- Choice of solvent (MeCN vs H2O) decides rate-limiting step in SNAr aminolysis of 1-fluoro-2,4-dinitrobenzene with secondary amines: Importance of Bronsted-type analysis in acetonitrile
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(Chemical Equation Presented) A kinetic study is reported for nucleophilic substitution reactions of 2,4-dinitro-1-fluorobenzene (DNFB) with a series of secondary amines in MeCN and H2O at 25.0°C. The reaction in MeCN results in an upward curva
- Um, Ik-Hwan,Min, Se-Won,Dust, Julian M.
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- Kinetic study on SNAr reaction of 1-(Y-Substituted-phenoxy)-2,4- dinitrobenzenes with cyclic secondary amines in acetonitrile: Evidence for cyclic transition-state structure
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A kinetic study is reported for SNAr reactions of 1-(Y-substituted-phenoxy)-2,4-dinitrobenzenes (1a-1h) with amines in MeCN. The plots of pseudo-first-order rate constant versus amine concentration curve upward, indicating that the reactions are catalyzed by a second amine molecule. The Br?nsted-type plots for the reaction of 1-(4-nitrophenyl)-2,4- dinitrobenzene (1a) with secondary amines are linear with βnuc = 1.10 and 0.85 for the uncatalyzed and catalyzed reactions, respectively, while the Yukawa-Tsuno plots for the reactions of 1a-1h with piperidine result in excellent linear correlations with ρY = 1.85 and r = 0.27 for the uncatalyzed reaction and ρY = 0.73 and r = 0.23 for the catalyzed reaction. The catalytic effect decreases with increasing amine basicity or electron-withdrawing ability of the substituent Y in the leaving group. Activation parameters calculated from the rate constants measured at five different temperatures for the catalyzed reaction of 1a with piperidine are ΔH? = 0.38 kcal/mol and ΔS? = -55.4 cal/(mol K). The catalyzed reaction from a Meisenheimer complex (MC ±) is proposed to proceed through a concerted mechanism with a cyclic transition-state rather than via a stepwise pathway with an anionic intermediate, MC-. Deuterium kinetic isotope effects provide further insight into the nature of the concerted transition state.
- Um, Ik-Hwan,Kim, Min-Young,Kang, Tae-Ah,Dust, Julian M.
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p. 7025 - 7031
(2014/08/18)
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- Dual nucleophilic substitution reactions of O,O-diethyl 2,4-dinitrophenyl phosphate and thionophosphate triesters
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The reactions of the title compounds with phenoxides, secondary alicyclic (SA) amines, and pyridines, in 44 wt% ethanol-water, at 25°C and an ionic strength of 0.2 M, were subjected to kinetic and product studies. From analytical techniques (HPLC and NMR), two pathways were detected (nucleophilic attack at the phosphoryl center and at the C-1 aromatic carbon) for the reactions of all the nucleophiles with the phosphate (2) and for the pyridinolysis of the thionophosphate (1). Only aromatic nucleophilic substitution was found for the reactions of 1 with phenoxides and SA amines. For the dual reactions, the nucleophilic rate constants (kN) were separated in two terms: documentclass{article}usepackage{amssymb} pagestyle{empty}begin{document}k-{rm N}^{rm P}end{document} and documentclass{article}usepackage{amssymb}pagestyle{empty}begin{document}k-{ rm N}^{{rm Ar}}end{document}, which are the rate constants for the corresponding electrophilic centers. The absence of a break in the Bronsted-type plots for the attack at P is consistent with concerted mechanisms. The Bronsted slopes, βAr 0.32-0.71, for the attack at the aromatic C-1, are in agreement with stepwise mechanisms where formation of a Meisenheimer complex is the rate-determining step. 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 202-211, 2013 Copyright
- Aguayo, Raul,Arias, Felipe,Canete, Alvaro,Zuniga, Carolina,Castro, Enrique A.,Pavez, Paulina,Santos, Jose G.
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supporting information
p. 202 - 211
(2013/03/14)
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- Mechanistic assessment of SNAr displacement of halides from 1-Halo-2,4-dinitrobenzenes by selected primary and secondary amines: Br?nsted and Mayr analyses
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Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for nucleophilic substitution reactions of 1-X-2,4-dinitrobenzenes (1a-d, X = F, Cl, Br, I) with various primary and secondary amines in MeCN and H2O
- Um, Ik-Hwan,Im, Li-Ra,Kang, Ji-Sun,Bursey, Samantha S.,Dust, Julian M.
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supporting information
p. 9738 - 9746
(2013/01/15)
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- Effect of Amine Nature on Reaction Rate and Mechanism in Nucleophilic Substitution Reactions of 2,4-Dinitrophenyl X-Substituted Benzenesulfonates with Alicyclic Secondary Amines
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Second-order rate constants have been measured for reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates with a series of alicyclic secondary amines. The reaction proceeds through S-O and C-O bond fission pathways competitively. The S-O bond fission occurs more dominantly as the amine basicity increases and the substituent X in the sulfonyl moiety becomes more strongly electron withdrawing, indicating that the regioselectivity is governed by the amine basicity as well as the electronic nature of the substituent X. The S-O bond fission proceeds through an addition intermediate with a change in the rate-determining step at pKa° = 9.1. The secondary amines are more reactive than primary amines of similar basicity for the S-O bond fission. The k1 value has been determined to be larger for reactions with secondary amines than with primary amines of similar basicity, which fully accounts for their higher reactivity. The second-order rate constants for the S-O bond fission result in linear Yukawa-Tsuno plots while those for the C-O bond fission exhibit poor correlation with the electronic nature of the substituent X. The distance effect and the nature of reaction mechanism have been suggested to be responsible for the poor correlation for the C-O bond fission pathway.
- Um, Ik-Hwan,Chun, Sun-Mee,Chae, Ok-Mi,Fujio, Mizue,Tsuno, Yuho
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p. 3166 - 3172
(2007/10/03)
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- Intramolecular Catalysis in the Reaction of 1-Fluoro-2,4-dinitrobenzene with Diamines in Benzene
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A kinetic investigation of the reaction of 1-fluoro-2,4-dinitrobenzene (FDNB) with saturated diamines in benzene shows that, when the two amino groups are suitable placed with respect to each other, catalysis by a second diamine molecule is kinetically insignificant throughout the diamine concentration range examined.A comparison with the reactivity of the same diamines towards 1-chloro-2,4-dinitrobenzene (CNDB) suggests that the rate-determining step is nucleophilic attack also for the FDNB system.This behaviour is attributed to efficient intramolecular assistance of the second amino group of a diamine molecule to decomposition of the tetrahedral reaction intermediate.
- Guanti, Giuseppe,Petrillo, Giovanni,Thea, Sergio,Pero, Francesca
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p. 2764 - 2771
(2007/10/02)
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