Pseudotsuga Menziesii

by | Mar 22, 2018 | Pseudotsuga Menziesii

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Toluene diisocyanate (TDI) is an organic compound with the formula CH3C6H3(NCO)2. Two of the six possible isomers are commercially important: 2,4-TDI (CAS: 584-84-9) and 2,6-TDI (CAS: 91-08-7). 2,4-TDI is produced in the pure state, but TDI is often marketed as 80/20 and 65/35 mixtures of the 2,4 and 2,6 isomers respectively. It is produced on a large scale, accounting for 34.1% of the global isocyanate market in 2000, second only to MDI.[3] Approximately 1.4 billion kilograms were produced in 2000.[4] All isomers of TDI are colorless, although commercial samples can appear yellow.

Synthesis

2,4-TDI is prepared in three steps from toluene via dinitrotoluene and 2,4-diaminotoluene (TDA). Finally, the TDA is subjected to phosgenation, i.e., treatment with phosgene to form TDI. This final step produces HCl as a byproduct and is a major source of industrial hydrochloric acid.[4]

Distillation of the raw TDI mixture produces an 80:20 mixture of 2,4-TDI and 2,6-TDI, known as TDI (80/20). Differentiation or separation of the TDI (80/20) can be used to produce pure 2,4-TDI and a 65:35 mixture of 2,4-TDI and 2,6-TDI, known as TDI (65/35).

Applications

The isocyanate functional groups in TDI react with hydroxyl groups to form carbamate (urethane) links. The two isocyanate groups in TDI react at different rates: The 4-position is approximately four times more reactive than the 2-position. 2,6-TDI is a symmetrical molecule and thus has two isocyanate groups of similar reactivity, similar to the 2-position on 2,4-TDI. However, since both isocyanate groups are attached to the same aromatic ring, reaction of one isocyanate group will cause a change in the reactivity of the second isocyanate group.[3] It is also sometimes used in rocket propellants.[5]

It is used in the production of rigid polyurethane foams with a high temperature stability.

Hazards

The LD50 for TDI is 5800 mg/kg for oral contact and LC50 of 610 mg/m3 for the vapour. Despite the indicated low toxicity, TDI is classified as "very toxic" by the European Community.[4]

In the United States, the Occupational Safety and Health Administration has set a permissible exposure limit with a ceiling at 0.02 ppm (0.14 mg/m3), while the National Institute for Occupational Safety and Health has not established a recommended exposure limit, due to the classification of toluene diisocyanate as a possible occupational carcinogen.[6] This chemical was one of many that were stored by the company whose chemical warehouse stationed in Tianjin, China was the site of massive explosions on August 12, 2015.[7]

Information is available on handling, personal protective equipment, exposure monitoring, transport, storage, sampling and analysis of TDI, dealing with accidents, and health and environmental themes.[8] All major producers of TDI are members of the International Isocyanate Institute,[citation needed] whose aim is the promotion of the safe handling of TDI in the workplace, community, and environment.

High-level exposure can result in reactive airways dysfunction syndrome.[citation needed]

See also

References

  1. ^ a b c d e f NIOSH Pocket Guide to Chemical Hazards. "#0621". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ "Toluene-2,4-diisocyanate". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  3. ^ a b Randall, D.; Lee, S. (2003). The Polyurethanes Book. New York: Wiley. ISBN 978-0-470-85041-1.
  4. ^ a b c Six, C.; Richter, F. "Isocyanates, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a14_611. ISBN 978-3527306732.{{cite encyclopedia}}: CS1 maint: multiple names: authors list (link)
  5. ^ "Ababil-100/Al Fat'h". GlobalSecurity.org. Archived from the original on 15 April 2019.
  6. ^ National Institute for Occupational Safety and Health (May 1994). "Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)". Centers for Disease Control and Prevention.
  7. ^ Ripley, Will; Jiang, Steven; Mullen, Jethro (13 August 2023). "Tianjin explosion: Dozens dead, areas of Chinese port city devastated". CNN. Retrieved 1 October 2023.
  8. ^ Allport, D. C.; Gilbert, D. S.; Outterside, S. M., eds. (2003). MDI and TDI: Safety, Health and the Environment: A Source Book and Practical Guide. Wiley. ISBN 978-0-471-95812-3.

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