Benzo hydrodesulfurization

The positive identification of the sulfur compounds in crude oils is a difficult problem often complicated by the lack of reference compounds. This difficulty has been overcome by hydrodesulfurization (see Section VIII), which converts the sulfur compounds into known hydrocarbons. Treatment of a petroleum oil fraction with calcium hexammine converts the benzo[6]thiophenes present into aryl mercaptans, which are readily separable from accompanying aromatic hydrocarbons (e.g., naphthalene) and then identified by hydro-... 

Unwanted sulfur-containing components may be removed from petroleum oils by hydrodesulfurization over a Co-Mo catalyst at high temperatures under pressure ( unifining or hydrofining ).38 However, benzo[6]thiophene is hydrodesulfurized with difficulty over a molybdenum catalyst89 40 and it is difficult to remove completely from petroleum oils by hydrofining.41... 

Various hydrobenzo[6]thiophenes have been identified in petroleum oils (Section II, A). The chemistry of hydrobenzo[6]thiophene-1,1-dioxides and hydrodesulfurization of benzo[6]thiophenes are discussed in Sections VI, P, 2,/and VIII, respectively. 

The use of hydrodesulfurization in the determination of the structures of unknown benzo[6]thiophenes is becoming increasingly recognized about 100 examples have now been recorded. Two sets of experimental conditions are commonly used the benzo[6]thiophene may be treated with Raney nickel alloy directly in alkaline medium (the method of Papa et al.7M), or it may be boiled in ethanol with Raney nickel of varying reactivity (commonly W-7). Even under mild conditions, nonaromatic double bonds are usually saturated, halogens are removed, and nitro groups are reduced. Raney cobalt has about one-tenth the activity of Raney nickel in the hydrodesulfurization of benzo [6]thiophenes.765... 

Hydrodesulfurization of the mixture of isomers obtained by the nitration of benzo[6]thiophene gives a mixture of amines, the identification of which indicates the possible orientations of the nitro groups.84,412 It should be noted, however, that 5- and 7-nitrobenzo[6]-thiophene both give m-ethylaniline in this reaction. 

Hydrodesulfurization of certain hydroxy-437 and methoxy-sub-stituted615 alkybenzo[6]thiophenes is a useful means of preparing some otherwise inaccessible alkyl-substituted phenols [e.g., Eq. (15)].015 Various p-methoxyphenylbenzo[6]thiophenes have been employed similarly to prepare the corresponding hydroxydiphenyl-alkanes.464 Catalytic hydrodesulfurization of a-alkyl-/ -(3-benzo[6]-thienyl)propionic acids affords a convenient method of preparing a,y-disubstituted y-phenylbutyric acids.636 Treatment of / -(3-benzo[6]thienyl)acrylic acid with Raney nickel alloy, sodium meth-oxide, and deuterium oxide affords the deuterated acid (366).667... 

Hydrodesulfurization of 4-phenyl- or 4-(o-, m-, or p-tolyl)benzo[6]-thiophene affords 2-ethyl- or 2-, 3-, or 4-methyl-2 -ethyldiphenyl, respectively.356 It is of interest that 4-aryl-6,7-dihydrobenzo[6]thio-phenes afford 2-ethyl-4,5-dihydrodiphenyls.356... 

The mechanism of hydrodesulfurization of benzo[6]thiophene and its derivatives involves, as a first step, chemisorption of the molecules (through the sulfur atom lone pair of electrons) in a more or less perpendicular fashion to the catalyst surface. Removal of the sulfur is then thought to produce a diradical which, on subsequent hydro-... 

The olefin (369) is thought to arise by reaction of the intermediate diradical (368) with hydrogen before subsequent hydrogenation of 369 to 370.767-769 When benzo[6]thiopheno[3,2-6]benzo[6]thiophene (154) is hydrodesulfurized, bibenzyl, (rans-stilbene, and 2-phenyl-benzo[6]thiophene are obtained in amounts determined by the catalyst and reaction conditions.768 This result lends support to the view that removal of sulfur precedes hydrogenation in hydrodesulfurization reactions. 

The rates of hydrodesulfurization of benzo[6]thiophene 770,771 and its 3-methyl derivative 772 have been compared with those of other sulfur compounds using hydrogen and a C0O3-M0O3-AI2O3 catalyst. 

The use of hydrodesulfurization to identify benzo[6]thiophenes in petroleum oils has been discussed in Section II, A. 

The reduction of benzo-l,2-dithiole-3-thiones (77b) to various polythiols (74ACS(B)827, 63LA(661)84) may be accomplished by lithium (78BEP867155), lithium aluminum hydride, or by catalytic hydrogenation, and Raney nickel hydrodesulfurization gives products by complete elimination of sulfur (B-66MI43100). 

Hatanaka, S., Yamada, M., and Sadakane, O. Hydrodesulfurization of catalytic cracked gasoline. 1. Inhibiting effects of olefins on HDS of alkyl(benzo)thiophenes contained in catalytic cracked gasoline. Industrial Engineering Chemistry Research, 1997, 36, 1519. 

The use of hydrodesulfurization by Raney nickel as a means of determining structures of benzo[b]thiophenes has been largely superseded by spectroscopic methods. 

Acylenamines, PhC(NHEt)=CHCOR (R = Et, t-Bu, or H), of known stereochemistry have been obtained in high yield by hydrodesulfurization of 2-acyl-3-ethylaminobenzo[b]thiophenes.383 An SMe substituent on the benzo[b]thiophene nucleus can be removed without rupture of the thiophene ring by using Raney nickel in acetone.299... 

Ruthenium clusters were evaluated for catalytic activity for hydrodesulfurization (HDS) of benzo[b]thiophene. At 423 43 K and 100 atm, hydrogen benzo[b]thiophene was converted to 2,3-dihydrobenzo[b]thiophene and 2-ethylthiophenol. The best catalyst precursor was H4Ru4(CO)g(PPh3)4, which gave 81% conversion to 2,3-dihydro-benzo[b]thiophene after 384 h at 443 K about 5% ethylbenzene was also formed, showing some HDS activity. The clusters were more active than the monometallic precursor Ru(CO)3(PPh3)2. However, the reaction conditions are rather severe and the involvement of decomposition products is very possible. ... 

Hydrodesulfurization [HDS, Eq. (1)] is the process by which sulfur is removed from fossil materials upon treatment with a high pressure of H2 (3.5-17 MPa) at high temperature (300-425 °C) in the presence of heterogenexius catalysts, generally transition metal sulfides (Mo, W, Co, Ni) supported on alumina [1]. About 90% of the sulfur in fossil materials is contained in thiophenic molecules, which comprise an enormous variety of substituted thiophenes, and benzo[b]thiophenes, di-benzo[b,d]thiophenes as well as other fused-ring thiophenes, most of which are generally less easily desulfurized over heterogeneous catalysts than any other sulfur compound in petroleum feedstocks (e.g., thiols, sulfide, and disulfides). 

Hydroprocessing of fossil fuel feedstocks for the removal of sulfur, nitrogen, and residual metals is a large-scale refinery process. Sulfru in fossil materials is found in various compounds, such as thiols, sulfides, disulfides, thiophenes, benzo-thiophenes, and dibenzothiophenes. The removal of sulfur from these fossil materials is commonly referred to as hydrodesulfurization (HDS), which is important in order to reduce the amount of sulfur introduced into the atmosphere since this contributes to acid rain. Secondly, the poisoning of catalysts in downstream processing has to be reduced. 

Studies of nucleophilic attack on the 7r-bound benzo[b]thiophene (BT) complexes [CpRu(BT)] and [Cp Ir(BT)] have been undertaken as potential models for the reactions of BT on hydrodesulfurization (HDS) catalysts. In these complexes, the BT coordinates to the metal via the benzene rather than the thiophene ring. A range of nucleophiles, including hydrides and sulfides which are proposed to be present on HDS catalyst surfaces, add to the benzene ring to give primarily C-7 adducts see Eq. (24). However, products that might be precursors to, or are similar to, proposed intermediates in the HDS of BT, such as... 

---