AbstractThe hydrolysis of 14C fenpropathrin (I) (RS)‐α‐cyano‐3‐phenoxybenzyl 2,2,3,3‐tetramethylcyclopropanecarboxylate was studied in buffer solutions at pH 1.9–10.4, and in natural river and sea water at 25, 40, 55 and 65°C under laboratory conditions. The hydrolysis ofIproceeded predominantly through neutral (pH independent) and base‐catalysed processes in the regions below pH 3.9 and above pH 7.0, respectively, whereas both reactions occurred between pH 3.9 and 7.0. The rates of hydrolysis ofIin buffer solutions were similar to those in one sample of river and one sample of sea water. If this obtains generally, it may be expected that the half‐life ofIin natural waters, normally within the range pH 5–9, will range from 1.54 to 1080 days at 40°C, 11.3 to 8520 days at 25°C and, by extrapolation of the data obtained in buffer solutions, 106 to 83 000 days at 10°C. The rate constants for hydrolysis ofIin aqueous media can be expressed by:documentclass{article}pagestyle{empty}begin{document}$$ k_H = k_N+ k_B {rm OH}^{rm - } $$end{document}Where logkN= 9.60–(5.56 × 103T−1) and logkB= 7.32–(2.56 × 103T−1). The calculated rate constants were in good accord with the observed values in buffer solutions. Cleavage of the ester linkage was more rapid than hydration of the cyano group
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