Canadian Journal of Chemistry p. 1678 - 1685 (2006)
Update date:2022-08-23
Topics:
Biswas, Supriya
Ali, Mahammad
Rappoport, Zvi
Salim, Hatim
The aminolysis of α-isobutyl-α-(methylthio)methylene Meldrum's acid 7 with primary amines, namely, n-butylamine, glycinamide, and methoxyethylamine in DMSO-H2O (50:50, v/v) at 20°C is overall second-order but first-order in both 7 and amines. The reaction with aminoacetonitrile (AA) is overall third-order, first-order in substrate, and second-order in amine at low amine concentration, while at high amine concentration and high pH the dependence on amine is first-order. A general three-step mechanism has been proposed for all these reactions. For the former group of amines, the first step is a rate-limiting attack of the amine to form the tetrahedral intermediate (TA±), followed by a fast acid-base equilibrium and a fast RNH3+- or H 2O-assisted leaving group expulsion. For AA, general base catalysis was confirmed from the dependence of kA on [AA]f and on [OH-]. For all four amines, a good Bronsted plot of log k 1 vs. pKaAH in DMSO-H2O (50:50, v/v) with βnuc = 0.34 ± 0.02 was observed. These observations are consistent with the suggested mechanism.
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