Noriyuki Kameda

Electronic effect of substituents on the hydrodesulfurization of ring substituted benzenethiols

Abstract To clarify the electronic factors of the reactants affecting hydrodesulfurization (HDS) reactivity, the o -, m - and p -isomers of aminobenzenethiol (ABT), methoxybenzenethiol (MBT) and toluenethiol (TT) were hydrogenolyzed by a batch method over CoS 2 , NiS 2 , and a presulfided commercial HDS catalyst. In the hydrogenolysis of all the isomers of ABT, MBT and TT, HDS by cleavage of the CS bond occurred selectively and was promoted by the presence of electron-releasing substituents in the ortho - and para -positions. Among the quantities obtained from the MINDO/3 calculation for a reactant, the next three are especially interesting: these are the coefficients of the ipso -carbon and the sulfur atoms in the highest occupied π-orbital (π-HOMO), C C HOMO and C S HOMO , and the energy level of π-HOMO. The differences in reactivity among the isomers of a substituted benzenethiol can be interpreted by use of the frontier π-electron densities (FED), 2(C C HOMO ) 2 and 2 (C C HOMO ) 2 . On the other hand, the differences in reactivity among the molecules, i.e., ABT, MBT, TT, and benzenethiol, shows a close correlation with the ratio of the two FEDS, (C C HOMO /C S HOMO ) 2 , and also with the energy level of π-HOMO. It is suggested that the energy level and the FED assume an important role in the HDS reactivities and that the magnitudes of the FEDs on the positions of both the sulfur and the ipso carbon atoms affect the reactivities not independently but concertedly.

Homogeneous catalytic hydrogenation of olefins using RhH2(Ph2N3)(PPh3)2 in tetrahydrofuran

Abstract The catalytic hydrogenation activity of RhH2(Ph2N3)(PPh3)2in tetrahydrofuran with different unsaturated compounds (allyl alcohol, cinnamic alcohol, cinnamaldehyde, acrylic acid, acrolein, cinnamic acid, acrylonitrile, cinnamonitrile and styrene) has been studied. The results obtained with acrolein, acrylic acid and acrylonitrile showed reduction, although other substrates did not. The highest activity was observed with acrylonitrile. A possible mechanism for this reaction is suggested.

Homogeneous catalytic hydrogenation of olefins by use of RhH2(Ph2N3)(PPh3)2 in dimethyl sulfoxide

Abstract A complex RhH2(Ph2N3) (PPh3)2 1 has been shown to be an efficient catalyst for the homogeneous hydrogenation of unsaturated compounds (styrene, acrylonitrile, cinnamic acid, cinnamic alcohol and cinnamonitrile) in dimethyl sulfoxide (DMSO) under mild conditions. DMSO appears to play an important role in generating the active catalytic species for hydrogenation of styrene. No catalytic activity for styrene hydrogenation was observed for 1 in solvents such as benzene, toluene, acetone, tetrahydrofuran and N,N-dimethylformamide. The results are discussed in relation to the mechanism of styrene hydrogenation.