Kinetic determination of selectivity constants of anion extraction in phase-transfer catalytic systems

A kinetic method has been developed to measure selectivity constants of pairs of anions in phase-transfer catalytic systems. The method is based on the study of the poisoning effect produced by the presence of catalytic amounts of different salts in the kinetic behaviour of the phase-transfer-catalysed isomerization of 4-allylanisole to 4-methoxy-β-methylstyrene in basic medium. The kinetic profiles experimentally obtained for this reaction are numerically analysed and K^sel values for different anions are subsequently derived. Particular attention is given to alkoxide anions, formed in situ by contact of alcohols with concentrated NaOH. A selectivity constant parameter that includes the acidity of the alcohols is defined.