Amplification of Chirality and Enantioselectivity in the Asymmetric Autocatalytic Soai Reaction

Abstract

From a kinetic analysis of the "dimer model", which is the most prominent mechanism of the Soai reaction, an equation is derived predicting the amplification of enantiomeric excess as a function of initial conditions. The role played by the enantioselectivity of the catalyst-product is also taken into account. Comparison with experimental data obtained at 0 degrees C by Soai et al. shows that the predicted enantiomeric excesses are lower than the experimental values by up to four orders of magnitude, and thus revision of the dimer model in the low-temperature regime is warranted. A kinetic analysis including the formation of tetramers is presented that fits the data at 0 degrees C and indicates that 2:2 heterochiral tetramers are more stable than homochiral and 3:1 heterochiral tetramers. A DFT study on diastereomers of barrel-like tetramers indeed shows higher stability of 2:2 heterochiral tetramers and thus lends support to the above kinetic analysis.