Mechanism of Carboxylic Acid-Catalyzed Reduction of Substituted Nitrosobenzenes by 1-Benzyl-3,5-bis(1-pyrrolidinylcarbonyl)-1,4-dihydropyridine in Acetonitrile

Article abstract of DOI:10.1246/bcsj.59.3117

Mechanism of carboxylic acid-catalyzed reduction of substituted nitrosobenzenes by 1-benzyl-3,5-bis(1-pyrrolidinylcarbonyl)-1,4-dihydropyridine has been studied in acetonitrile at 25 deg C.The major product was hydroxylamine when the dihydropyridine was used in excess over nitrosobenzene, while that was azoxybenzene in the reverse case.The observed second-order rate constant k^R₂ are dependent on acid concentration in a first-order manner with the acid-catalyzed third-order rate constant k^R_H.The Hammett relationship for k^R_H for substituted nitrosobenzenes gave a ρ=-0.93.The Broensted plot of log k^R_H vs. pK_a of acids gave a straight line with a slope of -0.34.The deuterium isotope effect for the catalysis by dichloroacetic acid was found to be k^R_H/k^R_D=2.80.These results indicate that a general acid catalysis by carboxylic acids plays an important role in the reduction of nitrosobenzene by dihydropyridine in acetonitrile.