Electrochemical Behavior of 3,3′-Methylenebis-(4-hydroxycoumarine) (dicoumarol) Derivatives in DMF

Summary

Dicoumarol, 3,3′-methylenebis-(4-hydroxycoumarine) (I), is well known as an effective anticoagulant agent. The electrochemical behaviour of (I) and some its derivatives, (3,3′-ethylenebis-(4-hydroxycoumarine) (II),3,3′-propylenebis-(4-hydroxycoumarine) (III), 3,3′-isobutylenebis-(4-hydroxycoumarine) (IV), 3,3′-benzylidenebis-(4-hydroxycoumarine) (V), has been investigated in DMF solutions containing 0.5 F (Et₄N)ClO₄ as supporting electrolyte. At a D.M.E. a two-step reduction takes place with every compound investigated. The first step is relative to the discharge of solvated H+, the second to the hydrogen in the undissociated species HB⁻. The acidic strength of various HB⁻ in DMF has been evaluated from spectrophotometric determinations of the constants (relative to the concentrations) of the equilibrium: HB⁻ + S ⇆ HS⁺ + B²⁻.

The half-wave potential values for the discharge of solvated H⁺ originated by compounds II–V are coincident, or slightly more positive, than the values for the solvated H⁺ ion issuing from HClO₄ or dicoumarol. The values of E _1/2″ for the hydrogen reduction in the HB⁻ anion of compounds II–V are arranged in the same order as the pK values of the second dissociation step.

These results are discussed on the basis of specific variations of the local dielectric constant of the solvent. According to Sanfeld and Hurwitz such deviations may cause the ion pair formation constants or the weak acid dissociation constants, to undergo some variations from their bulk values.