Issue 9, 2008

Aminolysis of 4-nitrophenyl phenyl carbonate and thionocarbonate: effects of amine nature and modification of electrophilic center from C[double bond, length as m-dash]O to C[double bond, length as m-dash]S on reactivity and mechanism

Abstract

A kinetic study is reported for the reactions of 4-nitrophenyl phenyl carbonate (5) and thionocarbonate (6) with a series of alicyclic secondary amines in 80 mol% H2O–20 mol% DMSO at 25.0 ± 0.1 °C. The plots of kobsdvs. amine concentration are linear for the reactions of 5. On the contrary, the plots for the corresponding reactions of 6 curve upward as a function of increasing amine concentration, indicating that the reactions proceed through two intermediates (i.e., a zwitterionic tetrahedral intermediate T± and its deprotonated form T). The Brønsted-type plot for the reactions of 5 with secondary amines exhibits a downward curvature, i.e., the slope decreases from 0.98 to 0.26 as the pKa of the conjugate acid of amines increases, implying that the reactions proceed through T± with a change in the rate-determining step (RDS). The kN values are larger for the reactions of 5 with secondary amines than for those with primary amines of similar basicity. Dissection of kN values for the reactions of 5 into the microscopic rate constants (i.e., k1 and k2/k−1 ratio) has revealed that k1 is larger for the reactions with secondary amines than for those with isobasic primary amines, while the k2/k−1 ratio is nearly identical. On the other hand, for reactions of 6, secondary amines exhibit larger k1 values but smaller k2/k−1 ratios than primary amines. The current study has shown that the reactivity and reaction mechanism are strongly influenced by the nature of amines (primary vs.secondary amines) and electrophilic centers (C[double bond, length as m-dash]O vs. C[double bond, length as m-dash]S).

Graphical abstract: Aminolysis of 4-nitrophenyl phenyl carbonate and thionocarbonate: effects of amine nature and modification of electrophilic center from C [[double bond, length as m-dash]] O to C [[double bond, length as m-dash]] S on reactivity and mechanism

Supplementary files

Article information

Article type
Paper
Submitted
25 Jan 2008
Accepted
27 Feb 2008
First published
14 Mar 2008

Org. Biomol. Chem., 2008,6, 1618-1624

Aminolysis of 4-nitrophenyl phenyl carbonate and thionocarbonate: effects of amine nature and modification of electrophilic center from C[double bond, length as m-dash]O to C[double bond, length as m-dash]S on reactivity and mechanism

I. Um, S. Yoon, H. Park and H. Han, Org. Biomol. Chem., 2008, 6, 1618 DOI: 10.1039/B801422A

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