Mirror-symmetry breaking in the Soai reaction: a kinetic understanding.
Kinetic modeling using nonlinear differential equations is proposed to analyze the spontaneous generation of enantiomeric excess in the autocatalytic addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction). Our approach reproduces experimentally observed giant chiral amplification from an initial enantiomeric excess of <10(-6)% to >60%, high sensitivity and positive response to the presence of minute amounts of chiral initiator at concentrations <10(-14) M, and spontaneous absolute asymmetric synthesis from achiral starting conditions. From our numerical simulations using kinetic schemes derived from the Frank model, including stereospecific autocatalysis and mutual inhibition, we have shown that it is possible to reproduce the mirror-symmetry-breaking behavior of the Soai reaction under batch conditions leading to a bimodal enantiomeric product distribution. Mirror-symmetry breaking was found to be resistant to a loss of stereoselectivity up to 30%. While the mutual inhibition between enantiomers seems to originate from the presence of dimerization equilibria, the exact nature of the autocatalytic stereoselective process still remains to be revealed. From the kinetic viewpoint, simple autocatalysis involving monomers as the catalytic species is consistent with all reported experimental effects of the Soai reaction.
Islas
Jesús Rivera
JR
Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Avenida Universidad 1001, Colonia Chamilpa, 62209 Cuernavaca, Morelos, Mexico.
Lavabre
Dominique
D
Grevy
Jean-Michel
JM
Lamoneda
Ramón Hernández
RH
Cabrera
Haydée Rojas
HR
Micheau
Jean-Claude
JC
Buhse
Thomas
T