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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 19, Number 6
BKCSDE 19(6)
June 20, 1998 

Formation and Dissociation Kinetics of Tetraaza-Crown-Alkanoic Acid Complexes of Cerium(Ⅲ)
Ki-Young Choi, Dong Won Kim, Yong Soon Chung, Chang Suk Kim, Choon Pyo Hong, Young-Ill Lee
The formation and dissociation rates of Ce3+ Complexes of the 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-NN', N",N"'-tetraacetic acid (1), 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetramethylacetic acid (2), and 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetrapropionic acid (3) have been measured by the use of stopped-flow spectrophotometry. Observations were made at 25.0±0.1 ℃ and at an ionic strength of 0.10 M NaClO4. The complexation of Ce3+ ion with 1 and 2 proceeds through the formation of an intermediate complex (CeH3L2+)* in which the Ce3+ ion is incompletely coordinated. This may then lead to be a final product in the rate-determining step. Between pH 4.76 and 5.76, the diprotonated (H2L2-) from is revealed to be a kinetically active species despite of its low concentration. The stability constants (logK(CeH3L2+)) and specific water-assisted rate constants (kOH) of intermediate complexes have been determined from the kinetic data. The dissociation reactions of Ce3+ complexes of 1, 2, and 3 were investigated with Cu2+, ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The effect of buffer and Cu2+ concentration on the dissociation rate has also been investigated. The ligand effect on the dissociation rate of Ce3+ complexes is discussed in terms of the side-pendant arms and the chelate ring sizes of the ligands.
671 - 676
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