The vapour pressure of parathion and related compounds

Abstract

In view of the widespread interest in insecticidal formulations based on parathion, the vapour pressures of the pure material and a number of related compounds likely to be encountered in the commercial product have been measured at various temperatures within the range 25–92° C. The materials examined include : (a) pure parathion, O,O′‐diethyl O‐P‐nitrophenyl thiophosphate, (b) S‐ethyl isomer of (a), O,S‐diethyl 0‐P‐nitrophenyl phosphate, (c) S‐phenyl isomer of (a), O,O′‐diethyl S‐p‐nitrophenyl phosphate, (d) commercial parathion, which contains mainly pure parathion together with small quantities of various related compounds, (e) O,O′,O″‐triethyl thiophosphate, (f) O,O′‐diethyl S‐ethyl phosphate, (g) O‐ethyl O,O′‐bis‐P‐nitrophenyl thiophosphate. Compounds (a) to (d) and (g) were examined by an effusion technique. Compounds (e) and (/) were examined in a liquid U‐tube manometer. Details of the preparation of the materials are given. The vapour pressures have been shown to be low at ordinary temperatures (generally of the order of 10⁻⁴ mm. mercury, or lower, at 20° C).The data provided will be of use in assessing the toxic hazards of exposure to the vapour of parathion and related compounds, and the permanence of insecticidal deposits of the material.