J Incl Phenom Macrocycl Chem
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Fig. 7 Effect of hydrochloric acid concentration on percentage
stripping of rare earth metal ions loaded on 6 with 1, 2, and 4 M HCl
were not completely stripped with 1 or 2 M hydrochloric
acid, while 4 M hydrochloric acid resulted in complete
stripping of all the rare earth metal ions examined.
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A cone conformation diphosphonic acid derivative of cal-
ix[4]arene, 6, incorporating two different spacer groups po-
sitioned at distal positions has been prepared as a reagent for
investigating the extraction behavior of rare earth metal ions.
This reagent exhibited heavy rare earth metal selectivity,
coupled with high extraction ability and good separation
efficiency towards rare earth metals. The high extraction and
good separation efficiency are in part attributed to the con-
vergence of the reagent’s functional groups as well as to the
preorganized metal-binding domain which reflects the cyclic
structure and cone conformation of calix[4]arene backbone.
Although 6 was synthesized with the expectation that its
extraction ability might be somewhat suppressed, it never-
theless showed improved separation efficiency and its ex-
traction ability was still comparable to the
propylenephosphonic acid derivative, 3. Strong chelate ef-
fect varied from unstable 7-membered ring to stable
13. Ohto, K., Yano, M., Inoue, K., Yamamoto, T., Goto, M.,
Nakashio, F., Shinkai, S., Nagasaki, T.: Solvent extraction of
trivalent rare earth metal ions with carboxylate derivatives of
calixarenes. Anal. Sci. 11(6), 893–902 (1995)
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4. Ohto, K., Ota, H., Inoue, K.: Solvent extraction of rare earths with
a calix[4]arene compound containing phosphonate groups. Sol-
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5. Ohto, K., Matsufuji, T., Yoneyama, T., Tanaka, M., Kawakita,
H., Oshima, T.: Preorganized, cone-conformational calix[4]arene
possessing four propylenephosphonic acids with high extraction
ability and separation efficiency for trivalent rare earth elements.
J. Incl. Phenom. Macrocycl. Chem. 71(3,4), 489–497 (2011)
6. Ohto, K., Takedomi, A., Chetry, A.B., Morisada, S., Kawakita,
H., Oshima, T.: The effect of phenoxy oxygen atoms on ex-
tremely high extraction ability and less separation efficiency of
trivalent rare earth elements with tetraphosphonic acid derivative
of calix[4]arene. J. Incl. Phenom. Macrocycl. Chem. 77(1–4),
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63–373 (2013)
7. Chetry, A.B., Matsufuji, T., Adhikari, B.B., Morisada, S.,
Kawakita, H., Ohto, K., Oshima, T.: Intramolecular synergism for
group separation extraction of trivalent rare earths with a cross
type calix[4]arene with phosphonic and carboxylic acid bifunc-
5
-membered ring clearly compensated by loss of comple-
mentarity and the presence of the two different phosphonic
acid groups. This conclusion may contribute to design more
effective extraction reagents. The extraction equilibrium
constants and separation factors were estimated from the
extraction data, along with the values of the other extraction
reagents prepared previously as well as for the commercial
reagent 10 (PC-88A). Full stripping of all the rare earth metal
ions loaded on the present reagent 6 was completely
achieved with 4 M hydrochloric acid.
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8. Ohto, K., Shiratsuchi, K., Inoue, K., Goto, M., Nakashio, F.,
Shinkai, S., Nagasaki, T.: Extraction behavior of copper(II) ion
by calixarene carboxylates derivatives preorganized by sodium
ion. Solvent Extr. Ion Exch. 14(3), 459–478 (1996)
9. Yoneyama, T., Sadamatsu, H., Kuwata, S., Kawakita, H., Ohto,
K.: Allosteric coextraction of sodium and metal ions with cal-
ix[4]arene derivatives 2: first numerical evaluation for the
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