Thiol sulfides

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

The System described in the previous section has been extended with a sulfur chemiluminescence detector (SCO) for the detection of Sulfur compounds (32). The separated fractions were thiols + sulfides + thiophenes (as one group), benzothio-phenes, dibenzothiophenes and benzonaphtho-thiophenes. These four groups have been subsequently injected on-line into and separated by the GC unit. Again, no overlap between these groups has been detected, as can be seen from Figure 14.20, in which the total sulfur compounds are shown and from Figure 14.21 in which the separated dibenzothiophenes fraction is presented. The lower limit of detection of this method proved to be 1 ppm (mg kg ) sulfur per compound. 

Thiols, the sulfur analogs of alcohols, are usually prepared by Sjv 2 reaction of an alkyl halide with thiourea. Mild oxidation of a thiol yields a disulfide, and mild reduction of a disulfide gives back the thiol. Sulfides, the sulfur analogs of ethers, are prepared by an Sk2 reaction between a thiolate anion and a primary or secondary alkyl halide. Sulfides are much more nucleophilic than ethers and can be oxidized to sulfoxides and to sulfones. Sulfides can also be alkylated by reaction with a primary alkyl halide to yield sulfonium ions. 

The progress on S-C bond activation, which covers the reduction of a C-S bond to a C-H bond, cross coupling reaction of sulfides with main group organometaUic nucleophiles, ring opening reactions of thietanes and thiiranes, and desulfurization of thiols, sulfides, and thiophenes has already been reviewed elsewhere [6-10], and... 

Certain reduced sulfur compounds such as thiols, sulfides, disulfides, and trisulfides, specifically those having the functionality... 

The l3C chemical shifts of methyl derivatives with sulfur substituents [e.g., SH, -S, -SCH3, -SSCH3, -SSSCHj, -S(0)CH3, -S02CH3, -S(CH3)2+, -SC(0)CH3, -SC(S)CH3, and -SC(S)SCH3] (130,131) and of vicinal and gem-inal bis-sulfides (290) have been reported. Freeman and co-workers have published similar studies on thiols, sulfides, disulfides, and sulfinic and sulfonic acid derivatives (131,132,433) and Tseng and Bowler (434), on thiocarbamates, their S-oxides and S,5-dioxides [R-X-C(0)-NR 2 with X = S, SO, S02]. 

It is more than likely that when sulfur occurs in a crude oil or in coal (other than the pyrites), it is organically bound in one of the three forms listed in Table 8.3—the thiols, sulfides, or disulfides. The combustion of these compounds is very much different from that of other sulfur compounds in that... 

Methanethiol Methyl Mercaptan Thiols, Mercaptans Thiols, Sulfides, and Disulfides Thorium Tin... 

Kennerly and Patterson (13) studied the effect of several organic sulfur compounds, including thiols, sulfides, a disulfide, sulfonic acids, and a zinc dialkyl dithiophosphate, on the decomposition rate of cumene hydroperoxide in white mineral oil at 150 °C. In each case they found phenol as the major product. They suggested that the most attractive mechanism by which to explain these results involves ionic rearrangement catalyzed by acids or other electrophilic reagents (10) as... 

Sulfur can be found in most all petroleum fractions. In naphtha, distillates and some lube fractions, sulfur is a component of carbon and hydrogen containing molecules. In heavier fractions, sulfur may be bound in asphaltene and resin matrices in combination with nitrogen and oxygen. The organosulfur compounds present in most fuels are either thiols, sulfides or thiophenes. 

Irradiation of aliphatic thiols, sulfides, and disulfides with a mercury lamp produces gaseous products identified by the mass spectrograph. Thiols are the least stable to light, with the formation of hydrogen95-129 as the main product. Sulfides and disulfides yield, as the predominant products, saturated hydrocarbons of structures corresponding to the smallest alkyl radical attached to sulfur. Haines et al.95-97 have offered a mechanism to explain the predominant production of hydrogen during photolysis of thiols. 

Sulfonic acids are prepared on a commercial scale by the sulfonalion of organic substrates using a variety of sulfonating agents, including sulfur trioxidc (diluted in air), sulfur trioxide (in sulfur dioxide), sulfuric acid, oleum (fuming sulfuric acid), chlorosulfuric acid, sulfamic add, trialkylamine-sulfur trioxide complexes, and sulfite ions. Other methods of sulfonic acid production, practiced on an industrial scale, include the oxidation of thiols, sulfide, disulfides, sulfoxides, sulfones, and sulfinic acids. See also Sulfonalion and Sulfation. 

White et al. (65) positively identified a variety of thiophenes in a Bevier seam coal extract. Using low-voltage high-resolution mass spectrometry they were able to observe low concentrations of compounds in the extract that had molecular formulae consistent with those of some thiols, sulfides and disulfides. It should be emphasized however, that no thiol, sulfide or disulfide was positively identified in the extract. 

---