Green solvents definition

Ionic liquids, having per definition a melting point below 100 °C, and especially room temperature ionic liquids (RTIL) have attracted much interest in recent years as novel solvents for reactions and electrochemical processes [164], Some of these liquids are considered to be green solvents [165]. The scope of ionic liquids based on various combinations of cations and anions has dramatically increased, and continuously new salts [166-168] and solvent mixtures [169] are discovered. The most commonly used liquids are based on imidazolium cations like l-butyl-3-methylimidazolium [bmim] with an appropriate counter anion like hexafluorophos-phate [PFg]. Salts with the latter anion are moisture stable and are sometimes called third generation ionic liquids. 

Since chlorophyll can be removed readily from chloroplasts by mild solvent extraction, it might appear that it is simply dissolved in the lipid portion of the membranes. However, from measurements of dichroism (Gregory,226 p. Ill) it was concluded that the chlorophyll molecules within the membranes have a definite orientation with respect to the planes of the thylakoids and are probably bound to fixed structures. The absorption spectrum of chlorophyll in leaves has bands that are shifted to the red by up to 900 cm-1 from the position of chlorophyll a in acetone. Most green plants contain at least four major chlorophyll bands at 662, 670, 677, and 683 nm as well as other minor bands264 (Fig. 23-21). This fact suggested that... 

Figure 1.2 Definitions of cavities based on interlocking spheres. In black (dashed) the spheres centred on atoms A and B, in red the SAS, in cyan the shared parts of VWS and SES. In green the concave part of SES. In blue the crevice part of VWS. In black (dotted) some positions of tangent solvent probes (see Colour Plate section).

A reasonable working definition of green chemistry can be formulated as follows [10] Green chemistry efficiently utilizes (preferably renewable) raw materials, eliminates waste and avoids the use of toxic and/or hazardous reagents and solvents in the manufacture and application of chemical products. 

This metric is an attempt to define yield in terms of the mass of the product that is made from non-toxic materials. This was one of the first times that reagent and reactant toxicity were included as an important part of determining what is considered to be green, and it is something that was absent from traditional yield measures. Hudlicky et al. did make an attempt to define benign (i.e. those byproducts, reagents, or solvents that have no known environmental risk associated with them, for example, water, low-concentration saline, dilute ethanol, autoclaved cell mass, etc. ), but the explanation suffers from a lack of definitional clarity. 

Supercritical carbon dioxide extraction of natural products from solid plant matrices is currently an established application, with over one hundred industrial facilities of various sizes operating throughout the world. Several books have been published describing this process in detail - see, for example Brunner [1]. The main green credential of these processes is the replacement of volatile organic solvents. Their implementation resulted, however, from definite technological advantages. 

A note on nomenclature. The above definitions use the nomenclature of the lUPAC Green Book (1), in which a solute is called 8 and a solvent A In compilations and evaluations, the first-named component (component 1) is the solute, and the second (component 2 for a two-component system) is the solvent. The reader should bear these distinctions in nomenclature in mind when comparing nomenclature and theoretical equations given in this Introduction with equations and nomenclature used on the evaluation and compilation sheets. 

---