Ketene-forming elimination reactions from aryl thienylacetates promoted by R2NH/R2NH2 + in 70 mol % MeCN(aq). Effect of the β-aryl group

Bong-Rae Cho, Yong Pyun Sang

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Abstract

(Chemical Equation Presented) Ketene-forming eliminations from ArCH 2CO2C6H3-2-X-4-NO2 (Ar = thienyl, 1) promoted by R2NH/ R2NH2 + in 70 mol % MeCN(aq) have been studied kinetically. When X = CF3 and NO2, the reactions exhibit second-order kinetics as well as β = 0.30-0.64 and |β1g| = 0.31-0.52 that decrease with a better leaving group. Hence, an E2 mechanism is evident. As the leaving group is made poorer (X = H, OCH3, and CI), E2 transition state becomes more skewed toward the proton transfer, as revealed by the increase in Brönsted β to 0.5-0.64, and the Elcb mechanism competes. The changes in the k1 and k-1/k2 values with the reactant structure variation provide additional support for the competing Elcb mechanism. By comparing with existing data for 4-YC6H4CH2CO 2C6H3-2-X-4-NO2, the effect of β-aryl group on ketene-forming elimination is assessed.

Original languageEnglish
Pages (from-to)1098-1103
Number of pages6
JournalJournal of Organic Chemistry
Volume72
Issue number4
DOIs
Publication statusPublished - 2007 Feb 16

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Proton transfer
Protons
Kinetics
ketene

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Ketene-forming elimination reactions from aryl thienylacetates promoted by R2NH/R2NH2 + in 70 mol % MeCN(aq). Effect of the β-aryl group. / Cho, Bong-Rae; Sang, Yong Pyun.

In: Journal of Organic Chemistry, Vol. 72, No. 4, 16.02.2007, p. 1098-1103.

Research output: Contribution to journalArticle

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abstract = "(Chemical Equation Presented) Ketene-forming eliminations from ArCH 2CO2C6H3-2-X-4-NO2 (Ar = thienyl, 1) promoted by R2NH/ R2NH2 + in 70 mol {\%} MeCN(aq) have been studied kinetically. When X = CF3 and NO2, the reactions exhibit second-order kinetics as well as β = 0.30-0.64 and |β1g| = 0.31-0.52 that decrease with a better leaving group. Hence, an E2 mechanism is evident. As the leaving group is made poorer (X = H, OCH3, and CI), E2 transition state becomes more skewed toward the proton transfer, as revealed by the increase in Br{\"o}nsted β to 0.5-0.64, and the Elcb mechanism competes. The changes in the k1 and k-1/k2 values with the reactant structure variation provide additional support for the competing Elcb mechanism. By comparing with existing data for 4-YC6H4CH2CO 2C6H3-2-X-4-NO2, the effect of β-aryl group on ketene-forming elimination is assessed.",
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