Potentiometric determination of p-chloranil and the kinetic study of its alkaline hydrolysis, using a chloranilate selective electrode.
Two Ion-Selective Electrodes (ISEs), one commercial chloride ISE and one home-made chloranilate (Chl(2-)) ISE, were applied to study the alkaline hydrolysis of p-chloranil. This reaction proceeds through a very fast first step producing monochloranilate (Chl(-)) and chloride ions followed by a slow, rate determining step, producing chloranilate (Chl(2-)) and chloride ion. Kinetic equations specific for this reaction scheme, were derived to calculate reaction rate constants from E-t curves. The potentiometric selectivity coefficient K(pot) = 2.23 x 10(4) was determined for the response of the chloranilate electrode to Chl(-) anion and used for the kinetic calculations. The reaction rate constant for the slow step of the hydrolysis was found to be 0.227 M(-1) . sec(-1) at 25 degrees and the activation energy 1.56 x 10(4) Cal/mol. The total potential change following the completion of the first fast step is proportional to the log C of chloranil. Concentrations of chloranil 5-500 ppm can be determined with a precision of about 2%. This potentiometric method was evaluated for the determination of chloranil in fungicide preparations (Spergon) and the results obtained were compared with those of the official iodometric method. Good agreement was found.
Veltsistas
P G
PG
Laboratory of Analytical Chemistry, University of Ioannina, University Campus, Dourouti, Ioannina 45110, Greece.
Karayannis
M I
MI
Koupparis
M A
MA