Sulfide aerobic oxidation

Dunn, B. W., Bur. Explos. Accid. Bull., Amer. Rail Assoc., 1917, 25, 36 Fused sodium sulfide in small lumps is liable to spontaneous heating from aerobic oxidation, temperatures of up to 120°C being observed after exposure to moisture and air. Packing in hermetically closed containers is essential [1]. Previously, similar material packed in wooden barrels had ignited in transit [2]. 

Mixtures of sodium sulfide and finely divided carbon exhibit an exotherm on exposure to air. As indicated by the low MRH value, this is probably not a direct interaction, but arises from co-promotion of aerobic oxidation of the individual components. 

This is remarkable in view of the small standard Gibbs energy decrease. Some species of the archaeobacteri-um Sulfolobus are able either to live aerobically oxidizing sulfide to sulfate with 02 (Eq. 18-22) or to live anaerobically using reduction of sulfur by Eq. 18-33 as their source of energy.369... 

PV2M010O40 has usually been used in the acid form. H5PV2M010O40 catalyzes aerobic oxidative cleavage of cycloalkanes, 1-phenylalkanes, and ketones. For example, the oxidation of 2,4-dimethyl cyclopentanone and 2-methylcyclo-hexanone gives 5-oxo-3-methylhexanoic acid and 6-oxoheptanoic acid, respectively, in yields higher than 90% [285, 286). Bromination of arenes with HBr [287), oxidative dehydrogenation of cyclohexadiene [288, 289) and a-terpinene [290), oxidation of 2,4-dimethylphenol [291) and sulfides [292) are other examples. 

Reaction of the sandwich-type POM [(Fc(0H2)2)j(A-a-PW9034)2 9 with a colloidal suspension of silica/alumina nanopartides ((Si/A102)Cl) resulted in the production of a novel supported POM catalyst [146-148]. In this case, about 58 POM molecules per cationic silica/alumina nanoparticle were electrostatically stabilized on the surface. The aerobic oxidation of 2-chloroethyl ethyl sulfide (mustard simulant) to the corresponding harmless sulfoxide proceeded efficiently in the presence of the heterogeneous catalyst and the catalytic activity of the heterogeneous catalyst was much higher than that of the parent POM. In addition, this catalytic activity was much enhanced when binary cupric triflate and nitrate [Cu(OTf)2/Cu(N03)2 = 1.5] were also present [148],... 

Another argument against the oxo-transfer mechanism in our catalytic aerobic oxidation protocol is the lack of formation of sulfoxides from sulfides, N-oxydes from amines and phosphine oxydes from phosphines. Alkenes also proved to be inert towards oxidation no epoxide formation could be detected under our reaction conditions. 

The sulfides that may be contained in the feed stream and which have not been eliminated in the previous physical-chemical process become sulfates, as a result of the aerobic-oxidant conditions of the process. Figure 41.8 shows that they disappear in the bioreactor or in permeate. 

The chemotrophic (colorless) sulfur bacteria obtain energy from the chemical aerobic oxidation of reduced sulfur compounds. The overall reactions occurring, concerning the biological oxidation of sulfide, are the formation of sulfur (at low oxygen concentrations) and the formation of sulfate (when there is an excess of oxygen) ... 

The use of Thiobacillus species has been studied quite extensively. Sublette and Sylvester especially focused on the use of Thiobacillus denitrificans [50-52] for aerobic or anaerobic oxidation of sulfide to sulfate. In the anaerobic oxidation NOs was used as an oxidant instead of oxygen (confirm Table 2). Buisman used a mixed culture of Thiobacilli for the aerobic oxidation of sulfide to elemental sulfur and studied technological applications [53-55]. Visser showed the dominant organism in this mixed culture to be a new organism named Thiobacillus sp. W5 [6]. 

An example in which formation of a carbon radical is not the initial reaction is provided by the atmospheric reactions of organic sulfides and disulfides. They also provide an example in which rates of reaction with nitrate radicals exceed those with hydroxyl radicals. 2-dimethylthiopropionic acid is produced by algae and by the marsh grass Spartina alternifolia, and may then be metabolized in sediment slurries under anoxic conditions to dimethyl sulfide (Kiene and Taylor 1988), and by aerobic bacteria to methyl sulfide (Taylor and Gilchrist 1991). It should be added that methyl sulfide can be produced by biological methylation of sulfide itself (HS ) (Section 6.11.4). Dimethyl sulfide — and possibly also methyl sulfide — is oxidized in the troposphere to sulfur dioxide and methanesulfonic acids. 

Sulfur/sulfide oxidizing bacteria (e g., Thiobacillus) Aerobic Oxidize sulfide (S2-) to elemental sulfur (S), sulfide to sulfate (SO4 ), or sulfur to sulfate. Strains that produce sulfate (e g., Thiobacillus) create sulfuric acid (H2S04) H+ (lower pH)... 

The activities of other nitrate-containing sulfoxidation catalysts were also evaluated. The known sulfide oxidation catalysts (NH4)2Ce (N03)6 (/7) (entry 7) and titanium nitrate (entry 8) have moderate activity. The data demonstrate the essential role of both nitrate and proton in the catalytic, aerobic oxidation of the sulfide CEES. 

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