Elemental sulfur atomizers

The described reaction proceeds slowly for aryl-thiolate DNICs and is fast for alkyl-thiolate complexes. Trapping of the elemental sulfur atoms by phosphine inhibits oxidation [137]. The fate of the sulfide ligands in reactions of biological iron-sulfur clusters with NO remains unknown, although analogically it is expected that sulfur by-products must be sequestered from the vicinity of the iron atoms in order for the DNICs to remain stable. It was shown that the cluster reassembly... 

The adsorption of the dextrin molecule at the sulfur surface is achieved by the attachment of a portion of the molecule. Yet the magnitude of the adsorption is weaker than at a graphite surface, as suggested by the significantly smaller portion of the dextrin molecule that sticks to the sulfur surface. Due to the similar hydrophobic character of the sulfur surface, which is composed of elemental sulfur atoms, the observed partial adsorption of the dextrin molecule at the sulfur surface is explained in the same way dextrin adsorption at the graphite surface is explained. 

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

Sulfur Donors. MBSS, DPTH, and the thiuram disulfides (see Table 2) ate examples. The morpholine disulfide and caprolactam disulfide examples in Table 4 can also donate one atom of sulfur from their molecular stmcture for cross-linking purposes. Monosulfide cross-links provide better thermal stabiUty than the sulfur—sulfur bonds in di- and polysulfide cross-links, which predominate when elemental sulfur is used. 

Spent Acid or Burning. Burners for spent acid or hydrogen sulfide are generally similar to those used for elemental sulfur. There are, however, a few critical differences. Special types of nozzles are required both for H2S, a gaseous fuel, and for the corrosive and viscous spent acids. In a few cases, spent acids maybe so viscous that only a spinning cup can satisfactorily atomize them. Because combustion of H2S is highly exothermic, carehil design is necessary to avoid excessive temperatures. 

Heating or irradiating alkenes in the presence of sulfur gives relatively low yields of thiiranes. For example, a mixture of sulfur and norbornadiene in pyridine-DMF-NHa at 110 °C gave a 19% yield of the monoepisulfide of norbornadiene as compared with a 78% yield by the method of Scheme 120 (79JCS(Pi)228). Often 1,2,3-trithiolanes are formed instead of thiiranes. The sesquiterpene episulfides in the essential oil of hops were prepared conveniently by irradiation of the terpene and sulfur in cyclohexane (Scheme 135) (80JCS(Pl)3li). Phenyl, methyl or allyl isothiocyanate may be used as a source of sulfur atoms instead of elemental sulfur. 

Tlie thermal reaction of dithiiranes is of particular interest in relation with the dithiirane/thioketone 5-sulfide manifold. Heating 5-oxodithiiranes (4) in solution led to both isomerization to 6,7-dithia-8-oxabicyclo[3.2.1]-octanes 74 and desulfurization to 5-oxothiones 75, the ratio of which was dependent on the reaction conditions employed. The intramolecular [3 + 2] cycloaddition of the thioketone 5-sulfide 76, generated by ring-opening, provides a straightforward explanation for the formation of 74. Meanwhile, 75 is probably formed by a nucleophilic attack on the sulfur atom by another molecule of 4 and/or by elemental sulfur formed during the reaction. 

As in phenoxatellurines, phenothiatellurine [95AHC(63)1] and benzotellura-zoles (89KGS757), 10-alkylphenotellurazines 43 react with elemental sulfur at elevated temperature by replacing the ring tellurium atom by sulfur (85KGS757). The yield of this reaction is about 50%. 

Sulfur Compounds. All crude oils contain sulfur in one of several forms including elemental sulfur, hydrogen sulfide, carbonyl sulfide (COS), and in aliphatic and aromatic compounds. The amount of sulfur-containing compounds increases progressively with an increase in the boiling point of the fraction. A majority of these compounds have one sulfur atom per molecule, but certain aromatic and polynuclear aromatic molecules found in low concentrations in crude oil contain two and even three sulfur atoms. Identification of the individual sulfur compounds in the heavy fractions poses a considerable challenge to the analytical chemist. 

Although Zn2+ is essential to human nutrition, compounds of the two elements below zinc in the periodic table. Cd and Fig. are extremely toxic. This reflects the fact that Cd2+ and Flg2+, in contrast to Zn2+, form very stable complexes with ligands containing sulfur atoms. As a result, these two cations react with and thereby deactivate enzymes containing —SH groups. 

The ionization energy of the sulfur atom shows that it is even more reluctant than phosphorus to lose electrons. The common compounds of sulfur are the sulfides, which may be formed by reactions of elemental sulfur with a large number of metals. Typical reactions are... 

The realization that the better ordering criterion is atomic number rather than atomic weight invites us to consider triads of atomic numbers. This reveals a most remarkable fact, namely that —50% of all conceivable triads on a conventional periodic table are in fact exact. For example, the elements sulfur, selenium, and tellurium have atomic numbers of 16, 34, and 52, respectively, thus showing that the atomic number of the middle of these three... 

Although belonging to a slightly different class of reactions, the reaction of trifluoromethyl radicals with sulfur vapor has been shown to provide a route to trifluoromethyl polysulfide compounds (20). Instead of using sulfur halides, which undoubtedly would also give positive results, elemental sulfur (Ss) was vaporized and dissociated into atomic and polyatomic sulfur species. 

With the exception of ionic sulfides formed from highly electropositive elements (i.e., Na, K, Ca, Mg), sulfur bonding in natural environments is covalent. When fully oxidized, however, the covalently bonded sulfur atom exists... 

Abstract Molecular spectroscopy is one of the most important means to characterize the various species in solid, hquid and gaseous elemental sulfur. In this chapter the vibrational, UV-Vis and mass spectra of sulfur molecules with between 2 and 20 atoms are critically reviewed together with the spectra of liquid sulfur and of solid allotropes including polymeric and high-pressure phases. In particular, low temperature Raman spectroscopy is a suitable technique to identify single species in mixtures. In mass spectra cluster cations with up to 56 atoms have been observed but fragmentation processes cause serious difficulties. The UV-Vis spectra of S4 are reassigned. The modern XANES spectroscopy has just started to be applied to sulfur allotropes and other sulfur compounds. 

Despite the fact that natural elemental sulfur contains 0.75% of the isotope [4] with a nuclear spin of 7 = /2 no NMR spectra of elemental sulfur have ever been reported. Such spectra are however well-known for compounds containing just one or two sulfur atoms [5]. Electron spin resonance spectra of irradiated elemental sulfur samples and of quenched sulfur vapor have been reviewed elsewhere [6-8]. 

Abstract Inorganic polysulfide anions and the related radical anions S play an important role in the redox reactions of elemental sulfur and therefore also in the geobio chemical sulfur cycle. This chapter describes the preparation of the solid polysulfides with up to eight sulfur atoms and univalent cations, as well as their solid state structures, vibrational spectra and their behavior in aqueous and non-aqueous solutions. In addition, the highly colored and reactive radical anions S with n = 2, 3, and 6 are discussed, some of which exist in equilibrium with the corresponding diamagnetic dianions. 

The composition of sodium polysulfide solutions saturated with sulfur of zero oxidation number (S°) has also been studied at 25 and 80 °C (solutions in contact with elemental sulfur) [76]. In this case the ratio 8° 8 per polysulfide ion increases with increasing alkahnity. The maximum average number of sulfur atoms per polysulfide molecule was obtained as 5.4 at 25 °C and 6.0 at 80 °C and pH values of >12. Equilibrium constants for reactions as in Eqs. (26) and (27) have been derived assuming various models with differing numbers of polysulfide ions present. 

Reaction of cyclic tetrasulfido complexes of heavier group 14 elements bearing bulky substituents such as Tbt(Ar)MS4 (M=Si, Ar=Tip M=Ge, Ar=Tip M=Sn, Ar=Ditp) with 3 equivalents of phosphines afforded the successful isolation of the first stable double-bonded compounds between heavier group 14 elements and sulfur atom (heavy ketones), Tbt(Ar)M=S, accompanied by the quantitative formation of the corresponding phosphine sulfides (Scheme 40) [13, 15, 112, 113]. On the other hand, their lead an-... 

The sulfur-rich oxides S 0 and S 02 belong to the group of so-called lower oxides of sulfur named after the low oxidation state of the sulfur atom(s) compared to the best known oxide SO2 in which the sulfur is in the oxidation state +4. Sulfur monoxide SO is also a member of this class but is not subject of this review. The blue-green material of composition S2O3 described in the older literature has long been shown to be a mixture of salts with the cations S4 and Ss and polysulfate anions rather than a sulfur oxide [1,2]. Reliable reviews on the complex chemistry of the lower sulfur oxides have been published before [1, 3-6]. The present review deals with those sulfur oxides which contain at least one sulfur-sulfur bond and not more than two oxygen atoms. These species are important intermediates in a number of redox reactions of elemental sulfur and other sulfur compounds. 

---