KR9800034

New Calix[4]arene Dibenzocrown Ethers for Selective Sensing of Cesium in Aqueous Environment

Jong Seung Kim,* Jong Kuk Kim, * Wang Kyu Choi, Kune Woo Lee, and Won-Zin Oh1

Department of Chemistry, Konyang University, Nonsan 320-711, Korea. Department of Chemical Engineering, Konyang University, Nonsan 320-711, Korea. ^Korea Atomic Energy Research Institute, Taejon 305-600, Korea.

ABSTRACT 1,3-Dialkoxycalix[4]arene dibenzocrown ethers (6-9) were successfully synthesized in the fixed 1,3-alternate conformation with over 90 % yields by the reaction of corresponding l,3-dialkoxycalix[4]arenes 2-5 with dibenzodimesylate 13 in acetonitrile as a solvent in the presence of cesium carbonate as a base. In view of cyclization yield, the use of dimesylate is found to be better than that of dibenzoditosylate. With an unusual AB pattern in *H NMR spectrum for compound 9, it is suggested that conformational structure of 1,3-diallyloxy calix[4]arene dibenzocrown ether be less flexible than that of usual 1,3-alternate calixcrown ether, probably due to steric effects of two allyl groups. Complexation of the corresponding calix[4]arene 6-9 toward using single flux method through bulk liquid membrane system was found to give a high cesium selectivity.

INTRODUCTION Calix[4]arene molecule, cyclic tetramer of phenols, has been proven to be a useful three dimensional molecular building block for the synthesis of molecules with specific properties.1 Much attention has been paid to the conformational behaviors of calix[4]arene by means of solid state, solution state, molecular mechanics, and NMR experiment.2"4 It is known

To whom correspondence should be addressed. -92- that the calix[4]arenes are able to exist in the following four different conformations: cone, partial cone, 1,2-alternate, and 1,3-alternate.5'6 Several groups have succeeded in demonstrating that calix[4]arenes serve as an excellent receptor for the specific binding of guest atoms and molecules.7"9 Gutsche10 and Shinkai11 have found that water-soluble calix[4]arene can form a variety of host-guest complexes with organic guests in water. Ungaro,l2Mckervey,13 and Chang14 have found that calixaryl esters have a latent potential to be counted as the third generation of supramolecules. 1,3-Distal capping of calix[4]arene at the lower rim has been achieved with polyether linkage such as calixcrown ether,15 calix- doubly-crowned,16 double-calix-crown.17 Shinkai reported that the calix[4]arene crown-4 shows very high selectivity in ion-selective electrodes.18 Recently, interestingly, Reinhoudt and Ungaro have reported that l,3-dialkoxycalix[4]arene-crown-6 derivatives were successfully prepared and they are exceptionally selective ionophores for cesium ion when they are fixed in the 1,3-alternate conformation.19 Those observation was due to a complexation of cesium ion not only with the crown ether moiety but also with the two rotated aromatic nuclei (cation/ K -interaction) of the 1,3-alternate conformation.

It has been deeply considered that the burial of vitrified reprocessed high level activity liquid wastes (HLW) and medium level activity liquid wastes (MLW) are of very importance in view of our environment. Recently, it was reported that MLW containing radioactive metal ions having 20-30 years half life such as Sr2+, Cs+, and Co3+ etc., can be treated by evaporation or other techniques such as chemical precipitation and ion exchange to concentrate their radioactive waste into the smallest possible volume, so to speak, volume reduction process. 20 With these reasons, we have paid attention to prepare a series of calixcrown ethers as organic carrier able to selectively separate the cesium ion from MLW. Now we report successful syntheses of new l,3-dialkoxycalix[4]arene crown ether derivatives containing dibenzo groups which make the ether linkage more rigid and give them more flat as well as the calixarene molecule more lipophilic. Upon the use of bulk liquid membrane process, cesium selectivity out of alkali metal ions was measured with varying lipophilicity on the lower rim of corresponding calix[4]arene.

EXPERIMENTAL Melting points were taken by the use of a Mel-Temp of Fisher-Johns melting point apparatus without any correction. IR spectra were obtained with a Perkin-Elmer 1600 Series -93- FT-IR on potassium bromide pellet and on deposited KBr window in the case of soild product and oil, respectively, are recorded in reciprocal centimeters. 'H and I3C NMR spectra were recorded with a 400 MHz (Bruker ARX-400) and an 100 MHz spectrometer, respectively, the chemical shifts (8) reported downfield from the internal standard, tetramethylsilane. Elemental analysis was performed by Vario EL of Elemental Analyzer in Korea Basic Science Institute in Seoul, Korea. FAB+ mass spectra was obtained from JEOL-JMS-HX 110A/110A High Resolution Tendem Mass Spectrometry in Korea Basic Science Institute in Taejon, Korea. Unless specified otherwise, reagent grade reactants and solvents were obtained from chemical suppliers and used as received. Dry solvents were prepared as follows: tetrahydrofuran was freshly distilled from metal ribbon or chunks; benzene and pentane were stored over sodium ribbon, respectively; dichloromethane was freshly distilled from aluminum hydride. Acetonitrile was pre-dried from molecular seives (3A) and distilled over diphosphorous pentaoxide. Compounds I,27, 10,2B and II25 were prepared as described in the literatures.

Transport of Alkali Metal Ions in a Bulk Liquid Membrane System. Liquid membrane transport experiments were carried out as reported earlier using a bulk liquid membrane apparatus.26 Two separated water phase (one containing the salt to be transported) were separated by a dichloromethane phase which constituted the membrane. The interior of the tube above the organic media is filled with the source phase which is a 0.8 mL of solution of 0.1 M lithium, sodium, potassium, , and cesium , respectively, using a single flux method. The outer cylinder is filled with 5.0 mL of deionized water as a receiving phase. The details of the transport conditions are summarized in the footnotes of Table 1. Each experiment was repeated three times in a room thermostated to 25 ± 1 °C then 3 mL of the receiving phase was taken. The flux values (moles transported / sec m2) for corresponding metal ion concentration were determined by the use of a Perkin -Elmer 2380 atomic absorption spectrophotometer. Blank experiments for which no calix[4]arene dibenzocrown ether is present were performed to determine a membrane leakage.

Synthesis. General Procedures for the syntheses of l,3-dialkoxycalix[4]arenes are same as those in reported literature19 except the amount of K2CO3 added and recrystallization process. To a suspension of calix[4]arene 1 (5.0 g, 11.8 mmole) in 150 mL acetonitrile were added 1- -94- iodopropane (4.20 g, 24.7 mmole) and K2CO3 (1.63 g, 11.8 mmole) and the reaction mixture refluxed for 24 h under nitrogen atmosphere. The solvent was removed in vacuo and 50 mL of 10 % aqueous HC1 solution and 50 mL of CH2CI2 were added. The organic layer was separated and washed with water (2X50 mL). Organic phase was dried over anhydrous MgSO4 and the CH2CI2 was removed in vacuo to give a colorless oil which can be easily recrystallized from 100 mL of co-solvents (diethyl ether / hexanes : 7/3) except for compound 4 which can be recrystallized in hexane only. Pure products were obtained with over 90 % yields. 25,27-Bis(l-propyloxy)calix[4]arene (2) and 25,27-Bis(l-octyloxy)calix[4]arene (4).19 were provided in 90 % and 93 % yields, respectively. For both two compounds 2 and 4 physical properties and spectral data for conformational analysis are same as that in literature. 25,27-Bis(l-butyIoxy)calix[4]arene (3). The yield was 93 %. mp 227-229 °C; IR (KBr pallet, cm"1); 3400 (O-H), 1254, 1196; *H NMR (CDCI3) S 8.28 (s, ArOH, 2 H), 7.04 (d, /= 7.48 Hz , 4 H, Ar//), 6.87 (d, J= 7.48 Hz , 4 H, ArH), 6.69-6.61 (m, 4 H, Ar//), 4.30 (d,

J= 13.0 Hz, 4 H, ArC//2Ar), 3.99 (t, J= 6.2 Hz, 4 H, OC//2(CH2)2CH3), 3.35 (d, J = 13.0 Hz,

4 H, ArC//2Ar), 2.06-1.99 (m, J= 6.2 Hz, 4 H, OCH2C//2CH2CH3), 1.82-1.73 (m, J = 6.2 Hz, 13 4 H, O(CH2)2C//2CH3), 1.08 (t, J = 6.2 Hz, 6 H, O(CH2) 3CH3); C NMR (CDCI3): ppm 153.9, 152.5, 134.0, 129.5, 129.0, 128.7, 125.9, 119.5, 77.1, 32.9, 32.0. 20.0, 14.7; FAB MS + m/z (M ) calcd 536.80, found 536.82. Anal. Calcd for C36H4o04: C, 80.59; H, 7.46. Found: C, 80.66; H, 7.49. 25,27-Bis(l-allyloxy)calix[4]arene (5). The yield was 90 %. mp 208-210 °C; IR (KBr pallet, cm1); 3400 (O-H), 1253, 1197; !H NMR (CDCI3) 8 7.99 (s, ArOH, 2 H), 7.05 (d, J = 7.40 Hz , 4 H, Ar//), 6.80 (d, J = 7.40 Hz , 4 H, Ar//), 6.73-6.63 (m, 4 H, ArH), 6.29-

6.20 (m, 2 H, OCH2C//=CH2), 5.78 (dd, 2 H, OCH2CH=C//2), 5.42 (dd, 2 H, OCH2CH=C//2),

4.89 (d, 4 H, OC//2CH=CH2), 4.33 (d, J= 13.0 Hz, 4 H, ArC//2Ar), 3.35 (d, J= 13.0 Hz, 4 H, 13 ArC//2Ar); C NMR (CDC13): ppm 153.8, 152.3, 134.0, 133.4, 129.6, 129.1, 128.7, 126.1, 119.6, 118.5, 77.3, 32.0; FAB MS m/z (M+) calcd 504.66, found 504.50. Anal. Calcd for C34H32O4: C, 80.95; H, 6.34. Found: C, 80.77; H, 6.42. General Procedures for the Synthesis of Calix[4]arene Dibenzocrown-8 (6-9). 25, 27-dialkoxycalix[4]arene 2 (2.0 mmole) was dissolved in 50 mL of acetonitrile and added to an excess of CS2CO3 (1.62 g, 5.0 mmole) and l,5-bis[2-(2'-mesyloxyethyloxy)phenoxy]-3- oxapentane (1.12 g, 2.1 mmole) under nitrogen atmosphere. The reaction mixture was

-95- refluxed for 24 h. Then acetonitrile was removed in vacuo and the residue extracted with 100 mL of methylene chloride and 50 mL of 10% aqueous HC1 solution. The organic layer was separated and washed twice with water. After the organic layer was separated and dried over anhydrous magnesium sulfate followed by removing the solvent in vacuo to give a brownish oil. With TLC analysis, all of four compounds (6-9) are found to show an only one spot (Rp0.4). Filtration column chromatography with ethyl acetate : hexane = 1 : 6 as eluents provied pure 1,3-alternate calix[4]arene dibenzocrown ethers as a white solid in over 90 % yield. 25,27-Bis(l-propyloxy)calix[4]arene dibenzocrown-8, 1,3-alternate (6) was recrystallized from the oil residue with 5/1 diethyl ether- hexanes: 90 % yield; mpl78- 1 ! 181 °C; IR (KBr pallet, cm ); 3068 (Ar-H), 1501, 1451, 1254, 1196; H NMR (CDC13) S 7.02-6.87 (m, 16 H), 6.78-6.70 (m, 4 H), 4.22 (t, J = 5.1 Hz, 4 H), 4.08 (t, J = 5.1 Hz, 4 H),

3.89 (t, J = 5.1 Hz, 4 H), 3.76 (t, J = 5.1 Hz, 4 H), 3.70 (s, 8 H, ArC//2Ar), 3.41 (t, J = 7.4 Hz,

4 H, OC//2CH2CH3), 1.47-1.38 (m, J = 7.4 Hz, 4 H, OCH2C//2CH3), 0.77 (t, J = 7.4 Hz, 6 H, I3 OCHsCHsCtfi); C NMR (CDC13): ppm 157.4, 156.8, 150.7, 149.8, 134.4, 134.3, 130.6, 130.5, 123.1, 122.8, 122.6, 122.3, 118.3, 116.1, 73.4, 71.1, 70.6, 69.8, 38.1, 23.7, 10.8; FAB MS m/z (M+) calcd 850.31, found 850.30. Anal. Calcd for C54H58O9: C, 76.20; H, 6.82. Found: C, 76.18; H, 6.87. 25,27-Bis(l-butyloxy)calix[4]arene dibenzocrown-8, 1,3-alternate (7) was crystallized from the oil residue with 5/1 diethyl ether- hexanes: 92 % yield; mp 146-148 °C; IR (KBr pallet, cm"1); 3068 (Ar-H), 1501, 1455, 1258, 1208; 'H NMR [DMSO-d^CDC^ 1/3 (v/v)] S 7.01-6.90 (m, 16 H), 6.75-6.70 (m, 4 H), 4.20 (t, /= 5.1 Hz, 4 H), 4.01 (t, 7=5.1 Hz,

4 H), 3.86 (t, J = 5.1 Hz, 4 H), 3.67 (s, 16 H, Ar-C//2-Ar, and O-C//2CH2O-), 3.42 (t, J = 7.4

Hz, 4 H, OC//2CH2CH2CH3), 1.46-1.32 (m, J = 7.4 Hz, 4 H, OCH2Ctf2CH2CH3), 1.25-1.16 13 (m, 4 H, OCH2CH2C//2CH3), 1.89 (t, J = 7.4 Hz, 6 H, OCHzCHzCHjCtfj); C NMR

[DMSO-d6/CDCl3= 1/3 (v/v)]: ppm 156.3, 155.5, 149.3, 148.3, 133.2, 133.0, 129.4, 121.8, 121.7, 121.4, 121.0, 116.3, 114.5,70.4,69.7,69.0,68.9.68.4,36.8,31.3, 18.4, 13.8; FAB MS + m/z (M ) calcd 878.30, found 873.40. Anal. Calcd for C56H62O9: C, 76.53; H, 7.06. Found: C, 76.48; H, 7.16. 25,27-Bis(l-octyloxy)calix[4]arene dibenzocrown-8, 1,3-alternate (8) was recrystallized from the oil residue with hexanes only: 92 % yield; mp 124-127 °C; IR (KBr

1 ] pallet, cm ) 1593, 1501, 1455, 1254, 1208; H NMR (CDC13) 5 7.08-6.91 (m, 16 H), 6.78-

-96- 6.70 (m, 4 H), 4.23 (t, J = 5.1 Hz, 4 H, -OC//2CH2O-), 4.08 (t, J = 5.0 Hz, 4 H, -OC#2CH2O-),

3.88 (t, J = 5.1 Hz, 4 H, -OC//2CH2O-), 3.73 (t, 7 = 5.1 Hz, 4 H, -OC//2CH2O-), 3.71 (s, 8 H,

ATCH2AT), 3.44 (t, 7 = 7.4 Hz, 4 H, OC//2(CH2)6CH3), 1.80-1.40 (m, J = 7.4 Hz, 4 H, 13 OCH2(C//2)6CH3), 0.91 (t, J = 7.4 Hz, 6 H, OCH2(CH2)6C//J); C NMR (CDC13): ppm 157.5, 156.8 150.7, 149.8, 134.5, 134., 130.6, 130.5, 123.1, 122.9, 122.7, 122.3, 118.3, 116.1, 71.9,

71.1, 70.6, 69.97, 69.90, 38.2 (ArCH2Ar),32.6, 30.43, 30.41, 30.13, 26.6, 23.4 + (OCH2(CH2)6CH3), 14.8 (OCH2(CH2)6CH3); FAB MS m/z (M ) calcd 990.20, found 990.10.

Anal. Calcd for C64H78O9: C, 77.57; H, 7.87. Found: C, 77.60; H, 7.77. 25,27-Bis(l-allyloxy)calix[4]arene dibenzocrown-8, 1,3-alternate (9) was recrystallized from the oil residue with 5/1 diethyl ether- hexanes: 92 % yield; mp 166- 1 168 °C; IR (KBr pallet, cm" ) 3010, 1501, 1455, 1258, 1200; *H NMR (CDC13) 5 7.02-6.93

(m, 16 H), 6.77-6.67 (m, 4 H), 5.83-5.74 (m, 2 H, OCH2C//=CH2), 5.11-5.00 (m, 4 H,

OCH2CH=C//2), 4.20 (t, J = 5.1 Hz, 4 H, -OC//2CH2O-), 4.08-4.03 (m, 4 H, -OCH2C//2O-,

OC//2CH=CH2), 3.84 (t, J = 5.1 Hz, 4 H, -OCU2CH2O-), 3.63 (AB quatet, J = 14.8 Hz A 13 v= 11.07 Hz, , 8 H, ArC//2Ar); C NMR (CDC13): ppm 156.8, 156.7, 150.9, 150.1, 134.6, 134.5, 134.2, 131.8, 130.9, 123.3, 123.3, 122.7, 122.63, 118.3, 117.0, 116.6,71.3,71.4,71.1, 70.7, 70.3, 38.1; FAB MS m/z (M+) calcd 856.30, found 846.30. Anal. Calcd for C54H54O9: C, 76.57; H, 9.21. Found: C, 76.60; H, 9.17. l,5-Bis[2-(2-hydroxyethyloxy)phenoxy]-3-oxapentane (12). Under nitrogen, to a

suspension of LiAlH4 (2.8 g, 73.9 mmole) in 150 mL of THF was added dropwise a solution of l,5-bis[2-(carboxymethyloxy)phenoxy]-3-oxapentane (11) (6.67 g, 16.4 mmole) dissolved in 50 mL of THF during a period of 30 min at 0°C. Upon the complete addition, reaction mixture was refluxed for 20 h under nitrogen atmosphere. After cooling down to 0°Cwith ice- bath, 10 mL of ethyl acetate and 10 mL of 10% NaOH aqueous solution were added dropwise to destroy the unreacted LiAlH4. The reaction mixture was allowed to stir for an additional 1 h at room temperature. White solid was filtered and washed with 100 mL of THF. After the organic solvent of filtrate was removed in vacuo, the residue was poured into a separatory funnel with 100 mL of CH2C12. The organic layer was separated and washed with 10 % HC1 solution followed by washing with 100 mL of brine and dried over anhydrous MgSC>4. The solvent was removed in vacuo to give a colorless oil. Recrystallization from 100 mL of diethyl ether provided 5.11 g (82%) of a white solid, mp 89-90°C: IR (KBr pallet, cm"1) 3400 (O-H),

1115 (C-O); 'H NMR (CDC13) S 6.91 (s, 8 H, Ar-H), 4.726 (br s, 2 H, -CH2CH2O//), 4.25-

-97- 4.19 (m, 4 H, -CH2CH2O-), 4.09-4.05 (m, 4 H, -CH2C#2O-), 3.99-3.84 (m, 8 H, -CH2C//,OH, and -CH2CH2O-), FAB MS m/z (M+) calcd 378.21, found 378.20. Anal. Calcd for C20H26O7: C, 63.49; H, 6.87. Found: C, 63.21; H, 6.90. l,5-Bis[2-(2-methanesulfonyloxyethyloxy)phenoxy]-3-oxapentane (13). Under nitrogen, to a solution of 5.0 g (13.2 mmole) of 12 and 4.08 rnJL (2.94 g, 29.0 mmole) of triethylamine in 100 mL of dry CH2CI2 was added dropwise 2.14 mL (3.33 g, 29.0 mmole) of methanesulfonyl chloride during a period of 30 min at 0°C. Upon the complete addition, reaction mixture was stirred for 5 h at 0°C. Reaction temperature was slowly rasied upto room temperature and stirred for additional 10 h. 50 mL of 10 % aqueous sodium bicarbonate solution was added and CH2CI2 layer was separated. The organic layer was washed with water (2 X 20 mL) and brine (2 x 20 mL) followed by drying over anhydrous magnesium sulfate. Removal of CH2CI2 in vacuo provided a colorless oil which was recrystallized from 100 mL of diethyl ether to give 6.20 g (92 %) of desired product, mp 98-99 °C: IR (KBr pallet, cm"1)

1597, 1516, 1350 (SO2), 1181 (SO2); 'H NMR (DMSO-d6) 5 7.00-6.88 (m, 8 H, Ar-tf),

4.57-4.45 (m, 4 H, -C//2CH2O-), 4.26-4.05 (m, 8 H, -CH2CH2O-), 3.85-3.75 (m, 4 H), 3.23 (s, + 6 H, CtfjSO2OCH2CH2-); FAB MS m/z (M ) calcd 534.12, found 534.20. Anal. Calcd for

C22H3oOnS2: C, 49.43; H, 5.61. Found: C, 49.21; H, 5.78.

RESULTS AND DISCUSSION Syntheses of 1,3-Alternate Dialkoxy Calix[4]arene Dibenzocrown Ethers To study an influence of lipophilicity of the organic carrier when the calix[4]arene dibenzocrown ether complexes with specific metal, a series of diametrically O-alkylated calix[4]arene 2-5 was prepared in the cone form. Synthetic route for the precursors was depicted in Scheme 1. It has been reported that the reaction of calix[4]arene with alkylating agents in acetonitrile in the presence of K2CC>3 is a well established synthetic method to obtain l,3-dialkoxycalix[4]arene in the cone form.19 They described that the use of 2.5 equivalents of

K2CC>3 as a base provided the 1,3-dialkoxy calix[4]arene with 50-65 % yields. Fortunately, however, we found the improved synthetic method that the use of only one equivalent of

K2COj gives one spot on TLC analysis (R/ 0.6, ethyl acetate : hexanes= 1 : 9) and provided the product in more than 90 % yield (see experimental). For all of four compounds (2-5), AB quartet splitting pattern (7=13 Hz, AV= 378 Hz, chemical shift difference value) in 'H NMR spectra was observed, indicating a characteristic cone conformation. The corresponding diallyl

-98- ether of calix[4]arene (5) and its crown ether analogues are of specially interest due to synthetic utilities that it affords.21

OH K2CO3 // \\ Rl CH3CN

R 2 C3H7 3 C4H9

4 C8H17 5 CH2=CH-CH2-

OR

CS2CO3 13 CH3CN

R 6 C3H7 7 C4H9 8 C8H17 9 CH2=CH-CH2-

Scheme 1. Synthetic route for the preparation of 1,3-dialkoxy calix[4]arene dibenzocrown ethers.

Cyclization reaction of 1,3-dialkoxy calix[4]arene with proper polyethylene glycol ditosylates in the presence of CS2CO3 has been also studied in many literatures.15"1719'22 It is

-99- known that the cyclization reaction to give the 1,3-alternate conformers is favored by the cesium template ion. 19 The yield was reported to give around 65-75 %. Also, for ditosylation of diol, reaction of diol and p-toluenesulfonyl chloride in the presence of aqueous NaOH 23 or pyridine 24 as a base has been widely used. However, because of a fish and disgusting smell, handling and treatment of p-toluenesulfonyl chloride or pyridine in laboratory is not recommendable. Also, the yield of tosylation by the use of known method is around 50-70%. In addition, in the present study, when we applied the previously reported method19 to dibenzo ditosylate with 1,3-dipropoxy calix[4]arene, we obtained the desired product as an almost same yield (65-70 %). Because of these reasons, we tried the dimesylation of dibenzo diol instead of ditosylation using methanesulfonyl chloride in the presence of triethylamine and obtained the dibenzo dimesylate with an over 90 % yield without any handling difficulties. Furthermore, surprisingly, cyclization yield using the dimesylate with 1,3- dialkoxycalix[4]arene in the presence of CS1CO3 was much more improved (over 90 %) than that of the corresponding ditosylate, resulting in a successful preparation of 1,3-dialkoxy calix[4]arene dibenzocrown ethers in the 1,3-alternate conformation. No other isomers were observed. The synthetic route for the preparation of corresponding dibenzodimesylate is described in Scheme 2. Reaction of l,5-bis(2-hydroxyphenoxy)-3-oxapentane (10) as a starting material with 2-bromoacetic acid in the presence of NaH as a base in THF provided l,5-bis[2-(carboxymethyloxy)phenoxy]-3-oxapentane (11) as a 90% yield.25 Subsequently, reduction of diacid with lithium aluminum hydride in THF gave a corresponding diol with an over 88 % yield. Mesylation of diol with methanesulfonyl chloride in the presence of triethylamine in CH2CI2 provided K5-bis[2-(2-methanesulfonyloxyethyloxy)phenoxy]-3- oxapentane (13) in a 92 % yield.

-100- NaH

BrCH2CO2H

11

LiAIH4 Methanesulfonyl Chloride >> THF/Reflux Triethylamine / CH2CI2

HO

12

Scheme 2. Synthetic route for the preparation of dibenzodimesylate.

*H NMR Behavior Three compounds (6-8) are blocked in the 1,3-alternate conformation as inferred from the !H NMR spectra (CDCI3) which show a singlet peak of 8 3.71 for the bridging methylene hydrogens of the calix[4]arene moiety. The 13C NMR spectra of compound 6-8 reveal one signal around 38 ppm, indicating the characteristic of 1,3-alternate conformation.

Interestingly, however, for compound 9 small AB quartet (J = 14.8 Hz AV=11.07 Hz, chemical shift difference value) was observed at S 3.64. The 13C NMR spectrum of compound 9 shows a signal at 38 ppm as well. This 'H NMR pattern in 1,3-alternate conformation seems to be unusual. To give a conformational identification, HOMO and

-101- HETERO COSY spectra were taken and the structure was well matched with the 1,3-alternate conformation. To further study the solvent effect on the conformational mobility and conformational identification of compound 9, *H NMR spectra were taken in two different deuterated solvents. Interestingly, the small AB splitting pattern of methylene hydrogens in CDCI3 is almost collapsed to show one singlet peak (not a perfect singlet) in CDCl3/DMSO-d6 (1:1 v/v) which corresponds to 1,3-alternate conformation. This indicates that the conformational flexibility increases in more polar solvent, resulting in a nearly magnetical equivalence on NMR time scale. Unfortunately and curiously, the compound 9 was not soluble in DMSO-d6 even at high temperature. That is why we use CDCh/DMSO-de (1:1 v/v) as a co-solvent. It has been known that when two protons attached on the calix[4]arene skeleton are magnetically nonequivalent, Hexo and Hendo being assigned to the higher and lower magnetic field, and then with increasing temperature the peak of AB system are gradually broadened and finally coalesce into one peak.1'2 In this study, however, when the temperature was raised from 10 "Cup to 60 °Cin CDCI3, the AB quartet peak did not change. Summarizing above solvent effect and temperature variable experiment, we can demonstrate that structure of 1,3-alternate 1,3- diallyloxy calix[4]arene dibenzocrown ether 9, probably due to bulkier diallyl group than «-alkyl chain, is slightly distorted or has less flexible conformation resulting in the fact of that Hexo and Hend0 are not exactly equivalent on NMR time scale.

Single Ion Transport Through Bulk Liquid Membrane Previously Reinhoudt and coworkers have reported the carrier-mediated transport of alkali metals through bulk liquid membrane and supported liquid membrane.19'28 Bulk liquid membrane system was preferentially adapted in this study to determine the transport amounts of metal ions. Source and receiving phase are made up of 0.8 mL of 0.1 M alkali metal nitrate and 5.0 mL of deionized water, respectively. Organic medium is composed of a solution of 3.0 mL of 1.0 mM calix[4]arene dibenzocrown ether in dichloromethane. The measured flux values from single transport experiment in bulk liquid membrane was described in Table 1 and depicted in Figure 1. For compound 6, stirring for 24 h at room temperature gave 0.00, 1.92, 1.28, 2.35, and 11.87 (10~8 mole • s"1 • m2) of flux values for Li, Na, K, Rb, and Cs ion, respectively. No transport of lithim ion was observed. High cesium ion selectivity in this single ion transport indicates that ring size of dibenzocrown ether linkage containing -102- calix[4]arene network has a good fitting with a diameter of cesium ion. In this study, although no evidence could be obtained for the ;r-interaction between p-orbital on benzene ring in calixarene framework and cesium ion, we assume a similar mechanistic fashion for the metal ion complextion from Reinhoudt's concept19 which the complexed ion interacts not only with the crown ether moiety but also with the two rotated aromatic nuclei (cation / K -interaction) of the 1,3-alternate conformation. It is thought that 1,3-alternate calix[4]arene dibenzocrown ether having two benzo groups would allow the downward ethereal linkage to be more rigid and flatter due to two benzo moieties. As a result, a good selectivity and efficiency of cesium ion among other alkali metal ions is ascribed not only to Reinhoudt's n -complexation concept but also to these rigidity and flatness of crown ether framework. Detailed X-ray crystal structure will be required in order to obtain a qualitative picture for the solid structure of metal ion complexation with calix[4]arene dibenzocrown ether 6.

Table 1. Single ion transport values of alkali metal ions through bulk liquid membrane using 1,3-dialkoxy calix[4]arene dibenzocrown ethers (6-9).

Compound Flux (10" mole • s" • m"2)b

Li* Na+ K+ Rb+ Cs+

6 0.00 1.92 1.28 2.35 11.87 7 0.00 0.60 0.64 1.37 8.12 8 0.00 1.51 0.77 1.03 2.90 9 0.00 0.57 0.68 1.51 8.11

a Transport conditions: source phase (aqueous solution of nitrate, 0.8 mL), M (NO3) = 0.1 M; membrane phase (CH2C12, 3.0 mL), (carrier) = 1.0 mM; i.d. of glass vial = 18 mm, stirred by 13 mm Teflon-coated magnetic stirring bar driven by a Hurst Synchronous motor; receiving phase (deionized water, 5.0 mL). b The average value of three independent determinations. The experimental values deviate from the reported values by an average of 10 %.

Lipophilicity of two alternate 1,3-dialkoxy groups was varied from propyl to butyl, to octyl, and to allyl. As lipophilicity of the alkoxy group increases, the selectivity and efficiency (flux value: 11.87, 8.12 and 2.90 for compound 6, 7 and 8 , respectively) for cesium ion

-103- gradually decrease. This plausibly indicates that when the metal ion complexed in organic medium with a highly lipophilic carrier, the solubility of complexed ligand-metal ion in organic solvent is so good that decomplexation of metal ion on the membrane surface between organic medium and the receiving phase could not be easily occurred. For 9 in which diallyloxy is substituted, 0.00, 0.57, 0.68, 1.51, and 8.11 of flux value for Li, Na, K, Rb, and Cs ion, respectively, were also observed to lead us think that there would be another factor like steric congestion besides lipophilicity of organic carrier for the controlling the complexation of cesium ion.

6 7 8 9 Organic carrier

Figure 1. Profile for single ion flux values of alkali metal ions through bulk liquid membrane.

In conclusion, syntheses of 1,3-dialkoxy calix[4]arene dibenzocrown ether in the 1,3- alternate conformation from the reaction of 1,3-dialkoxy calix[4]arene in the cone conformation with dibenzodimesylate in the presence of cesium carbonate in acetonitrile were succeeded with an over 90% yields which are better than the use of ditosylate. Single ion transport of alkali metal ion through bulk liquid membrane was conducted to show an excellent cesium ion selectivity. So far, we learned that compound 6 in which dipropoxy was substituted for 1,3-dialkoxy group shows the one of the best flux values for cesium in single ion transport experiment. Therefore, to optimize the selectivity and efficiency for cesium ion

-104- transport, the syntheses of 1,3-diethoxy and 1,3-dimethoxy calix[4]arene dibenzocrown ether which are much less lipophilic are planned and will be reported.

Acknowledgement This research was fully supported by the Korea Atomic Energy Research Institute in Taejon, Korea.

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