What is green chemistry?
Green chemistry is the intention of chemical products and the developments that are used to decrease and remove the creation of hazardous substances. Green chemistry should be applied in every part of the chemical’s life cycle from its creation and manufacture to its disposal (US EPA, 2019). Green chemistry begins at molecular level and applies to all sectors of chemistry. Through advances in chemical creations and scientific solutions it helps to counteract the production of pollution. Green chemistry has many benefits not only for human health but for the environment in which we live and work in while also being better for the economy and businesses. It can reduce and remove hazards from existing creations and procedures.
Green chemistry differs from traditional chemistry which generally requires the cleaning up of pollution from waste water streams and other associated ecological sources.
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Why use green chemistry?
Using green chemistry requires the use of less synthetic steps, which as a result allows for a faster manufacturing process of products thus maximizing output of goods and reducing energy consumptions/costs. The use of green chemistry saves a significant amount of waste which leads to less hazardous material being produced which reduces the costs to the consumer due to significant reduction in corrective clean up required.
Fewer synthetic steps often allowing faster manufacturing of products, increasing plant capacity, and saving energy/water. Reduced waste, eliminating costly, hazardous waste disposal and end-of-the-pipe treatments. Green chemistry allows the replacement of a purchased feedstock by a waste product
How good is it?
Some benefits of green chemistry include (US EPA 2019 (2)): cleaner air-the reduction of hazardous chemicals into the atmosphere which will help protect our lungs. Cleaner water:- the reduction of hazardous chemicals into water supplies can ensure that we have cleaner drinking water.
It can also reduce the impact on the workers in chemical manufacturing meaning less toxic exposure leading to safer working environment, less personal protective equipment required and a reduction in the associated accidents. Safer products for the customer
Safer food, requires fewer toxic pesticides If there is a reduction in the amount of toxic chemicals released into the environment then vegetation and livestock will see a reduction in the affects of toxic chemicals
Green chemistry can also lead to a fall in the impending potential for global warming
Fewer chemicals used in the environment will see less interference of ecosystems
The use of the green chemistry will also reduce the amount that is sent to landfills on a regular basses.
Developments in newer environmentally friendly chemicals can aim to see an increase in yields from these chemicals while decreasing the amounts of raw materials needed to obtain the same product/reaction.
Reactions & structures
Reactions play a vital role in synthesis. The idea of Green chemistry commands the creation of new chemical reactivities and responses that benefit synthesis resources, efficient energy supplies and ecological safety.
Atom economy
Initially the acquiring the largest yield and product selectivity were the main influences of chemical synthesis. Scant thought was offered to using several reagents in stoichiometric (calculation of reactants and products in chemical reactions) amounts which was not frequently included into the target molecule which can produce considerable side products. In a calculated chemical reaction a cyclo addition combines all the atoms of the preliminary material into the finishing product.
This was thought of by (Trost 1991) when he posed a set of principles for assessing the effectiveness of certain chemical processes called atom economy. This was then integrated into the “Twelve Principles of Green Chemistry” and has changed the method in how many chemists outline and develop their synthesis. The atom economy pursues to increase the integration of the principle materials into the end product. As a result, if the greatest integration can’t be attained then the side products should be insignificant and ecologically friendly.
There is a difference in the way a reaction yield and the atom economy yield are determined.
The reaction yield only deals with the amount of the preferred product that is separated in relation to the theoretical amount of product. Atom economy accounts for all reagents and products both desired and undesired.
Examples include: substitutions and eliminations signify a significant amount of wasteful reactions in which inevitable wastes are produced.
Direct conversion of C-H Bonds
Direct transformation of C-H bond organic molecules into preferred structures without additional chemical alterations is an ideal reaction, (Naota. T 1998). In nature organic compounds can be oxidized by oxygen and oxygen suppliers in cells of fungi, bacteria, plants and in vertebrates. Hydroxylation of liner alkanes to create end stage alcohols can be used in the synthesis of fuels and chemicals.
The direct conversion of C–H bonds into C–C bonds is useful to produce more effective syntheses of products with a reduction in steps required to produce the product, (Reitleng.V 2002). Several methods to develop C-C bonds directly from two different C-H bonds with an oxidizing agent through a cross-dehydrogenative coupling catalysed by transition metals have been generated lately, Li. Z (2006). For instance: NH)-indoles and tetrahydroisoquinolines were converted directly into alkaloids by using such a coupling (Li.Z 2005).
Applications of green chemistry
An example of a procedure that has a high atom efficiency delivered by over the counter anti-inflammatory drugs is Ibuprofen. There are two ways to produce Ibuprofen intermediate, p – isobutylacetophenone. (Doble, M. and Kruthiventi, A. K. 2007)
The first was developed by Boots Pure Drug company in the 1960’s. This process required six steps with stoichiometric reagents which produced little atom efficiency (40%) along with inorganic salt forming. It also produced vast amounts of waste and by-products. A new process to create ibuprofen was created by Boots-Hoechst-Celanese (BHC) company in the 1980’s. This new more efficient method only required three catalytic steps, (Elango .V et al 1991). Both methods of creating Ibuprofen start with the same staring material. The staring step requires the use of anhydrous hydrogen fluoride as a catalyst and solvent in a friedel-crafts acylation. The hydrogen fluoride is recycled and so there is little waste generated. The next steps involve hydrogenation, carbonylation and are 100 % atom efficient. The BHC ibuprofen procedure was produced on a large scale in 1992. The BHC procedure was had high atom efficiency (77%) (Doble.M and Kruthiventi. AK, 2007). The recovery and recyclability of hydrogen fluoride was achieved with 99.9% efficiency. Due to their being no other solvents used the procedure offers simply product recovery and limited emissions. The time to create a batch and costs to make were greatly reduced in the BHC procedure compared to the Boots Pure Drug company method.
The Boots pure drug company used aluminium trichloride in a stoichiometric amount and was then transformed into aluminium trichloride hydrate waste. The BHC method was so successful that it won the Presidential Green Chemistry Challenge award in 1997 and the Kirpatrick chemical Engineering Achievement Award in 1993.
Sildenafil citrate
Pfizer has revamped the way in which it synthesis many of its drug based products in our to decrease the amount of harmful waste produced. Alterations were made in the synthetic pathway of sildenafil citrate which is an active ingredient in Viagra Dunn et al (2004). This led to a more effective process that reduced the need for extraction and solvent recovery steps. The E-factor (Sheldon, 1992) for this procedure was 6kg waste/kg product. “The E-factor measures the efficiency of a chemical process and is defined as kg waste products/kg product” ( Sheldon 1994)
This is a lower E-factor than most other pharmaceutical procedures ( 25-100). Chlorinated solvents were removed from the process. Solvent usage was greatly reduced over the years from 1816L/kg in 1990 (medicinal chemistry stage), reduced to 139L/kg with optimisation of the process to 31L/kg during commercial production in 1997 to 10L/kg with solvent recoveries in 1997. Pfizer replaced t-butanol/t-butoxide cyclization with an ethanol/ethoxide cyclization. Doing this and including the overall improvements resulted in a yield of 76-80%.
Other applications of green chemistry include
Energy: Green chemistry is important in creating new methods to produce renewable energy to replace fossil fuels like oil, coal and gas. Green chemistry uses solar cells to that collect energy from the sun and exists in forms such as solar panels. Green chemistry is used to discover the best biomass feedstock, conversion methods and production parameters. Once the solar energy is collected it must be stored until its needed. New ways to store this energy is being developed, Eg. Using catalysts to split H20 into hydrogen and oxygen which can be deposited separately. When needed the hydrogen and oxygen are combined to release energy. (Lancaster. M, 2010)
Wastewater treatment: Pollution in water comes from many sources. Chlorine is added to water to reduce waterborne illnesses and raw sewage. Chlorine is dangerous as it can react with other composites to form carcinogens. This is dangerous as both humans and animals then consume this. Through the use of green chemistry the amount of pollution can be decreased before it is discharged.(Matlack. A, 2010). Many current treatments produce increased volumes of toxic waste due to dangerous chemicals used to withdraw pollutants.
Agriculture: Pest control is the largest problem for agriculture now a days. Vast acres of managed, enriched fields of harvests are ideal supports for pests. With a vast food network leading to large communities of pests. The use of pesticides to fight against these pests increases risk to human health and the surrounding environment. Pesticides only last for so long and then pests begin to acclimatize to the pesticides making them less effective. Green chemistry is needed to reduce the impact that pesticides have on the environment. Dow AgroSciences’s creation of Spinosad a pesticide created by the decomposing of an organism is efficient in small doses and breaks down in the presence of sun (Renneboog, R, 2019). It also is kind for the surrounding ecosystem.
Importance of green chemistry
Green chemistry is important for now and future generations as it will have a significant impact on the lives we live. Its up to the scientific community to come together as one to help reduce the amount of chemical waste and toxic biproducts generated when producing pharmaceutical products. By using eco-friendly constituents the amount of dangerous contaminants can be lessened. Greener chemistry is helping analysts to improve their work with the use of greener chemicals to create a safer working environment. Green chemistry needs to be considered at all stages of a products life cycle. In doing so it can help to :- produce cleaner air, cleaner water, deliver safer products, healthier livestock and reduce global warming.
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