Toluene diisocyanate
Toluene diisocyanate
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Names |
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2,4-diisocyanato-1-methyl-benzene |
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Other names Tolylene diisocyanate Methyl phenylene diisocyanate |
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Identifiers |
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Jmol 3D model |
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CZ6300000 | |
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Properties |
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C9H6N2O2 | |
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174.2 g/mol | |
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Appearance |
Colorless to pale yellow liquid |
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sharp, pungent[1] | |
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1.214 g/cm3, liquid | |
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21.8 °C (71.2 °F; 294.9 K) | |
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251 °C (484 °F; 524 K) | |
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Reacts | |
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0.01 mmHg (25°C)[1] | |
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Hazards |
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See: data page | |
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EU classification (DSD) |
Very toxic (T+) |
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127 °C (261 °F; 400 K) | |
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0.9%-9.5%[1] | |
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Lethal dose or concentration (LD, LC): |
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LC50 (median concentration) |
14 ppm (rat, 4 hr) 13.9 ppm (guinea pig, 4 hr) 9.7 ppm (mouse, 4 hr) 11 ppm (rabbit, 4 hr)[2] |
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US health exposure limits (NIOSH): |
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PEL (Permissible) |
C 0.02 ppm (0.14 mg/m3)[1] |
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REL (Recommended) |
Ca[1] |
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IDLH (Immediate danger) |
Ca [2.5 ppm][1] |
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Related compounds |
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Related isocyanates |
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Related compounds |
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Refractive index (n), Dielectric constant (εr), etc. | |
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Thermodynamic data |
solid–liquid–gas |
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?) |
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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]
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]
References[edit]
- ^ Jump up to: a b c d e f "NIOSH Pocket Guide to Chemical Hazards #0621". National Institute for Occupational Safety and Health (NIOSH).
- Jump up ^ "Toluene-2,4-diisocyanate". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
- ^ Jump up to: a b Randall, D.; Lee, S. (2003). The Polyurethanes Book. New York: Wiley. ISBN 978-0-470-85041-1.
- ^ 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
- 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.
- 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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