Reaction, greenness solvents

Keywords Low melting mixtures, sugars, multi component reactions, green solvent, 1,4 dihydropyridines. 

S., Kula, M.R., and Kragl, U. (2003) Enzymatic Condensation Reactions in ionic liquids, in Ionic Liquids as Green Solvents, ACS Symposium Series, Vol. 856 (eds R.D. Rogers and... 

The same authors have also reported the application of green solvents in additions of terminal alkynes to aldehydes in the presence of Zn(OTf)2 and l,8-diazabicyclo[5,4,0]-7-undecene (DBU, Scheme 109).287 The reactions proceeded very slowly, but afforded desirable alcohols 195 in moderate to good yields. 

Overall, green solvents appear to be a valuable alternative to conventional solvents in addition reactions of diverse organozinc reagents to aldehydes. 

In recent years, supercritical fluids such as scC02 were considered to be modern green solvents they were non-toxic, readily available, inexpensive, and environmentally benign. They are studied as a reaction medium for catalytic applications because of their interest in product separation and catalyst recovery, and... 

A typical atom transfer sensitization process is shown in Figure 3.7 the alkylation of an unsaturated acid via a radical produced from an alcohol by hydrogen abstraction (in a green solvent, water). This principle has been applied to a large series of radical alkylation reactions, where the radical precursor is an alcohol, an ether, or even an alkane. ... 

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. 

More recently, Shen et al. reported on a green and efficient three-component one-pot synthesis of 2-aryl-pyridines with the same starting materials as the Hanztsch reaction, under solvent-, catalyst-, and heat-free conditions. This methodology does... 

We begin with a brief summary of some of the review articles that have been written on the subject of ionic liquids. Wilkeswrote a short history of ionic liquids describing the chronological development of ionic liquids with an emphasis on listing the names and pictures of those involved in the research. Holbrey and Seddon and Earle and Seddon reviewed the literature of ionic liquids composed entirely of ions which were mainly of interest to electrochemists. Recently, however, it has become apparent that, inter alia, their lack of measurable vapor pressure characterizes them as green solvents, and that a wide range of chemical reactions (reviewed here) can be performed in them. Wassercheid and Keim reviewed the literature of ionic liquids, not only the synthesis and physical properties of the ILs, but also their use as... 

The use of various solvents as reaction media for diverse reactions is summarized in Reichardt (1988), and Marcus (1998). The following is a partial list of organic reactions requiring solvents. In chapters 5 through 7 we will look at green solvents and provide some examples of more environmentally benign alternatives to some of the more toxic solvents. 

The discussion of green solvents will include chemistry, ecology, and philosophy. The choice of solvents will include new criteria in addition to the traditional considerations of synthesis yield (if we are dealing with reactions), perfect product recovery (separations), or commercial usefulness. 

Examples of organic reactions in green solvents abound. One example is described in the oxidation of cyclohexenes with 30% hydrogen peroxide (Sato et al., 1998). Cur-rendy, the industrial production of adipic acid uses nitric acid oxidation of cyclohexa-... 

Since the complications due to solvent structure have already been discussed, the remainder of this chapter is mainly devoted to a discussion of the complications introduced into the theory of reaction rates when the collision of solvent molecules does not lead to a complete loss of memory of the molecules about their former velocity. Nevertheless, while such effects are undoubtedly important over some time scale, the differences noted by Kapral and co-workers [37, 285, 286] between the rate kernel for reaction estimated from the diffusion and reaction Green s function and their extended analysis were rather small over times of 10 ps or more (see Chap. 8, Sect. 3.3 and Fig. 40). At this stage, it is a moot point whether the correlation of solvent velocity before collision with that after collision has a significant and experimentally measurable effect on the rate of reaction. The time scale of the loss of velocity correlation is typically less than 1 ps, while even rapid recombination of radicals formed in close proximity to each other occurs over times of 10 ps or more (see Chap. 6, Sect. 3.3). 

Diaz-Ortiz, A., De la Hoz, A. andLanga, F., Microwave irradiation in solvent-free conditions an eco-friendly methodology to prepare indazoles, pyrazolopyridines and bipyrazoles by cycloaddition reactions, Green Chem., 2000, 2, 165-172. 

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