Alkyl benzothiophenes

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... 

The sulfur-heterocyclic compounds in the mid-distillate range are primarily the thiacyclane derivatives, benzothiophene derivatives and dibenzothiophene derivatives. with lesser amounts dialkyl-, diaryl- and aryl-alkyl sulfides. Sulfur compounds are significant contributors to the vacuum gas oil fraction (Ma et al., 1997). The major sulfur species are alkyl benzothiophene derivatives, dibenzo-... 

The results in Figure 4 clearly show that a number of alkyl benzothiophenes and dibenzothiophenes can be metabolized (or co-metabolized) by microorganisms and the biodesulfurization studies suggest that other OSC can undergo biodegradation. Yet, the metabolism of only a few OSC has been studied in detail. 

TMBT, 2,3-DMBT, and the minor species 2,3,5-TMBT and 2,3,6-TMBT. The more detailed analyses of a diesel fuel by Ma et al. (1994) showed 61 sulfur compounds. These were, again, almost exclusively alkyl benzothiophenes and alkyl dibenzothiophenes. An example for the sulfur composition of gasoline is given in Table 10.13. 

In addition, gasoline contains benzothiophenes and alkylated benzothiophenes, while dibenzothiophene and alkylated dibenzothiophenes can be detected in jet fuels and diesel. Polycyclic sulfur compounds with three or more rings are found in heavy fuel oils [109]. A typical sulfur compound of diesel fuel is 4,6-dimethyldibenzothio-phene [109]. 

Another strain R. erythropolis KA2-5-1 was found to desulfurize alkyl derivatives of benzothiophene in addition to DBT and its alkyl derivatives [36], Specifically, it was able to desulfurize various methyl, ethyl, and multi-alkyl derivatives of DBT and of BT however, it could not desulfurize BT itself or 2-methyl, 5-methyl, 7-methyl, or 5,7-dimethyl derivatives of BT. The product of desulfurization of 3-methyl BT was... 

Rhodococcus sp. Strain WU-K2R A Rhodococcus strain capable of sulfur-specific desulfurization of benzothiophene, naphthothiophene (NT), and some of their alkyl derivatives was reported [35]. The metabolites of BT desulfurization were BT sulfone, benzo[c][l,2]oxanthiin S-oxide, benzo[c][l,2]oxanthiin S,S-dioxide, o-hydroxystyrene, 2,(2 -hydroxyphenyl)ethan-l-al, and benzofuran. The NT metabolites were NT sulfone, 2 -hydroxynaphthyl ethene, and naphtho[2,l-b]furan [35], The exact biochemical pathway was not determined, however, part of the pathway for BT desulfurization was speculated to be similar to Paenibacillus All-2. 

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. 

Matsui, T. Hirasawa, K. Konishi, J., et al., Microbial Desulfurization of Alkylated Diben-zothiophene and Alylated Benzothiophene by Recombinant Rhodococcus Sp. Strain, T09. Appl. Microbiol. Biotechnol., 2001. 56(1-2) pp. 196-200. 

The researchers from Waseda University have been following the most recent GE strategy for developing improved biocatalysts with desulfurization activity. They hold two patents, the first concerns with the use of Mycobacterium frei WU-0103 strain in a method for decomposing heterocyclic sulfur compounds [169], This bacterium has the ability for desulfurizing DBTs, benzothiophenes, naphthothiophene, and their alkyl derivatives, at 50°C. Details about this strain and the method can be found in Section 2.2.3 in Chapter 3. 

The oxidation of thiophene and its derivatives with H202 was studied using a Ti-Beta molecular sieve. The oxidation product is very dependent from the aromaticity of model compounds. The thiophene oxidation product was mostly sulfates and the benzothiophene oxidation product was benzothiophene sulfone. Oxidation of mono and di-alkyl thiophenes also produced sulfates and sulfones. The diffusivity and aromaticity of the relevant sulfur compounds, intermediates and stable product, as well as the proposed new mechanism of oxidation will be discussed. This proposed new reaction pathway is different from current literature, which reports the formation of sulfones as a stable oxidation product. 

A recent report indicates that thiophenes (not benzothiophenes) may be formed from alkyl phenyl ketones by treatment with a slight excess of thionyl chloride in the cold.58 Propiophenone, for example, yields 3,4-dibenzoyl-thiophene (47). Adipic acid and related carboxylic acids yield thiophene derivatives upon treatment with thionyl chloride in the presence of pyridine.59... 

The method described in this preparation of mesitoic acid avoids the preparation of bromomesitylene,13 and the yield of acid is essentially the same as that from the two-step synthesis.2-13 This procedure appears to be general and can be used to prepare such acids as a- and /3-naphthoic acids,14 cumenecarboxylic acid, 2,5-dimethylbcnzoic acid, and durenecarboxylic acid. Carboxylic acids could not be obtained from benzothiophene, vera-trole, -dimethoxybenzene, and ferrocene under the conditions of this reaction. Although there has been no exhaustive study, this procedure is probably applicable to a variety of aromatic compounds, especially alkylated aromatics. Aromatic compounds which readily undergo oxidation, e.g., ferrocene, catechol, and hydroquinone, do not lend themselves to this method. 

In a series of studies, substituents were introduced or varied at the 2-positions of the thiophene rings of di(benzothienyl)ethenes. The reactions of 3-bromo-2(n-aIkyl)-l-benzothiophene with BuLi and octafluorocyclo-pentene gave bis(2-n-alkyl-l -benzothiophen-3-yl)perfluorocyclo-pentenes 60 containing alkyl substituents with a different chain length at position 2 of the benzothiophene ring. The authors stated that the Et-, Pr-, and Bu-containing derivatives exhibit photochromic properties even in the crystalline state (06JPP(A)162). 

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... 

As mentioned earlier, the MOPAC-PM3 calculations also helped to determine the importance of bond order in the hydrogenative route to desulfurization. Figure 28 shows the calculated bond orders of all bonds in a wide variety of thiophenes, benzothiophenes, and dibenzothiophenes (38). These values were correlated with the rates of desulfurization of sterically hindered alkyl-substituted benzothiophenes and alkyl-substituted 1,1 -diox-... 

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