The properties and uses of piperylene sulfone as a new, recyclable dipolar, aprotic solvent for conducting organic reactions are presented.

Tunable solvent systems couple homogeneous catalytic reactions to heterogeneous separations, thereby combining multiple unit operations into a single step and subsequently reducing waste generation and improving process economics. In addition, tunable solvents can require less energy than traditional separations, such as distillation. We extend the impact of such solvents by reporting on the application of two previously described carbon dioxide tunable solvent systems: polyethylene glycol (PEG)/organic tunable solvents (POTS) and organic/aqueous tunable solvents (OATS). In particular, we studied: (1) the palladium catalyzed carbon-oxygen coupling of 1-bromo-3,5-dimethylbenzene and o-cresol to potassium hydroxide to produce o-tolyl-3,5-xylyl ether and 1-bromo-3,5-di-tert-butylbenzene to potassium hydroxide to produce 3,5-di-tert-butylphenol in PEG400/1,4-dioxane/water and (2) the rhodium-catalyzed hydroformylation of p-methylstyrene in water/acetonitrile to form 2-(p-tolyl) propanal. In addition, we introduce a novel tunable solvent system based on a modified OATS where propane replaces carbon dioxide. This represents the first use of propane in a tunable solvent system.

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Conventional acid-catalyzed reactions use homogeneous catalysts that generate large amounts of waste due to neutralization processes. We can eliminate such waste with the use of switchable solvents such as butadiene sulfone and piperylene sulfone, which can act as reaction media and generate reversible, in-situ acid catalysts. These solvents enable separation through use of a thermal switch, which shifts the equilibrium from the nonvolatile, polar aprotic solvent to highly volatile products. This equilibrium generates sulfurous acid through the addition of water, enabling acid-catalyzed reactions and easy separation due to the unstable nature of the acid at reversal temperatures. In this work, we use these switchable solvents to complete the hydrolysis of β-pinene to α-terpineol. We show a kinetic study of the hydrolysis reaction, illustrating high activity and selectivity in the novel reaction media. Further, we illustrate recycle of the solvent and catalyst five times without loss in activity or need for neutralization processes.