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Pure and Applied Chemistry

The Scientific Journal of IUPAC

Ed. by Burrows, Hugh / Weir, Ron / Stohner, Jürgen

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Online
ISSN
1365-3075
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Volume 81, Issue 4 (Jan 2009)

Issues

Kinetics and mechanism of the aminolysis of thioesters and thiocarbonates in solution

Enrique A. Castro
  • Corresponding author
  • Faculty of Chemistry, Pontifical Catholic University of Chile, Casilla 306, Santiago 6094411, Chile
Published Online: 2009-01-01 | DOI: https://doi.org/10.1351/PAC-CON-08-08-11

The aminolysis reactions of thioesters and thiocarbonates, in either aqueous solution or in 44 wt % aqueous ethanol at 25 °C, are subjected to a kinetic investigation. The Brønsted-type plots (lg kN vs. amine pKa, where kN is the nucleophilic rate constant) obtained for these reactions can be grouped in three categories: linear plots with slopes 0.8-1, biphasic plots (two linear portions and a curve in between), and linear plots with slopes 0.4-0.6. The two former plots are attributed to stepwise reactions through a zwitterionic tetrahedral intermediate. The latter plots are associated with a concerted mechanism. The fact that some reactions are stepwise and others concerted depends on the stability of the zwitterionic tetrahedral intermediate. This work shows how the experimental data allows one to assess the mechanism of these reactions. Also discussed are the factors that affect the stability of this intermediate, which in turn determines the pathway followed by the reaction. The factors analyzed in this work are (i) the leaving group of the substrate, (ii) the nature of the amine, (iii) the non-leaving group of the substrate, (iv) the electrophilic group of the substrate (CS vs. CO), and (v) the solvent.

Keywords: aminolysis; kinetics; mechanism; thiocarbonates; thioesters

Conference

International Conference on Physical Organic Chemistry (ICPOC-19), International Conference on Physical Organic Chemistry, ICPOC, Physical Organic Chemistry, 19th, Santiago de Compostela, Spain, 2008-07-13–2008-07-18

References

About the article

Published Online: 2009-01-01

Published in Print: 2009-01-01


Citation Information: Pure and Applied Chemistry, ISSN (Online) 1365-3075, ISSN (Print) 0033-4545, DOI: https://doi.org/10.1351/PAC-CON-08-08-11.

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