Functionalization sulfurated intermediates

Disproportionation reactions do not cause a net oxidation of the sulfur species, yet they have a key function in sulfide oxidation. Disproportionation provides a shunt in the sulfur cycle whereby the H S formed by this reaction may be oxidized again to the same sulfur intermediate by metal oxides. Manganese oxide, for example, rapidly oxidizes H S to S without participation of bacteria, but does not oxidize the S further to sulfate (Burdige 1993). The elemental sulfur may, however, be disproportionated (Eq. 8.19) whereby a fourth of it is oxidized completely to sulfate while the remaining three fourths return to the sulfide pool. Through repeated partial oxidation of sulfide to elemental sulfur with manganese oxide and subsequent disproportionation of the elemental sulfur to sulfate and sulfide a complete oxidation of sulfide to sulfate by manganese oxide may be achieved (Fig. 8.16 Thamdrup et al. 1993 Bdttcher and Thamdmp 2001) ... 

The process implications of equation 3 go beyond the weU-known properties (27—29) of NMP to faciUtate S Ar processes. The function of the aminocarboxylate is also to help solubilize the sulfur source anhydrous sodium sulfide and anhydrous sodium hydrogen sulfide are virtually insoluble in NMP (26). It also provides a necessary proton acceptor to convert thiophenol intermediates into more nucleophilic thiophenoxides. A block diagram for the Phillips low molecular weight linear PPS process is shown in Eigure 1. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

A iD-Corticoids have been important intermediates since it was shown ° that substitution at C-9 enhances anti-inflammatory activity. These olefins are usually obtained from 11a- or 11)5-alcohols, and consequently several refined methods have been devised for effecting this dehydration. It is desirable that such methods be compatible with the presence of A" -3-ketone and 17-hydroxy functions. The first direct procedure for which high yields were claimed was described in a patent issued to Upjohn. According to this method, the alcohol (11a or )5) is treated first with A-bromoacetamide in pyridine, then with sulfur dioxide. Recently it has been claimed " that the A-haloamide/sulfur dioxide method gives results superior to other methods, although the methanesulfonyl chloride/sulfur dioxide procedure (see below) apparently was not compared (see also ref. 94). 

The mechanism of the Cook-Heilbron reaction between a-aminonitriles and dithioformic ester 6 proceeds via an acyclic intermediate 7, as proven by its isolation in several cases. Nucleophilic attack of the amine function on the sulfur-bearing carbon leads to the elimination of hydrogen sulphide. Cyclization of the acyclic thiacetoamide results in a five membered ring which aromatises favourably to give 5-amino-2-benzylthiazole 8. 

Several reviews on the synthesis of aziridines have been published in the previous year. These publications include a review on the silver catalyzed addition of nitrenes (among other intermediates such as carbene) across a double bond <06EJOC4313> a review on sulfur ylide addition to imines to form aziridines <06SL181> a review on nitrogen addition across double bonds <06ACR194> a general review on functionalization of a,p-unsaturated esters with some discussion of aziridination <06TA1465>... 

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