and using competition kinetics with thiocyanate as the reference solute. The rate of the reaction k (OH + SCN ) was remeasured to be 9.60 1.12 x 109 M 1 s 1, in reasonable agreement with recent literature determinations. The rates of reaction of the hydroxyl radical with the organosulfur compounds were found to decrease in the order DMSO (k = 5.4 0.3 x 109 M-i s 1) > MSA (k = 4.7 0.9 x 107 M l S 1) > DMS02 (k = 2.7 . 15 x 107 M 1 s ). The implications of the rate constant for the fate of MSA in atmospheric water are discussed. 

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