Reaction, greenness environmental concern

Industry, in fact, has a major interest in these diesters as building blocks for nylon 6,6 and nylon 7,7 in the production of polyesters and polyamides. However, their present synthesis raises an environmental concern. For instance, the oxidation of cyclohexanone by nitric acid (for the preparation of adipic acid), accounts for more than 10% of the total yearly release of N2O, which is among the main gases responsible for the greenhouse effect. The reaction of Scheme 4.14 represents an eco-friendly alternative synthesis of a,(i)-diesters which uses green reagents and, relevantly, has a 100% atom economy. The overall process is mechanistically described as a retro-Claisen condensation. 

Friedel-Crafts (FC) alkylation, acylation, and sulfonylation reactions are important C-C or C-S bond forming reactions in organic chemistry [60-64], Since the seminal works of Charles Friedel and James Mason Crafts published in 1877 in which they report the use of A1C13 for alkylation reactions [65], the search for more active catalysts, especially for acylation reactions, continues. Due to increasing environmental concerns, the need for green catalysts and processes for the FC reaction has gained significant importance. Bi(III) salts have shown to be efficient and recoverable catalysts with applicability in this area [13]. 

Acyclic and cyclic ketones may be oxidized to esters or lactones, respectively, by a variety of oxidants including peracids or peroxides associated with suitable catalysts. This reaction is known as Baeyer-Villiger (BV) oxidation and it was originally applied to the oxidation of menthone and tetrahydrocarvone with monopersulfuric acid (equation 69). With the increase of environmental concern, much research has focused on the development of catalytic BV processes based on green and cheap oxidants like hydrogen peroxide and relatively non-toxic metals (Re, Pt, Ti). ... 

Organic synthesis relies largely on solution phase chemistry. Owing to the safety problems inherent in the use of volatile organic materials, as well as environmental concerns, it has become important to reduce dependency on organic solvents in favor of a reaction medium that can be considered to be green and where the following... 

A great deal of the environmental concern associated with chemical manufacture comes from not merely the chemicals that are made or the chemicals from which they are made, but from all of the substances associated with their manufacture. In the manufacture, processing, formulation and use of chemical products, there are a variety of associated substances that contribute to the environmental loading from chemical manufacture. The most visible of these associated substances are the solvents used in reaction media, separations and formulations. Many solvents, especially the widely used volatile organic solvents, have come under increased scrutiny and regulatory restriction based on concerns for their toxicity and their contributions to air and water pollution. It is for these economic and environmental reasons that much of the research and development in Green Chemistry reaction conditions is focussed on alternative solvents. 

Whatever the final target, a successful synthesis is characterized by brevity and high overall yield. The starting materials should be readily available, preferably commercially, and inexpensive. The principles of green chemistry need to be addressed (see Real Life 3-1), minimizing safety and environmental concerns, such as potentially dangerous reaction conditions and ingredients and the production of toxic waste. 

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]. 

It is clear from the above that there is a long way before photochemistry acquires an important role in industrial chemistry. However, there are in fact some peculiar characteristics in these reactions that makes them indeed green , or at least suitable candidates for green procedures. Therefore, it may be expected that as far as concern about the environmental aspects of chemical synthesis grows, application of photochemistry will take a more important role. 

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