Soai’s discovery of chiral amplification in the autocatalytic alkylation of pyrimidine-5-carbaldehyde
with diisopropylzinc is one of the most noteworthy findings of the last decade of the
20th century. This is the first experimental confirmation of an early theoretical rationalisation
of autocatalysis as a mechanism for the evolution of biological homochirality from a racemic
environment (Frank, 1953).
This thesis describes kinetic and spectroscopic investigations that were conducted with the aim
of better understanding the mechanism under which chiral amplification is achieved in the Soai
system. The methodology used to perform the kinetic studies that are presented in this thesis
focuses on the use of reaction calorimetry as in-situ tool coupled with the appropriate analytical
technique for enantiomeric excess measurements.
Observations of an unusual temperature effect on the reaction rate and a profound induction
period are reported together with extensive kinetic investigations. Kinetic experiments were
designed and carried out following Reaction Progress Kinetic Analysis methodology, which is
described in detail. These experiments were carried out in order to ascertain the concentration
dependence of the substrates and the reaction product, and revealed a 1.6 order in pyrimidyl
aldehyde, a zero order in diisopropylzinc and a first order in the reaction product.
Meticulous NMR studies of the alkoxide product at low temperature demonstrated its tendency
to form tetrameric complexes, which could be either directly involved in the autocatalysis or be
the precursors of the active catalytic species.
Possible mechanisms that involve tetramers formation are proposed and supported by simulations
carried out using COPASI simulation software.
This thesis also includes a separate Chapter on the MIB mediated alkylation of benzaldehyde
with diethylzinc, a system characterised by a marked nonlinear effect. Kinetic studies demonstrate
how the high degree of chiral amplification comes at the expense of the reaction rate.