Carbon-sulfur bonds selectivity

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

A one-pot synthesis of alkyl perfluoroalkyl ketones has been developed. Phosphoranes, generated in situ, are acylated with a perfluoroacyl anhydnde, and the resultmg phosphonium salts are hydrolyzed with alkali [4S (equation 48) Hydrolysis of a carbon-sulfur bond in 2-chloro-2,4,4-trifluoro-1,3-dithietane-S-trioxide, which can be obtained from 2,2,4,4-tetrachloro-l,3-dithietane by fluor-mation with antimony trifluoride followed by selective oxidations, opens the nng to produce 2-chloro-1,1,2-trifluorodimethyl sulfone [49] (equation 49)... 

Kirimura K, T Furuya, R Sato, Y Ishii, K Kino, S Usami (2002) Biodesulfurizarion of naphthothiophene and benzothiophene through selective cleavage of carbon-sulfur bonds by Rhodococcus sp. strain WU-K2R. Appl Environ Microbiol 68 3867-3872. 

Biodesulfurization (BDS) is the excision (liberation or removal) of sulfur from organosul-fur compounds, including sulfur-bearing heterocycles, as a result of the selective cleavage of carbon-sulfur bonds in those compounds by the action of a biocatalyst. Biocatalysts capable of selective sulfur removal, without significant conversion of other components in the fuel are desirable. BDS can either be an oxidative or a reductive process, resulting in conversion of sulfur to sulfate in an oxidative process and conversion to hydrogen sulfide in a reductive process. However, the reductive processes have been rare and mostly remained elusive to development due to lack of reproducibility of the results. Moderate reaction conditions are employed, in both processes, such as ambient temperature (about 30°C) and pressure. 

Kirimura, K. Furuya, T. Sato, R., et al., Biodesulfurization of Naphthothiophene and Ben-zothiophene Through Selective Cleavage of Carbon-Sulfur Bonds by Rhodococcus Sp Strain WU-K2R. Applied and Environmental Microbiology, 2002. 68(8) pp. 3867-3872. 

A viscosity reducing method based on the selective cleavage of carbon sulfur bonds of aromatic heterocyclic molecules containing a sulfur heteroatom. The physicochemical properties of these heterocycles contribute to the liquid viscosity. The method comprises contacting the liquid with an effective amount of a biocatalytic agent. 

In the approach followed in this invention [29], a biocatalytic agent converts the sulfur heterocycles into different molecules that do not exhibit the hydrophobic interactions. This is achieved by selectively cleaving carbon-sulfur bonds. The selectivity of the biocatalytic agent employed is limited to the carbon-sulfur bonds and no attack to the carbon-carbon skeleton was reported. Thus, it is expected that the proposed biocatalytic reduction of viscosity would not diminish the fuel value of the treated petroleum liquids. The biocatalyst employed consisted of the strain ATCC No. 53968 (see Section 20 and references therein), in an aqueous culture conventionally prepared by fermentation under aerobic conditions. The fermenting bioreactor is fed with a suitable nutrient medium, which comprises a conventional carbon source (dextrose and glycerol are recommended carbon sources. To confer maximal biocatalytic activity for the desired cleavage of organic C—S bonds, the bacteria was kept in a state of sulfur deprivation. 

The bacterial strains were submitted to the National Collection of Microorganism Cultures of the Pasteur Institute (CNCM) and included R. erythropolis CNCM 1-2204, -2205, -2207, and -2208, and/or R. rhodnii 1-2206. The activity of the microorganisms includes a selective attack on the carbon-sulfur bonds in the organic molecules without significant alteration of the carbon atom structure. As usual, strains were isolated and subjected to successive enrichment phases, in media containing various sources of carbon and DBT as the only sulfur source, then a purification of the enhanced culture led to the fifteen DBT specific strains. From those strains, a subset of ten strains was selected... 

Oxidation reactions using mediators are possible under very mild conditions with high selectivity. In fact, the oxidative cleavage of the carbon-sulfur bond of thio ether (16) was easily possible by using mediator (17) (Scheme 6) [46]. 

Thus, as compared with direct electrolysis, not only a gain in energy can be obtained but also the selectivities can be enhanced. The selectivity of the reaction in this case is determined by the potential differences between the different functional groups of the substrate and the mediator in combination with the rate of the respective follow-up reaction. A typical example of this type is the cleavage of a carbon-sulfur bond using tris(4-bromophenyl)amine as organic mediator ) (Eq. (12)). 

Thus, oxidation reactions are possible under very mild conditions and with high selectivities. Therefore, this method is especially useful for oxidative deprotections. For example, the oxidative cleavage of the carbon-sulfur bond is easily possible according to Eq. (103). In this way, disulfides and follow-up products of carbenium... 

Electrochemical reduction of specific oriented chemisorbed intermediates is also very selective [77-79]. For example, reduction of chemisorbed thioph-enols (and mercaptans) result in selective scission of the carbon-sulfur bond to yield an unadsorbed hydrocarbon and an adsorbed sulfur atom. 

The different reactivities of the two substituents on C-l allow selective replacement and conversion of them. Alkyl monothio-acetals [proposed as intermediates in mercury(II)-catalyzed demer-captalation reactions—see Section IV,l,b] have been prepared from a-bromothioethers by the combined action of an alcohol and silver(I) carbonate the introduction of S-nucleophiles is discussed in Section 11,6. Reduction of 81 by lithium aluminum hydride effects hydrogen-olysis of the carbon-halogen bond, whereas the action of Raney nickel on the derived S-ethyl O-methyl monothioacetal specifically cleaves the carbon-sulfur bond to afford the pentaacetate of 1-0-methyl-D-galactitol.327... 

Allylsilanes react with alkoxymethyl and phenylthiomethyl chlorides in the presence of Lewis acids (Scheme 53), and dithioacetals, similarly, where substantial stereoselection can be achieved with large aryl groups on the sulfur atoms (Scheme 54). Monothioacetals react selectively with cleavage of the carbon-sulfur bond when tin(IV) chloride is used as the Lewis acid (Scheme 55). ° ... 

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