Dialkyl phosphorothionates

Dialkyl phosphonates form with sulfur, in the presence of ammonia, dialkyl phosphorothionates, which are in equilibrium with their thiolo isomers (Jonas, 1949). 

With alkylating agents, the salts of dialkyl phosphorothionates form 0,0,S-trialkyl phosphorothioates. Dialkyl phosphonate can also be used as an alkylating agent (Melnikov et al., 1965). 

Correlation of the P NMR chemical shift with the position of bond critical points (BCP) in 0,0-dialkyl O-aryl phosphorothionates has been reported. The first isolable dialkyl iodophosphates were obtained by iodination of bis-(hexa-fluoroisopropyl)phosphites with NIS. Reactions of vinyl phosphites (19) with iodine produce dealkylated intermediates, the highly reactive phosphoroiodi-dates (20) which are efficient phosphorylation reagents to prepare biologically relevant vinylphosphates (21) (Scheme 2). ... 

Of the other older dialkyl-aryl phosphorothionates, fenthion is still widely used. Fenthion has a better residual efficiency than parathion and methyl parathion and is probably less toxic to fish — 0.01 mg/1 at 24 hours exposure results in 100% mortality in mosquitoes (Aedes aegypti), whereas 1 mg/1 does not kill any guppy (Lebistes reticulatus) during 48 hours exposure. 

Chemical Shift. - Kuivalainen et showed that the P chemical shift measured in 16 substituted G,G-dialkyl 0-aryl phosphorothionates correlate very well with the average value of the BCP-P distances for the P-S and the three P-0 bonds (r = 0.95). The shortening of the average BCP-P distance causes more effective electronic shielding of the phosphorus nucleus. 

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