Solvent effects

Abstract: INTRODUCTION SOLUTE-SOLVENT INTERACTIONS Solutions Intermolecular Forces Solvation Preferential Solvation Micellar Solvation (Solubilization) Ionization and Dissociation CLASSIFICATION OF SOLVENTS Classification of Solvents According to Chemical Constitution Classification of Solvents Using Physical Constants Classification of Solvents in Terms of Acid-Base Behaviour Classification of Solvents in Terms of Specific Solute/Solvent Interactions Classification of Solvents Using Multivariate Statistical Methods SOLVENT EFFECTS ON THE POSITION OF HOMOGENEOUS CHEMICAL EQUILIBRIA General Remarks Solvent Effects on Acid/Base Equilibria Solvent Effects on Tautomeric Equilibria Solvent Effects on other Equilibria SOLVENT EFFECTS ON THE RATES OF HOMOGENEOUS CHEMICAL REACTIONS General Remarks Gas-Phase Reactivities Qualitative Theory of Solvent Effects on Reaction Rates Quantitative Theories of Solvent Effects on Reaction Rates Specific Solvation Effects on Reaction Rates SOLVENT EFFECTS ON THE ABSORPTION SPECTRA OF ORGANIC COMPOUNDS General Remarks Solvent Effects on UV/Vis Spectra Solvent Effects on Infrared Spectra Solvent Effects on Electron Spin Resonance Spectra Solvent Effects on Nuclear Magnetic Resonance Spectra EMPIRICAL PARAMETERS OF SOLVENT POLARITY Linear Gibbs Energy Relationships Empirical Parameters of Solvent Polarity from Equilibrium Measurements Empirical Parameters of Solvent Polarity from Kinetic Measurements Empirical Parameters of Solvent Polarity from Spectroscopic Measurements Empirical Parameters of Solvent Polarity from Other Measurements Interrelation and Application of Solvent Polarity Parameters Multiparameter Approaches SOLVENTS AND GREEN CHEMISTRY Green Chemistry Reduction of Solvent Use Green Solvent Selection Non-Traditional Solvents Outlook APPENDIX: PROPERTIES, PURIFICATION, AND USE OF ORGANIC SOLVENTS Physical Properties Purification of Organic Solvents Spectroscopic Solvents Solvents as Reaction Media Solvents for Recrystallization Solvents for Extraction and Partitioning (Distribution) Solvents for Adsorption Chromatography Solvents for Acid/Base Titrations in Non-Aqueous Media Solvents for Electrochemistry Toxicity of Organic Solvents

Abstract: sorption results9 revealed that the iron surface was mostly covered by promoter oxides of AI, Ca, and K. Postreaction XPS results also revealed a C( Is) XPS peak of weak to moderate intensity centered at 284.1-283.7 eV. This binding energy approaches those (ca. 283.5 eV) reported for iron cat bide^.^^*'^ More convincing evidence for carbide formation was obtained from TPHT results collected after reaction studies like those displayed in Figure 1 in which methane was the only product. After reaction at temperatures below 340 OC, only small amounts of reactive carbon could be distinguished with maximum methane desorption rates near 300 OC. However, for higher reaction temperatures, large amounts of methane were produced with a maximum rate just above 400 OC. Since XPS results revealed only small amounts of carbonaceous residue on top of the catalyst surface, this reactive carbon must be associated with carbiding of the catalyst. Consequently, it appears that the active carbon incorporation catalyst is carbided iron. This conclusion is well supported by bulk carbon to iron stoichiometries of 0.1-0.25 estimated from the TPHT peak areas which were adequate to represent 40-60'36 conversion to bulk carbides such as Fe,C or FeSC2. Moreover, preliminary results from studies using bona fide iron carbides have shown similar catalytic b e h a ~ i o r . ~

Abstract: The technological utility of enzymes can be enhanced greatly by using them in organic solvents rather than their natural aqueous reaction media. Studies over the past 15 years have revealed not only that this change in solvent is feasible, but also that in such seemingly hostile environments enzymes can catalyse reactions impossible in water, become more stable, and exhibit new behaviour such as 'molecular memory'. Of particular importance has been the discovery that enzymatic selectivity, including substrate, stereo-, regio- and chemoselectivity, can be markedly affected, and sometimes even inverted, by the solvent. Enzyme-catalysed reactions in organic solvents, and even in supercritical fluids and the gas phase, have found numerous potential applications, some of which are already commercialized.