Benign solvent

In conclusion, the above summary of oxidation methods shows that there is still room for further improvements in the field of selective olefin epoxidation. The development of active and selective catalysts capable of oxidizing a broad range of olefin substrates with aqueous hydrogen peroxide as terminal oxidant in inexpensive and environmentally benign solvents remains a continuing challenge. 

Use of less hazardous solvents - Since the reaction is two phase, simple benign solvents can often be used since PTC avoids the need to find a solvent that will dissolve all reactants, e.g. dipolar aprotic solvents such as dimethyl formamide. In some cases an organic solvent may not be required at all, the substrate forming the second phase. 

As a cautionary note PTC should not be considered a panacea for all of the problems associated with green chemistry. Two-phase reactions involving water are often difficult to deal with industrially, particularly if the water is contaminated with trace amounts of hazardous organic substances. In some cases it may be more practical, cost effective and environmentally prudent to avoid production of aqueous waste in favour of a recyclable less benign solvent. 

Increasingly it is being shown that the greatest opportunities for step-change developments come from collaborative projects, for example from using a new catalyst and a new benign solvent in a new intensified reactor. 

Opt for solventless reactions, recycle solvents, or use benign solvents (e.g., water, ionic liquids, supercritical media). 

An excluded-volume random-coil conformation will be achieved when the solvent quality exceeds the theta point, the temperature or denatu-rant concentration at which the solvent-monomer interactions exactly balance the monomer—monomer interactions that cause the polymer to collapse into a globule under more benign solvent conditions. A number of lines of small-angle scattering—based evidence are consistent with the suggestion that typical chemical or thermal denaturation conditions are good solvents (i.e., are beyond the theta point) and thus that chemically or thermally unfolded proteins adopt a near random-coil conformation. 

The research has inspired related investigation into the coupling reaction between aromatic aldehydes and benzyl bromide or chloride in water. The yields are slightly higher than the results for allylation despite the fact that aqueous benzylation is intrinsically more difficult than allylation. It is also found that the coupling reaction is chemoselective for aromatic aldehydes over aliphatic aldehydes, and also for aromatic aldehydes over aromatic ketones.98 Aqueous Grignard chemistry is attractive for its use of an environmentally benign solvent, and has been the subject of several... 

Because of the physical properties and chemical behavior concerning corrosiveness and toxicity, it may be used in existing high-pressure plants and facilities at fine chemical industry production sites. This allows a fast and easy change to an environmentally benign solvent. 

Besides the advantages of process design, special emphasis is also put on water, which is an environmentally benign solvent for industrial purposes. 

In principle, solvent extraction is an environmentally friendly process with no air or water pollution, provided the plant flows are properly designed. It could, therefore, replace many of the present polluting processes. A particular problem, however, is the solvent extraction effluents, which may contain biochemically active substances posing new hazards to the environment. These can be handled by various solid sorbents, which then can be incinerated, but the advantage of the solvent extraction process may be lost. There is, therefore, a demand for biodegradable and environmentally benign solvent phases. In the future, additional attention is required to this field. 

The development of alternative reaction conditions, including the use of more benign solvents and greater attention to the kinds of wastes released to the environment... 

The Lewis acid-catalyzed condensation of a,/3-unsaturated ketones 277 with amides 278 furnished 2,4,6-trisubsti-tuted-6//-l,3-oxazines 279. An environmentally benign solvent-free version of this process, based on the application of montmorillonite K-10 clay and a brief microwave irradiation, provided oxazines 278 in higher yields than in the conventional solution-phase method (Equation 26) <2004BCJ2265>. 

The substitution of more benign solvents in many formulations will have global ramifications. For example, water-reducible coatings are products where the solvent system used to disperse and suspend solids is primarily water. The remainder of the solvent system may contain liquids that are classified as flammable or combustible liquids. Inherent limitations in these systems relate to product viscosity, accuracy in predicting overall fire hazard, abihty to assess physical changes of state when a product is tested, and test method rehabihty and ease of use (Scheffey and Tabar, 1996). 

Organic Reactions in Micro-Organized Media—Why and How Water-Promoted Organic Reactions The design of green oxidants Water as a solvent for chemical reactions Water as a benign solvent for chemical syntheses... 

The implementation of the Montreal Protocol, the Clean Air Act, and the Pollution Prevention Act of 1990 has resulted in increased awareness of organic solvent use in chemical processing. The advances made in the search to find green replacements for traditional solvents have been tremendous. With reference to solvent alternatives for cleaning, coatings, and chemical reaction and separation processes, the development of solvent databases and computational methods that aid in the selection and/or design of feasible or optimal environmentally benign solvent alternatives for specific applications have been discussed (Sherman et al., 1998). 

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