EQUILIBRIUM BETWEEN N-BENZYL-N-METHYLPIPERIDINIUM ION AND N-BENZYLPYRIDINIUM ION . CARBON BASICITY OF NITROGEN

The equilibrium constants for the reaction between N-benzyl-N-methylpiperidinium halides and pyridine to form N-benzylpyridinium salts and N-methylpiperidine (eq 2) have been measured in organic solvents, principally benzyl alcohol and nitrobenzene, at temperatures from 140 to 105°. The temperature coefficient of the equilibrium has been determined from the linear plot of log K vs. 1/T, and the equilibrium constant at 25° in benzyl alcohol has been obtained. Similar measurements have been made on the equilibrium between N,N-dimethylpiperidimum bromide and pyridine. Measurements of equilibrium concentrations have been made by two independent methods—electrometric titration of N-methylpiperidine in nonaqueous solution with perchloric acid in dioxane and comparisons of nmr absorptions of the product mixture, The relative pKa values for N-methylpiperidine and pyridine in benzyl alcohol at 25° have been determined; combination of these data and the equilibrium constants shows that, under the conditions specified, N-methylpiperidine is a stronger base than pyridine toward the proton by a factor of 2.5 × 106. The ratio of carbon basicities of N-methylpiperidine compared with pyridine is much smaller, however; for the N-benzyl-N-methylpiperidinium reaction, the corresponding ratio is 1.7 × 102, and, for the N,N-dimethylpiperidinium case, the ratio is 1.4 × 103. © 1969, American Chemical Society. All rights reserved.