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New Crown Ether Compounds and Their Alkali Metal Ion Complexation

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New Crown Ether Compounds and Their Alkali Metal Ion Complexation NEW CROWN ETHER COMPOUNDS AND THEIR ALKALI METAL ION COMPLEXATION by LOKMAN TORUN, B.S., M.S. A THESIS IN CHEMISTRY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved May, 1994 fie Copyright 1994, Lokman Torun ACKNOWLEDGMENT I would like to acknowledge Dr. Richard A. Bartsch for his guidance, help and understanding. I would also like to thank all faculty members of the Chemistry Department, whose guidance made this work possible. I would like to recognize the friendly co-workers of the Bartsch's group. I would like to thank University of Yuzuncu Yil for much of the financial support. 11 TABLE OF CONTENTS ACKNOWLEDGEMENTS ii LIST OF TABLES vi LIST OF FIGURES vii LIST OF SCHEMES ix CHAPTER I. INTRODUCTION 1 Discovery of Crown Ethers 1 Proton-Ionizable Crown Ethers 8 Crown Ethers with Naphthalene Subunits 15 Statement of Research Goals 19 II. SYNTHESIS AND COMPLEXATION STUDIES OF NOVEL BENZOIC ACID CROWN ETHERS 20 Synthesis of Benzoic Acid Crown Ethers 62 and 63 20 ^H-NMR Spectroscopic Results 25 Experimental Procedures 37 Instrumentation and Reagents 37 o-Methylbenzoyl Chloride (66) 38 t-Butyl o-Methylbenzoate (67) 38 t-Butyl 2-(Bromomethyl)benzoate (NBS method) (68) 39 iii t-Butyl 2-(Bromomethyl)benzoate (Brom 55P method) (68) 39 Benzyl-protected Solketal (70) 40 3-(Benzyloxy)-1,2-propanediol (71) 40 2-(Benzyloxymethyl)-12-crown-4 (76) 41 Tetraethyleneglycol Ditosylate (72) 42 2-(Benzyloxymethyl)-15-crown-5 (73) 42 Hydroxymethyl-15-crown-5 (74) 43 Hydroxymethyl-12-crown-4 (77) 44 t-Butyl 2-[ (0xymethyl-15-crown-5)methyl] benzoate (79) 44 t-Butyl 2-[(0xymethyl-12-crown-4)methyl] benzoate (78) 45 2-[(Oxymethyl-12-crown-4)methyl]benzoic acid (62) 46 2-[(0xymethyl-15-crown-5)methyl]benzoic acid (63) 47 General Procedure for Preparation of Sodium, Potassium, Rubidium and Cesium Crown Ether Carboxylates 47 Preparation of Lithium Crown Ether Carboxylates 48 III. SYNTHESIS AND STRUCTURE OF DI (1,8-NAPHTHYL) CROWN ETHERS 4 9 Results and Discussion 50 Synthesis of Bis-1,3-(8-hydroxy-l-naphthoxy) propane (104) 50 Synthesis of sym-Di(1,8-naphtho)-16-crown-4 (99) and sym-Methylene-di(1,8-naphthyl)-16- crown-4 (100) and the Solid State Structure of Crown Ether 100 52 IV Attempted Synthesis of sym-(Hydroxy)di (1,8-naphtho)-16-crown-4 (113), sym-(Keto) di (1,8-naphtho)-16-crown-4 (115) and sym- (Dimethylene)di(1,8-naphtho)-16-crown-4 (116) 58 Summary 62 Experimental Procedures 64 1,8-Dihydroxynaphthalene (102) 64 Monobenzyl-protected 1,8-Dihydroxynaphthalene (106) 64 Bis-1,3-(8-Hydroxy-l-naphthoxy)propane (104) 65 Dimesylate of 1,3-Propanediol (108) 66 sym-(Methylene)dinaphtho-16-crown-4 (100) 66 Di(1,8-naphtho)-16-Crown-4 (99) 67 REFERENCES 69 LIST OF TABLES 1. Metal cation and crown ether cavity diameters 7 2. Chemical shifts (5), changes in chemical shift (A5), and the chemical shift differences (AD) for the benzylic protons of crown ether carboxylic acids 62-64 and their alkali metal salts 29 VI LIST OF FIGURES 1. Illustration of the template effect 4 2. Illustration of typical cation/ligand arrangements in crystalline crown ether complexes 8 3. Illustration of metal ion complexation by a proton-ionizable crown ether 10 4 Some examples of proton-ionizable crown ethers 12 5. Some examples of naphtho- and dinaphtho-crown ethers. 16 6. Equilibration of enantiomeric conformations of l,5-naphtho-22-crown-6 (55) 18 7. Proton-ionizable crown ethers that may exhibit an AB pattern when they complex with alkaline metal cations 20 8. Preparation of alkali metal salts for ^H-NMR study 27 9. The change in chemical shift of the benzylic hydrogens in going from the lariat ether carboxylic acid to the corresponding alkali metal lariat ether carboxylate as a function of radius of the alkali metal cation 30 10. Crown ether analogous of 62-64 33 11. An illustration of the complexes 34 12. Crystal structure of simi-methylanedinaphtho-16- crown-4 (100) 57 Vll LIST OF SCHEMES 1. Synthesis of dibenzo-18-crown-6 (8) by Pedersen 2 2. Five general methods for the synthesis of crown ethers 5 3. Synthesis of bromo t-butyl ester 68 22 4. Synthesis of hydroxymethyl crown ethers 74 and 77 23 5. Synthesis of crown ether carboxylic acids 62 and 63 2 6 6. Synthesis of intermediate 104 51 7. Synthesis of dinaphtho-16-crown-4 99 53 8. Synthesis of 1,8-naphtho-8-crown-2 (109) 54 9. Synthesis of sym-methylenedinaphtho-16-crown-4 (100) 55 10. Attempted synthesis of methylenedinaphtho-16- crown-4 100 by use of a LiH-THF base-solvent system 55 11. Attempted synthesis of sym-(Hydroxy)di(1,8- naphtho)-16-crown-4 (113) 59 12. Attempted synthesis of ketodinaphtho-16-crown-4 (115) 61 13 Synthesis of methylene-1,8-naphtho-8-crown-2 (111)63 Vlll CHAPTER I INTRODUCTION Discovery of Crown Ethers Although the first crown ether 1 was reported in 1937, the fascinating aspects of cyclic polyethers were not appreciated until after the accidental rediscovery of crown ethers by Pedersen in 1967-1'2 The first "accidental" crown ether was dibenzo-18-crown-6 (2). Pedersen was attempting to synthesize an acyclic phenolic ligand to study the catalytic properties of the vanadyl ion VO+2. The desired product of the reaction was bis-[2-(o-hydroxyphenoxy] ethyl ether (8) (Scheme 1) . However, he did not purify the product obtained from the first step, which is protection of catechol (3) with dihydropyran (4). Therefore about 10% of the catechol was left unprotected. The second step involved the reaction of this unpurified mixture with OH + H+, EtjO OH O 4 1-butanoI H+ CH, OH + O R ^ "O O o o o o Scheme 1: Synthesis of dibenzo-18-crown-6 (2) by Pedersen^'^ bis-(2-chloroethyl) ether (6) under basic conditions in 1- butanol to give 7. Hydrolysis under acidic conditions gave desired compound 8. In addition to 8, Pedersen isolated a 3 white solid from an "unattractive goo." The isolated white crystalline compound was identified as the cyclic polyether 2. Pedersen named such cyclic polyether compounds "crown ethers" due to their crown-like shape. Pedersen prepared more than 60 crown ethers which show interesting physical properties.^'^ Pedersen developed five general synthetic methods which were based on catechol or substituted catechols as reactants.2 The usual solvent for these reactions was 1- butanol. The methods are shown in Scheme 2 where R, S, T, U, V, and W represent bifunctional organic groups. Method II is the most versatile route for the preparation of compounds containing two or more benzo groups. It also gives the highest yields.^ A notable feature is that surprisingly good yields of the cyclic polyethers may be obtained without using high dilution techniques (0.1 mole in 300-500 ml of solvent) .'^'5'^ The reason high dilution is not needed is due to a "template effect" (Figure 1).'^'8 This shows a favoring of the intramolecular reaction by such a template effect, complexation of acyclic polyether with cations to bring the two chain ends into close proximity- This is a favored and very useful method for improving product yields in crown ether synthesis. 5'^'^'^"^ The template effect has been studied by Mesci and co-workers.18,19 They Method I 2NaOH OH Cl-R-Cl O R OH O Method II ,OH HO. 2NaOH O^T--o. Cl-T-CI O o^s^o O-^S-0' Method m OH 4NaOH ,o^u-o. 2 Cl-U-CI Q Q OH ^o—u-o" Method IV ,OH ,o^v^o. 2NaOH Q Q O-^^^Cl ^o-^v^o" Method V H2 (l(X)0-1500psi) ,CKW--O. ruthenium dioxide Q • dioxane ^o-^w-o" Scheme 2: Five general methods for the synthesis of crown ethers used the Okahara procedure^^'^i^ 22 ^o study cyciization yields of differentpolyethylene glycols in the presence of sodium, potassium and cesium cations. They found that the highest yielding reactions were for the formation of the 15-crown-5, 18-crown-6 and 21-crown-7 with sodium, potassium and cesium cations, respectively. This is expected from the principle of size complementary.8'23 Thus the cavity sizes of 15-crown-5, 18-crown-6 and 21-crown-7 best match the diameters of sodium, potassium and cesium cations, respectively. In a few cases cesium gives very good yields of cyciization products.^3 <r\ OTs TsO- Q I TsO TsO o. ^.a^^ .o. I KOH OH OH I c ^cr I ^O' V^° o o. Figure 1: Illustration of the template effect Pedersen found that a crown ether is capable of providing cation stabilization or solvation within its cavity, which is defined by the cyclic array of oxygen atoms. In the complex between a cation and an organic complexing agent, the cation is held by ion-dipole interaction between the cation and electron-rich oxygen atoms. Crown ether molecules complex not only with metal 6 cations but also organic species, such as diazonium ions^^ and primary and secondary alkyl ammonium salts.25,26 Although many crown ethers are sparingly soluble in methanol, they become quite soluble in the presence of appropriate metal salts. While trying to explain the unusual solubility characteristics of this new class of compounds, Pedersen proposed several factors which influence the stability of a crown ether-metal salt complex: (i) the relative size of the cation and the cavity of the crown ether ring; (ii) the number of oxygens in the crown ether ring; (iii) coplanarity of the oxygens; (iv) symmetrical placement of the oxygens; (v) basicity of the oxygen atoms; (vi) steric hindrance in the crown ether ring, which may hinder formation of the complex; (vii) the tendency of the ion to associate with the solvent; and (viii) the electrical charge on the ion.2 The strength of complexation between the crown ether "host" and the cationic "guest" depends on the cavity size of the polyether ring and the relative size of the cation (Table 1).27,28,29,30 Best complexation occurs when the size of the cation matches well with the size of the crown ether cavity.
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