Three series of proton-ionizable sym-dibenzo-16-crown-5 ethers with sterically demanding 1naphthyl, 2-naphthyl, and 9-phenanthryl geminal groups are synthesized and characterized. Variation of the proton-ionizable group includes oxyacetic acid and N-(X)sulfonyl oxyacetamide units with X = Me, Ph, C 6 H 4 -4-NO 2 , and CF 3 . For the latter series, variation of X provides 'tunable' acidity of the ligand. The metal ion-complexing properties of the proton-ionizable sym-(aryl)dibenzo-16-crown-5

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... ounds are probed by competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform. variation of the electron-withdrawing properties of X 'tunes' the acidity of the functional side arm. The influence of sterically hindered geminal aryl groups on metal ion complexation is evaluated in competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform. Results and Discussion Synthetic routes The synthetic routes to the new proton-ionizable sym-(1-naphthyl)-and sym-(2naphthyl)dibenzo-16-crown-5 ethers are shown in Scheme 1. General procedure for the synthesis of N-(X)sulfonyl sym-(1-naphthyl)dibenzo-16-crown-5oxyacetamides 10-13 Benzene (50 mL), 6 (1.20 g, 2.26 mmol) and oxalyl chloride (1.20 mL, 13.56 mmol) were combined in a 1-necked flask and stirred at room temperature for 1.5 h. The benzene was evaporated in vacuo and an IR spectrum of the residue was taken. Disappearance of the C=O peak at 1731 cm -1 and appearance of a C=O peak at 1824 cm -1 verified formation of acid chloride 8. The sulfonamide salt was prepared under nitrogen by adding NaH (0.54 g, 22.6 mmol) and THF (20 mL) to a 3-necked flask. A solution of the appropriate sulfonamide (2.71 mmol) in THF (20 mL) was added over a 10-min period. The mixture was stirred at room temperature for 1.5 h followed by the dropwise addition of a solution of the acid chloride 8 in THF (20 mL). The reaction mixture was stirred overnight (3 h when X = C 6 H 4 -4-NO 2 ) at room temperature and cooled to 0 o C. Water (15 mL) was added dropwise to destroy the excess NaH. The THF was evaporated in vacuo and then 40 mL of distilled water was added to the residue. The mixture was extracted with CH 2 C1 2 (100 mL then 50 mL). The combined organic extracts were washed with 10% aq K 2 CO 3 (2×50 mL). The combined aq layers were extracted with CH 2 C1 2 (2×50 mL). The combined organic layers were dried over MgSO 4 and evaporated in vacuo to give a solid that was purified by chromatography and recrystallization. N-Methanesulfonyl sym-(1-naphthyl)dibenzo-16-crown-5-oxyacetamide (10) was chromatographed on alumina with EtOAc-hexanes (1:1) as eluent. Recrystallization from the same solvent gave 0.82 g (75%) of white solid with mp 100 o C. ν max (film)/cm -1 : 3342 (N-H), 1723 (C=O), 1257, 1061 (C-O), 1343, 1158 (SO 2 ). δ H 3.09 (s, 3H), 3.85-3.99 (m, 2H), 4.02-4.15 (m, 2H), 4.15-4.28 (m, 4H), 4.80 (s, 2H), 4.91 (dd, J 10, 30, 4H), 6.74-7.84 (m, 4H), 6.84-6.91 (m, 2H), 6.91-6.99 (m, 2H), 7.45-7.59 (m, 3H), 7.86-7.94 (m, 3H), 8.71 (d, J 10, 1H), 9.52 (s, 1H). H, 5.47; N, 2.30%. N-Benzenesulfonyl sym-(1-naphthyl)dibenzo-16-crown-5-oxyacetamide (11) was chromatographed on alumina with EtOAc-hexanes (1:1) as eluent followed by recrystallization from the same solvent to give 0.65 g (65%) of white solid with mp 100 o C. ν max (film)/cm -1 : 3332 (N-H), 1723 (C=O), 1257, 1060 (C-O); 1353, 1160 (SO 2 ). δ H 3.78-3.87 (m, 2H), 3.91-4.00 (m, 2H), 4.00-4.08 (m, 2H), 4.09-4.21 (m, 2H), 4.71 (s, 2H), 4.65-4.75 (dd, J 20, 11, 4H), 6.70-7.75 (m, 2H), 6.75-6.85 (m, 4H), 6.88-6.99 (m, 2H), 7.27-7.36 (m, 2H), 7.43-7.59 (m, 4H), 7.80-7.95 (m, 5H) 8.64 (t, J 3, 1H), 9.67 (s, 1H). N, 2.09%. N-(4-Nitrobenzene)sulfonyl sym-(1-naphthyl)dibenzo-16-crown-5-oxyacetamide (12) was chromatographed on alumina with EtOAc-hexanes (1:1) as eluent. Recrystallization from the same solvent gave 0.64 g (55%) of yellow solid with mp 125-126 o C. ν max (film)/cm -1 : 3474 (N- General procedure for the synthesis of N-(X)sulfonyl sym-(2-naphthyl)dibenzo-16-crown-5oxyacetamides 14-17 Benzene (50 mL), carboxylic acid 7 (0.74 g, 1.39 mmol), oxalyl chloride (0.74 mL, 8.46 mmol), and DMF (1 drop) were added to a 1-necked flask. The solution was stirred under reflux for 1.5 h and evaporated in vacuo. The residue was analyzed by IR spectroscopy. A carbonyl peak at 1824 cm -1 indicated completion of the reaction. The sulfonamide salt was prepared by adding NaH (0.17 g, 7.05 mmol) and THF (20 mL) to a 3-necked flask under nitrogen. A solution of the appropriate sulfonamide (1.69 mmol) in THF (20 mL) was added dropwise via an addition funnel. The mixture was stirred for 1.5 h at room temperature. A solution of acid chloride 9 in THF (20 mL) was added dropwise and the mixture was stirred overnight (3 h when X = C 6 H 4 -4-NO 2 ). After cooling to 0 o C, water (15 mL) was added dropwise to destroy the excess NaH. The THF was evaporated in vacuo and water (40 mL) was added to the residue. The mixture was extracted with CH 2 C1 2 (100 mL then 50 mL). The combined organic extracts were washed with 10 % aq K 2 CO 3 (2×50 mL). The aqueous washes were back extracted with CH 2 C1 2 (2×50 mL). The organic extracts and back extracts were combined, dried over MgSO 4 , and evaporated in vacuo. The residue was dissolved in CH 2 C1 2 and the sulfonyl salt precipitated. The product was acidified with 3 N HCl to pH 1. The organic layer was separated, washed with distilled water Issue in Honor of Prof. Richard Bartsch ARKIVOC 2010 (vii) 98-117 Extraction procedure An aqueous solution of the alkali metal chlorides with hydroxides for pH adjustment (when X = CF 3 , 0.10 M HCl was utilized for pH adjustment) (2.0 mL, 10.0 mM in each alkali metal ion species) and 2.0 mL of 1.0 mM ligand in chloroform in a capped, polypropylene, 15-mL centrifuge tube was vortexed with a Glas-Col Multi-Pulse Vortexer for 10 min at room temperature. The tube was centrifuged for 10 min for phase separation with a Becton-Dickinson Clay Adams Brand® centrifuge. A 1.5-mL portion of the organic phase was removed and added to 3.0 mL of 0.10 M HCl in a new, 15-mL, polypropylene centrifuge tube. The tube was vortexed for 10 min and centrifuged for 10 min. The alkali metal cation concentrations in the aqueous phase from stripping were determined with a Dionex DX-120 ion chromatograph with a CS12A column. The pH of the aqueous phase from the initial extraction step was determined with a Fisher Accumet AR25 pH meter with a Corning 476157 combination pH electrode.