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

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: σα-S 0.30, σβ-S–0.08, and σβ-N 0.49.