1. Field of the Invention
The present invention relates to calix[4]arene dibenzo crown ether compounds, their preparation process and their use as extractants which can selectively separate cesium ions (Cs.sup.+). More particularly, the present invention relates to calix[4]arene dibenzo crown ethers able to selectively extract the cesium ions present in the state of traces in aqueous effluents from nuclear fuel cycle facilities, their preparation process and their use in extraction of cesium ions. Useful as ionophores for separating cesium ions from radioactive wastes, the compounds of the present invention are represented by the following structural formula 1: ##STR1## wherein R is a C.sub.1 -C.sub.10 normal alkyl, a phenyl or a methoxyphenyl, R' is hydrogen, p-tert-butyl or a C.sub.1 -C.sub.10 normal alkyl, R" is hydrogen or a C.sub.1 -C.sub.10 normal alkyl, and n is an integer of 0-2.
2. Description of the Prior Art
As industry has been highly advanced, environmental pollution is aggravated. In the present days, nuclear power is extensively used as an important energy source by virtue of its economical favorability in terms of, for example, investment cost in equipment, so more radioactive wastes are now generated mostly from atomic power plants. Therefore, the techniques for disposing radioactive wastes safely and in as little space as possible must be settled without delay.
The concentration technique by evaporation which has been employed for the disposal of radioactive waste liquids thus far, is very good in desalting, but produces a large amount of the wastes to be solidified because it treats all nuclides and salts together. In order to dispose of such wastes, of particularly interest are extractants which are capable of selectively separating heat-generating nuclides and long half-life nuclides. Active and extensive research has been and continues to be directed to the development of the extractants.
A special control is required for cesium upon solidification after disposal of radioactive wastes because it is much longer in half-life (about 30 years) than other fission products, such as cobalt (5.72 years) and iodine (8 days), and generates heat. Thus, if the cesium ions contained in radioactive wastes are selectively separated, a great effect can be brought about on the disposal of radioactive wastes in terms of stability and energy efficiency.
The host-guest chemistry is a science field in which the interaction of the compounds, ions and/or molecules having intramolecular holes is researched. Since 1971 in which Helv. Chim. Acta, 54, 268, 1971, issued to professor Moff, describes that most of the ionophores present in nature are able to selectively transport cations through cell membranes, functioning as antibiotics, the chemistry has been of great interest and continues to be utilized in extensive research.
Calixarenes, which have interesting structures, compose a branch of the host-guest chemistry. For the past twenty years, the research in the calixarene chemistry has been focused on the synthesis and structural specificity of calixarenes and their derivatives. Particularly, recent research has reported that the calixarene crown ether compounds based on calix[4]arenes are able to selectively extract the metals such as cesium and be applied for the solidification of the concentrated radioactive waste liquids, which could cause serious problems in the aspect of environmental pollution if they are not treated properly.
The word calixarene is the compound word of calix and arene, both derived from Greek, meaning a benzene ring-containing macrocyclic compound with a shape of a wine cup (Vogtel and Weber, Host Guest Complex Chemistry Macrocycles, 378, Springer-Verlag, 1985).
p-tert-Butyl calixarene, representative of calixarenes, was synthesized from the reaction of p-tert-butyl phenol and formaldehyde in the presence of sodium hydroxide, as shown in the following scheme 1 (Cornforth et al., J. Pharmacol., 73, 10, 1995): ##STR2##
From the p-tert-butylcalix[4]arene 2, Gutsche et al., easily synthesized a calix[4]arene 3 by eliminating the p-tert-butyl group with the aid of an AlCl.sub.3 catalyst, as shown in the following scheme 2 (J. Org. Chem., 5795-5802, 50, 1985) ##STR3##
D. N. Reinhoudt et al., succeeded in the synthesis of calix[4]arene-crown-6-ether and the isolation of its four stereoisomers. During a study on the use of these calix arene compounds as macrocyclic ligands to absorb alkali metals, they found that 1,3-alternate calix[4]arene-crown-6-ether is of high selectivity for cesium ions (J. Am. Chem. Soc., 117, 2767, 1995).
Dozol disclosed the synthesis of a biscrown calix[4]arene in PCT/FR93/01161 and a calix[4]arene crown ether in PCT/FR94/00432 and asserted that these macrocyclic ligands were superior in selectivity and efficiency for cesium ions to any other crown ether known. However, these crown ethers are problematic in practical use as an ion extractant because their binding capacity to ions or their ion-extracting performance is reduced.