A series of substituted diethyl arylphosphonates was synthesized by the microwave‐assisted Arbuzov reaction of triethyl phosphite and aryl bromides in the presence of NiCl2 as the catalyst under solvent‐free conditions in good yields. The resulting phosphonates were hydrolyzed to the corresponding arylphosphonic acids whose acidity was evaluated by physicochemical methods.
Determination of the proton dissociation constants of several arylphosphonic acid derivatives was carried out to investigate the accuracy of the Hammett equations available for this family of compounds. For the measurement of the pK values modern, accurate methods, such as the differential potentiometric titration and NMR-pH titration were used. We found our results significantly different from the pK values reported before (pK: MAE = 0.16 pK: MAE=0.59). Based on our recently measured pK values, refined Hammett equations were determined that might be used for predicting highly accurate ionization constants of newly synthesized compounds (pK=1.70-0.894σ, pK=6.92-0.934σ).
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