Pyrolysis sulfur transfer

The molybdenum and tunsten diphenylacetylene compounds have been chemically useful primarily as precursors to the quadruple metal-metal bonded dimers [M(Por)]2, formed by solid-state vacuum pyrolysis reactions. However. Mo(TTP)()/"-PhC CPh) is also a useful substrate in atom-transfer reactions, reacting with Sx or Cp2TiS i to form Mo(TTP)=S. The reaction can be reversed by treatment of Mo(TTP)=S with PPh (which removes sulfur as PhxP=S) and PhC CPh. The order of preference for ligand binding to molybdenum 11) has been established to be PPh < PhC CPh < 4-picoline. ... 

The first example of asymmetric induction in transfer of chirality from the chiral sulfur atom to the prochiral carbon atom was described by Goldberg and Sahli in 1965 (197). It concerns the pyrolysis of the optically active p-tolyl tra s-4-methylcyclohexyl sulfoxides 258. It was found that on pyrolysis at 200 to 250°C, optically active sulfoxides (R)-258 and (5)-258 yield optically active 4-methylcyclohexenes-l 259, with the absolute R and S configurations, respectively, at the newly formed chiral carbon atoms (Scheme 25). The optical purities of the 4-methylcyclohexenes-l that were formed depended largely on the temperature of pyrolysis. Thus, the values of 42 and 70% optical purity were noted for 259 at 250° and 200°C, respectively. The formation of the cycloolefins 259, whose absolute configurations are the same as those of the starting optically active sulfoxides 258, indicates that the pyrolysis reaction proceeds... 

As the name implies, the acid hydrolysis pretreatment is intended to partially hydrolyze the lignocellulosic feedstock as well as remove alkali from it. This process converts hemicellulose to pentose sugar as well as removes alkali. Biomass was added to a 5 wt % solution of sulfuric acid in the proportion of about 150 g biomass for every liter of solution and boiled for 2 how s. The mixture was transferred to the glass column and excess liquid drained from the bottom. At this point 2 L of distilled water was pumped through die column at a superficial velocity of 0.08 mm/s to rinse acid from the biomass. The pretreated biomass was then dried at 105°C for subsequent pyrolysis. 

The formation curve of hydrogen sulfide started to evolve after 550 "C and reached a maximum around 750 °C, indicating the contribution of main chain random scission of the sulfur groups as the major path in the pyrolysis process. The monomer benzenethiol was the next abundant species. It started to form at 550 "C, reached a maximum between 700 °C and 750 C and then drastically reduced after 850 °C, indicating that depolymerisation was also one of the major pyrolysis paths. The formation of carbon disulfide indicated the contribution of the scission of the incompletely carbonised solid residue after 850 °C. This implied that the chain transfer of carbonisation increased gradually to become the dominating mechanism in the transition from lower to higher pyrolysis temperature. 

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