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Nonlinear Taft Polar Free Energy Relationship: Reactions of N‐Substituted Benzyl Amines with Benzyl Bromide in Methanol
Author(s) -
Ravi R.,
Sanjeev R.,
Jagannadham V.
Publication year - 2013
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20818
Subject(s) - chemistry , benzyl bromide , polar effect , medicinal chemistry , bromide , amine gas treating , nucleophile , alkyl , methanol , reaction rate constant , organic chemistry , kinetics , catalysis , physics , quantum mechanics
The rates of reactions of N‐substituted benzyl amines with benzyl bromide were measured using a conductivity technique in methanol medium. The reaction followed a total second‐order path. The end product of the reaction is identified as dibenzyl alkyl amine (C 6 H 5 CH 2 N(R)CH 2 C 6 H 5 ). The rates increased with a decrease in the electron‐donating capacity or with an increase in the Taft σ* value of electron‐donating alkyl substituents (R) such as t ‐butyl (σ* = −0.3), i ‐propyl (σ* = −0.19), n ‐butyl (σ* = −0.13), and ethyl (σ* = −0.1) on nitrogen of the amine until the Taft σ* value becomes zero for the methyl group ( σCH 3 * = 0.00), and then the rates decreased with an increase in the electron‐withdrawing capacity or with an increase in the Taft σ* value of electron‐withdrawing substituents (R) such H and C 6 H 5 ( σ H * = 0.49 and σ C 6H 5 * = 0.6). The locus of the Taft polar free energy relationship has a maximum near the point for N ‐methyl benzyl amine, showing that there is a sharp change in the rate‐determining step. A mechanism involving formation of an S N 2‐type transition state between the amine nucleophiles and the benzyl bromide and its subsequent decomposition is proposed. Activation parameters were calculated and are discussed.