Ion-pair extraction of metalloporphyrins into a mixture of acetonitrile with water

Extraction mechanism and solvent structure were studied for the solvent ext raction of cationic porphyrin (5,10,15,20-tetrakis(1-methyl-pyridinium-4-yl ) porphyrin; H-2(tmpyp)(4+)) and its metalloporphyrins (MP(n+2+)) into an a cetonitrile phase separated from a 1:1 (v/v) mixture of acetonitrile with w ater by addition of sodium chloride. Mn+ denotes Cu2+, Co3+, Fe3+, Li+, Mn3 +, and Zn2+ and H2P4+ is the free base form of H(2)tmpyp(4+). The separated acetonitrile phase contains a lot of water (more than 4 mol dm(-3)) and so dium chloride (1 x 10(-2) mol dm(-3)) that are necessary to extract the hig hly charged chemical species of the above porphyrin or metalloporphyrins wh ich can not be extracted into normal organic solvents such as chloroform. T he extracted chemical species dissociate in the acetonitrile phase and exis t in ionized forms. X-ray diffraction analysis indicates the formation of clusters of acetonitr ile in the mixed-aqueous organic solvent. An acetonitrile molecule interact s with 2 neighbors at 3.45 Angstrom in antiparallel and 4.10 Angstrom in pa rallel through dipole-dipole interaction. Water molecules that form hydroge n bonding between water molecules surround the acetonitrile clusters. The p orphyrin or metalloporphyrins are preferentially solvated by acetonitrile m olecules and are surrounded by acetonitrile clusters.