Kinetics and Mechanism of the Anilinolysis of (2R,4R,5S)-(+)-2-Chloro-3,4-dimethyl -5-phenyl-1,3,2-oxazaphospholidine 2-Sulfide in Acetonitrile
2012; Wiley; Volume: 33; Issue: 3 Linguagem: Inglês
10.5012/bkcs.2012.33.3.1037
ISSN1229-5949
AutoresHasi Rani Barai, Hai-Whang Lee,
Tópico(s)Chemical Reactions and Mechanisms
ResumoThe nucleophilic substitution reactions of (2R,4R,5S)-(+)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide (3) with substituted anilines ( $XC_6H_4NH_2$ ) and deuterated anilines ( $XC_6H_4ND_2$ ) are investigated kinetically in acetonitrile at $5.0^{\circ}C$ . The anilinolysis rate of 3 involving a cyclic five-membered ring is considerably fast because of small negative value of the entropy of activation ( ${\Delta}S^\neq=-2cal\;mol^{-1}\;K^{-1}$ ) over considerably unfavorable enthalpy of activation ( ${\Delta}H^\neq=18.0\;kcal\;mol^{-1}$ ). Great enthalpy and small negative entropy of activation are ascribed to sterically congested transition state (TS) and bulk solvent structure breaking in the TS. A concerted $S_N2$ mechanism with a backside nucleophilic attack is proposed on the basis of the secondary inverse deuterium kinetic isotope effects, $k_H/k_D$ < 1.
Referência(s)