Nucleophilic Addition to Olefins. 14. Kinetics of the Reaction of 1,3-Indandione Anion with Benzylidene-1,3-indandione

Article abstract of DOI:10.1021/ja00309a024

The rate and equilibrium constants of the reversible addition of 1,3-indandione anion (ID(1-)) to benzylidene-1,3-indandione (BID) have been determined in 50percent Me2SO-50percent water at 20 deg C: k₁=7.23*10³ M^-1 s^-1, k_-1=9.35*10^-3 s^-1, K₁=7.73*10⁵ M^-1.The intrinsic rate constants for this reaction is about 300-fold lower than for the analogous reaction of malononitrile anion (MN(1-)) with benzylidenemalonotrile (BMN).This is consistent with numerous previous observations according to which reactions involving more strongly resonance-stabilized carbanions have lower intrinsic rates (higher intrinsic barriers).The ratio of 300 in the intrinsic rate constants is large than the corresponding ratios in the addition of hydroxide ion to BMN vs.BID, or the addition of MN(1-) vs.ID(1-) to benzaldehyde.This is not surprising since the reactions of ID(1-) with BID and the one of MN(1-) with BMN both involve two carbanionic sites.Our results, as well as similar findings in the comparison of the MN(1-)/BMN system with the nitromethane anion/β-nitrostyrene system, constitute Marcus-type behavior, although the quantitative adherence to a modified Marcus equation is not very good.The pK_a values of both the keto and the enol form of the BID/ID(1-) adduct and proton-transfer rates involving the keto form were determined.The enol content of the adduct is much higher than that of ID itself.This is attributed to intramolecular hydrogen bonding in the adduct.Proton transfer at carbon of the adduct is, for a given ΔpK, slower by a factor of ca. 12 than at carbon of ID, showing the operation of a steric effect.