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

• Published in: International journal of chemical kinetics 2013-08, Vol.45 (8), p.478-486
• Main Authors: Fiori, Simone, de Carvalho, Fernando Rodrigues, Tessaro, André Luiz, Meyer, Emerson, Caetano, Wilker, Politi, Mario José, Hioka, Noboru
• Format: Article
• Language: English
• Subjects: Kinetics; Propane; Scholarships & fellowships
• ISSN: 0538-8066; 1097-4601
• DOI: 10.1002/kin.20784

ABSTRACT The alkaline hydrolysis reaction rates of 1,n‐bis(4‐cyanopyridinium)alkane derivatives Cnbis(CP)2+ with n = 3, 6, and 8 were studied and compared to the reaction rate of the N‐methyl‐4‐cyanopyridinium (MCP+). C6bis(CP)2+ and C8bis(CP)2+ obeyed the first‐order kinetic law. However for C3bis(CP)2+ data fitted to a consecutive two‐step model reaction, the observed rate constants (kobs) of C8bis(CP)2+ and C6bis(CP)2+ are approximately 50% and 100%, respectively, higher than those for MCP+, an effect mainly assigned to the higher charge density of these two derivatives. For C3bis(CP)2+, the kobs of the second (slow) step is almost twofold the value observed for C6bis(CP)2+, whereas the first (fast) step is approximately six times higher. As for MCP, the hydrolysis of Cnbis(CP)2+ generates pyridone (Po) and carbamidopyridinium (A+) units. For C3bis(CP)2+, 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− inserted between the rings is proposed. This structural effect in the C3bis(CP)2+ due to the conformational effect justifies the (i) two kinetic steps, (ii) high rate constants, (iii) high Po/A+ ratios, (iv) observed temperature and salt effects, and (v) the formation of the new product.