OO-Diethyl 0-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 pg.) in spray and dust, by reduction with zinc, diazotization and coupling with an amine to give an int ise 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 purifled 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 /S-ethyl ester, but it may also be due to the formation of paroxan itself 0 II 

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