Evidence against phosphacylium cation participation in nucleophilic displacement at tetracoordinated phosphorus

Biomimetic Chemistry as a Useful Tool for Studying Reactive Metabolites of Pesticides

“…Because the formation of 18 O-enriched sulfonic acid is strongly favored, it is assumed that the mechanism of solvolysis does not involve separation into ion pairs but rather a nucleophilic attack at sulfur; otherwise, the 18 O would equally label both acids. Similar evidence for S−O rather than P−O bond cleavage was found from hydrolysis of 18 O-enriched thiophosphorus−sulfonic mixed anhydrides …”

Thiophosphinic Acids: Historic Overview and Recent Advances in their Synthesis and Applications

“…The same reactions were performed with selenium in the place of sulfur, giving the same results implying that both elements follow the same stereochemical course. Continuation of this work appeared in 1980 [15] and and in 1998 [16]. Optically active (-)-(S P )-38a (obtained from the resolution of the racemic (±)-38 by -phenylethylamine) reacted with methanesulfonylchloride/triethylamine and under conditions of spontaneous hydrolysis in 2:8 acetone-water complete inversion of configuration was observed in the product (+)-(R P )-38b (Scheme 14).…”

“…Optically active (-)-(S P )-38a (obtained from the resolution of the racemic (±)-38 by -phenylethylamine) reacted with methanesulfonylchloride/triethylamine and under conditions of spontaneous hydrolysis in 2:8 acetone-water complete inversion of configuration was observed in the product (+)-(R P )-38b (Scheme 14). The fact that the absolute value of the optical rotation remains unchanged (only the sign changed) is a new example of Walden inversion in phosphorus chemistry [15].…”

“…If an ion pair was involved during the reaction, the position of 18 O should equilibrate among the three oxygens. Since this was not observed, it was concluded that only the S-O bond is cleaved, leaving the P-O bond intact [15].…”

Trigonal Planar Phosphorus Cations

“…For a long time, the transient formation of oxophosphonium ions (or phosphacylium) via nucleophilic displacement at tetracoordinated phosphorus has been discussed . However, in the 1980s, this hypothesis was ruled out, and in fact, so far, no oxophosphonium ions have been reported in the literature.…”