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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 6
BKCSDE 32(6)
June 20, 2011 

Kinetics and Mechanism of the Anilinolysis of Dicyclohexyl Phosphinic Chloride in Acetonitrile
Md. Ehtesham Ul Hoque, Hai Whang Lee *
Phosphoryl transfer reaction, Anilinolysis, Dicyclohexyl phosphinic chloride, Deuterium kinetic isotope effects
The nucleophilic substitution reactions of dicyclohexyl phosphinic chloride [3; cHex2P(=O)Cl] with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at 60.0 oC. The anilinolysis rate is too slow to be rationalized by the stereoelectronic effects. The rate is contrary to expectations for the electronic influence of the two ligands and exhibits exceptionally great negative deviation from the Taft’s eq. The deuterium kinetic isotope effects (DKIEs) involving deuterated anilines invariably change from primary normal (kH/kD > 1; max kH/kD = 1.10 with X = 4-MeO) with the strongly basic anilines (X = 4-MeO, 4-Me, 3-Me) to secondary inverse (kH/kD < 1; min kH/kD = 0.673 with X = 3-Cl) with the weakly basic anilines (X = H, 4-F, 4-Cl, 3-Cl). A concerted SN2 mechanism is proposed on the basis of both secondary inverse and primary normal DKIEs. The obtained DKIEs imply that the fraction of a frontside attack increases as the aniline becomes more basic. A hydrogen-bonded, four-center-type transition state is suggested for a frontside attack, while the trigonal bipyramidal pentacoordinate transition state is suggested for a backside attack.
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