Kaur K, Qian Y, Gandour RD, Matson JB. Hydrolytic Decomposition of S-Aroylthiooximes: Effect of pH and N-Arylidene Substitution on Reaction Rate.
J Org Chem 2018;
83:13363-13369. [PMID:
30347157 DOI:
10.1021/acs.joc.8b02151]
[Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The hydrolytic decomposition of four peptides containing S-aroylthiooximes (SATOs) with variable N-arylidene substituents was investigated in 10 aqueous buffer solutions at pH values ranging from 6.0 to 10.9. UV-vis spectroscopy was employed to study the reaction kinetics, which revealed V-shaped pH-rate profiles for all peptides with a minimum near pH 8, suggesting a change from an acid-catalyzed to a base-activated reaction. Hammett plots showed positive ρ values above pH 8 and negative ρ values below pH 8, providing further evidence for a mechanism change. Based on these data, along with mass spectral evidence, we propose specific acid catalysis under mildly acidic and neutral conditions and multiple base-promoted decomposition reactions under mildly basic conditions.
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