The reaction medium plays a critical role in determining the success of a particular reaction, the rate at which it proceeds, and whether any undesirable side-products are formed.  The selection of a solvent is often empirical or based on somewhat rudimentary properties (H-bond donor/acceptor abilities, dielectric constant, solubility parameters, etc.).  Furthermore, there is limited customization in solvent choice as many reactions are performed in one of a handful of common laboratory solvents or a simple blend of these solvents.  For this reason, choosing an optimal (or simply improved) solvent for a particular reaction has significant application potential in liquid-phase chemistry.  <br/>From an optimization point of view, this problem is challenging for two main reasons: (1) there are virtually an infinite number of potential structures to choose from and (2) any blend of solvents requires the additional determination of mole fractions.  In this work, we propose the use of the COSMO solvation model and its –RS and –SAC post-processing steps to calculate solvation free energies and thereby estimate reaction rates.  The use of COSMO presents a distinct advantage over other approaches as COSMO-RS and –SAC estimates of any composition require only a single calculation for each component of a mixture.  Incorporating these methods into an efficient optimization framework necessitates the development of semi-empirical methods (specifically, group contribution methods) These provide estimates to sigma profiles, which are averaged representations of charge density versus surface area and are key in calculating mixture properties.   <br/>The design space of the optimization (molecular structures and mole fractions) is projected into a much lower-dimensional space, specifically that of the statistical moments of the sigma profiles of each component of the solvent mixture.  This enables the use of efficient derivative-free optimization methods to quickly design solvents for specific reaction-rates applications.  This approach will be discussed in detail and applied to several solvent design problems.

COSMO-based approach for the design of solvents to optimize reaction rates

251st National Meeting (2016)

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