Chemical of the Week 9 – Toluene Diisocyanate

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The news reports last week of the major chemical explosions in Tianjin, a major port in China, were very worrying. Current reports put the death toll at over 100 with massive devastation of the port area. It is thought the first explosion had a power equivalent to three tonnes of TNT detonating, whilst the second was the equivalent of 21 tonnes, the power was so great some thought it was a nuclear explosion. One of the chemicals being stored at the facility where the explosions occurred was toluene diisocyanate (IUPAC name is 2,4-diisocyanato-1-methyl-benzene). It is primarily used as a chemical intermediate in the production of polyurethane products, of which 11.7 million tonnes are produced annually. The global market for toluene diisocyanate was $ 6195.6 million in 2014. The worry is that toluene diisocyanate is extremely toxic from both acute and chronic exposures. Acute exposure to high levels of the chemical results in severe irritation of the skin and eyes and affects the respiratory, gastrointestinal, and central nervous systems. This explosion highlights the safety issues that surround the transport and storage of chemicals involved in major processes.

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Polyurethane is an interesting polymer as it can be tailored to be either flexible or rigid and is found in everything from car seats and mattresses to insulation foam. It is a condensation polymer made using the following difunctional monomers :- a diol and a diisocyanate. They react to produce a urethane linkage and any functionality found between the functional groups can dictate what type of properties the polyurethane has (for example hydroxyl groups can lead to cross linking of the chains which increases the rigidity of the polymer).

https://pubs.acs.org/cen/whatstuff/84/8402foam.html

Condensation polymers are on the A2 syllabus and I know that pupils do find the application questions based on these challenging (as soon as I saw this reaction all I could think was, ‘there’s a neat little application question’). Not only is the production of the polymer interesting but the production of toluene diisocyanate is very relevant as well. The starting material is methylbenzene which is nitrated, reduced (two reactions that are met at detail at A2) and then reacted with phosgene.

This blast has shone a light onto the importance of safety within the Chinese chemical industry. Questions have been asked as to why more than one dangerous chemical was been stored at the same site and the hope is that lessons will be learned from this tragic event to prevent it ever happening again. So as we lie on our memory foam mattress tonight it’s important to remember that the great benefits we gain from the chemical industry must be aligned with a responsible and safe approach to chemical production where safety comes before profit.

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