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copper catalyst. Non-toxic ascorbic acid is used as a reducing agent to regenerate the active catalyst (124). . Tributyltin hydride, a known neurotoxin, can be replaced by a hypophosphite salt in reductive termination of free-radical reactions (125). Organo- tin antifoulants (e.g. tributyltin oxide) used on ships are bioaccumulative and have reproductive toxicity; an isothiazolone alternative was developed having low bioconcentration properties and excellent bio- degradability (126). . The use of structure-activity relationships has revealed that the acute toxicity of nitrile compounds is related to the ease of radical formation at the a-carbon. This elucidated a simple design guideline for synthetic chemists to prepare less toxic nitriles (127). The rapidly growing field of nanotechnology has seen theinventionofmyriadnovelmaterials,butverylittle evaluation of environmental and human health risks. Nanoparticles based on arsenic, cadmium, and other toxic materials present clear concerns, but other hazards have not been fully explored. Some nano- particles are able to cross the bloodbrain barrier; others may pass through cell membranes, increasing the risk of mutagenicity and carcinogenicity. Activity at the nanoparticle surface, such as generation of damaging radicals, adsorption and transport of substances, and interactions with biochemicals are largely unknown (128). A recent review has focused on green nanosynthesis, the wet chemistry that has been invented to produce and manipulate nanoma- terials. The review proposes guidelines for design and evaluation of novel materials according to green chemistry principles. Progress in development of green synthetic methods has been summarized, such as reduced dependence on solvents and reagents (reducing agents for metals, stabilizers, and phase- transfer reagents), use of more efficient purification techniques, and use of microreactors for better control of reaction conditions and facilitation of scale-up. Biology also offers greener routes to nano- particles, through use of biomolecules as templates for growth of inorganic structures, or production of nanoparticles by whole organisms (129). Designing molecules for biodegradability reduces the chance that a molecule can exert a toxic effect on a life form. A recent review of small molecule biodegradability presents some generalizations that can be made from examining structure-degradability relationship data, and provides commentary on specific cases with relevance to industrial chemistry. A summary of modeling software and database information is also provided (130). Additional exam- ples of design for degradation have been reported for textile dyeing auxiliaries (131). With the exception of natural polymers, and those derived from renewable resources, most high-molecular weight chemicals are extremely resistant to microbial attack. One strategy for imparting degradability to traditional polymers is chemical modification with degradable functional groups; a poly(styrene-co-maleic anhydride) was derivatized with monosaccharides and disaccharides, leading to a significant increase in biodegradation rate (132). Biodegradable polymers will be further discussed under the heading of ‘renewable resources’ below. Renewable resources One of the major goals of green chemistry is to derive chemical feedstocks from renewable resources instead of petroleum. Renewable biomass is produced by natureonthescaleofabout180billionmetrictons/ year, of which only about 4% is currently utilized by humans. Most (about 75%) is in the form of carbohydrates, about 20% is lignin, and the remain- der includes fats, proteins, and terpenes. A recent review summarizes strategies for converting biomass into useful materials, including chemistry of glucose fermentation products, chemical transformations of mono- and disaccharides, and reactions of oils, fatty acids, and terpenes (133). Currently, the major non- food uses of carbohydrates are production of ethanol, furfural, d-sorbitol sweetener, lactic acid, surfactants, and pharmaceuticals (e.g. penicillin). However, routes are available for converting low-value carbohydrates into a much wider range of industrially useful products (134). Biomass has been utilized in many inventive ways by green chemists: . Amino acids and vegetable oils can be used to prepare antimicrobial surfactants having low toxi- city and excellent biodegradability. In many cases the synthesis can be achieved through biocatalysis (135). . Simple amino acids, by adsorbing onto metal sur- faces, behave as natural corrosion inhibitors, slow- ing damage to steel or aluminum in concentrated HCl solution (136,137). The amino acids can replace conventional inhibitors such as nitrites, benzoates, phosphonates, and quaternary ammonium salts, which are often biohazardous and difficult to dispose of safely (138). . All-natural UV protectant can be prepared by enzymatically incorporating ferulic acid (derived from plants) into soybean oil. By encapsulation in starch, aqueous dispersions of the material can be prepared without surfactants, and the UV-blocking properties were enhanced (139). . While terpenes comprise only a small percentage of biomass, they can be used to prepare thermoplastics Green chemistry: the emergence of a transformative framework 17PDF Image | Green chemistry: the emergence of a transformative framework
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