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Redox Chemistry of Third Phases Formed in the Cerium/Nitric Acid/Malonamide‐ n ‐Dodecane Solvent Extraction System
Author(s) -
Ellis Ross J.,
Antonio Mark R.
Publication year - 2012
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201100022
Subject(s) - chemistry , cerium , bulk electrolysis , dodecane , third phase , redox , solvent , inorganic chemistry , electrolysis , nitric acid , aqueous solution , cerium nitrate , aqueous two phase system , cyclic voltammetry , valence (chemistry) , electrochemistry , phase (matter) , nuclear chemistry , electrode , organic chemistry , electrolyte
Upon solvent extraction of the colorless solution 0.1 M Ce(NO 3 ) 3 ⋅6H 2 O in 3 M HNO 3 with DMDBTDMA ( N , N ′‐dimethyl‐ N , N ′‐dibutyltetradecyl malonamide) at a concentration of 0.5 M in n‐ dodecane (also a colorless solution), a yellow third phase is formed. In keeping with previous observations reported in the historical literature of solvent extraction, the yellow color was initially interpreted as an indication of the presence of tetravalent cerium, which is, coincidentally, yellow in aqueous HNO 3 . The valence quandary arising from the visual assessment led us to extract a freshly prepared solution of 0.1 M cerium(IV) nitrate, which was obtained by exhaustive bulk electrolysis of 0.1 M Ce(NO 3 ) 3 ⋅6H 2 O in 3 M HNO 3 . A red third phase was obtained. Under ambient light, the red third phase reverts to the yellow color of the third phase formed upon solvent extraction of Ce III . These observations, in combination with results obtained by UV/Visible and X‐ray absorption spectroscopies as well as electrochemical studies of the yellow and red third phases, demonstrate that the colors are directly correlated with changes in Ce valence, where Ce III obtains in the yellow third phase and Ce IV in the red one, and the formation of coordination complexes with DMDBTDMA. By use of three‐phase electrode voltammetry and controlled potential electrolysis techniques, the one‐electron Ce III /Ce IV redox chemistry in the third phases was examined in a manner not realized beforehand. These results, demonstrating reversible electrochromism, stand at the intersection of the fields of electroanalytical chemistry, on the one hand, and separations science, on the other, thus providing original insights into third phase phenomena and ion transfer across the aqueous–organic liquid interface in the extraction system.