【Paper】
Highly Selective Extraction of Palladium（II）with Alkyl Xanthine Derivatives
Katsuya Kaikake* and Yoshinari Baba**
* Technical center. Faculty of Engineering, University of Miyazaki
** Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki
† Correspondence should be addressed to Katsuya Kaikake:
Faculty of Engineering, University of Miyazaki
（1-1 Gakuenkibanadai-Nishi Miyazaki-shi, Miyazaki, 889-2192 Japan）

Abstract
Extraction equilibria of palladium（II）from acidic chloride media were studied at 303K to examine the potential use of three kinds of xanthine derivatives（＝RN）, caffeine, theophylline, and theobromine, as selective extractants. Xanthine derivatives have exhibited high selectivity for palladium（II）over copper（II）and platinum（IV）. The extraction reaction of palladium（II）was elucidated by examining effects of hydrochloric acid, chloride ion, hydrogen ion, and extractant concentration as PdCl2＋2RN ⇔〓 PdCl2（RN）2 for caffeine, theophylline, and theobromine derivatives Using the xanthine derivatives, palladium（II）was extracted selectively from mixtures containing the 25-fold amounts of copper（II）or platinum（IV）. In addition, it was easy to strip the palladium（II）extracted with the xanthine derivatives using an ammonia or thiourea solution. The stripping percentage of palladium（II）was more than 60％ using single batchwise processing.

Key words: caffeine, xanthine derivatives, palladium（II）, selective extraction, stripping