Various derivatives of diaza-crown ethers and the polymers containing cryptands were synthesized and their ion-binding properties were investigated by solvent extraction, transport through liquid membrane and conductance measurements.
N,N'-Bis(aminoalkyl) derivatives of three different diaza-crown ethers, diaza18-crown-6(DA-18-C-6), DA-15-C-5, and DA-12-C-4, were synthesized via Gabriel synthesis and other substituted diaza-crown ethers including propyl, hydroxyalkyl, and phthalimidoalkyl derivatives were prepared by alkylation with the corresponding bromo compounds. Four different polymers, i.e., polyamide, polyurea, polyimide, and polysulfone, which contain cryptand moiety on their backbones were prepared from the diaza-crown ethers and their aminoalkyl derivatives. Polymers were obtained in 80-100% yield and showed inherent viscosity values in the range of 0.2-0.4 dl/g.
In the solvent extractions of picrate salts from aqueous phase into $CH_2Cl_2$ or $CHCl_3$ by cryptands showed that N-alkylated derivatives exhibited enhanced extraction properties compared with their corresponding parent diaza-crown ethers, and phthalimidoalkyl derivatives showed distinct size-selectivity. The most interesting to note was the extremely high but non-selective extraction efficiency of the aminoalkyl derivatives.
The polymers prepared by the reaction of DA-18-C-6 and hexamethylene diisocyanate exhibited notably decreased extraction efficiency, and no selectivity towards metal ions was observed. However with the polymers prepared from N-alkylated cryptand moiety the extraction property of the cryptand was retained, even though selectivity was somewhat reduced.
Liquid membrane study with water/chloroform/water system indicated that the ion-transport efficiency exhibited by derivatives of cryptands were found to be in accordance with their extraction behavior. However, aminoalkyl derivatives were particular in that very inefficient carrier activity was observed in spite of their high carrier saturation values. Among the substituted cryptands, alkyl derivative was the most effective carrier and the relative efficiency of derivatives as ion carriers were in the order of alkyl＞phthalimidoalkyl＞hydroxyalkyl＞aminoalkyl derivatives.
All the polymeric cryptands investigated carried various metal ions at somewhat lower transport rates compared with low molecular weight analogs, but carrier behaviors were similar in trend to those of the corresponding low molecular weight derivatives. Among the polymers studied the polyimide prepared from N,N'-bis (aminopropyl) derivatives of DA-18-C-6 and DA-15-C-5 and pyromellitic dianhydride was the most effective carrier with good selectivity, implying certain applications as a new, efficient ion-chelating material.
Changes in solution conductance of alkali metal tetraphenylborates by complex formation with cryptands were also investigated in acetone. Complex formation constants estimated from the conductance measurements confirmed the results which were obtained from extraction and transport studies. The log $K_f$ values of aminoalkyl derivatives of DA-18-C-6 for potassium ion was estimated to be much larger than 5, being most selective toward potassium ion. This is in contrast with the results of solvent extraction and transport studied. The decrease in equivalent conductance values were much larger with polymeric cryptands, and was about 40 $ohm^{-1}㎠mol^{-1}$. The equivalent conductance did not become constant even after the 1:1 stoichiometry of crown-to-cation ratio was reached. However the break in the conductance curve was observed in the range of 2 and 3 of crown-to-cation ratio, though it was not clearly defined. The large cesium ion was not complexed by polymers which contain 15-C-5 moiety. This observation confirms the enunciation that cryptands situated on the polymer backbones do not take the conformation such that 2:1 sandwich-type complex can be formed with large size metal cations.
Diaza-crown ether (DCE)의 여러 유도체와 cryptand를 포함하는 중합체를 합성하고 이들의 ion-binding 특성을 용매추출, 액체막을 통한 수송 및 전기전도도 측정에 의해 연구하였다.
DCE의 N-amino 알킬유도체는 Gabriel 합성법에 의하여 합성하였으며 propyl, 히드록시알킬 및 phthalimido알킬유도체들은 대응하는 브로모화합물에 의한 알킬화에 의해 얻었다. 주쇄에 cryptand를 포함하는 4종의 중합체 즉, 폴리아미드, 폴리우레아, 폴리이미드, 폴리술폰을 DCE 또는 이의 N-amino알킬유도체로 부터 합성하였으며, 이때 중합수득율은 80~ 100%가 점도는 0.2-0.4 dl/g이 얻어졌다.
피크린산금속염의 dichloromethane 또는 chloroform 용액으로의 용매추출실험에서는 DCE의 N-알킬화된 유도체 모두의 추출성이 DCE에 비해 증가하였으며 특히 phthalimido알킬유도체가 명확한 이온 선택성을 보여 주었다. N-amino알킬유도체들의 경우에는 매우 크지만 비선택적인 추출성을 보였다. DCE와 diisocyanate의 반응에서 얻어진 중합체는 추출성이 크게 감소하였으며 이때 여러 금속이온들에 대한 선택성도 또한 불분명해졌다. 이에 반하여 cryptand 부분이 손상되지 않은 N - 알킬화된 cryptand를 포함하는 중합체에 있어서는 다소 선택성은 감소하였으나 cryptand 부분의 추출특성이 유지되는 것을 볼 수 있었다.
Chloroform 액체막을 통한 피크린산 금속염수송의 일반적인 특성은 추출실험결과와 유사하였으나, amino 알킬유도체는 매우 큰 추출 효율에도 불구하고 낮은 수송효율을 나타내었다. 이는 amino알킬유도체가 매우 안정한 착물을 형성하기 때문이라고 생각할 수 있다. 여러 치환된 DCE중 알킬유도체가 가장 효과적인 carrier로 작용하였으며 상대적인 효율성은 알킬＞phthalimido 알킬＞히드록시알킬＞amino 알킬유도체 순이었다. 사용된 cryptand를 포함하는 중합체 모두는 저분자 유도체에 비해 다소 낮은 수송속도를 나타내었으나 수송거동은 유사하였으며 그중 polyimide가 가장 좋은 선택성을 가져 새로운 킬레이트 수지로의 이용 가능성을 시사해 주고 있다.
여러 cryptand에 의한 알칼리금속 tetraphenylborate의 전기전도도 변화를 acetone용액중에서 측정하였다. 전기전도도 측정으로부터 구한 착물형성 상수 값은 앞 두 실험에서 얻어진 결과와 일치된 경향을 보이나 diaza-18-crown-6의 amino알킬유도체는 $K^{+}$ 이온에 대하여 착물형성상수 ($logK_f$) 값이 5보다 큰 것으로 나타났으며 $Na^{+}$, $Cs^{+}$ 이온에 대하여 선택성을 나타내어 용매추출 및 액체막 실험결과와 대조되었다.
중합체에 있어 당량전도도의 감소는 매우 커서 $40 ohm^{-1}㎠mol^{-1}$ 가까이 되는 경우도 있었으며 1:1 이론적 종말점을 지난후에도 전도도는 계속 감소하여, 분기점은 명확하지는 않았으나 2 - 3 당량의 cryptand가 가해진 후에야 얻어졌다. 이온크기가 큰 $Cs^{+}$ 이온의 경우 15-crown-5 부분을 포함하는 중합체에 의해 착물이 이루어지지 않았으며 이로써 주쇄에 존재하는 cryptand는 2:1 sandwich형의 착물을 형성하지 못함을 확인할 수 있었다.
