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La Chimica Verde/Sostenibile
Green/Sustainable Chemistry

An Overview

The term green chemistry is defined as: The invention, design and application of chemical products and processes to reduce or to eliminate the use and generation of hazardous substances.

While this short definition appears straightforward, it marks a significant departure from the manner in which environmental issues have been considered or ignored in the upfront design of the molecules and molecular transformations that are at the heart of the chemical enterprise.

Looking at the definition of green chemistry, the first thing one sees is the concept of invention and design. By requiring that the impacts of chemical products and chemical processes are included as design criteria, the definition of green chemistry inextricably links hazard considerations to performance criteria.

Another aspect of the definition of green chemistry is found in the phrase “use and generation”. Rather than focusing only on those undesirable substances that might be inadvertently produced in a process, green chemistry also includes all substances that are part of the process.

Therefore, green chemistry is a tool not only for minimizing the negative impact of those procedures aimed at optimizing efficiency, although clearly both impact minimization and process optimization are legitimate and complementary objectives of the subject.
Green chemistry, however, also recognizes that there are significant consequences to the use of hazardous substances, ranging from regulatory, handling and transport, and liability issues, to name a few. To limit the definition to deal with waste only, would be to address only part of the problem.

Green chemistry is applicable to all aspects of the product life cycle as well.
Finally, the definition of green chemistry includes the term “hazardous”. It is important to note that green chemistry is a way of dealing with risk reduction and pollution prevention by addressing the intrinsic hazards of the substances rather than those circumstances and conditions of their use that might increase their risk.
Why is it important for green chemistry to adopt a hazard-based approach?
To understand this, we have to revisit the concept of risk. Risk, in its most fundamental terms, is the product of hazard and exposure:

Risk = Hazard X Exposure

A substance manifesting some quantifiable hazard, together with a quantifiable exposure to that hazard, will allow us to calculate the risk associated with that substance. Virtually all common approaches to risk reduction focus on reducing exposure to hazardous substances. Regulations often require increases in control technologies and treatment technology, and in personal protective equipment such as respirators, gloves, etc., in order to reduce risk by restricting exposure.

By achieving risk reduction through hazard reduction, green chemistry addresses concerns about the cost and potential for failure of exposure controls. Regardless of the type of exposure control, ranging from engineering controls through personal protective gear, there is always going to be an upfront capital cost; to what degree this cost can be recouped will be situation-specific, but it will always be there. In contrast, there is no additional upfront capital cost necessarily associated with green chemistry.

While some green chemistry options may require capital investment, others may actually lower total cost of operations from the outset. This result is frequently the case in some of the easiest ways of implementing green chemistry technologies. Exposure controls, because they rely on either equipment or human activity to accomplish their goals, are capable of failing.

Respirators can rupture, air scrubbers can break down, and so forth. When failure occurs, risk is maximized because the resultant exposure is to a constant hazard. Green chemistry, in contrast, does not rely on equipment, human activity, or circumstances of use but, instead, changes the intrinsic hazard properties of the chemical products and transformations. Consequently, green chemistry is not as vulnerable to failure, as are the traditional approaches to hazard control.

The definition of green chemistry also illustrates another important point about the use of the term “hazard”. This term is not restricted to physical hazards such as explosiveness, flammability, and corrosibility, but certainly also includes acute and chronic toxicity, carcinogenicity, and ecological toxicity.

Furthermore, for the purposes of this definition, hazards must include global threats such as global warming, stratospheric ozone depletion, resource depletion and bioaccumulation, and persistent chemicals. To include this broad perspective is both philosophically and pragmatically consistent.

It would certainly be unreasonable to address only some subset of hazards while ignoring or not addressing others. But more importantly, intrinsically hazardous properties constitute those issues that can be addressed through the proper design or redesign of chemistry and chemicals.

Thematic areas of Green Chemistry
As defined by OCSE in 1999

Use of alternative feedstocks
The use of feedstocks that are both renewable rather than depleting and less toxic to human health and the environment.

Use of innocuous reagents
The use of reagents that are inherently less hazardous and are catalytic whenever feasible.

Employing natural processes
Use of biosynthesis, biocatalysis, and biotech-based chemical transformations for efficiency and selectivity.

Use of alternative solvents
The design and utilization of solvents that have reduced potential for detriment to the environment and serve as alternatives to currently used volatile organic solvents, chlorinated solvents, and solvents that damage the natural environment.

Design of safer chemicals
Use of molecular structure design and consideration of the principles of toxicity and mechanism of action to minimize the intrinsic toxicity of the product while maintaining its efficacy of function.

Developing alternative reaction conditions
The design of reaction conditions that increase the selectivity of the product and allow for dematerialization of the product separation process.

Minimizing energy consumption
The design of chemical transformations that reduce the required energy input in terms of both mechanical and thermal inputs and the associated environmental impacts of excessive energy usage

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