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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
Author(s) -
Fiori Simone,
Carvalho Fernando Rodrigues,
Tessaro André Luiz,
Meyer Emerson,
Caetano Wilker,
Politi Mario José,
Hioka Noboru
Publication year - 2013
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20784
Subject(s) - chemistry , reaction rate constant , reactivity (psychology) , kinetic energy , hydrolysis , kinetics , medicinal chemistry , crystallography , stereochemistry , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics
The alkaline hydrolysis reaction rates of 1, n ‐bis(4‐cyanopyridinium)alkane derivatives C n bis(CP) 2+ with n = 3, 6, and 8 were studied and compared to the reaction rate of the N ‐methyl‐4‐cyanopyridinium (MCP + ). C 6 bis(CP) 2+ and C 8 bis(CP) 2+ obeyed the first‐order kinetic law. However for C 3 bis(CP) 2+ data fitted to a consecutive two‐step model reaction, the observed rate constants ( k obs ) of C 8 bis(CP) 2+ and C 6 bis(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 C 3 bis(CP) 2+ , the k obs of the second (slow) step is almost twofold the value observed for C 6 bis(CP) 2+ , whereas the first (fast) step is approximately six times higher. As for MCP, the hydrolysis of C n bis(CP) 2+ generates pyridone (P o ) and carbamidopyridinium (A + ) units. For C 3 bis(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 C 3 bis(CP) 2+ due to the conformational effect justifies the (i) two kinetic steps, (ii) high rate constants, (iii) high P o /A + ratios, (iv) observed temperature and salt effects, and (v) the formation of the new product.