David J. Heldebrant

Green chemistry: Reversible nonpolar-to-polar solvent

Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

CO2-triggered switchable solvents, surfactants, and other materials

Waste CO2 at atmospheric pressure can be used to trigger dramatic changes in the properties of certain switchable materials. Compared to other triggers such as light, acids and oxidants, CO2 has the advantages that it is inexpensive, nonhazardous, non-accumulating in the system, easily removed, and it does not require the material to be transparent. Known CO2-triggered switchable materials now include solvents, surfactants, solutes, catalysts, particles, polymers, and gels. These have also been described as “smart” materials or, for some of the switchable solvents, “reversible ionic liquids”. The added flexibility of switchable materials represents a new strategy for minimizing energy and material consumption in process and product design.

Organic liquid CO2 capture agents with high gravimetric CO2 capacity

We report a new class of CO2 binding organic liquids that chemically capture and release CO2 much more efficiently than aqueous alkanolamine systems. Mixtures of organic alcohols and amidine/guanidine bases reversibly bind CO2 chemically as liquid amidinium/guanidinium alkylcarbonates. The free energy of CO2 binding in these organic systems is very small and dependent on the choice of base, approximately −9 kJ mol−1 for DBU and Bartons base and +2 kJ mol−1 for 1,1,3,3-tetramethylguanidine. These CO2 capturing agents do not require an added solvent because they are liquid, and therefore have high CO2 capacities of up to 19% by weight for neat systems, and slightly less when dissolved in acetonitrile. The rate of CO2 uptake and release by these organic systems is limited by the rate of dissolution of CO2 into and out of the liquid phase. Gas absorption is selective for CO2 in both concentrated and dilute gas streams. These organic systems have been shown to bind and release CO2 for five cycles without losing activity or selectivity.

In Situ Multinuclear NMR Spectroscopic Studies of the Thermal Decomposition of Ammonia Borane in Solution

The development of condensed phase hydrogen storage materials for fuel cell powered vehicles capable of meeting the 2015 system target goals of >82 g H2 L-1 volumetric density and >90 g H2 kg-1 gravimetric density has attracted recent interest. The details of the mechanisms for hydrogen release from AB are not completely understood; however, significant progress has been made in furthering our understanding of these mechanisms. This work was funded by the Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE) as part of the Chemical Hydrogen Storage Center and carried out at the Pacific Northwest National Laboratory (operated by Battelle for DOE).

Coordination of aminoborane, NH2BH2, dictates selectivity and extent of H2 release in metal-catalysed ammonia borane dehydrogenation

In situ(11)B NMR monitoring, computational modeling, and external trapping studies show that selectivity and extent of H(2) release in metal-catalysed dehydrogenation of ammonia borane, NH(3)BH(3), are determined by coordination of reactive aminoborane, NH(2)BH(2), to the metal center.

Reversible Uptake of COS, CS2, and SO2: Ionic Liquids with O-Alkylxanthate, O-Alkylthiocarbonyl, and O-Alkylsulfite Anions

CO(2)-binding organic liquids (CO(2)BOLs) are mixtures of a base (typically an amidine or guanidine) and an alcohol, and have been shown to reversibly capture and release CO(2) with low reaction energies and high gravimetric CO(2) capacity. We now report the ability of such liquid blends to chemically bind and release other acid gases such as CS(2), COS, and SO(2) analogously to CO(2). These systems bind with sulfur-containing acid gases to form colored ionic liquids with new O-alkylxanthate, O-alkylthiocarbonyl, and O-alkylsulfite anions. The capture and thermal stripping of each acid gas from these systems and their applicability towards flue gas desulfurization is discussed.

Liquid polymers as solvents for catalytic reductions

Nonvolatile solvents eliminate the health and environmental risks associated with volatile solvent use, but may pose their own risks and separation problems. Several liquid polymers are compared in terms of environmental risk, solvent polarity, and performance as solvents for homogeneously-catalyzed and whole-cell-catalyzed reductions. Asymmetric catalyst use and recycling was demonstrated using a combination of liquid polymer and supercritical CO2. A polymeric solvent was also found to protect air-sensitive catalysts from inactivation due to exposure to air.

Formanilide and carbanilide from aniline and carbon dioxide

Abstract Earlier syntheses of formamides from the catalytic hydrogenation of CO 2 in the presence of amines were only successful for the preparation of dialkylformamides. After an analysis of the reason for the failure of the reaction using aniline as a starting material, formanilide has been prepared, for the first time, from CO 2 , H 2 and aniline with the use of 1,8-diazabicyclo[5.4.0]undec-7-ene. Omission of the H 2 reductant causes the selectivity to switch to the production of carbanilide (1,3-diphenylurea).

A reversible zwitterionic SO2-binding organic liquid

N,N-Dibutylundecanolamine is a liquid that chemically binds SO2 to form a viscous zwitterionic liquid that contains 35% by wt. SO2 at standard temperature and pressure. SO2 is chemically bound to the alcohol component as an alkylsulfite, which is then stabilized by the amine. The zwitterionic liquid can be reverted to its non-ionic form and recycled by thermally stripping the SO2 under vacuum at temperatures near 70 °C. N,N-Dibutylundecanolamine is a potential flue gas desulfurizing solvent because it is chemically selective to bind SO2 but not basic enough to chemically bind CO2.

The diammoniate of diborane: crystal structure and hydrogen release

[(NH(3))(2)BH(2)](+)[BH(4)](-) is formed from the room temperature decomposition of NH(4)(+)BH(4)(-), via a NH(3)BH(3) intermediate. Its crystal structure has been determined and contains disordered BH(4)(-) ions in 2 distinct sites. Hydrogen release is similar to that from NH(3)BH(3) but with faster kinetics.