Philip G. Jessop

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.

Searching for green solvents

Academic research in the area of green solvents is focused on neither the industries that use solvents most nor the types of solvents that the research community believes have the best hope of reducing solvent-related environmental damage. Those of us who are primarily motivated by a desire to reduce such damage would do well to look at the major uses of solvents, to determine the problems that currently make those applications less-than-green and focus our research efforts on potential solutions to those problems. As a contribution to such efforts, I present four grand challenges in the field of green solvents: finding a sufficient range of green solvents, recognizing whether a solvent is actually green, finding an easily-removable polar aprotic solvent and eliminating distillation.

Reactions of transition metal dihydrogen complexes

A. Introduction (i) The scope of the review (ii) The preparation of dihydrogen complexes (a) Preparation from dihydrogen gas (b) Protonation of a hydride complex (c) Other methods of preparation B. Homolytic splitting of coordinated dihydrogen (i) Introduction (ii) Observing the dihydrogen-dihydride equilibrium (iii) Factors influencing the dihydrogen-dihydride equilibrium (iv) Thermodynamics of the dihydrogen-dihydride equilibrium (v) Kinetics of the dihydrogen-dihydride equilibrium (vi) Rapid dihydrogen-dihydride equilibrium or elongated H ... H ligand? ..... (vii) Other dihydrogen to dihydride reactions (viii) Intermolecular homolytic cleavage of a dihydrogen ligand C. Exchange of H atoms between dihydrogen and other hydrogen-donor ligands .... (i) Introduction (ii) Intramolecular H atom exchange for a three-hydrogen system M(H,)H ..... (a) Mechanisms of H atom exchange (b) Observing H atom exchange for a three-hydrogen system M(H,)H .... (c) Complete line-shape analysis (d) Activation parameters from complete line-shape studies (e) Slow exchange with incomplete T, averaging (f) Line-shape coalescence (g) No line-shape decoalescence (h) Intramolecular exchange of isotopes (iii) Intramolecular H atom exchange for dihydrogenpolyhydride systems M(H,)H, (a) Mechanisms (b) Line-shape coalescence (c) No line-shape decoalescence (d) Intramolecular exchange of isotopes (iv) H/D exchange in the reaction of M(H,)L, with D, (v) Intramolecular H atom exchange in bimetallic systems D. Heterolytic cleavage of the dihydrogen ligand 159 160 161 162 162 163 163 163 164 170 174 178 182 185 187 188 188 189 189 193 194 197 198 201 203 203 206 206 207 209 211 212 214 215

Homogeneous Catalysis in Supercritical Fluids

Supercritical fluids (SCFs), compounds heated and pressurized beyond the critical point, have many unusual properties. Homogeneous molecular catalysts, which have far greater control over selectivity than heterogeneous solid catalysts, are now being tested in SCFs, and early results show that high rates, improved selectivity, and elimination of masstransfer problems can be achieved. As industry moves away from toxic or environmentally damaging solvents, supercritical carbon dioxide may be an ideal replacement medium for nonpolar or weakly polar chemical processes. More than simply substitutes for nonpolar solvents, SCFs can radically change the observed chemistry. Supercritical carbon dioxide is also an excellent medium for its own fixation, as demonstrated by studies of its hydrogenation.

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.

A solvent having switchable hydrophilicity

A new kind of switchable solvent, a switchable-hydrophilicity solvent, is hydrophobic and has very low miscibility with water when in air but is hydrophilic and has complete miscibility with water when under an atmosphere of CO2. We report here the first example of such a solvent, N,N,N′-tributylpentanamidine. Solvents such as these could be used for the extraction of low-polarity organic products, such as vegetable oils, followed by the removal of the solvent from the product by carbonated water. Carbonated water is able to extract the solvent from the product because the CO2 converts the solvent to its hydrophilic form. The solvent can then be separated from the carbonated water upon removal of the CO2, because this removal triggers the conversion of the solvent back to its hydrophobic, water-immiscible form. Importantly, distillation is not required for removal of the solvent from the product.

Tertiary amine solvents having switchable hydrophilicity

Several tertiary amines serve as switchable-hydrophilicity solvents, meaning that they are hydrophobic solvents having very low miscibility with water when under air but hydrophilic solvents having complete miscibility with water when under an atmosphere of CO2. Unlike the only previously reported switchable-hydrophilicity solvent, these amines are easily prepared and, in some cases, commercially available. The effect of temperature, gas flow rates, choice of amine and additives on the switching process is described. These solvents can be applied to the recycling of polystyrene foam.

Switchable hydrophilicity solvents for lipid extraction from microalgae for biofuel production

A switchable hydrophilicity solvent (SHS) was studied for its effectiveness at extracting lipids from freeze-dried samples of Botryococcus braunii microalgae. The SHS N,N-dimethylcyclohexylamine extracted up to 22 wt.% crude lipid relative to the freeze-dried cell weight. The solvent was removed from the extract with water saturated with carbon dioxide at atmospheric pressure and recovered from the water upon de-carbonation of the mixture. Liquid chromatography-mass spectrometry (LC-MS) showed that the extracted lipids contained high concentrations of long chain tri-, di- and mono-acylglycerols, no phospholipids, and only 4-8% of residual solvent. Unlike extractions with conventional organic solvents, this new method requires neither distillation nor the use of volatile, flammable or chlorinated organic solvents.

Asymmetric hydrogenation of α,β-unsaturated carboxylic acids in supercritical carbon dioxide

Hydrogenation of tiglic acid in supercritical CO2 catalyzed by a chiral H8-BINAP-Ru(II) complex proceeds cleanly with cis stereochemistry to afford 2-methylbutanoic acid in up to 89% ee and over 99% yield.