Substituted dialkyl-phenyl phosphates and phosphorothioates

The first example of this most important group of phosphorus esters, diethyl-p-nitrophenyl phosphate (paraoxon, 15), was prepared by Schrader (1948a) by the reaction of diethyl phosphorochloridate (16) with sodium p-nitrophenolate  

The strong insecticidal and acaricidal effect of this compound is linked with a high toxicity to warm-blooded animals (ld q for rats is 3 mg/kg), so that it has not been used in agriculture. In ophthalmology it is used as a miotic agent under the name Mintacol . 

The thio analogue of paraoxon, diethyl-p-nitrophenyl phosphorothioate (parathion, 17), is practically more adequate because of its lower toxicity to warmblooded animals and higher stability against hydrolysis. It was prepared by Schrader in 1944, and the elucidation of its biological properties was due to Kiikenthal and Unterstenhofer (Schrader and Kukenthal, 1948 Unterstenhofer, 1948 Schrader, 1952b). 

Its industrial manufacture began in 1947 in the USA, and in 1948 in FRG. Because of its excellent practical properties, it soon became an indispensable tool in modern plant protection. Since then, several new phosphorus ester insecticides have been developed, but parathion has maintained its leading role and is still the first among insecticides of a similar type with respect to world production capacity. 

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