HDS Chemistry

Some early proposals for the modes of adsorption of thiophenes on metal sulfides have been probed by comparisons with the structures of well-characterized metal complexes this has allowed the identification of the most reasonable alternatives and of new possibilities not previously considered. Tlieoretical studies on such complexes at increasing levels of sophistication have also contributed in an Important manner to provide a clear and consistent picture of the different possible bonding modes of thiophenes to metal centers. When these theoretical and experimental results from molecular chemistry are combined with the information available from surface techniques and heterogeneous catalysis, the chemisorption of this type of organosulfur compounds on metal sulfides arises as a very well understood phenomenon. This is no doubt one of the most important achievements of the organometallic modeling approach to HDS chemistry. 

Stenzenberger HD. Chemistry and properties of addition polyimides. In Wilson D, Stenzenberger HD, Hergenrother PM, eds. Polyimides. Glasgow Blackie 1990. pp. 79—128. 

J. D. Collins, L. S. Stone, and P. A. Juvner, Background Chemistry for Development ofEiquid Kocket Oxidizers, HD-18-283, CaHery Chemical Co., CaHery,... 

H. Topsoe, B. S. Clausen, N. Topsoe, andj. Hyldtoft, Symposium on the Mechanism of HD S / HDN Reactions, Vol. 38, No. 3, Division of Petroleum Chemistry, Preprints, American Chemical Society, Chicago, lU., July 1993. 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Contribution No. 3176 from the Gates and Crellin Laboratories of Chemistry, California Institute of Technology, Pasadena, California. This work was supported by grant No. HD-00347 from the National Institute of Child Health and Human Development. 

Patai, S., Hd. The Chem tstry of Functional Groups, The Chemistry of Peroxides, Wiley Chichester, UK, 1983,... 

This chapter follows the organization used in the past. A summary of the electronic properties leads into reports of electrocyclic chemistry. Recent reports of studies of HDS processes and catalysts are then summarized. Thiophene ring substitution reactions, ring-forming reactions, the formation of ring-annelated derivatives, and the use of thiophene molecules as intermediates are then reported. Applications of thiophene and its derivatives in polymers and in other small molecules of interest are highlighted. Finally, the few examples of selenophenes and tellurophenes reported in the past year are noted. 

Wageningen Agricultural University, Department of Food Chemistry, Bomenweg 2, 6703 HD Wageningen, The Netherlands, fax +31 317 484893... 

A New Improved Synthesis of Tricycle Thienobenzazepines Apphcation of chemistry recently developed by Knochel" combined with the well-described halogen dance (HD) reaction, allowed preparation of our key intermediate A in only three synthetic transformations (Scheme 6.4). In this respect, treatment of 2-bromo-5-methylthiophene with hthium diisopropylamide followed by dimethylformamide afforded aldehyde 11 in good yield, lodo-magnesium exchange with conunercial 4-iodo-3-nitro anisole followed by reaction with 11 afforded the thiophene catbinol 12. Dehydroxylation of 12 provided our key intermediate A which presented the requisite functionality to examine our approach to the construction of the seven-member ring system. 

Prof. Dr. hd ltd Department of Chemistry, Tohoku University, Sendai, Japan 980... 

Foss BJ, Sliwka HR, Partali V, Kopsel C, Mayer B, Martin HD, Zsila F, Bikadi Z, and Simonyi M. 2005b. Optically active oligomer units in aggregates of a highly unsaturated, optically inactive carotenoid phospholipid. Chemistry-A European Journal 11(14) 4103—4108. 

HD Gould, E. S. Mechanism and Structure in Organic Chemistry, p. 436. New York Holt, Rinehart and Winston 1959. 

Skipper HD, Gilmour CM, Furtick WR (1967) Microbial versus chemical degradation of atrazine in soils. Soil Sci Soc Am Proc 31 653-656 Sliwinski MK, Goodman RM (2004) Comparison of cienarchaeal consortia inhabiting the rhizosphere of diverse terrestrial plants with those in bulk soil in native environments. Appl Environ Microbiol 70 1821-1826 Stumm W, Morgan JJ (1996). Aquatic chemistry - chemical equlibrium and rates in Natural Waters (3rd edn). Wiley, New York Vega D, Bastide J (2003) Dimethylphthalate hydrolysis by specific microbial esterase. Chemosphere 51 663-668... 

Birkhofer H, Beckhaus HD, Ruchardt C (1986) ImViehe HG, JanousekZ,MerenyiR (Eds) Substituent Effects in Radical Chemistry, D. Reidel Publishing, Dordrecht, p 199... 

Roth HD (1992) Structure and Reactivity of Organic Radical Cations. 163 131-245 Rouvray DH (1995) Similarity in Chemistry Past, Present and Future. 173 1-30 Roy R (1997) Recent Developments in the Rational Design of Multivalent Glycoconjugates. 187 241-274... 

Zinn AA, Brandt L, Kaesz HD, Hicks RFF (1994) The Chemistry of Metal CVD, Kodas TT, Hamden-Smith MJ (eds), VCH, Weinheim, Germany... 

Craker LE, Simon JE (eds) (1986) Herbs, Spices, and Medicinal Plants Recent Advances in Botany, Horticulture and Pharmacology, vol 1. Food Products, New York Belitz HD, Grosch, W, Schieberle P (2004) Food Chemistry, 3rd edn. Springer, Berlin Heidelberg New York... 

In seeking new and improved ways for achieving the ultralow levels of sulfur in the fuels of the future, it is important to understand the nature of the sulfur compounds that are to be converted (especially PASCs), as described in Section III. It is equally important to understand how these transformations occur through interactions with catalytic surface species, the pathways involved during these transformations, and the associated kinetic and thermodynamic limitations. These considerations dictate the process conditions and reactor process configurations that must be used to promote such transformations. In this section, we describe the reactor configurations and process conditions being used today what is known about the catalyst compositions, structure, and chemistry and what is known about the chemistry and reaction pathways for conversion of PASCs in conventional HDS processes. 

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... 

For example, data obtained by this technique are shown in Table VIII and Fig. 12a for HDS of dibenzothiophene catalyzed by a CoMo/carbon (41). In these experiments, 3,3 -dimethylbiphenyl was used as the biphenyl analog, as the chemistries are identical and only small differences in adsorption behavior are expected. As shown in Table VIII, the ratio of rate constants ((kDo + /chs / hpi) was estimated to be 62. With this ratio held constant, the other rate constants in the HDS pathway matrix were estimated using curve-fitting techniques. 

Many of these studies utilized noble metals such as Ir, Os, Rh, Ru, or Re, whereas others used more conventional metals such as Mn, Fe, Mo, or Co. The particular metal on which the observations were made is not important at this point. What is important is that all of the important steps required for direct sulfur removal and hydrogenation of thiophene and more condensed derivatives have been shown to occur with soluble metal complexes. Thus, organometallic complex chemistry can be of great value in elucidating the mechanisms involved in conventional HDS processes and perhaps can point the way to improved catalyst formulations. 

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