OO-Diethyl O-p -nitrophenyl phosphorothionate parathion

This is a reasonably stable substance (VI) Schrader called it E-605 and prepared it as follows  

Chlorobenzene was the solvent preferred by the Germans for carrying out the reaction in step (b). 

The pure compound is a pale yellow, nearly odourless oil, soluble in organic solvents, but almost insoluble in water. Averell and Norris describe the detection of minute quantities of parathion (20 /ig.) in spray and dust, by reduction with zinc, diazotization and coupling with an amine to give an intense magenta colour. It is effective (at concentrations of 25-600 p.p.m.) against many insect species, but of course, like the majority of organo-phosphorus insecticides, it is toxic to man and to animals. 

Parathion when highly purified has low anti-cholinesterase activity in vitro compared to its activity in vivo. Diggle and Gage considered this to be due to isomerization to the iS-ethjd ester, but it may also be due to the formation of paroxan itself O 

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