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The solubility of potassium fluoride (KF) in dimethylformamide (DMF) and the dielectric constant of the solvent have been determined in the temperature range (25-125) °C by means of electrical conductivity and capacity measurements. The solubility of KF in this aprotic solvent seems to be almost temperature independent (mean value (0.33 ( 0.03) × 10 -3 mol‚dm -3 ). The speciation of KF in DMF is also discussed in relation to the concentration dependence of the molar conductance. It is concluded that ion pairs could account for around 50 to 70% of the species and that triple ions could be present in the concentration range studied.

The halogen exchange reaction of 2,4-dichloronitrobenzene with potassium fluoride in dimethylformamide containing tetrabutylammonium salts has been studied employing an electrochemical detection methodology based upon the use of square wave voltammetry to follow the loss of reactant and the formation of the product and intermediates. The results obtained show that the kinetics of loss of parent material behave on one hand as a dissolution-rate-controlled process and on the other as a homogeneous chemical process. Initially homogeneous reaction dominates the observed kinetics as the presaturated solution is stripped of fluoride ion; at longer time, the observed kinetics are controlled by the rate of KF dissolution. Modeling the system using a fully implicit finite difference method with Richtmyer modification (FIRM algorithm) yielded a mean value for the homogeneous rate constant for the formation of 2,4-dinitrofluorobenzene by reaction of 2,4-dichloronitrobenzene with fluoride ion in DMF at 85 °C of 640 ± 250 mol-1 cm3 s-1 and a mean value for the saturation concentration of fluoride ion of (6.5 ± 0.5) × 10-6 mol cm-3. Ultrasound was found not to significantly enhance the rate of the reaction in the intensity range studied. Furthermore, the utility of microelectrodes for obtaining simple quantifiable voltammetric responses from compounds of which the macroelectrode responses are complicated by chemical followup steps is demonstrated. Ultrasonically induced mixing has been shown to facilitate reproducible microelectrode responses in intrinsically heterogeneous systems.

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