Parathion 
0,0-Dimethyl O-p-nitrophenyl phosphorothioate (I) Methyl Parathion 
0,0-Diethyl O-p-nitrophenyl phosphorothioate (II) Parathion 
Exposure of parathion to light resulted in the formation of cholin- 
esterase inhibitors chromatographically different from parathion (Cook, 

1957c; Payton, 1953; Frawley et al., 1958; Sandi, 1958; Koivistoinen, 
1963a,b). The material resulting from the ultraviolet light treatment was 
a mixture of parathion, paraoxon, S-ethyl parathion, S-phenyl parathion and 
other oxidation and degradation products. That the mixture was less subject 
to diazotization and coupling suggested some destruction of the p-nitro- 
phenol moiety. Exposure of the three identified products from parathion 
gave rise to many compounds, which did not separate into distinct spots 
on the chromatogram. Methyl parathion gave rise only to the corresponding 
paraoxon, which in turn gave rise to a less polar compound. Parathion 
also underwent isomerization at elevated temperatures (Emmett and Jones, 1911). 
When p32 
-labeled methyl parathion was applied to cotton leaves, 
analyses indicated a half-life of 24 hours. Four compounds containing p32 
were found in the residue. Two were identified as methyl parathion and 
methyl paraoxon and two were unidentified. Under conditions of high 
temperatures more of the methyl parathion in the cotton leaf was converted 
to methyl paraoxon. Other studies with plants have shown the presence of 
phosphoric, dialkyl thiophosphoric, dealkyl thiophosphoric and dealkyl 
phosphoric acid (David, 1957). When applied to rice plants, methyl para- 
thion gave rise to methyl paraoxon and to desmethyl methyl parathion 
(Miyamoto et al., 1963a,b). 
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