Toluene diisocyanate

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Toluene-2,4-diisocyanate

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]

Contents

 [hide] 

• 1 Synthesis
• 2 Applications
• 3 Hazards
• 4 See also
• 5 References
• 6 External links

Synthesis[edit]

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 crude 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[edit]

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 used in the production of flexible polyurethane foams

Hazards[edit]

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.^[5]

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.^[6] 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.

See also[edit]

• Methylene diphenyl diisocyanate
• Hexamethylene diisocyanate
• Isophorone diisocyanate

References[edit]

1. ^ Jump up to: ^{a b c d e f} "NIOSH Pocket Guide to Chemical Hazards #0621". National Institute for Occupational Safety and Health (NIOSH).
2. Jump up ^ "Toluene-2,4-diisocyanate". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
3. ^ Jump up to: ^{a b} Randall, D.; Lee, S. (2003). The Polyurethanes Book. New York: Wiley. ISBN 978-0-470-85041-1.
4. ^ Jump up to: ^{a b c} Six, C.; Richter, F. (2005), "Isocyanates, Organic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a14_611
5. Jump up ^ 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.
6. Jump up ^ 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.

External links[edit]

• International Chemical Safety Card 0339
• IARC Monograph: "Toluene Diisocyanates"
• NIOSH Pocket Guide to Chemical Hazards
• NIOSH Safety and Health Topic: Isocyanates, from the website of the National Institute for Occupational Safety and Health (NIOSH)
• International Isocyanate Institute http://www.diisocyanates.org

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