Journal of the American Chemical Society p. 6146 - 6149 (1983)
Update date:2022-08-23
Topics:
Ercolani, Gianfranco
Mandolini, Luigi
Masci, Bernardo
Alkali and alkaline-earth metal ions exert a remarkable catalytic effect (template effect) on the cyclizatiion of o-hydroxyphenyl 3,6,9,12-tetraoxa-14-bromotetradecyl ether (ArOH) to benzo-18-crown-6 (B18C6) in MeOH solution.This phenomenon is interpreted as resulting from two opposing factors, a rate-enhancing factor due to an increased proximity of chain ends in the cation-associated precursor ArO- and a rate-retarding factor due to interaction of the nucleophilic end of ArO- with the metal ion.Combination of previous equilibrium data with kinetic measurements from the present work provides a complete set of equilibrium constants for association of seven cations Na+, K+, Rb+, and Cs+ and Ca2+, Sr2+, and Ba2+ with the four ligands ArOH, ArO-, B18C6, and T<*>, the latter being the transition state for cyclization.Following our earlier suggestion, according to which the proximity effect is viewed as a sort of macrocyclic effect, i. e., the one in which the cyclic ligand is T<*> and the acyclic ligand is ArO-, we now present an extrathermodynamic treatment indicating that the magnitude of the above macrocyclic effect is well represented by the KB18C6/KArOH ratio.This ratio provides an estimate for the upper limit of the template effect.The actually observed values are lower by a factor of ca. 4 because of reduction of nucleophilicity due to cation association.
View MoreShangyu Sanhechemicals Co.,LTD.
Contact:86-0571-56696839
Address:Num.2952,Nanhuan Road,Binjiang District,Hangzhou,China
Nanjing distinctions Medical Technology Co., Ltd.
Contact:+86-15996203785 13914714059
Address:nanjing,jiangsu , China
Changsha Goomoo Chemical Technology Co.Ltd
Contact:+86-731-82197655
Address:No.649,Chezhan Rd.(N),Changsha,Hunan,China
Qingdao S. H. Huanyu Imp. & Exp. Co., Ltd.
Contact:86-532-88250866
Address:Room 615, World Trade Centre Building B, Hongkong Middle Roda 6#, Qingdao, Shandong, China
Contact:021-61840961 021-61840962
Address:No.157,Zhuguang Rd, Qingpu, Shanghai, China
Doi:10.1021/ol990856c
(1999)Doi:10.1021/jacs.0c11010
(2021)Doi:10.1016/0301-0104(91)85004-Z
(1991)Doi:10.1080/00397919808007049
(1998)Doi:10.1016/S0040-4039(98)01867-X
(1998)Doi:10.1134/S0023158416030174
(2016)