4,6-Dimethyl-dibenzothiophene

Two patents were awarded on microbial desulfurization of sulfur-containing heterocyclic compound [155,156], the first targeting DBT and alkylated DBTs and the other benzothiophenes and alkylated benzothiophenes. In both cases, the selective cleavage of the C—S bonds is reported as the main mechanism. The claimed bacteria strains are Mycobacterium G3 strain (PERM P-16105) and R. erythropolis KA2-5-1 strain (PERM P-16277), respectively. Special emphasis was made to the desulfurization of the recalcitrant 4,6-dimethyl-dibenzothiophene. The main product from DBT... 

Montiel C, Terres E, Dominguez JM et al (2007) Immobilization of chloroperoxidase on silica-based materials for 4,6-dimethyl dibenzothiophene oxidation. J Mol Catal B Enzym 48 90-98... 

A year earlier Dalliige et al. had reported more or less the same separation [37]. In their study, these authors used a ToF MS to detect and identify all the different sulphur compounds, including 4,6-dimethyl-dibenzothiophene, one of the compounds that is very refractory to hydrogenation. 

When hydrotreating to lower and lower sulfur levels, it becomes necessary to remove sulfur from those compounds which are the most difficult to desulfurize/ The most refractive sulfur compounds are higher molecular weight dibenzothiophenes that contain side chains in positions close to the sulfur atom (Figure 1). Two such compounds that are known to be difficult to desulfurize are 4-methyl dibenzothiophene (4-MDBT) and 4,6-dimethyl dibenzothiophene (4,6-DMDBT). These compounds are normally found in a higher concentration in aromatic feeds such as cycle oils and coker gas oils. 

An analysis of the ESR spectrum of the dibenzothiophene radical anion46 yields the following hfs (hyperfine splitting) constants (gffuss) 5.16, 4.48, 1.46, and 0.86. The theoretical values based on HMO data for Model A2 are considerably smaller 2.84, 2.48, 1.47, and 0.27, respectively, which led the authors to make spin-density calculations by the Hartree-Fock method. Quite recently, the spin densities have been calculated for Model B (8S = 1, pcs = 0.566),466 and the following constants were obtained 5.03,3.99,0.75, and — 1.23. A study of the ESR spectrum of the radical derived from 2,8-dimethyl-dibenzothiophene permitted the assignment of the lowest hfe constant value to the proton in position 2. In contrast to the dithiins, experimental data for dibenzothiophene radicals are better reproduced by Model B. 

Treatment of 5,6-dichloro-2,3-dimethyl- -benzoquinone with sodium sulfide followed by oxidation with nitric acid yields the thianthrene derivative (60). Sulfur extrusion from 60 with peracetic acid leads to 2,3,7,8-tetramethyl-l,4,6,9-dibenzothiophene tetrone (61) (overall yield 57%). ... 

Three NiMo-HNaY-alumina catalysts with similar composition were prepared by different methods and tested in the hydrodesulfurization of dibenzothiophene (DBT) and 4,6-dimethyl-DBT. It was found that the catalyst preparation method induces some changes of the characteristics of the deposited metallic species as well as of the acidic properties of the zeolite component. These changes affect the catalytic behavior in the hydrodesulfurization of DBT and 4,6-DMDBT. Acidic properties of the catalyst seem to be more important for the conversion of alkyl-substituted DBT. 

In detail, several alkylated and nonalkylated polycyclic aromatic compounds (PAHs) were detected and dominated by acenaphthene with a maximum concentration of 24 pg/L in sample B. Total concentrations of methyl- and dimethylnaphthalenes reached 5.1 pg/L and 24 pg/L, respectively. Tricyclic aromatic compounds and oxygenated PAH species were detected comprising e.g. phenanthrene, 9H-fluorenone and acenaphthenone. Methylated and dimethylated benzo(b)thiophenes as well as dibenzothiophene were also present. 

Phenylmercapto-cyclohexcn fuhrt ebenfalls nur in 6%iger Ausbeute zu 1,2,3,4-Tetra-hydro- dibenzothiophen)i, und aus dem folgenden Sulfid wird l-Oxo-3,3-dimethyl-l,2,3,4-tetrahydro- dibenzothiophm) (F 100-102°) ebenfalls nur mit einigen Prozent erhalten5 ... 

Dibenzothiophene, dimethyl- (at least four isomers detected 3547, 4249 ... 

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