Angew. Chem. Int. Ed. http://dx.doi.org/10.1002/anie.201102813 (2011)
Complex mixtures of different chemical components can, under the correct conditions, undergo a self-sorting process to form a specific set of products — any living organism offers a practical and powerful example of this phenomenon. In synthetic systems, however, the highly evolved biological machinery that often mediates this sorting is typically absent, and so careful design of the components — and the reactions they can undergo — is required. In particular, reversible interactions between the components are critical so that undesired products can be recycled back into an equilibrating mixture.
Now, Karolina Osowska and Ognjen Miljanić from the University of Houston have combined the self-sorting of a dynamic covalent library of imines with the simultaneous act of physically separating the products. In their initial experiment, two aldehydes (1 and 2) were mixed with two amines (A and B) to produce an equilibrating mixture of four different imines. When this mixture was distilled, the most volatile imine 1A — made up of the lowest-molecular-weight aldehyde and amine — was removed from the system. As 1A is depleted, the equilibrium shifts, and 2A and 1B are recycled to form more of 1A. Once 1A has been completely removed from the system, all that remains is 2B and so two different compounds are isolated in high purity from a mixture of four possible products.
The principle is also shown to work on larger libraries — the sequential distillation at increasing temperatures of a mixture comprising five aldehydes and five amines gives just five different imines as the major products from a potential pool of 25 compounds. This strategy could prove useful for other reactions (such as esterification) and may also be relevant for industrial processes.
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Cantrill, S. Simple sorting solution. Nature Chem 3, 655 (2011). https://doi.org/10.1038/nchem.1137