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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 24, Number 7
BKCSDE 24(7)
July 20, 2003

Title	Kinetics and Mechanism of the Aminolysis of Phenacyl Bromides in Acetonitrile
Author	Ikchoon Lee, Hai Whang Lee, Young-Kab Yu
Keywords	Bronsted b values, Aminolysis of phenacyl bromides, Stepwise mechanism, Cross-interaction constant
Abstract	In the aminolysis of phenacyl bromides (YC6H4COCH2Br) with benzylamines (XC6H4CH2NH2) in acetonitrile, the Bronsted bX ( bnuc) values observed are rather low ( bX = 0.69-0.73). These values are similar to those ( bX @ 0.7) for other aminolysis reactions of phenacyl compounds with anilines and pyridines, but are much smaller than those ( bX = 1.1-2.5) for the aminolysis of esters with benzylamines which are believed to proceed stepwise with rate-limiting expulsion of the leaving group. The relative constancy of the bX values ( bX @ 0.7) irrespective of the amine, leaving group and solvent can be accounted for by a bridged type transition state in the rate-limiting expulsion of the leaving group. Thus the aminolysis of phenacyl derivatives are proposed to proceed stepwise through a zwitterionic tetrahedral intermediate (T±), with rate-limiting expulsion of the leaving group from T±. In the transition state, the amine is bridged between the carbonyl and a-carbons, which leads to negligible effect of amine on the leaving group expulsion rate.
Page	993 - 998
Full Text	PDF

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