Accumulation of Hydrogen-Bonding and Electrostatic Binding Sites: Stabilization of Salts in Hydroxylic Media via Intramolecular Hydrogen Bonding

Article abstract of DOI:10.1021/jo00026a009

Pyridyl-bisresorcinol derivative 1a and dodecyl phosphate (5) form a pyridinium-phosphate salt which is stabilized via hydrogen-bonding interaction between the bisresorcinol moiety and bound phosphate anion.The salt-formation constants (K) are relatively insensitive to solvent polarities; K_1a(5) = 1.2*10³ (water-methanol (2:1)), 1.2*10³ (methanol), 1.1*10³ (ethanol), and 6.9*10² M^-1 (2-propanol).On the other hand, the salt formation with 2-picoline (3) as a less crowded reference host takes place with much difficulty and is highly solvent dependent; K₃(5) = 2.1*10² (water-methanol (2:1)), 3.2*10 (methanol), 1.6*10 (ethanol), and 9.2 (2-propanol).The selectivities K_1a(5)/K₃(5) thus increase with respect to change in solvents in the order, water-methanol (2:1) (6) < methanol (37) < ethanol (72) < 2-propanol (75).The role of a pair of hydroxyl groups in the bisresorcinol moiety is discussed in terms of intramolecular microsolvation.