Reagents, environmentally benign

The standard Hantzsch procedure does not involve the use of additive or reagent, but to improve reaction time and yield, the use of a large variety of catalysts has been developed, which makes possible to operate at room temperature in some cases. In the last few years, particular efforts have been devoted to the utilization of low cost, nontoxic, environmentally benign and reusable catalysts [22, 29 0]. 

Water is cheap, relatively abundant in many part of the world, safe, and, when pure, environmentally benign [40]. It is also true that some reactions show unusual selectivity and/or rate enhancements when run in, or more accurately, on water [41]. However, a closer examination of many reactions in water reveals that in fact one or more liquid reagents have been used in large excess, so they are in fact biphasic reactions. There is also a misguided perception that water, after use as a reaction medium, can be poured down the drain [42]. On an industrial scale, there can be a considerable cost and environmental burden associated with remediation of waste water streams contaminated with solvents and organic and metal residues-see Chapters 2 and 3. 

A new reagent, AMiydroxyphthalimide combined with Co(acac)n (n = 2,3), transforms alkylbenzenes to ketones, whereas methylbenzenes give the corresponding carboxylic acids.1121 Phthalimide N-oxyl was found to be the key intermediate. Novel oxoperoxo Mo(VI) complexes mediate the cost-effective and environmentally benign oxidation of methylbenzenes to carboxylic acids.1384 Similar green oxidation of p-xylene to terephthalic acid was reported by using a Ru-substituted heteropolyanion.1385... 

Interestingly, the same reaction can be performed with the polymer-supported reagent 18 in water, because the reagent 18 was found to be considerably stable in this solvent. A mechanistic rationale of the catalytic activation of iodosobenzene 5 by potassium bromide is given in Scheme 14. This reaction provides a very facile and environmentally benign method for the alcohol oxidation. 

X-ray fluorescence,1516 surface acoustic waves (SAW) for determining volatile organic compounds (VOCs),17 18 and immunoassays19-21 are examples of direct analytical techniques (in which a sample preparation step is unnecessary) that are environmentally friendly. In addition, there are environmentally benign procedures from which reagents and solvents have been eliminated or their quantities minimized (calculated per analytical cycle) ... 

In addition, other techniques, in which quantities of reagents and solvents per one analytical cycle are limited, are part of environmentally benign procedures. These include... 

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