Title: Oxidation of diphenylmethanol to form benzophenone
Author: Emma Halloran
Student ID: G00325352
1) To perform an oxidation of diphenylmethanol to form a high yield of benzophenone product.
2) Design a green chemistry experiment.
3) Take into count health and safety considerations in designing this experiment.
4) Design a method that can be preformed within two hours as it is a first-year lab as part of the chemistry syllabus.
6) Use a combination of analytical techniques such as TLC, IR spectroscopy, NMR and GC to determine the yield and purity of product formed.
(i) Green Chemistry
One of the main aims of this experiment is not only to synthesis benzophenone by oxidation of diphenylmethanol but to incorporate green chemistry throughout this entire experiment. Green chemistry was quiet a foreign concept until 1970 when the Environmental Protection Agency was set up. Green chemistry is an effective way to deal with one of the most immanent problems in the world pollution. Pollution is the source of many problems in the world currently, such as the destruction of eco systems and threats to wildlife. Over the past 35 years in the US some of the major environmental legislation such as the Clean Water Act, the Clean Air Act, the Resource recovery and Conservation Act and the superfund in the US have centred around pollution and its effects. Green chemistry was developed as an initiative of pollution prevention. The term green chemistry is also known as clean chemistry and refers to the design of chemicals and processes that minimize the use and production of toxic substances and aims towards a more environmentally friendly approach.
By mid-20th century the long term negative effect of toxic chemicals could no longer be ignored. There were holes in the earth’s ozone, increasing global warming. Acid rain deteriorated forest health. Some chemicals in use were linked to human cancer and other human and environmental and health outcomes. Green chemistry became more recognised following Rachel Carson’s publication in 1962 and the founding of the European Protection Agency (EPA) in the 1970s. Rachel Carson was an environmental activist and following her publication of “Silent Spring” in 1962 it raised many questions about the use of pesticides especially Dichlorodiphenyltrichloroethane (DDT) pesticide used to control malaria by killing the malaria mosquitoes, which eventually led it to being banned for agricultural use in the US in 1972. DDT was seen as the ideal solution at the time to malaria, it was also inexpensive to make, non-toxic to humans and worked persistently eliminating need for retreatment. During the 1960s it became increasing noticed as it was accumulating widely in the environment. It started accumulating in the fatty tissues of animals as it was insoluble in water, mainly in birds and the effects could be seen in the offspring eggs as they were extremely thin. DTT was banned and replaced in the 1970s by a less environmentally persistent costly insecticide organo-phosphates. The EPA often references its existence as the shadow of Rachel Carson’s who sparked the growth of green chemistry practices. The EPA was designed to protect human and environmental health through setting and enforcing environmental law and regulations. By the 1980s the EPA established the Office of Pollution and Prevention and Toxics, by 1990 the pollution and prevention act was enforced, it was designed to enforce eco-friendly strategies and provide grants to states in an effort to reduce source waste. President Bill Clinton in his time in office devised the Presidential Green Chemical Challenge Awards which recognised and awarded outstanding chemical technologies which incorporates the principals of Green Chemistry. Experts claim that the primary step towards green chemistry practise is assessing material that is unsustainable and working alongside manufacturers to replace and develop more safe and sustainable product.
The challenge on the pharmaceutical industry in the 21st century is to continue to provide the benefits continually achieved from pharmaceuticals in an economically viable manner but without adverse environmental effects. The twelve principals of green chemistry show how this can be sustained and achieved. Atom economy is one of the most important of these twelve principals, it is a measurement of how many atoms end up in the final product and how many end up in by-products or waste. A major benefit of atom economy is that it can be calculated prior to the reaction taking place from a balanced equation. Most multinational and global pharmaceutical companies aim to achieve the maximum amount of product they can from the raw material and the success of this can be calculated by a simple percentage yield calculation however from a green chemistry point of view this is not the entire picture. The yield itself is calculated by considering only one final product, atom economy comes into play here as a reaction may have a high percentage yield but also make a significant amount of waste product, this kind of reaction would be seen to have a low atom economy. Therefore both yield and atom economy must be taken into account when designing any chemical reaction.
Waste production is a huge part of green chemistry. Manufacturers are also very much aware of the cost of treatments and disposing of chemical substances. The more toxic the substance the more costly it is to dispose of. “In an ideal chemical factory there is, strictly speaking, no waste but only products. The better a real factory makes use of its waste, the closer it gets to its ideal, the bigger is the profit” A. W. von Hofmann (First President of The Royal College of Chemistry, London) 1848. Legislation plays an important role in waste minimisation. Certain noxious substances are illegal to dispose of for obvious reasons. Legislation set by the Environmental Protection Agency encourages cleaner technology and greener chemistry and set a national hazardous waste management plan for all companies to adhere to. Taxes and regulations mean companies worldwide are looking for greener methods. Unfortunately, no matter how much work is put into greener methodologies it is rare to convert one hundred percent of the raw material to one hundred percent pure product. A treatment plan for the waste has to be put in place. These methods of treatment can include chemical or physical treatment or through biodegradation pathways should be considered.
Green chemistry also focuses on technology that can significantly improve process and energy efficiency as well as reduce cost. Use of alternative forms of energy is not a novice approach although its use is becoming more enticing to manufacturing industries. Energy efficiency technology and improved process chemistry has resulted in energy consumption per tonne of product declining significantly over the past few years. Microwave heating chemistry has received phenomenal research over the past few years in the realisation in can provide a rapid method for screening reactions. With a heating rate of 10 degrees Celsius per second, reaction rates could be significantly shortened and more energy efficient. Solvent free reactions are especially suited to microwave heating. In the eradication of solvent, radiation is directly absorbed by the reactants hence giving enhanced energy efficiency. Microwave chemistry also shows high yields for oxidation reactions as well as significantly shortened reaction times. Unfortunately, chemistry related industrial applications of this technology are very limited.
Many environmental agencies state that the unsustainable uses of resources is a direct result of profit driven capitalist and competitive society that can been seen amongst manufacturing companies today. Even though chemical waste has been vastly reduced there is still more to be achieved within the pharmaceutical sector to achieve a greener society. Upcoming chemists need to be concerned about water, energy efficiency and safer design when entering into industry. When developing new synthetic procedures green chemistry will be at the forefront of the experiment and the chemist will automatically turn to benign solvent system and simplicity over complexity will become the trademark for a greener organic synthetic procedure. Regulation and the cost of implementing greener processes can act as a real deterrent for companies however more incentives are being given to companies to introduce greener processes. By following and implement the 12 principals of green chemistry chemists can contribute to sustainable development.
(ii) Oxidation reactions
The classical oxidation procedure for oxidising secondary alcohols to ketones usually involves the use of chromium (VI) reagent. However, chromium (VI) is a highly toxic reagent, over the years more alternative oxidising reagents have become more available for the oxidation of secondary alcohols to ketones. The conversion can be preformed with a wide variety of oxidising agents due to the stability of ketones. Some examples of these oxidation reactions include jones reagent, Collins reagent, Swern oxidation, Dess Martin oxidation, TEMPO. These are some of the numerous methods available however the development of new methods is considered a challenge.
Scientists have been keenly interested in selective and total oxidation processes for decades. The interest developed from an eagerness to develop a catalyst that was better than previous. Oxidation is an important and valued reaction and is used in many chemical processes. These are many examples of oxidation reactions that prove it is of huge commercial value. In previous years trial and error was the main technique used in designing oxidation catalysts however nowadays high throughput screening is used, this has opened up the possibility of a generic method being developed for the design of a catalyst in oxidation reactions. It is critical to be selective if one considers the amount of possible active elements for oxidation reactions. The nature of the active site of the catalyst should be considered when the process of catalyst optimisation is under way. Typically supported metal complexes or oxides have a range of active sites and this should be considered when decide on a catalyst. The most commonly used catalysts are based upon various metals such as Pd, Cu, Ru, and Co. Although some of these reported systems suffer from a high reagent load, difficult reaction conditions, high cost and toxic metal usage. Although iron shows some fundamental differences to these metals listed above as it is cheaper, chemoselective, and a greater catalyst. Its fundamental role in biological processes such as oxygen transportation and electron transfer make it a strong candidate in catalyst design. In 2002 the first iron(III) catalysed alcohol oxidation was reported. Hence iron complexes such as clafen (iron (III) nitrate supported on montmorillonite k-10) or zeofen (zeolite HZSM-S and ferric nitrate) have gained a huge amount of population in the oxidation of alcohols.
All this information must therefore be considered when designing an experiment for the oxidation of diphenylmethanol. Overall Green chemistry reduces pollution at its source by eliminating or lessening the effect of hazardous chemicals and should be the main priority when designing any experiment.
The oxidation of alcohols to the corresponding carbonyl compounds is one of the most important synthesis in organic chemistry. The development of new selective oxidative and green chemistry procedures is still considered a challenge nowadays.
Methodology / Materials and Methods:
? This chapter should consist of a description of the experimental or other methods employed (including relevant references)
? The rationale behind the choice of methodology used should be clearly stated, keeping in mind any required company confidentiality
? The make and model of items of equipment or instrumentation used should also be recorded
? Sufficient detail should be included to allow another researcher to replicate the work carried out
? This chapter should document the key sources of data and the methods used to obtain such data
Materials and Methods:
Place diphenylmethanol (1.00g) in a beaker and add iron(III) nitrate (2.4g). Heat this mixture on the hotplate in the fumehood (set to 150C) until the solids have completely melted. Next add 2 spatulas of silica gel and stir until the powder is obtained. Heat for a further 30 minutes stirring briefly every 5-10 minutes until a fine dark brown powder is obtained. Remove from the hotplate. Once cold add 15cm3 of ethyl acetate and a few drops of water. Filter this using a bucker funnel and wash the flask into the funnel with additional ethyl acetate. Immediately place the brown solid in waste containers found in the fumehood.
Dry the ethyl acetate solution by the addition of magnesium sulphate. Decant the ethyl acetate solution into a weighed evaporating dish making sure to avoid transferring any of the magnesium sulphate. Using the steambath evaporate off the solvent. The oil remaining is benzopheone. This oil should solidify when it is cooled on ice.
Transfer crude product to a small conical flask. Add 10cm3 of petroleum ether and heat on the steam bath until a solution is obtained. Add a spatula of activated carbon. Boil it on the steam bath for 30 seconds. Filter it through fluted filter paper using a preheated funnel into a beaker. Cool the solution on ice. White needles should appear in the beaker.
Oxidation of Alcohols to Ketones