Neoteric

Ionic liquids are now widely recognized as an important component of green chemistry. This chapter, after exploring the field of green chemistry, explains some of the unique features of these neoteric solvents, and suggests that they should be part of the arsenal of solvents used by all synthetic chemists. 

Neoteric is defined in the Oxford English Dictionary as meaning recent, new, modern. 

Seddon, K. R., Room-temperature ionic liquids—neoteric solvents for clean catalysis, Kinet. Catal., 1996, 37(5), 693-697 Seddon, K. R. Room-temperature ionic liquids— neoteric solvents for clean catalysis, Kinet. Katal, 1996, 37(5), 743-748. 

J. S. Wilkes, A short history of ionic liquids—from molten salts to neoteric solvents , Green Chemistry, 2002, 4, 73-80. 

K. R. Seddon, in Room-Temperature Ionic Liquids Neoteric Solvents for Clean Catalysis , www http //www.ch.qub.ac.uk/resources/ionic/review/review.html (22.05.1997). 

Because ILs are neoteric (i.e., new) solvents that have the potential to be used on a large scale in the future, it is important that the impact on the environment of each IL should be thoroughly investigated before it is brought to market. It is to be hoped that in common with other chemicals, ILs would be properly disposed of, preferably by treatment/recovery, and if this is not possible, by landfill or incineration. Although landfill has traditionally provided a cheap means of waste disposal, it is becoming increasingly impractical and expensive to implement now that suitable landfill sites... 

Neoteric Solvents as the Basis of Alternative Approaches to the Separation of Actinides and Fission Products... 

The subject of alternative reaction media (neoteric solvents) also touches on another issue which is very relevant in the context of this book recovery and reuse of the catalyst. This is desirable from both an environmental and an economic viewpoint (many of the catalysts used in fine chemicals manufacture contain highly expensive noble metals and/or (chiral) ligands. 

Molten salts at room temperature, so-called ionic liquids [1, 2], attracting the attention of many researchers because of their excellent properties, such as high ion content, liquid-state over a wide temperature range, low viscosity, nonvolatility, nonflammability, and high ionic conductivity. The current literature on these unique salts can be divided into two areas of research neoteric solvents as environmentally benign reaction media [3-7], and electrolyte solutions for electrochemical applications, for example, in the lithium-ion battery [8-12], fuel cell [13-15], solar cell [16-18], and capacitor [19-21],... 

Several thermodynamic and kinetic behaviors of enzyme-catalyzed reactions performed in ILs, with respect to enzymatic reactions carried out in conventional solvents, could lead to an improvement in the process performance [34—37]. ILs showed an over-stabilization effect on biocatalysts [38] on the basis of the double role played by these neoteric solvents ILs could provide an adequate microenvironment for the catalytic action of the enzyme (mass transfer phenomena and active catalytic conformation) and if they act as a solvent, ILs may be regarded as liquid immobilization supports, since multipoint enzyme-1L interactions (hydrogen. Van der Waals, ionic, etc.) may occur, resulting in a flexible supramolecular not able to maintain the active protein conformation [39]. Their polar and non-coordinating properties hold considerable potential for enantioselective reactions since profound effects on reactivities and selectivities are expected [40]. In recent years attention has been focused on the appUcation of ILs as reaction media for enantioselective processes [41—43]. 

The outlook of syntheses, based on using SC-CO2 or appropriate IL/SC-CO2 biphasic system for developing integral green chemical processes due to the physical and chemical characterishcs of these neoteric solvents and the enhanced enzyme catalytic properties seems promising. 

This ion interaction retention model of IPC emphasized the role played by the electrical double layer in enhancing analyte retention even if retention modeling was only qualitatively attempted. It was soon realized that the analyte transfer through an electrified interface could not be properly described without dealing with electrochemical potentials. An important drawback shared by all stoichiometric models was neglecting the establishment of the stationary phase electrostatic potential. It is important to note that not even the most recent stoichiometric comprehensive models for both classical [17] and neoteric [18] IPRs can give a true description of the retention mechanism because stoichiometric constants are not actually constant in the presence of a stationary phase-bulk eluent electrified interface [19,20], These observations led to the development of non-stoichiometric models of IPC. Since stoichiometric models are not well founded in physical chemistry, in the interest of brevity they will not be described in more depth. 

The model was recently tested to determine whether it was able to model analyte retention in the presence of novel and unusual IPRs (see Chapter 7) such as chaotro-pic salts and ionic liquids. Chaotropes that break the water structure around them and lipophilic ions (classical IPRs and also ionic liquids) that produce cages around their alkyl chains, thereby disturbing the ordinary water structure, are both inclined to hydrophobic ion-pairing since both are scarcely hydrated. This explains the success of the theory, that is predictive in its own right, when neoteric IPRs are used [64]. Recently a stoichiometric model (vide supra) was put forward to describe retention of analytes in the presence of chaotropic IPRs in eluents [18] but its description of the system is not adequate [64]. 

The model is inclusive the retention equation quantitatively predicts the behavior of charged, multiply charged, neutral, and zwitterionic solutes in the presence of both classical and neoteric IPRs, and can also quantitatively consider the influences of organic modifier concentration and ionic strength. 

Even if anionic chaotropes are the most popular neoteric IPRs, polarizable cations such as sulfonium and phosphonium reagents showed single selectivity toward polarizable anions their behavior was rationalized on the basis of their chaotropicity. Probe anion retention generally increases in the order of tributylsulfonium < tetrabutylammonium < tetrabutylphosphonium. Interestingly, retention was found to be influenced by the kosmotropic/chaotropic character of both the IPR and the probe anion [93] and this confirms the peculiarities of hydrophobic ion-pairing. Quaternary phosphonium salts provided increased selectivity compared to ammonium in the IPC of heavy metal complexes of unithiol [112]. 

For the use of sc-fluids as reaction media in synthesis, see reviews [211-217, 224, 225, 228-230] and Section 5.5.13, which describes applications of some neoteric solvents such as ionic liquids, perfluorohydrocarbons, and sc-fluids in organic synthesis and catalysis. 

Reactions in Biphasic Solvent Systems and in Neoteric Solvents... 

In addition to fluorous solvents and ionie liquids, supercritical fluids sc-fluids, scf s), sueh as supercritical carbon dioxide (se-C02), constitute a third class of neoteric solvents that can be used as reaction media. Although sc-fluids have been known for a long time and have been advantageously used as eluants in extraction and chromatography processes (see Sections A.6 and A.7 in the Appendix), their application as reaction media for chemical processes has become more popular only during the last decade. Some of their physical properties and the supercritical conditions necessary for their existence have already been described in Section 3.2 (see Figure 3-2 and Table 3-4) see also references [209, 211-220, 224-230] to Chapter 3 for reviews on sc-fluids and their applications (particularly for SC-CO2 and SC-H2O). 

However, a more qualitative LCA approach has been used by Clark and Tavener to assess the neoteric solvents described in this book (Figure 1.4). The solvent must first be manufactured, usually from petroleum. This is relatively straightforward for simple and aromatic hydrocarbons that are obtained... 

Jessop, P.G. Stanley, R.R. Brown, R.A. Eckert, C.A. Liotta, C.L. Ngo, T.T. Pollet, P. Neoteric solvents for asymmetric hydrogenation supercritical fluids, ionic liquids, and expanded ionic liquids. Green Chem. 2003, 5 (2), 123-128. 

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