Reactive sulfur species

In a practical HDS process for gas oil, both aromatic species existing in the feed and various types of sulfur compounds compete for the active sites on the catalyst surface. Moreover, H2S and some other hydrocarbons produced in the early stages of the desulfurization appear to inhibit the HDS of the less reactive sulfur species. The reactivities of refractory sulfur compounds and the effects of inhibitors in gas oils need to be fully understood for the development of an improved economical desulfurization process. 

As discussed in Section III, when the sulfur content is lowered from 0.20 to 0.05%, the chemistry of HDS of gas oils is essentially the chemistry of alkyl-substituted dibenzothiophenes. Though gas oils initially contain mostly alkyl-substituted benzothiophenes, these are completely removed by the time 0.20% S is achieved. Thus, this review will deal predominantly with the reaction pathways involved in the HDS of alkyl-substituted dibenzothiophenes. There are many excellent reviews on reaction pathways of the more reactive sulfur species such as thiophenes and benzothiophenes (2, 5, 8, 23, 24), and the reader is referred to those reviews for information on the reaction pathways and mechanisms of HDS for the more reactive... 

The sulfenylation of metalloimines is equally applicable to ketones, although using more reactive sulfur electrophiles it is possible to bring about reaction on the unmetallated enamine. ° Sulfenylation of ketone enol silyl ethers also proceeds well with the more reactive sulfur species. Sulfenamides and their derivatives e.g. 11) are particularly suited to the direct sulfenylation of ketones and active methylene compounds such as -diketones, -keto esters and malonates, which undergo facile reaction at room temperature (equation 5). This procedure, however, does not appear to have been exploited for the dehydrogenation of active methylene compounds icf. Section 2.2.4.1). By preparing the dianion (13)... 

Figures 4-7 and 4-8, which show VjF, plotted against the integrals in (J) and (K), were prepared by graphical integration, with Fig. 4-5 used for the relations of X, to 7s6 nd jsg. The values of the integrals are given in the last two columns of Table 4-7. We see that in contrast to Fig. 4-6, based on S2, the data do not fall on a straight line as required by Eqs. (J) and (K). Also, the points for various reactants ratios are not in agreement. We conclude that a second-order mechanism based on either 85 or Sg as the reactive sulfur species does not agree with the experimental data.

Figure 7.2. The activation of parathion to species that destroy cytochrome P450 is proposed to involve oxidation of the thiophosphonate to reactive sulfur species that bind to protein residues. The reactive species can be envisioned to be a sulfur atom with six electrons or HSOH.

First Storable Source of Diatomic Sulfur S2. Access to diatomic sulfur (a very reactive sulfur species) was limited to methods involving deconposition of reactive intermediates like triph-enylphosphane ozonide or bis(thiobenzoyl)biphenyl (generated in situ from BCI3 and 2,2 -dibenzoylbiphenyl). Their spontaneous decomposition produced the 2-sulfur-transfer reagent. The inconveniencies of this approach lead to a series of ingenious... 

A series of catalysts in two successive layers to remove reactive sulfur species and in the first layer, and to remove remaining refractory sulfur species to less than 10 ppm under the presence of H2S, NH3 and other remaining inhibitors, such as nitrogen species and aromatic compounds, in the other layer. 

Fig. 2 illustrates the sulfur distribution of a current 300 ppm diesel fuel (HSRGO). Comparison of its sulfur distribution to that of the straight run gas oil (SRGO) revealed that 100% of reactive sulfur species and 80% of refractory sulfur species are removed to obtain 300 ppm by current HDS units. The nitrogen species in the 300 ppm diesel are also illustrated in the same figure, showing carbazole of 50 ppm. 

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... 

The polysulfidic moieties of the silanes are unstable, and cleavage of the sulfur groups results in active sulfur species. A notorious problem with this kind of coupling agents is the balance between its reactivity towards the silica, requiring a temperature of at least 130°C to obtain an acceptable speed, and its eagerness to react with the rubber polymer, which starts to become noticeable at temperamres above 145°C. Furthermore, the primary and secondary reactions are chemical... 

The detector is based on the combustion of sulfur-containing compounds in a hydrogen rich air fleuie of a FID to form sulfur monoxide. The hydrogen/air flow rate ratio is the most critical parameter controlling the production of sulfur monoxide. Under optimum conditions sulfur monoxide may account for up to 20% of the sulfur species in the flame. Sulfur monoxide is a free radical and a very reactive species that is short lived however, it can be stabilized in a vacuum, and a ceramic probe under reduced pressure can be used to sample it in the flame and transfer it to... 

In connection with the chemistry of the reactive transient species, nitrene, the chemistry of azepines is well documented u. Also, the chemistry of oxepins has been widely developed due to the recent interest in the valence isomerization between benzene oxide and oxepin and in the metabolism of aromatic hydrocarbons 2). In sharp contrast to these two heteropins, the chemistry of thiepins still remains an unexplored field because of the pronounced thermal instability of the thiepin ring due to ready sulfur extrusion. Although several thiepin derivatives annelated with aromatic ring(s) have been synthesized, the parent thiepin has never been characterized even as a transient species3). 

---