Electrochemical behaviors of protonated diamines at the micro-water/1,2-dichloroethane interface

• The IT and FIT of a series of protonated diamines (DA+ and DA2+) were studied.
• DA2+ is dominated at low pH whereas at high pH it is mostly due to the DA+ transfer.
• Some basic thermodynamic parameters for both processes have been calculated.
• The mechanism for facilitated ion transfer (FIT) has also been evaluated.

The simple ion transfer (IT) and facilitated ion transfer (FIT) of a series of protonated diamines ([H3N(CH2)nNH3]2+ (DA2+) or [H2N(CH2)nNH3]+ (DA+), n = 2, 3, 4, 6, 8) at the micro-water/1,2-dichloroethane (μ-W/DCE) interface supported at the tip of a micropipette are reported. The effect of pH on both transfer processes has been studied in detail. For the IT process at low pH, DA2+ is dominated whereas at high pH it is mostly due to the DA+ transfer. The experimental results also demonstrate that dibenzo-18-crown-6 (DB18C6, L) can facilitate the transfer of protonated diamines at such interface. The complexation between ion and ligand is 1:1 at all experimental pH when CDAz+≫CLCDAz+≫CL (where z   can be 0, 1 or 2 depending on the pH of solutions). For CDAz+≪CL,CDAz+≪CL, the ion to ligand stoichiometry is 1:1 when pH is high, and is 1:2 when pH is low. The association constants for both cases are also calculated. Among these five diamines, the association constant for protonated 1,3-propanediamine has the biggest values.