2,3及び4位にアルキル置換基を持つN-アルキルピリジニウムイオンのイオン会合抽出性と抽出性に及ぼす置換基の寄与

2,3,4位にアルキル基を持つN-アルキルピリジニウム塩(アルキル基:CH(3)-,C(2)H(5)-,C(3)H(7)-)26種を合成し,イオン会合抽出性について検討した.水-クロロホルム抽出系で,対イオンとしてエチルオレンジのジクロロ誘導体(Cl(2)-EO(-))を用いて抽出定数(logK(ex))を求めた.アルキル基の炭素数が増すと抽出性も増し,抽出定数への寄与分は2,3,4位の置換基では平均0.59,N-置換基では平均0.54であった.アルキル基が同じ場合には,抽出定数は4位>3位>2位置換体の順に小さくなる.2位置換体は隣接のN-置換基との重なり効果の結果,3,4位置換体よりも小さくなる.基本骨格(C(5)H(5)N(+)-)の抽出性の尺度(C:>N(+)<を基準C=0とする)は約2.2となり,メチレン基の数から単純計算した値(0.59×5=2.95)よりも0.75小さい.これはベンゼン環(-C(6)H(5))の単純計算値と実測値との差(0.64)とほぼ一致しており,閉環効果による抽出性(疎水性)の減少分と見なされる.

Twenty-six derivatives of alkyl-N-alkylpyridinium ions, where the alkyl groups were the methyl, ethyl and propyl groups, were synthesized. These pyridinium ions (C(+)) could be extracted into chloroform as their ion associates with Cl(2)-EO(-)(dichloro derivatives of Ethyl Orange, A(-) ), and thus each extraction constant K(ex)(=[C(+)・A-)] (o)/[C(+)][A(-)]) was obtained in this work. The longer the alkyl chains, the larger the values of log K(ex) were. The contribution of a methylene group to log K(ex) was on average 0.59 for alkyl groups substituted at a pyridine ring, and 0.54 for N-alkyl groups. The position effect (P(p)) was 0.11 and 0.28 for 3-substituted and 4-substituted derivatives, respectively. The overlapping effect (P(o)) occurred between an N-alkyl group and a 2-substituted group, and was estimated to be -0.20. P(o) must be considered for pairs of ethyl groups, and ethyl and propyl groups. The extractability parameter of the skelton (C(5)H(5)N(+)-) was determined to be an average 2.2, which is 0.75 smaller than the value of 2.95 (=0.59×5) calculated by using the contribution value of the methylene group, 0.59. This difference is almost the same as that in the benzene ring, 0.64, and is considered to be the effect of ring closure.