Nucleophilic Addition to Olefins. 13. Kinetics of Hydrolysis of Benzylidene-1,3-indandione

Article abstract of DOI:10.1021/ja00309a023

A complex kinetic analysis of the four-step hydrolysis of benzylidene-1,3-indandione into benzaldehyde and 1,3-indandione in 50percent Me2SO-50percent water is reported.The four steps (see Scheme 1) are (1) nucleophilic addition of hydroxide ion or water to form the adduct T_OH(1-), (2) carbon protonation of T_OH(1-) to form T_OH0, (3) oxygen deprotonation of T_OH0 to form T_O(1-), and (4) breakdown of T_O(1-) into benzaldehyde and 1,3-indandione or its anion.There is also a direct water-catalyzed pathway from T_OH0 to benzaldehyde and 1,3-indandione.Rate and equilibrium constants of the various steps are compared with analogous parameters in the hydrolysis of benzylidenemalononitrile, β-nitrostyrene, benzylidene Meldrum's acid, and 1,1-dinitro-2,2-diphenylethylene.The following conclusions emerge. (1) The equilibrium constants of the carbanion-forming steps (step 1 forward, step 2 reverse, step 4 forward) correlate fairly well with the pK_a values of the corresponding parent carbon acids 1,3-indandione, malononitrile, nitromethane, Meldrum's acid, and 1,1-dinitroethane, although steric as well as other factors make the correlations less than perfect. (2) The intrinsic rate constants (k for K=1) for the carbanion-forming steps (step 1 with OH(1-), and step 4) decrease with increasing resonance stabilization of the carbanion, just as is the case for the deprotonation of the corresponding parent carbon acids.However, the effect of the activating substituent(s) on the intrinsic rates of these steps is only about half (on a logarithmic scale) as large as for the proton transfer. (3) The effect of the activating substituent(s) on the intrinsic rates of water addition to the olefin, and of the direct water-catalyzed breakdown of T_OH0 to products, is significantly smaller than for step 1 (OH(1-) attack) and k₄, and in some cases even reversed, with the intrinsic rate being higher for the system with substituents capable of strong resonance.This is attributed to a special transition-state stabilization by internal hydrogen bonding from the water to the oxygen anion in these water-catalyzed reactions.