Dibenzothiophenes alkylation

Dibenzothiophene, 1,2,3,4-tetrahydro-4-keto-synthesis, 4, 905 Dibenzothiophenes alkylation, 4, 724 Birch reduction, 4, 775 C NMR, 4, 11... 

The two principal categories of compounds studied have been diaryl or aryl alkyl sulphones (not dialkyl sulphones, which are polarographically not reducible) and S-dioxides of certain heterocyclic compounds, such as thiophene (also benzo- and dibenzothiophenes) and phenothiazines. The first named have half-wave potentials in the region of — 2.0 V, the thiophene dioxides near — 1.0 V. Some examples of each category may be given. 

In dibenzothiophene-S,S-dioxide the S atom is in a ring, and hence more constrained. The yield of SOz in the radiolysis is linear with the dose to about 13 Mrad after which it levels off as in p,p -ditolyI sulfone. However, the yield of S02 in this case is much lower (a factor of 25) than in the case of p,p -ditolyl sulfone (G = 0.002 compared to G = 0.05). This stability of the dibenzothiophene sulfone could be partially due to back reaction to reform the parent sulfone and partially due to more efficient energy delocalization. The expected biphenylene product was not detected due to limitations of the analytical method. Bowmer and O Donnell70 studied the volatile products in y-radiolysis of dialkyl, alkyl aryl and diaryl sulfones. Table 2 gives the radiolytic yields of S02 and of the hydrocarbon products of the alkyl or aryl radicals. The hydrocarbon products are those obtained either by H atom abstraction or by radical combination. The authors69 suggested the mechanism... 

Figure 15. Relative removal of dibenzothiophenes and benzothiophenes from the middle-distillate cut of OB oil in the presence (left frame) and absence (right frame) of sulfate. Compounds are ranked in order of their relative depletion. Bars with solid and hatched lines represent the sum of the results for alkylated compounds with n pendant carbons, with CO indicating the unalkylated parent open bars in the left frame represent individual dibenzothiophenes. In the right frame, the bars represent sum of alkylated analogs for each carbon number. Figure reproduced from Ref. [86],...

Kobayashi, M. Onaka, T. Ishii, Y., et al., Desulfurization of Alkylated Forms of Both Dibenzothiophene and Benzothiophene by a Single Bacterial Strain. Ferns Microbiology Letters, 2000. 187(2) pp. 123-126. 

Omori, T. Saiki, Y. Kasuga, K., and Kodama, T., Desulfurization of Alkyl and Aromatic Sulfides and Sulfonates by Dibenzothiophene-Desulfurizing Rhodococcus Sp Strain Syl. Bioscience Biotechnology and Biochemistry, 1995. 59(7) pp. 1195-1198. 

Folsom, B. R. Schieche, D. R. DiGrazia, P. M., et al., Microbial Desulfurization of Alkylated Dibenzothiophenes From a Hydrodesulfurized Middle Distillate by Rhodococcus Erythropo-lis 1-19. Applied and Environmental Microbiology, 1999. 65(11) pp. 4967-4972. 

Kobayashi, M. Horiuchi, K. Yoshikawa, O., et al., Kinetic analysis of microbial desulfurization of model and light gas oils containing multiple alkyl dibenzothiophenes. Bioscience Biotechnology and Biochemistry, 2001. 65(2) pp. 298-304. 

Matsui, T., and Maruhashi, K., Isolation of Carotenoid-Deficient Mutant From Alkylated Dibenzothiophene Desulfurizing Nocardioform Bacteria, Gordonia Sp TM414. Current Microbiology, 2004. 48(2) pp. 130-134. 

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... 

Treatment of dibenzothiophene with alkyl halides in the presence of silver tetrafluoroborate or triaryloxonium tetrafiuoroborate has recently been shown to yield the corresponding 5-alkyl salts of type g0 96,359 Compounds thus prepared include 5-methyl- (93%), 5-ethyl-(98%), and 5-isopropyldibenzothiophenium tetrafiuoroborate (14%). The products were thermally unstable, reverting to dibenzothiophene, although the corresponding perchlorates were more stable. 5-Methoxy-... 

Dibenzothiophene 5-oxide is sufficiently nucleophilic to be alkylated at the oxygen atom by alkyl halides in the presence of silver perchlorate (96). Such compounds were found to be readily hydrolyzed back to the sulfoxide. The reaction of 96 with amines is discussed in Section VI, E, 3. 

An attempt to methylate the diketone (97) with methanolic hydrogen chloride gave the dimethoxy derivative (98), presumably by alkylation of the j8-dicarbonyl system by the activated aromatic nucleus. The possibility therefore exists of synthesizing polymethoxy derivatives of dibenzothiophene by the 2-chlorocyclohexanone route (Section IV, A), using this modification of the ring-closine step. 

Two novel monoaminodibenzothiophenes, 9b-amino-l,4,4a,9b-tetra-hydrodibenzothiophene (113) and 9b-amino-l,2,3,4,4a,9b-hexayhydro-dibenzothiophene (114) have been synthesized from the corresponding carboxylic acid sulfones 32 and 33 by treatment with sodium methoxide and bromine followed by reduction of the resultant sulfone carbamates with LAH. A -Alkylation of both 113 and 114 gives compounds which possess CNS depressant activity. ... 

The transformation of lithio derivatives of dibenzothiophene into alkyl, alkenyl, hydroxyalkyl, formyl, acetyl, carboxylic acid, alkyl and arylsilyl, boronic acid, aryl and carbinol derivatives of dibenzothiophene is dealt with in the appropriate sections. In addition, the four mono-tritio derivatives of dibenzothiophene have been prepared from the corresponding lithio derivatives via hydrolysis with tritiated water (Section III, 0,2). ... 

There are several potential sources of error. Both methods of analysis use a binary model mixture, composed of sulfidic and thiophenic components. Thickness effects in the XANES of these model systems would alter the calibrations. There may be contributions from species not adequately represented by a simple dibenzothiophene-dibenzylsulfide model. While the XPS data are represented by 163.3 eV and 164.1 eV components, the model compound data base is as yet limited and not sufficient for a definitive interpretation in terms of alkyl sulfide and thiophenic forms. Examination by both XPS and XANES of a wider variety of model compounds and multiple component model compound mixtures will better define the sulfur species represented by these quantification methods. 

Wasserscheid and coworkers were the first to attempt to use ILs for the desulfurization of model solutions (dibenzothiophene [DBT], in n-dodecane) and real diesel fuels [41]. For extraction, the authors used ILs with l-alkyl-3-methylimidazolium cations ([C CiIm], n = 2, 4, 6) and various anions. Also, binary mixtures of l-alkyl-3-methylimidazolium chloride with AICI3 (Lewis-acidic ILs), the equimolar mixture of cyclohexyldiethylammonium and tri-butylammonium mefhanesulfonates (Brnnsted-acidic IL) and the equimolar mixture of cyclohexyldiefhylmethylammonium and tributylmefhylammo-nium methanesulfonafes were tested. 

More than 70 individual sulfur species were further identified by gas chromatography-atomic emission detection (GC-AED) and by gas chromatography-mass spectroscopy (GC-MS) (12). Figure 5 illustrates the composition of the sulfur components of the gas oil. The major components are individually identified on the figure. It can be seen that alkylbenzothio-phenes and dibenzothiophenes are the major components. The size of the alkyl substituents ranges up to 16 carbons on benzothiophene and up to 7 carbons on dibenzothiophene. 

As discussed in Section III, when the sulfur content is lowered from 0.20 to 0.05%, the chemistry of HDS of gas oils is essentially the chemistry of alkyl-substituted dibenzothiophenes. Though gas oils initially contain mostly alkyl-substituted benzothiophenes, these are completely removed by the time 0.20% S is achieved. Thus, this review will deal predominantly with the reaction pathways involved in the HDS of alkyl-substituted dibenzothiophenes. There are many excellent reviews on reaction pathways of the more reactive sulfur species such as thiophenes and benzothiophenes (2, 5, 8, 23, 24), and the reader is referred to those reviews for information on the reaction pathways and mechanisms of HDS for the more reactive... 

Though it has long been known that the more highly condensed thiophene structures, such as dibenzothiophene and especially their alkyl-substituted derivatives, have low HDS reactivity (21, 25-29), it is only recently that study in this area has intensified. Researchers throughout the world are now actively seeking understanding of the fundamental causes of low reactivity and attempting to find means to circumvent the problems (29-33). 

Having established reliable values for all of the important rate constants as a function of alkyl substitution on dibenzothiophenes, it is now possible to examine critically how these rate constants (and associated changes in product selectivity) are affected by other components of commercial gas oils and by the H2S that is produced during the HDS process. It is also possible to evaluate how these various rate constants are affected by changes in catalyst composition and by process conditions. Knowledge of the details of these effects can lead to novel catalyst modifications and process configurations that may be able to reach the new stricter standards of 0.05% S. These topics are discussed in later sections. However, for perspective, we will first summarize what is known about present-day catalyst compositions and catalytic mechanisms that bring about the transformations observed in HDS processes. 

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