Additive-free formation of aldol and polyacetone from acetone under pressure

Abstract

Pressure-induced polymerization (PIP) provides a route towards the controlled synthesis of topological polymeric compounds from the basic molecular units. In general, PIP is a green chemical process that does not require solvents, additives or catalysts. Siloxane, a backbone polymer containing alternating silicon–oxygen linkages with organic side chains, is commercially known as silicone oil. Herein, we report a new class of polymeric compound formed from molecular acetone using crystal structure predictions assisted by first-principles calculations at high pressure (P ≥ 20 GPa). Acetone forms a polymeric compound with alternating carbon–oxygen linkages, [–(Me)₂C–O–C(Me)₂–]_n analogous to the polydimethylsiloxane (PDMS) structures. This polymeric structure is dynamically stable over a wide range of pressures and thermally stable at room temperature. The present finding establishes the first example of carbon-based PDMS-type structure and should motivate further exploration in novel polymerization protocols. At an intermediate pressure P = 10 GPa, acetone self-dimerizes into the aldol (diacetone alcohol, DAA). While aldol formation from acetone traditionally requires external acid or base catalysts, pressure in itself suffices for this reaction. The self-dimerization of acetone occurs via a hydrogen-bonded keto–enol co-crystal formed in situ under pressure.