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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 3
BKCSDE 32(3)
March 20, 2011 

 
Title
Nucleophilic Substitution Reactions of N-Methyl α-Bromoacetanilides with Benzylamines in Dimethyl Sulfoxide
Author
Keshab Kumar Adhikary, Hai Whang Lee*
Keywords
Benzylaminolysis, N-Methyl-α-bromoacetanilides, Cross-interaction constant, Deuterium kinetic isotope effect, Biphasic nonlinear free energy correlation
Abstract
Kinetic studies of the reactions of <EM>N</EM>-methyl-Y-α-bromoacetanilides with substituted X-benzylamines have<BR>been carried out in dimethyl sulfoxide at 25.0 <SUP>o</SUP>C. The Hammett plots for substituent X variations in the<BR>nucleophiles (log <EM>k</EM><SUB>N</SUB> vs <EM>σ</EM><SUB>X</SUB>) are slightly biphasic concave upwards/downwards, while the Brönsted plots (log <EM>k</EM><SUB>N</SUB><BR>vs p<EM>K</EM><SUB>a</SUB>) are biphasic concave downwards with breakpoints at X = H. The Hammett plots for substituent Y<BR>variations in the substrates (log <EM>k</EM><SUB>N</SUB> vs <EM>σ</EM><SUB>Y</SUB>) are biphasic concave upwards/downwards with breakpoints at Y = H.<BR>The cross-interaction constant <EM>ρ</EM><SUB>XY</SUB> values are all negative: <EM>ρ</EM><SUB>XY</SUB> = −0.32 for X = Y = electron-donating; −0.22<BR>for X = electron-withdrawing and Y = electron-donating; −1.80 for X = electron-donating and Y = electronwithdrawing;<BR>−1.43 for X = Y = electron-withdrawing substituents. Deuterated kinetic isotope effects are<BR>primary normal (<EM>k</EM><SUB>H</SUB>/<EM>k</EM><SUB>D</SUB> &gt; 1) for Y = electron-donating, while secondary inverse (<EM>k</EM><SUB>H</SUB>/<EM>k</EM><SUB>D</SUB> &lt; 1) for Y = electronwithdrawing<BR>substituent. The proposed mechanisms of the benzylaminolyses of <EM>N</EM>-methyl-Y-α-bromoacetanilides<BR>are a concerted mechanism with a five membered ring TS involving hydrogen bonding between hydrogen<BR>(deuterium) atom in N-H(D) and oxygen atom in C = O for Y = electron-donating, while a concerted<BR>mechanism with an enolate-like TS in which the nucleophile attacks the α-carbon for Y = electronwithdrawing<BR>substituents.
Page
857 - 862
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