BASE-CATALYZED HYDROGEN-DEUTERIUM EXCHANGE IN SOME PYRIDINE N-OXIDES . CHLORO AND N-OXIDE RATE FACTORS AND MECHANISM

Rates of deuterium-hydrogen exchange for deuterated pyridine N-oxide (I) and 3-chloro- (II) and 3,5-dichloro-pyridine N-oxide (III) in CH3ONa-CH3OH were obtained by nmr methods. At 138° relative rates for I-4, 1-3,5, and I-2,6 are 1.0, 10, and 1500, respectively. At 50° relative rates for II-4, I-2,6, II-6, III-4, II-2, and III-2,6 are 0.37, 1.0, 12.2, 1370, 1840, andll800. Log rate factors (relative to benzene) at 50° for C1 and N-oxide groups are o-Cl = 3.27 ± 0.24; p-Cl = 0.95 ± 0.14; o-NO = 9.58, and p-NO = 5.88. The N-oxide group is one of the most strongly activating groups for carbanion formation yet reported; its effect appears to be largely inductive. Exchange proceeds by direct deprotonation to give carbanions. © 1969, American Chemical Society. All rights reserved.