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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 12
BKCSDE 32(12)
December 20, 2011 

Kinetics and Mechanism of the Anilinolysis of Ethylene Phosphorochloridate in Acetonitrile
Hasi Rani Barai, Hai Whang Lee *
Phosphoryl transfer reaction, Anilinolysis, Ethylene phosphorochloridate, Biphasic concave upward free energy correlation, Deuterium kinetic isotope effect
The nucleophilic substitution reactions of ethylene phosphorochloridate (1c) with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at 5.0 oC. The anilinolysis rate of 1c involving a cyclic five-membered ring is four thousand times faster than its acyclic counterpart (1a: diethyl chlorophosphate) because of great positive value of the entropy of activation of 1c (ΔS≠ = +30 cal mol–1 K–1) compared to negative value of 1a (ΔS≠ = –45 cal mol–1 K–1) over considerably unfavorable enthalpy of activation of 1c (ΔH≠ = 27.7 kcal mol–1) compared to 1a (ΔH≠ = 8.3 kcal mol–1). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. The free energy correlations exhibit biphasic concave upwards for substituent X variations in the X-anilines with a break point at X = 3-Me. The deuterium kinetic isotope effects are secondary inverse (kH/kD < 1) with the strongly basic anilines and primary normal (kH/kD > 1) with the weakly basic anilines and rationalized by the TS variation from a dominant backside attack to a dominant frontside attack, respectively. A concerted SN2 mechanism is proposed and the primary normal deuterium kinetic isotope effects are substantiated by a hydrogen bonded, four-center-type TS.
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