Bazı makro halkalı eterlerin sentezlerinde ve iyonofor özelliklerinin incelenmesi

Abstract

Bu çalışmada bazı makro eter sentezlerinde oldukça önemli olan bir sentez basamağı üzerinde çalışılmıştır. Genel olarak makro halkalı eter sentezlerinde aromatik dihidroksi gurupları bazlı ortamda dihalojenpolietilen glikoller ile eter halkasının oluşması sağlanmaktadır. Bu çalışmada dinitrohalojen benzerleri ile etilenglikol sodyum tuzu etkileştirilerek f eniletilenglikol türevi ha zırlanmıştır. Bu türevleri daha sonra nitro gurubunun monomerlik indirgenmesi ile amine ve daha sonra fenole dönüştürülmüştür. Elde edilen 4-nitro-2-hidroksifenoks» etanol'den çıkılarak 4 ' -Nitro-benzo makro eterler elde edilmiştir.

Since 1970, when the complexes of organic macrocyclic ligands were first reported, this area off coordination chemistry has seen intensive growth. Stimulations* procee ded from interest in metalloenzymes, homogeneous catalysis, electrical conductance, and magnetic-exchange processes. As a result, most of the research was focussed on transi tion-metal coordination. Multisite ligands which make possible a close neighborhood of more than one alkali »or alkaline earth metal ion are still rather rare. Although new practical applications are imaginable, mixed systems for the. comman complexation of alkali and transition-metal ions also known. The complexation of the alkaline earth metals is reminiscent of the behaviourof several of the naturally occurring antibiotics and, like the latter, the crown often exhibits remarkable selectivity for particular ions. The thermodynamic factors underlying the selectivity of many of the crowns have been studied in some depth and the results related to such parameters as cavity size, number of donar atoms present, possible ring conformations on complex formation and the solvation" energies of the various species involved. For small ring crowns, enhanced binding tends to occur yhen the ionic radius of the cation maches the cavity size of the crown in a flat conformation. For example, 18-crown- 6 has an estimated radius of approximately 1.38 A and, with the alkali metals, forms its strongest complex with KT" whose ionic radius has also been estimated tobel.38A" The X-ray structure of the KNCS complex of 18-crown-6 confirms that the K+occupies the macrocyclic cavity in an unstrained manner with the ether oxygens arranged regularly around this cation in a near planar fashion. With Na4", the X-ray structure of the NaNCS complex of 18-crown-6 appears to reflect the reason for the drop in stability relative to the K species. In this complex, the coordinated 18-crown 6 is bent such that one donor oxygen lies well out of the approximate plane formed by the other five. This non-pla- narity of the donor set appears to be a consequence of the less than ideal fit of the metal for the macrocyclic cavity of 18-crown-6 in a planar conformation. Nevertheless, the origins of the stability pattern illustrated in Figure 4.5 may not be quite as straightforward as suggested by simple hole-size considerations since there is evidence that sol vation effects also markedly influence the relative stabi lities of the crown complexes of these ions. Indeed, it has been demonstrated that the observed stability constant sequence shown in Figure 4.5 for 18-crown-6 (or the corres ponding sequences for its benzo or dibenzo derivatives)may vary in other solvents. The macrocycle types discussed so far tend to from very stable complexes with transition metal ions and, as mentioned previously, have properties which often resemble those of the naturally occurring porphyrins and corrins. The complexation behavior of these macrocycles contrasts in a number of ways with that of the second mojor category of cyclic ligands-the crown, polyethers. In 1967, a seminal paper describing the synthesis of thirty-theree cyclic polyethers was published |1|. All are simple monocyclic rings-a general macrocyclic category sometimes termed the coronands. In Pedersen1 s study, the first ligand was prepared because of the appearance of its molecular model and its ability, on coordination, to crown'a metal ion, this and other members of the series were referred to as crown compounds. The trivial names consist of, in order: (1) the number and kind of attached hydrocarbon rings, (2) the number of atoms in the polyether ring, (3) the class name, crown, and (A) the number of oxygens in the polyether ring. Following the original paper, reports of the syn thesis of new crowns and crown-like molecules prolifera ted. A typical property of these systems is their ability to from stable complexes with the alkali metal and alkaline earth ions. Prior to synthesis of the crowns, the coordi nation chemistry of the above ions with organic ligands had received very title attention. A further impetus to the study of such com]pexes was the recoanition of the important role of Na+, K4", M|^ an(i Ca2 ions in biolo gical systems. Apart from metal ions, many of these polyether com pounds also exhibit complexing ability (and often speci ficity), to arrange the other inorganic and organic cations as well as for a variety of neutral molecules. Complexes such as these, which contain species incorporated in the macrocyclic cavity, are usually known as 'inclusion comp lexes'; the general area covering the binding of all types of substrates in molecular cavities often being VI referred to as 'host-guest' chemistry. General Consideration In Crown Ether Synthesis Condensation reactions, often at medium to high dilution, have usually been used to obtain new crown polyethers |2|. For the majority of such crowns, two carbon atoms link consecutive ether oxygens in the res pective rings. This structure feature, in part, a ref lection of the ready availability of suitable precursors (such as catechol or ethylene oxide and their derivatives) for synthesizing rings of this type. Further, the cyclic products obtained from such precursors tend to from more stable metal complexes (containing five-membered chelate rings) than species inconporating longer or shorter bridges the oxygens. Representative Cycliz^tions- Typically, a given cyclization involves nucleophilic displacement of a halide or tosylate by alkoxide or phenoxide ion (that is, a Williamson systhesis) even though such reactions are frequently quite slow. Products may be converted into the corresponding cyclohexane deri vatives by hydrogenation, typically in butanol, over a ruthenium catalyst. A range of crowns incorporating furan or tetrahyd- rofuran heterocyclic rings have been synthesized. The general preparation of rings of this type has involved condensation of 2,5-bis ( hydroxymethyl) furan with a poly- ether ditosylate in tetrahydrofuran as solvent |3,A|. Effects Of Chain Length On Cyclization The effect of chain length on cyclization of a series of acyclic precursors of benzo-crowns has been studied. In accordance with kinetic data, calculations of the Monte Carlo type indicate that the probability of the cycilzation rate fron the small to medium rings. Template Contributions Alkali metal ions have been documented to play a tem- late role in a number of crown synthesis. Thus, for example the presence of K* been shown to promote the formation of 18-crown-6 in systheses |5|. The ideal template metal in such procedures appears, once again, to be one that best fits the cavity of the cyclic product. The small Li* has been used to aid formation of 12-crown-4 while larger Na+ Vll was used for 15-crown-5. Kinetic aspects of the use of alkali metals as temp lates for the formation of other crowns have been studied in some depth. The results of such investigations parallel the previous observations-namely, that the catalytic effi ciency of such ions in promoting cyclization shows a strong tendency to parallel their strength of binding with the crown products (this in turn often correlates with the fit of the metal ion for the macrocyclic cavity in the product). Metal-Ion Binding Properties Pedersen' s paper marked the beginning of a aew and major development in the study of the metal-ion chemistry of macrocyclic ligands. The crown exhibit a number of unusal properties such as,the ability to form complexes with alkali metal ions which, on certain cases, are stable in aqueous solution. Indeed, they also yield stable comp lexes öf a range of non-transition metal ions but tend to bind less strongly to transition metal ions. Pedersen showed that rings incorporating between five and ten oxygen atoms tended to form the most stable complexes and complexes with some or all of the following metal ions were isolated: Li+, Na+ K* Rb+, Csf Ag*, Auf Ca**, Sı**, Ba**, Cd**, Hg*" La*+, Tl+, Cİ and Pba+, In such compounds the ether-oxygen interactions with the metal cation were considered to be essentially electrostatic. Since this original work many hew crowns have been synthesized and their complex formaiton has been very exten sively studied. Complexes with many other ions (including weak complexes with several transition ions) have been characterized. Crystalline 1:1 (metal: ligand). 1:2, and 2:3 complexes as well as species of other stoichiometry have all been isolated. At tough the fact that several methods have been repor ted the synthesis of such compounds had to be improued due to expensive view of the preparations. We therefore tend to work on the better and low cost preparations, of the similar molecules. This work covers the facile and impro ved synthesis of large aligomer starting from cheap polyet hylene glycols. In the presented -work, the synthsis of the macrocyclic ethers has been improved regarding the ex-tention of ethyleneoxy group on the cyclic ether moiety. 17 general the crown ethers have been prepared starting from the dihydroxyphenols vixi by reacting dihalogenated polyethylene glycols in the presence of a strong base. Accordingly, dinitrohalogen- benzenes were reacted with sodio salt of ethylenegiycol in dioxane / PEGDIETHYLETHER to give the B-(2,4-dinitro- phenoxy) ethanol. The product was sten reduced to mono- amino derivative which was then converted to mononitrohyd- roxyphenyl derivative. The end product was reacted with dihalogenpolyethyleglycoles to obtain the 4 '-nitrobenzo crown ethers.