The eme reactions of α-ionones with singlet oxygen were examined to ascertain the effect of secondary Me interaction between the reactants on the reaction regiospecificity. Exclusive formation of 3-hydroxy-γ-ionones...The eme reactions of α-ionones with singlet oxygen were examined to ascertain the effect of secondary Me interaction between the reactants on the reaction regiospecificity. Exclusive formation of 3-hydroxy-γ-ionones found in the reactions reveals favorable interaction of singlet oxygen with the acyclic α-hydrogen atom,On the other hand,no formation of 3-hy- droxy-β-ionones implies that the steric requirement was not met for the bond formation between zwitterionic perepoxide with C_1-hydrogen in the process.The MMP21 and MNDO calculations indicate minus value of the secondary interaction energy for the aeyelie α-hydrogen abstrac- tion and a repulsion between the oxygen with C_1-hydrogen atom.Twisting tilting of the double bond may account for favorable attack of singlet oxygen on C_3.An explanation of the excellent regiospecificity was addressed and placed in proper mechanic prospective.展开更多
Nanosized solid superacids SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2),as well as MCM-41-supported SO_(4)^(2−)/ZrO_(2),were prepared.Their structures,acidities,and catalytic activities were investigated and compare...Nanosized solid superacids SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2),as well as MCM-41-supported SO_(4)^(2−)/ZrO_(2),were prepared.Their structures,acidities,and catalytic activities were investigated and compared using XRD,N2 adsorption-desorption,and in situ FTIR-pyridine adsorption,as well as an evaluation reaction with pseudoionone cyclization.The results showed that SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2)possess not only nanosized particles with diameters<7.0 nm,a BET sur-face greater than 140 cm2/g and relatively regular mesostruc-tures with pores around 4.0 nm,but also a pure anatase phase and strong acidity.Different from the Lewis acid nature of SO_(4)^(2−)/ZrO_(2)/MCM-41,SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2)exhibit mainly Brønsted acidities.The strongest Brønsted acid sites were produced on SO_(4)^(2−)/TiO_(2)promoted with H2SO4,while Lewis acid sites on S_(2)O_(8)^(2)−/TiO_(2)even stronger than those on SO_(4)^(2−)/ZrO_(2)/MCM-41 were generated when persulfate solu-tion was used as sulfating agent.Because of their distinct acid natures,SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2)exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO_(4)^(2−)/ZrO_(2)/MCM-41.It can be concluded that the existence of more Brønsted acid sites was favorable for proton participation in the cyclization reaction.展开更多
基金project supported by the National Natural Science Foundation of China.
文摘The eme reactions of α-ionones with singlet oxygen were examined to ascertain the effect of secondary Me interaction between the reactants on the reaction regiospecificity. Exclusive formation of 3-hydroxy-γ-ionones found in the reactions reveals favorable interaction of singlet oxygen with the acyclic α-hydrogen atom,On the other hand,no formation of 3-hy- droxy-β-ionones implies that the steric requirement was not met for the bond formation between zwitterionic perepoxide with C_1-hydrogen in the process.The MMP21 and MNDO calculations indicate minus value of the secondary interaction energy for the aeyelie α-hydrogen abstrac- tion and a repulsion between the oxygen with C_1-hydrogen atom.Twisting tilting of the double bond may account for favorable attack of singlet oxygen on C_3.An explanation of the excellent regiospecificity was addressed and placed in proper mechanic prospective.
文摘Nanosized solid superacids SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2),as well as MCM-41-supported SO_(4)^(2−)/ZrO_(2),were prepared.Their structures,acidities,and catalytic activities were investigated and compared using XRD,N2 adsorption-desorption,and in situ FTIR-pyridine adsorption,as well as an evaluation reaction with pseudoionone cyclization.The results showed that SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2)possess not only nanosized particles with diameters<7.0 nm,a BET sur-face greater than 140 cm2/g and relatively regular mesostruc-tures with pores around 4.0 nm,but also a pure anatase phase and strong acidity.Different from the Lewis acid nature of SO_(4)^(2−)/ZrO_(2)/MCM-41,SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2)exhibit mainly Brønsted acidities.The strongest Brønsted acid sites were produced on SO_(4)^(2−)/TiO_(2)promoted with H2SO4,while Lewis acid sites on S_(2)O_(8)^(2)−/TiO_(2)even stronger than those on SO_(4)^(2−)/ZrO_(2)/MCM-41 were generated when persulfate solu-tion was used as sulfating agent.Because of their distinct acid natures,SO_(4)^(2−)/TiO_(2)and S_(2)O_(8)^(2)−/TiO_(2)exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO_(4)^(2−)/ZrO_(2)/MCM-41.It can be concluded that the existence of more Brønsted acid sites was favorable for proton participation in the cyclization reaction.
