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Team:Leicester/Chemistry
From 2012.igem.org
Chemistry
Breakdown of polystyrene is the quest many scientists have faced in recent years. It is now more than ever before, where there is an urgency to find a biologically and chemical route to degrade polystyrene in an economical and environmental safe way as this is the only down side polystyrene poses. The organic chemists are responsible and are working alongside with the biochemist and the iGEM team to find a convenient and useful way to break down polystyrene.
Research into present techniques did not show anything so this surely suggests that we were entering new territory, which was something that was exciting to know. Equipped with knowledge from our two years of studying chemistry and our problem solving skills learnt we devised a synthetic chemical route to breakdown polystyrene. The iGEM team had found excellent support from a plastic company Styrofoam. This organisation converted plastics into lactic acids and then into polylactic acid which is easily biodegradable. It was then that a member of the iGEM team Christopher thought it could be possible that polystyrene could be converted to lactic acid and then polylactic acid. This was our starting point.
The first method we discovered was a simple robust chemical route. This route however has its downsides too because the elimination of groups can cause problems to the environment. Our main concern was that of benzene since it is a carcinogen.
The method follows that on styrene we add a blocking group to saturate its double bond such as water, and then add hydrogen with Fe catalyst to reduce benzene to cyclohexane thereby eliminating the formation of a carcinogenic benzene, and then just break that cyclohexane into a chain whereby one carbon will be a tertiary carbon atom depending on how its broken. Water can then be added since benzene only undergoes electrophillic attacks therefore water will attack the alkenes thereby we can hydrogenate benzene and so forth. Cyanide could be used in a safe manner when it is in solution already and so any direct contact can be avoided. The aim is to find a new method to incorporate a cleaner and less dangerous method. Seen below, you can see that cyanide is not used. Instead a methyl cation is used which would seem a better alternative. Theoretically this reaction may work but in practice it may be more difficult to achieve.
N:B Possible side reactions will be taken into account as will a written safety and hazard sheet for the chemicals used, reactants and products upon confirmation of all mechanisms.
Mechanism 1
The first mechanism shows the conversion of styrene (monomer of polystyrene) to lactic acid which can be converted to polylactic acid and further degraded in the environment easily. This mechanism involves the use of harsh and dangerous chemicals. The first step shows that benzyne is formed which is a carcinogen. It can be reduced to benzene and disposed of easily.
Mechanism 2
The second mechanism shows that as polystyrene is heated up, the intermolecular forces weaken and with the added fact that benzene can undergo electrophilic aromatic substitution; it is treated with nitric acid to afford a new compound that contains a new NO2 side group. The final product of this reaction is a benzene ring with an alcohol side group. We are still researching into practical uses and possible further reactions.
Mechanism 3
This is an alternative mechanism to that proposed in mechanism 2. Instead of placing an OH side group, a bromine group is added. Ultimately the formation of an acid anhydride chain is formed which is degradable in the environment. The hydrocarbon chain would need to be both weakened and then broken so as to afford pure anhydride monomers. Current research is onto this idea.
Mechanism 4
This final mechanism draws on the peroxyl product formation. Organic peroxyls are used in many chemical reactions in industry so it may be possible that this organic peroxyl will have a use in the near future. Research is being done into this route.
