Kinetic study of the base-catalysed reactions of benzaldehyde and thiophene-2-carbaldehyde with acetonitriles

Abstract

The reaction rates of the sodium methoxide-catalysed condensation of benzaldehyde and thiophene-2-carbaldehyde with heteroaromatic acetonitriles [ArCH₂CN; Ar = C₆H₅, C₆H₄CH₃(p), C₆H₄OCH₃(p), C₆H₄F(p), C₆H₄Cl(p), C₆H₄Br(p), 2-thienyl, 3-thienyl, 3-pyridyl] are measured in methanol. The reaction is third-order overall, first-order respect to each reactant. The reaction rates of thiophene-2-carbaldehyde with acetonitriles are lower than those of benzaldehyde indicating that the thienyl group behaves as an electron-donating substituent. The reactivity order with respect to acetonitriles is: 3-pyridylacetonitrile > thiophen-2-ylacetonitrile > phenylacetonitrile > thiophen-3-ylacetonitrile. From the Hammett treatment of the data of the reaction between benzaldehyde and acetonitriles the Cl constants for the heteroatoms are obtained: σ_α-S 0.30, σ_β-S–0.08, and σ_β-N 0.49.