Green chemistry/production

Costs of alternatives may initiaiiy be higherthan continued use of a chemical of very high concern, but increased demand for the alternative will drive costs down, particularly as competition increases among producers to supply the new market demand. Chemical producers will in turn find an expanded market for Green Chemistry products. 

By taking these steps towards a green chemistry production model, Argonne and the licensing manufacturers have also dramatically reduced their facilities vulnerability to accidents or deliberate acts against them. 

ISD requires the chemist and engineer to go back to the drawing board and think about alternative feedstocks, solvents, and synthetic pathways when developing a new process. It is about redesigning products. As an example, paint used to be made from oil-based materials, and its application created volatile organic compounds in the ambient air. Today, all paints are water-based (latex). They work the same as previous paints, but they are inherently less hazardous. Latex paint is a green chemistry product. 

A solventless synthesis of pyrazoles, a green chemistry approach, has been described where an equimolar amount of the diketone and the hydrazine are mixed in a mortar with a drop of sulfuric acid and ground up. After an appropriate length of time ( 1 h) the product is purified to provide clean products. Even acyl pyrazoles 42 were obtained under the solvent-less reaction conditions in good yields. 

A green chemistry variation makes use of solventless conditions to minimize the waste stream from reactions of this type. To a mortar are added aldehyde 67, ketone 68 and solid sodium hydroxide. The mixture is ground and within 5 minutes aldol product 69 is produced. Addition of the second ketone and further grinding affords the 1,5-diketone 70, which can be isolated and cyclized to pyridine 71 with ammonium acetate. The authors report that this method can substantially reduce the solid waste (by over 29 times) and is about 600% more cost effective than previously published procedures. 

Green chemistry (Chapter 11 Focus On) The design and implementation of chemical products and processes that reduce waste and minimize or eliminate the generation of hazardous substances. 

L9.96 Waste reduction is an important goal of the green chemistry movement. In many chemical syntheses in industry, not all the atoms required for the reaction appear in the product. Some end up in by-products and are wasted. Atom economy is the use of as few atoms as possible to reach an end product and is calculated as a percentage, using atom economy = (mass of desired product obtained)/(nrass of all reactants consumed) X 100%. 

Green chemistry also calls for design for biodegradable end products, principally, by employing chemicals from renewable sources, and dictates the use of real-time, on-line analysis for better process control. 

While this works progresses, a part of our attention should be focused on potential industrial applications. In this regard, the path is set, because important principles of green chemistry are inherent to cellulose derivatives, namely the raw material is renewable, and the products are biodegradable. With regard to these principles, consider the following ... 

We have reported a simple, green, bench top, economical and environmentally benign room temperature synthesis of MSe (M=Cd or Zn) nanoparticles using starch, PVA and PVP as passivating agents. The whole process is a redox reaction with selenium acting as the oxidant and MSe as the reduction product. An entire "green" chemistry was explored in this synthetic procedure and it is reproducible. The optical spectroscopy showed that all the particles are blue shifted from the bulk band gap clearly due to quantum confinement. Starch capped CdSe nanoparticles showed the presence of monodispersed spherical... 

One of the fundamental and most important principles of Green Chemistry is that of atom economy. This essentially is a measure of how many atoms of reactants end up in the final product and how many end up in byproducts or waste. The percentage atom economy can be calculated as 100 times the relative molecular mass (RMM) of all atoms used to make wanted product divided by the RMM of all reactants. Box 1.2. The real benefit of atom economy is that it can be calculated at the reaction planning stage from a balanced reaction equation. Taking the following theoretical reaction ... 

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. 

Oxidation reactions are frequently used in the production of both bulk and fine chemicals. Review the main differences in the processes usually used in each sector, discussing these differences in terms of the 12 principles of green chemistry. 

Maury, J. et ah. Microbial isoprenoid production example of green chemistry through metabolic engineering, in Biotechnology for the Future, Springer-Verlag, Berlin,... 

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