Aromatic sulphonates and the hydrolysis of 2-(p-nitrophenoxy)tetrahydropyran

The rate of hydrolyis of 2-(p-nitrophenoxy)tetrahydropyran was measured in a variety of buffers in water at 30 °C. At low ionic strength (μ = 0.05), 3,6-disulphonaphthoxyacetic acid catalysed the reaction. The second-order rate constant was 20 times faster than predicted from pKa. At high ionic strength (μ = 0.5), plots of kobs vs. total buffer concentration for both 3,6-disulphonaphthoxyacetic acid and 6,8-disulphonaphthyoxyacetic acid go through a maximum. Polyacrylic acid catalysed the reaction. The results are discussed in terms of aggregation and salt effects.