Chemical kinetics at a critical point

The rate of the Diels‐Alder reaction of isoprene with maleic anhydride has been measured in the vicinity of the upper critical solution points of two liquid‐liquid mixtures, and the rate of the Menschutkin reaction of ethyl iodide and triethylamine has been investigated near a lower critical solution point. Anomalous behavior has been observed, with the former reaction rate augmented by up to 40% and the latter apparently running 25–30% too slow. A possible explanation for these results is presented in terms of transition state theory and the abrupt behavior of the solution activities of dilute solutes near a critical point.