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Chemistry

The 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 biological and chemical route to degrade polystyrene in an economical and environmentally safe way as this is the only down side polystyrene poses. We, the organic chemists are responsible for coming up with syntheses to breakdown or convert polystyrene into useful products. We are working alongside with the biochemists and the iGEM team to find a convenient and useful way to break down polystyrene.

Research into present chemical techniques did not show anything useful 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 have devised synthetic chemical routes to breakdown and/or the conversion of polystyrene. The iGEM team have found excellent support from a plastic company Styrofoam. This organisation converts plastics into lactic acids and then into polylactic acids which in turns are easily biodegradable. It was thought that turning polystyrene into lactic acid and then into polylactic acid may be possible and this was our starting point for our research.

Mechanism Insight

Mechanism 1: This was our initial idea. We thought that decomposing would be this easy. Then we realised our mistake! We were undergoing the wrong route. (Decompose styrene, not polystyrene!)

Mechanism 2: Once the organic chemists checked this with each other, they realised how can this be possible as a heterogeneous catalyst Pd would not synthesis this reaction.

Mechanism 3: Out of the other two mechanisms, this is far the most realistic. Despite this, there is an urgency to find an enzyme that can regenerate a reactive oxygen species. This must then react further to oxidise the benzyl carbon as well as degrade the remaining aliphatic chain. A good example is peroxidise that may help.

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 or stablised by a transition metal.

This route, though may work for styrene, will however not work for the breakdown of the polymer itself as this shows the conversion of the monomer unit into lactic acid.

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 which can be easily broken down.

The mechanism above, in combination with mechanism 5 below, may work to break down polystyrene into smaller parts.

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.

This is a viable route. Conversion of the product to a smaller unit of benzoyl peroxide would have pharmaceutical uses. To add to the mechanism above, the use of a cytochrome P450 or a peroxidase may be able to generate a reactive oxygen species that will oxidise the benzyl carbon. Degradation of the aliphatic hydrocarbon chain may be possible via mechanism 5.

Mechanism 5

The fifth mechanism shows how we might be able to degrade polystyrene down if we were to pursue an inorganic method. This is an interesting concept as most chemical research today is influenced by inorganic chemistry. We believe this route below could serve as a template for future efforts to breakdown polystyrene. Key reagents are notably missing as this we have left this open to further research.

Hazards and Safety

To conclude, this research has shown us organic chemists that though there may not be a definite chemical route, we have pitched in our ideas and we are confident that in the near future that there will definetly be a cheap way to break down polystyrene that is both economical and safe. We set out to breakdown polystyrene completely and we feel that we have learnt much about the application of chemistry in synthesis.

References

Vincent N. Cavaliere, Marco G. Crestani, Balazs Pinter, Maren Pink, Chun-Hsing Chen, Mu-Hyun Baik, and Daniel J. Mindiola. Room Temperature Dehydrogenation of Ethane to Ethylene Journal of the American Chemical Society

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