Abstract:The introduction and removal of protecting groups is ubiquitous in multi-step synthetic schemes. From a green chemistry standpoint, however, alternative strategies that employ in situ and reversible protection and deprotection sequences would be attractive. The reversible reactions of CO2 with amines could provide a possible vehicle for realizing this strategy. Herein, we present (1) the products of reaction of benzylamines with CO2 in a variety of solvents with and without the presence of basic additives; (2) 498(4-aminomethyl)phenyl) methanol with isopropenyl acetate in acetonitrile containing DBU in the absence and presence of CO2.

The Suzuki coupling reaction of basic nitrogen containing substrates (2-bromo- and 2-chloro-4-aminopyridine, and 2-bromo and 2-chloropyridine) with phenylboronic acid using Pd(TPP)2Cl2/K3PO4 in acetonitrile-water biphasic solvent systems under a CO2 or a N2 atmosphere is discussed. It was observed that 2-halo-4-aminopyridine produced quantitative yields of coupled products under a CO2 atmosphere while the yields for the 2-halopyridines were poor. In contrast, the yields of coupled products for the 2-halopyridines substrates were quantitative under a N2 atmosphere while only poor yields were realized for the 2-halo-4-aminopyridines under the same conditions. Evidence is presented which suggests that the presence of CO2 alters the pH of the aqueous phase of the reaction system and the accompanying efficiency of the coupling process. Using a series of buffers to adjust the pH of the aqueous phase, the pH dependence associated with the efficiency of the coupling process is illustrated.

Water at elevated temperatures (WET) can act simultaneously as reactant, solvent, and catalyst in reaction processes.

John Prausnitz was never content to measure new data solely because the data were new. He always had an application in mind-a separation or even a process that required the data for implementation. We present here an advance in using designed changes in phase equilibria to enable the facile recovery and recycle of homogeneous catalysts. We show a new application of organic-aqueous tunable solvents (OATS) to run homogeneous reactions (fast rates and high selectivities) followed by facile and efficient heterogeneous separations and the recycle of the homogeneous catalysts. This is done by using CO 2 to manipulate the phase behavior of monophasic organic-water mixtures to form heterogeneous organic-rich and aqueous-rich phases. The example shown is the hydroformylation of hydrophobic p-methylstyrene catalyzed by rhodium catalyst to which is attached a hydrophilic phosphorus ligand. The OATS method increases the conversion rate of styrene to the aldehyde products by an order of magnitude compared to heterogeneously reported reactions. Also, the selectivity toward the branched aldehyde (the desired product) increases by 30 %. The hydrophobic product partitions into the organic-rich phase with more than 99 % removal efficiency, and the hydrophilic catalyst is retained in the aqueous-rich phase with 99.9 % efficiency. In addition, we recycle the catalyst for five consecutive reactions without significant loss of catalytic activity.