Sulfur compounds reactivity/reaction mechanisms

These reactions may be important for several reasons. It may be possible to use the chemiluminescent reaction of ozone with organic sulfides to monitor the low concentrations of sulfur compounds in urban atmospheres. Also, excited species are being formed, and these reactive intermediates may be important in high altitude atmospheric reactions. Finally, identifying these emitting species should give information about the mechanisms of gas phase ozone reactions. Current progress on these reactions by the authors is reviewed here. 

REACTIVITY AND REACTION MECHANISM OF VARIOUS SULFUR COMPOUNDS... 

The efficient decomposition of hydroperoxides by a non-radical pathway can greatly increase the stabilizing efficiency of a chain-breaking antioxidant. This generally occurs by an ionic reaction mechanism. Typical additives are sulfur compounds and phosphite esters. These are able to compete with the decomposition reactions (either unimolecular or bimolecular) that produce the reactive alkoxy, hydroxy and peroxy radicals and reduce the peroxide to the alcohol. This is shown in the first reaction in Scheme 1.69 for the behaviour of a triaryl phosphite, P(OAr)3 in reducing ROOH to ROH while itself being oxidized to the phosphate. 

Orotidine monophosphate decarboxylase, the mechanism of, 38, 183 Oxyacids of sulfur and their anhydrides, mechanisms and reactivity in reactions of organic, 17, 65 Oxygen isotope exchange reactions of organic compounds, 3, 123... 

Figure 3 shows the GC-FPD chromatograms that illustrate reactivities of various sulfur compounds in gas oil HDS for diesel fuel production. In deep HDS, the conversion of these key substituted dibenzothiophenes largely determines the required conditions. In gas oils, the reactivities of (alkyl-substituted) 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are much lower than those of other sulfur-containing compounds " . Gates and Topsoe pointed out in 1997 that 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are the most appropriate compounds for investigations of candidate catalysts and reaction mechanisms. 

The reaction of various A-tosylated a-amino acids (94) with benzene in concentrated sulfuric acid yielded diphenyl derivatives (95)." The mechanism proposed for the reaction (Scheme 9) involves initial protonation of the carboxyl group to give (96), which suffers decarbonylation to the A-tosyliminium salt (97). This reactive electrophile (97) interacts with benzene to give a monophenyl compound (98) which, via a Friedel-Crafts reaction, interacts with another molecule of benzene to yield the diphenyl compound (95)." Toluene and p-xylene reacted analogously to yield diarylated products. 

The high affinity of many platinum compounds for sulfur and the availability of many sulfur-containing biomolecules have raised the question whether Pt-sulfur biomolecule interactions could serve as a drug reservoir for platination at DNA, necessary for the antitumor activity of cis-Pt. Two reaction paths are possible, i.e., spontaneous release of plantinum from the sulfur, or nucleophilic displacement of platinum from sulfur by guanine (N7), for example. At the moment, there is no real evidence for the existence of such reactivation mechanisms. In fact, it has been reported that Pt-protein interactions in the plasma (albumin) are not reversible under normal conditions (161, 165). Further, a mixture of cis-Pt-methionine products does not show antitumor properties (166), indicating no induced platination of DNA. More research is required to investigate the existence of a reactivation mechanism. However, it is predicted that if such a reactivation phenomenon is operational, the most likely candidate is the labile Pt-methionine bond, as has been shown by its rapid reaction with Naddtc, STS, and thiourea (vide supra) (131). 

A given alcohol is treated with 25 percent excess of aqueous (48 per cent) hydrobromic acid together with sulfuric acid. The mixture is refluxed in order to convert the alcohol as completely as possible into the corresponding bromide, and the latter is then removed from the reaction mixture by distillation. Slight variations from this procedure depend upon the physical and chemical properties of the alcohol used, or of the bromide formed in the reaction. For example, in the preparations of ethyl and allyl bromides, the reaction mixture is not refluxed because of the volatility of the former compound, and because of the chemical reactivity of the latter in the preparation of wo amyl bromide, too large a proportion of sulfuric acid may produce appreciable decomposition while halides of high molecular weight, because of their low volatility, are separated from the reaction mixture mechanically, instead of by distillation. 

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