Carbocations such as tropylium and trityl cation, can be stable enough to be isolated and used without inert conditions. They can act as Lewis acids to lower the LUMO of electrophile, thus promoting reactions with nuc...Carbocations such as tropylium and trityl cation, can be stable enough to be isolated and used without inert conditions. They can act as Lewis acids to lower the LUMO of electrophile, thus promoting reactions with nucleophiles. Additionally, the interaction between carbocations and alcohols can form Bronsted acids with enhanced acidity. Furthermore, electrophoto activation of TAC^(+)(trisaminocyclopropenium ion)delivers the excited radical dication TAC·^(2+*), which is a strong oxidant and capable of oxidizing a range of challenging substrates. Moreover,^(n)Pr-DMQA^(+) is disclosed as a versatile photoredox catalyst as its excited state can be quenched through both oxidation and reduction. This review summarizes recent advance in carbocation-catalyzed reactions. These developed methods provide an environmentally friendly pathway for the synthesis of valuable compounds and will inspire chemists to discover more interesting transformations promoted by carbocations.展开更多
The first transition metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mech-anism triggered strategy is developed by using AI(OTf)_(3) as a hidden Br0nsted a...The first transition metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mech-anism triggered strategy is developed by using AI(OTf)_(3) as a hidden Br0nsted acid catalyst,which provides facile access to value-added acyclic tri-and tetra-substituted alkenes in good yields with high stereoselectivity under mild conditions.展开更多
The carbocationic polymerization of styrene（St） initiated by H2O/TiCl4 system was conducted at-60℃ in dichloromethane（CH2Cl2）/hexane（n-Hex）（50/50 V/V） in the presence of pyridine（Py）,2-methyl pyridine（MPy...The carbocationic polymerization of styrene（St） initiated by H2O/TiCl4 system was conducted at-60℃ in dichloromethane（CH2Cl2）/hexane（n-Hex）（50/50 V/V） in the presence of pyridine（Py）,2-methyl pyridine（MPy） and 2,6-dimethyl pyridine（DMPy）.A desirable polymerization process with a relative slow polymerization rate and PS products with relatively narrow molecular weight distribution（MWD,Mw/Mn ca.1.8） were obtained.Py and its derivants and/or their complexes with Lewis acid TiCl4 interact with the growing chain end to reduced its 'cationicity' and thus to decrease the polymerization rate,suppress chain transfer and termination reactions and narrow MWD.The experimental results also show that the monomer conversion as well as the molecular weight of polymer products increased but MWD almost kept unchanged with polymerization time.The number-average molecular weight of polymer increased linearly with monomer conversion but the line did not pass through the origin.展开更多
篢he carbocationic reaction between 2, 4, 4-trimethy1-2-chloropentane, which is a model compound of polyisobutylene’s end group, and 1, ldsdiphenyl ethylene was investigated by high pressure liquid chromatography, it...篢he carbocationic reaction between 2, 4, 4-trimethy1-2-chloropentane, which is a model compound of polyisobutylene’s end group, and 1, ldsdiphenyl ethylene was investigated by high pressure liquid chromatography, it was found that the reaction presents a strong reverse reaction even if at low temperature. The ceiling temperature is about -18℃. The reaction with tirne and effect of concentration of TiCl4, temperature, polarity of solvent on the reaction show that the main features of this reaction are very close to that of carbocationic polymerization of isobutylene. So the reaction would be ideal model reaction for the carbocationic polymerization.展开更多
In order to investigate the impact of U-ore on organic matter maturation and isotopic fractionation,we designed hydrous pyrolysis experiments on Type-II kerogen samples,supposing that the water and water–mineral inte...In order to investigate the impact of U-ore on organic matter maturation and isotopic fractionation,we designed hydrous pyrolysis experiments on Type-II kerogen samples,supposing that the water and water–mineral interaction play a role.U-ore was set as the variable for comparison.Meanwhile,anhydrous pyrolysis under the same conditions was carried out as the control experiments.The determination of liquid products indicates that the presence of water and minerals obviously enhanced the yields of C（15＋） and the amounts of hydrocarbon and nonhydrocarbon gases.Such results may be attributed to waterorganic matter reaction in the high-temperature system,which can provide additional hydrogen and oxygen for the generation of gas and liquid products from organic matter.It is found that δD values of hydrocarbon gases generated in both hydrous pyrolysis experiments are much lower than those in anhydrous pyrolysis.What is more,δD values are lower in the hydrous pyrolysis with uranium ore.Therefore,we can infer that water-derived hydrogen played a significant role during the kerogen thermal evolution and the hydrocarbon generation in our experiments.Isotopic exchange was facilitated by the reversible equilibration between reaction intermediaries with hydrogen under hydrothermal conditions with uranium ore.Carbon isotopic fractionations of hydrocarbon gases were somehow affected by the presence of water and the uranium ore.The increased level of i-C4/n-C4ratios for gas products in hydrous pyrolysis implied the carbocation mechanism for water-kerogen reactions.展开更多
The living cationic polymerization of 4-[2-(tert-butyldimethylsiloxy)ethyl]styrene (TBDMES) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) (50/50 V/V) solvent mixture at -80 degrees C. The initiator 1,...The living cationic polymerization of 4-[2-(tert-butyldimethylsiloxy)ethyl]styrene (TBDMES) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) (50/50 V/V) solvent mixture at -80 degrees C. The initiator 1,1-diphenylethylene (DPE) capped 2-chloro-2,4,4-trimethylpentane (TMPCl) was formed in situ in conjunction with titanium tetrachloride (TiCl(4)). The Lewis acidity of TiCl(4) was decreased by the addition of titanium(IV) isopropoxide (Ti(OiPr)(4)) to accomplish living polymerization of TBDMES. Hydrolysis of poly(TBDMES) in the presence of tetra-butylammonium fluoride yielded poly[4-(2-hydroxyethyl)styrene] (poly(HOES)). FT-IR, NMR and DSC demonstrated the hydrolysis was complete.展开更多
基金Financial support from National Natural Science Foundation of China (No. 21871053)the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang (No. 2019R01005)the Open Research Fund of School of Chemistry and Chemical Engineering, Henan Normal University (No. 2020ZD04) is gratefully acknowledged。
文摘Carbocations such as tropylium and trityl cation, can be stable enough to be isolated and used without inert conditions. They can act as Lewis acids to lower the LUMO of electrophile, thus promoting reactions with nucleophiles. Additionally, the interaction between carbocations and alcohols can form Bronsted acids with enhanced acidity. Furthermore, electrophoto activation of TAC^(+)(trisaminocyclopropenium ion)delivers the excited radical dication TAC·^(2+*), which is a strong oxidant and capable of oxidizing a range of challenging substrates. Moreover,^(n)Pr-DMQA^(+) is disclosed as a versatile photoredox catalyst as its excited state can be quenched through both oxidation and reduction. This review summarizes recent advance in carbocation-catalyzed reactions. These developed methods provide an environmentally friendly pathway for the synthesis of valuable compounds and will inspire chemists to discover more interesting transformations promoted by carbocations.
基金We gratefully acknowledge the financial support from the National Natural Science Foundation of China(Grant No.21901074)"Zijiang Scholar Program"of East China Normal University。
文摘The first transition metal-free highly stereoselective positional isomerization of various α-alkyl styrenes through a carbocation mech-anism triggered strategy is developed by using AI(OTf)_(3) as a hidden Br0nsted acid catalyst,which provides facile access to value-added acyclic tri-and tetra-substituted alkenes in good yields with high stereoselectivity under mild conditions.
文摘The carbocationic polymerization of styrene（St） initiated by H2O/TiCl4 system was conducted at-60℃ in dichloromethane（CH2Cl2）/hexane（n-Hex）（50/50 V/V） in the presence of pyridine（Py）,2-methyl pyridine（MPy） and 2,6-dimethyl pyridine（DMPy）.A desirable polymerization process with a relative slow polymerization rate and PS products with relatively narrow molecular weight distribution（MWD,Mw/Mn ca.1.8） were obtained.Py and its derivants and/or their complexes with Lewis acid TiCl4 interact with the growing chain end to reduced its 'cationicity' and thus to decrease the polymerization rate,suppress chain transfer and termination reactions and narrow MWD.The experimental results also show that the monomer conversion as well as the molecular weight of polymer products increased but MWD almost kept unchanged with polymerization time.The number-average molecular weight of polymer increased linearly with monomer conversion but the line did not pass through the origin.
文摘篢he carbocationic reaction between 2, 4, 4-trimethy1-2-chloropentane, which is a model compound of polyisobutylene’s end group, and 1, ldsdiphenyl ethylene was investigated by high pressure liquid chromatography, it was found that the reaction presents a strong reverse reaction even if at low temperature. The ceiling temperature is about -18℃. The reaction with tirne and effect of concentration of TiCl4, temperature, polarity of solvent on the reaction show that the main features of this reaction are very close to that of carbocationic polymerization of isobutylene. So the reaction would be ideal model reaction for the carbocationic polymerization.
文摘In order to investigate the impact of U-ore on organic matter maturation and isotopic fractionation,we designed hydrous pyrolysis experiments on Type-II kerogen samples,supposing that the water and water–mineral interaction play a role.U-ore was set as the variable for comparison.Meanwhile,anhydrous pyrolysis under the same conditions was carried out as the control experiments.The determination of liquid products indicates that the presence of water and minerals obviously enhanced the yields of C（15＋） and the amounts of hydrocarbon and nonhydrocarbon gases.Such results may be attributed to waterorganic matter reaction in the high-temperature system,which can provide additional hydrogen and oxygen for the generation of gas and liquid products from organic matter.It is found that δD values of hydrocarbon gases generated in both hydrous pyrolysis experiments are much lower than those in anhydrous pyrolysis.What is more,δD values are lower in the hydrous pyrolysis with uranium ore.Therefore,we can infer that water-derived hydrogen played a significant role during the kerogen thermal evolution and the hydrocarbon generation in our experiments.Isotopic exchange was facilitated by the reversible equilibration between reaction intermediaries with hydrogen under hydrothermal conditions with uranium ore.Carbon isotopic fractionations of hydrocarbon gases were somehow affected by the presence of water and the uranium ore.The increased level of i-C4/n-C4ratios for gas products in hydrous pyrolysis implied the carbocation mechanism for water-kerogen reactions.
基金supported by the Beijing Municipal Project for Developing Advanced Human Resources for Higher Education(Elastomers and Biomaterials).
文摘The living cationic polymerization of 4-[2-(tert-butyldimethylsiloxy)ethyl]styrene (TBDMES) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) (50/50 V/V) solvent mixture at -80 degrees C. The initiator 1,1-diphenylethylene (DPE) capped 2-chloro-2,4,4-trimethylpentane (TMPCl) was formed in situ in conjunction with titanium tetrachloride (TiCl(4)). The Lewis acidity of TiCl(4) was decreased by the addition of titanium(IV) isopropoxide (Ti(OiPr)(4)) to accomplish living polymerization of TBDMES. Hydrolysis of poly(TBDMES) in the presence of tetra-butylammonium fluoride yielded poly[4-(2-hydroxyethyl)styrene] (poly(HOES)). FT-IR, NMR and DSC demonstrated the hydrolysis was complete.
