Green-chemistry

Green polymer synthesis using starting materials derived from renewable resources (rather than petroleum) is discussed in Section 30.8. 

The Amberlyst A-26 resin consists of a complex hydrocarbon network with cationic ammonium ion appendages that serve as counterions to the anionic chromium oxidant, HCr04 . Heating the insoluble polymeric reagent with an alcohol results in oxidation to a carbonyl compound, with formation of an insoluble Cr by-product. Not only can the metal by-product be removed by filtration without added solvent, it can also be regenerated and reused in a subsequent reaction. 

With Amberlyst A-26 resin-HCr04, 1 ° alcohols are oxidized to aldehydes and 2° alcohols are oxidized to ketones. 

Many other green approaches to oxidation that avoid the generation of metal by-products entirely are also under active investigation. 

ProblGin 12.26 What carbonyl compound is formed when each alcohol is treated with Amberlyst A-26 resin-HCr04  

Green Separation Processes. Edited by C. A. M. Afonso and J. G. Crespo 

Copyright 2005 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

The costs of waste to a chemical manufacturing company are high and diverse (Fig. 1.1-1) and, for the foreseeable future, they will get worse. 

These costs and other pressures are now evident throughout the supply chain for a chemical product - from the increasing costs of raw materials, as petroleum becomes more scarce and carbon taxes penalize their use, to a growing awareness amongst end-users of the risks that chemicals are often associated with, and the need to disassociate themselves from any chemical in their supply chain that is recognized as being hazardous (e.g. phthalates, endocrine disrupters, polybromina-ted compounds, heavy metals, etc. Fig. 1.1-2) 

At about the same time as the establishment of the GCN, the Royal Society of Chemistry (RSC) launched the journal Green Chemistry . The intenhon for this journal was always to keep its readers aware of major events, initiatives, and edu- 

Green chemistry is an initiative that promotes the design and application of chemical products and processes that are compatible with human health and that preserve the environment. Green chemistry rests on a set of 12 principles  

Prevention It is better to prevent waste than to clean it up after it has been created. 

Atom Economy Methods to make chemical compounds should be designed to maximize the incorporation of all starting atoms into the final product. 

Less Hazardous Chemical Syntheses Wherever practical, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment. 

Design of Safer Chemicals Chemical products should be designed to minimze 

Green chemistry is also known as environmentally benign chemistry, or sustainable chemistry. Perhaps the most widely accepted definition of green chemistry is the one offered by chemists Paul Anastas and John Warner, who defined green chemistry as the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. 

Anastas and Warner formulated the twelve principles of green chemistry in 1998. These serve as guidelines for chemists seeking to lower the ecological footprint of the chemicals they produce and the processes by which such chemicals are made. 

Starting in 1996, outstanding examples of green chemistry have been recognized in the United States each year by the Presidential Green Chemistry Challenge (PGCC) awards. These are the only awards in chemistry that are bestowed at the presidential level. 

The EPA and the American Chemical Society (ACS) have played a major role in promoting research and development, as well as education, in green chemistry. In 2000 the GCI became a partner of the ACS. Chemical societies around the globe have recognized the importance of green chemistry and promote it through journals, conferences, educational activities, and the formation of GCI chapters. There are GCI chapter affiliates all over the world. 

The following real-world examples of green chemistry represent the accomplishments of several winners of the PGCC awards. They illustrate how green chemistry impacts a wide array of fields including pharmaceuticals, pesticides, polymers, and many others. 

Green chemistry embodies two main aspects. First, it emphasizes the efficient utilization of raw or natural materials and the eoneomitant 

The principles and concepts of green chemistry are the subjects of several monographs (18-22). Recent progress in enzyme-driven 

The different catalytic processes for the conversion of terpenes, triglycerides and carbohydrates to valuable chemicals and polymers have been reviewed (25). 

A basic task of green chemistry is to design chemical products and processes that use and produce less hazardous materials. The term hazardous covers several aspects including toxicity, flammability, explosion potential and environmental persistence (26). 

The s mthesis of maleic anhydride illuminates a possibility of multiple pathways. Maleic anhydride can be synthesized both from benzene and from butene by oxidation. In the first route, a lot of carbon dioxide is formed as an undesirable byproduct. Thus, the first route is addressed as atom uneconomic. In Table 1.1, some uneconomic and economic reaction types in organic chemistry are opposed. 

Rearrangement reaction Addition reaction Diels-Alder reaction Claisen reaction Substitution reaction Elimination reaction Wittig reaction Grignard reaction 

Of prime relevance for us, organometallic catalysis plays a key role in realizing many green aspirations, such as atom economy (Eq. 12.34), which measures the efficiency of incorporation of reactant atoms into products in the theoretical chemical equation. For example, the Monsanto process (Section 12.3) has 100% atom economy (MeOH -I- CO MeCOOH) but requires catalysis to activate the reactants. With their high selectivity, catalysts often avoid the need for separations and for protection/deprotection steps. 

Milstein modified this pathway with a catalyst that dehydrogenates the hemiaminal intermediate shown in Fig. 12.8 (right) to give the 

FIGURE 12.8 Two types of alcohol activation catalysis alcohol amination (left) and alcohol amidation right). 

Catalysts such as [Cp IrCl2]2 can help recovery of materials that would otherwise become waste. For example, after the desired enantiomer is removed from the mixture in a resolution step or enzymatically, the undesired isomer left behind can be catalytically racemized back to a 50-50 mixture of enantiomers via the sequence of Eq. 12.35. Dehydrogenation destroys the initial chirality so the hydrogenation step produces a 50-50 racemic mixture, from which more of the desired isomer can be extracted as before. 

MCRs that adhere to the standards set by green chemistry will be discussed. 

During the 1990s there was a revolutionary movement to a new type of chemistry collectively determined green chemistry , meaning environmentally friendly chemistry. On its Web site, the U.S. Environmental Protection Agency lists 12 Principles of Green Chemistry  

Use renewable feedstocks (often from agricultural products) 

Use catalysis, not stoichiometric reagents (catalysts are used in small amounts and re-used many times stoichiometric reagents are used once) 

Avoid chemical derivatives (blocking or protecting groups, once removed, may generate waste) 

Maximize atom economy (design processes so as not to waste atoms) 

Once yield was the primary factor that determined the success of a reaction, but increasingly, concerns about sustainability, environmental impact and related legislation, as well as toxicity, are incorporated into the design of an experiment. The Environmental Protection Agency (EPA) has defined twelve principles of Green Chemistry, which call for safer reactants and procedures, less chemical and energy waste, avoiding the use of environmentally persistent materials and unnecessary reactions, and the use of renewable feedstocks [75]. 

Several methods are aimed at quantifying the greenness of an experiment [76]. The Environmental or E-factor is one of the simplest. It calculates the ratio of total waste to total product (Eq. 9.25) [77]. While the type of waste, and not only the amount, is important, this simple calculation allows an estimation of environmental impact. Atom economy is calculated by dividing the molecular weight of the desired product by the total of the molecular weights of all the products and by-products of the reaction weighting as appropriate for a balanced equation (Eq. 9.26, where n is the molar coefficient from the balanced equation) [78]. This is another estimate of environmental impact. 

Let s hope disasters like this are never repeated. 

Maximize atom economy. Synthetic methods should maximize the incorporation of all materials used in a process into the final product so that waste is minimized. 

Use less hazardous processes. Synthetic methods should use reactants and generate wastes with minimal toxicity to health and the environment. 

Atom economy - the incorporation of as much of the starting materials as possible into the product - is a useful concept, but it should not overshadow the whole. 

No reaction can be green in its own right until all the aspects of the process in which it is involved have been analysed, which includes complete analysis of the green-ness of the origin of starting materials and reagents. 

Many aspects of green chemistry have been in use for years, because efficient chemical processes with minimum waste are also economically preferable, and in industry are also confined by legal controls on polluting practices, at least in some countries. 

Since many oxidation methods use toxic reagents (such as OSO4 and O3) and corrosive acids (such as H2SO4), or they generate carcinogenic by-products (such as Cr ), alternative reactions have been developed. One method uses a polymer-supported reagent—HCr04 -Amberlyst 

A-26 resin—that avoids the use of strong acid, and forms a Cr by-product that can be easily removed fr iitpi3i (J] ct ipo iotEnhanc er 

Safer Solvents and Auxiliaries The use of auxiliary substances (e.g., solvents, separation agents,) should be made unnecessary wherever possible and innocuous when used. 

Design for Energy Efficiency Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure. 

Use of Renewable Feedstocks A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable. 

Reduce Derivatives Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste. 

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The terms green chemistry and environmentally benign synthesis have been coined to refer to procedures explicitly designed to minimize the for mation of byproducts that present disposal problems Both the National Science Foundation and the Envi ronmental Protection Agency have allocated a por tion of their grant budgets to encourage efforts m this vein... 

S. C. DeVito, ia S. C. DeVito and R. L. Garrett, eds.. Designing Safer Chemicals Green Chemistry for Pollution Prevention, American Chemical Society Symposium Series 640, American Chemical Society, Washington, D.C., pp. 194—223. 

MLC enables to analyse drugs and active phamiaceutical substances without using special column and lai ge quantity of organic solvents. So, from the point of view of pharmaceutical analysis ecology and green chemistry conception, assay with MLC using will be better than conventional reversed-phase chromatography. 

Chase, V. (1995). Green chemistry The middle way to a cleaner environment. R D Magazine, 25-26. 

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. 

Ionic liquids have several important features that make them attractive for use as solvents, particularly in green chemistry ... 

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. 

Green Chemistry (Chapler 11), X-Ray Crystallography (Chapter 221, and Green Chemistry IJ Ionic Liquids (Chapter 24). 

NEW Chemistry Connections are multipart exercises that integrate many different concepts from several chapters. Many of these exercises incorporate illustrations of green chemistry. 

NEW Green chemistry promotes environmentally sound chemistry. Passages in the text created in consultation with Michael Cann and new end-of-chapter exercises are accompanied by a (IT). Topics include ionic liquids (Chapter 5), supercritical C02 (Chapter 8), yttrium in paint (Chapter 12), chelates as a substitute for chlorine bleach (Chapter 16), and transesterification (Chapter 19). 

Some contributed in substantial ways. Roy Tasker, University of Western Sydney, contributed to the Web site for this book, designed related animations, and selected the icons for the animation media links. Michael Cann, University of Scranton, opened our eyes to the world of green chemistry in a way that has greatly enriched this book... 

A newly emerging concern of chemistry is sustainable development, the economical utilization and renewal of resources coupled with hazardous waste reduction and concern for the environment. This sensitive approach to the environment and our planetary inheritance is known colloquially as green chemistry. Where we s think it appropriate to draw your attention to this important development, we dis- I ( play the small icon shown here in the margin. 

Green chemistry methods, which use nontoxic j[il 1 chemicals, are replacing elemental chlorine for the... 

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%. 

The Challenge Ahead Meeting the Requirements of Green Chemistry. .. 141... 

Green chemistry, principles of Green chemistry, application to cellulose... 

Another favorable aspect of these polymers is their conformity with the principles of green chemistry. The latter sets guidehnes for the chemical industry in order to secure sustainable development, while increasing process economy [3,4]. Briefly, green chemistry, and the related green engineering [5] call for an increase in, and/or upgrading of ... 

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. 

The green chemistry approach, and the surge of biopolymers as candidates for substituting synthetic ones in several applications require detailed understanding of the following aspects, at the molecular level ... 

The discussion is organized in the following order First the advantages of HRC scheme, relative to the industrial (i.e., heterogenous) process are briefly commented on second, the relevance of celMose activation and the physical state of its solution to optimization of esterification are discussed. Finally, the use of recently introduced solvent systems and synthetic schemes, designed in order to obtain new, potentially useful cellulose esters with controlled, reproducible properties is reviewed. A comment on the conformity of these methods with the concepts of green chemistry is also included. 

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