KINETIC-BEHAVIOR OF TETRACHLOROCYCLOPENTADIENYL-TYPE ANIONS - DEPROTONATION OF 1,2,3,4-TETRACHLORO-1,3-CYCLOPENTADIENE AND NUCLEOPHILIC-ADDITION TO 1,2,3,4-TETRACHLORO-6-PHENYLFULVENE IN 50-PERCENT ME2SO 50-PERCENT WATER

The kinetics of the reversible deprotonation of 1,2,3,4-tetrachloro-1,3-cyclopentadiene by OH-, piperidine, piperazine, 1-(2-hydroxyethyl)piperazine, morpholine, 1-piperazinecarboxaldehyde, n-butylamine, 2-methoxyethylamine, 2-chloroethylamine, and glycinamide and of reversible nucleophilic addition of piperidine and morpholine to 1,2,3,4-tetrachloro-6-phenylfulvene have been measured in 50% Me2SO/50% water at 20 °C. Bronsted coefficients and intrinsic rate constants have been determined for both the proton transfers and the nucleophilic additions. The intrinsic rate constant for deprotonation of 1,2,3,4-tetrachloro-1,3-cyclopentadiene by the secondary alicyclic amines (log k0 = 3.59) is about halfway between that for deprotonation by piperidine and morpholine of malononitrile (log k0 = 7.0) and phenylnitromethane (log k0 = -0.25), while the intrinsic rate constant for piperidine and morpholine addition to 1,2,3,4-tetrachloro-6-phenylfulvene (log k0 = 3.34) lies about halfway between that for piperidine/morpholine addition to benzylidenemalononitrile (log k0 = 4.94) and α-nitrostilbene (log k0 = 1.42). The significance of these intrinsic rate constants with respect to resonance effects in the tetrachlorocyclopentadienyl anions and transition-state imbalances is discussed. This papier also reports the first pKa determination of 1,2,3,4-tetrachloro-1,3-cyclopentadiene (pKa = 8.32). © 1990, American Chemical Society. All rights reserved.