排序方式: 共有12条查询结果,搜索用时 15 毫秒
11.
Detection and Reaction of Oxaphosphetanes Derived from Benzaldehyde and 1-Adamantylmethylidene Ylide
The Wittig reaction of (1-adamantylmethylidene)triphenylphosphorane (Ph(3)P=CH(1-Ad)) with benzaldehyde was investigated, and the results were compared with those of other ylides. The substituent effect in the reaction of the ylide with benzaldehydes was determined by competition experiments, which gave a Hammett rho value of 3.2. The rho value is much larger than those reported for analogous reactions of Ph(3)P=CH(CH(2))(2)CH(3) (rho = 0.20) and Ph(3)P=CH(CH(3))(2) (rho = 0.59), indicating that the reaction mechanism differs for Ph(3)P=CH(1-Ad) and the other ylides. The cis/trans ratio of the product alkene is 74/26 for the reaction with the parent benzaldehyde and highly depends on the position of the substituent; ortho substituted benzaldehydes gave the trans alkenes up to 90%. Monitoring the reaction by means of (31)P NMR revealed that both cis and trans oxaphosphetane intermediates were formed and that the formation and decomposition of the cis oxaphosphetane are 7-12 times faster than those of the trans oxaphosphetane. From the comparison of the reaction of Ph(3)P=CH(1-Ad) + benzaldehyde with those of Ph(3)P=CH(CH(2))(2)CH(3) + benzaldehyde and benzophenone, and Ph(3)P=CH(CH(3))(2) + benzophenone, it was concluded that all the reactions with these nonstabilized ylides proceed via an electron-transfer mechanism and that the rate-determining step changes from the electron transfer step to that of radical combination when the substrate or ylide becomes more sterically demanding. 相似文献
12.
Teruaki Toyota Tadashi Hanafusa Takashi Oda Iwane Koumura Takanori Sasaki Eiji Matsuura Hiromi Kumon Tsuneo Yano Toshiro Ono 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):295-300
Ion exchange is a simple and efficient method for separating no-carrier-added 64Cu from an irradiated Ni target. We developed a semi-automated two-round 64Cu separation system equipped with a strong-base anion exchange resin column. We first verified the efficiency of the system using a non-radioactive substitute consisting of 25 mg of Ni and 127 ng of Cu, and confirmed that Cu was completely eluted at the second round of the separation step. After the bombardment, separation of 64Cu from the Ni target was achieved with high radiochemical purity. 64Cu produced and separated in this study had an extremely low level of Ni impurity. It could be used for labeling monoclonal antibodies for antibody positron emission tomography imaging and synthesizing radiopharmaceuticals. 相似文献