Molybdenum compounds oxidation-reduction conversion

An efficient synthetic route to (10Z)- and (10 )-19-lluoro-la,25-dihydroxy vitamin D3 has been developed (488). The key feature of this pathway is the introduction of a 19-fluoromethylene group to a (5 )-19-nor-10-oxo-vitamin D derivative. The 10-oxo compound 445 has been obtained via a 1,3-dipolar cycloaddition reaction of (5 )-la,25-dihydroxyvitamin D with in situ generated nitrile oxide, followed by ring cleavage of the formed isoxazoline moiety with molybdenum hexacarbonyl. Conversion of the keto group of (5 )-19-nor-10-oxo-vitamin D to the E and Z fluoromethylene group has been achieved via a two-step sequence, involving a reaction of lithiofluoromethyl phenyl sulfone, followed by the reductive de-sulfonylation of the u-lluoro-j3-hydroxysulfone. The dye-sensitized photoisomerization of the (5 )-19-fluorovitamin D affords the desired (5Z)-19-fluorovitamin D derivatives, (10Z)- and (10 )-19-fluoro-la,25-dihydroxy-vitamin D3. 

Commercial heterogeneous HDS catalysts for refinery use consist, almost without exception, of nickel- and/or cobalt-promoted molybdenum oxide located on a high surface area (approx. 300 m g ) alumina or silica-alumina support. Cobalt and nickel promoters increase the catalytic activity, particularly towards thiophenes whether Co or Ni is used as a promoter depends on the specific function for which the catalyst should be optimal. The catalyst material is shaped into porous pellets, a few millimeters in size, and these pellets are loaded into the reactor, forming a catalyst bed of 30-200 m volume. During start-up of a freshly loaded reactor, the catalyst bed, which is in the oxidic form, is sulfided, typically by treatment with an oil feed which has been spiked with a reactive sulfur compound that readily generates H2S in situ. The oxidic precursor phases (non-stoichiometric CoMo or NiMo surface oxides) are thereby converted into sulfidic phases termed Co-Mo-S and Ni-Mo-S. The conversion from the oxidic phase to the sulfidic is accompanied by a reduction in Mo oxidation state from +6 to +4. 

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