Kinetic Study of the Alkaline Hydrolysis of 1, n‐Bis(4‐cyanopyridinium)alkanes: Charge Density and New Conformational Effects on the Reactivity of 1, 3‐Bis(4‐cyanopyridinium)propane. Issue 8 (24th June 2013)

• Record Type: Journal Article
• Authors: Fiori, Simone; de, Fernando Rodrigues; Tessaro, André Luiz; Meyer, Emerson; Caetano, Wilker; Politi, Mario José; Hioka, Noboru
• Is Part Of: International journal of chemical kinetics. Volume 45:Issue 8(2013:Aug.)
• Page Start: 478
• Page End: 486
• Publication Date: 2013-06-24
• Subjects: Chemical kinetics -- Periodicals; 541.394
• DOI: 10.1002/kin.20784
• Languages: English
• ISSNs: 0538-8066

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p>The alkaline hydrolysis reaction rates of 1, <italic>n</italic>‐bis(4‐cyanopyridinium)alkane derivatives C<italic><sub>n</sub></italic>bis(CP)<sup>2+</sup> with <italic>n</italic> = 3, 6, and 8 were studied and compared to the reaction rate of the <italic>N</italic>‐methyl‐4‐cyanopyridinium (MCP<sup>+</sup>). C<sub>6</sub>bis(CP)<sup>2+</sup> and C<sub>8</sub>bis(CP)<sup>2+</sup> obeyed the first‐order kinetic law. However for C<sub>3</sub>bis(CP)<sup>2+</sup> data fitted to a consecutive two‐step model reaction, the observed rate constants (<italic>k</italic><sub>obs</sub>) of C<sub>8</sub>bis(CP)<sup>2+</sup> and C<sub>6</sub>bis(CP)<sup>2+</sup> are approximately 50% and 100%, respectively, higher than those for MCP<sup>+</sup>, an effect mainly assigned to the higher charge density of these two derivatives. For C<sub>3</sub>bis(CP)<sup>2+</sup>, the <italic>k</italic><sub>obs</sub> of the second (slow) step is almost twofold the value observed for C<sub>6</sub>bis(CP)<sup>2+</sup>, whereas the first (fast) step is approximately six times higher. As for MCP, the hydrolysis of C<italic><sub>n</sub></italic>bis(CP)<sup>2+</sup> generates pyridone (P<sup>o</sup>) and carbamidopyridinium (A<sup>+</sup>) units. For C<sub>3</sub>bis(CP)<sup>2+</sup>, however at pHs above 11.5, one additional product is formed. From the existence of the new product and the kinetic evidence, a "sandwiched‐type" complex with the OH<sup>−</sup> inserted between the rings is proposed. This structural effect in the C<sub>3</sub>bis(CP)<sup>2+</sup> due to the conformational effect justifies the (i) two kinetic steps, (ii) high rate constants, (iii) high P<sup>o</sup>/A<sup>+</sup> ratios, (iv) observed temperature and salt effects, and (v) the formation of the new product.</p> </abstract>