Pyridinolysis of Diethyl Phosphinic Chloride in Acetonitrile

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The reactions of O,O-diethyl Z-S-aryl phosphorothioates with X-benzylamines are kinetically investigated in dimethyl sulfoxide at 85.0 °C. The Hammett (log k 2 vs σ X ) and Brönsted [log k 2 vs pK a (X)] plots are biphasic concave downwards for substituent X variations in the nucleophiles with a break point at X = H. The signs of the cross-interaction constants (ρ XZ ) are positive for both the strongly and weakly basic nucleophiles. Considerably great magnitude of ρ XZ (= 6.56) value is observed with the weakly basic nucleophiles, while ρ XZ = 0.91 with the strongly basic nucleophiles. Proposed reaction mechanism is a stepwise process with a ratelimiting leaving group expulsion from the intermediate involving a backside nucleophilic attack with the strongly basic nucleophiles and a frontside attack with the weakly basic nucleophiles. The kinetic results are compared with those of the benzylaminolysis of O,O-diphenyl Z-S-aryl phosphorothioates.

Kinetics and Mechanism of the Benzylaminolysis of O,O-Diethyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide

Adhikary¹,

Lee²

2011

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Kinetics and Mechanism of the Pyridinolysis of S-Aryl Phenyl Phosphonochloridothioates in Acetonitrile

Adhikary¹,

Lumbiny²,

Lee³

2011

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Kinetic studies on the reactions of Y-S-aryl phenyl phosphonochloridothioates with X-pyridines have been carried out in MeCN at 55.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H. The Hammett plots for substituent Y variations in the substrates are biphasic concave upwards with a break point at Y = H, and the sign of ρ Y is changed from unusual negative (ρ Y < 0) with the weaker electrophiles to positive (ρ Y > 0) with the stronger electrophiles. The stepwise mechanism is proposed on the basis of the ρ X , β X , and ρ XY values as follows: a ratelimiting leaving group departure from the intermediate involving a frontside attack and product-like TS for the stronger nucleophiles and weaker electrophiles; a rate-limiting leaving group departure from the intermediate involving a backside attack and product-like TS for the weaker nucleophiles and electrophiles; a rate-limiting bond formation involving a frontside attack for the stronger nucleophiles and electrophiles; a rate-limiting bond formation involving a backside attack for the weaker nucleophiles and stronger electrophiles. The substituent effects of X and Y on the pyridinolysis mechanisms of R 1 R 2 P(=S)Cl-type substrates are discussed.

Kinetics and Mechanism of the Anilinolysis of Diisopropyl Thiophosphinic Chloride in Acetonitrile

Hoque¹,

Lee²

2011

The nucleophilic substitution reactions of diisopropyl thiophophinic chloride (3) with substituted anilines (XC 6 H 4 NH 2 ) and deuterated anilines (XC 6 H 4 ND 2 ) are investigated kinetically in acetonitrile at 65.0 o C. The anilinolysis rate of 3 is rather slow to be rationalized by the conventional stereoelectronic effects. The obtained deuterium kinetic isotope effects (DKIEs; k H /k D ) are secondary inverse (k H /k D = 0.80-0.96). The anilinolyses of ten P=S systems in MeCN are reviewed on the basis of DKIEs and selectivity parameters to obtain systematic information on the DKIEs and mechanism for thiophosphoryl transfer reactions. The steric effects of the two ligands on reactivity, DKIEs, mechanism, and substituent effects of the nucleophile (X) on the DKIEs are discussed.