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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 5
BKCSDE 32(5)
May 20, 2011 

 
Title
Kinetics and Mechanism of the Aminolysis of O-Methyl S-Aryl Thiocarbonates in Acetonitrile
Author
Hyuck Keun Oh
Keywords
Nucleophilic substitution reaction, Concerted mechanism, Cross-interaction constant, Kinetic isotope effects, Four-center cyclic transition state
Abstract
The aminolysis of O-methyl S-aryl thiocarbonates with benzylamines are studied in acetonitrile at −45.0 oC. The βX (βnuc) values are in the range 0.62-0.80 with a negative cross-interaction constant, ρXZ = −0.42, which are interpreted to indicate a concerted mechanism. The kinetic isotope effects involving deuterated benzylamine nucleophiles (XC6H4CH2ND2) are large, kH/kD = 1.29-1.75, suggesting that the N-H(D) bond is partially broken in the transition state by forming a hydrogen-bonded four-center cyclic structure. The concerted mechanism is enforced by the strong push provided by the MeO group which enhances the nucleofugalities of both benzylamine and arenethiolate from the putative zwitterionic tetrahedral intermediate.
Page
1539 - 1542
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