Toluene diisocyanate

Toluene-2,4-diisocyanate
Names


Preferred IUPAC name 2,4-Diisocyanato-1-methylbenzene
Other names Toluene diisocyanate Toluene-2,4-diisocyanate Methyl phenylene diisocyanate Benzylene 2,4-diisocyanate 2,4-Di(nitrogencarbonyl)toluene
Identifiers
CAS Number	2,4: 584-84-9^Y 2,6: 91-08-7
3D model (JSmol)	2,4: Interactive image 2,6: Interactive image
Beilstein Reference	744602
ChEBI	2,4: CHEBI:53556^Y 2,6: CHEBI:53557
ChEMBL	2,4: ChEMBL1086446^Y 2,6: ChEMBL1443390
ChemSpider	2,4: 13835351^Y 2,6: 6773
ECHA InfoCard	100.008.678
EC Number	2,4: 209-544-5 2,6: 202-039-0
PubChem CID	2,4: 11443 2,6: 7040
RTECS number	2,4: CZ6300000 2,6: CZ6310000
UNII	2,4: 17X7AFZ1GH^Y 2,6: 78243HXH5O
UN number	2078
CompTox Dashboard (EPA)	2,4: DTXSID7026156 2,6: DTXSID2026157
InChI InChI=1S/C9H6N2O2/c1-7-2-3-8(10-5-12)4-9(7)11-6-13/h2-4H,1H3^Y Key: DVKJHBMWWAPEIU-UHFFFAOYSA-N^Y 2,4: InChI=1/C9H6N2O2/c1-7-2-3-8(10-5-12)4-9(7)11-6-13/h2-4H,1H3 Key: DVKJHBMWWAPEIU-UHFFFAOYAL 2,6: InChI=1S/C9H6N2O2/c1-7-8(10-5-12)3-2-4-9(7)11-6-13/h2-4H,1H3 Key: RUELTTOHQODFPA-UHFFFAOYSA-N
SMILES 2,4: Cc1ccc(cc1\N=C=O)\N=C=O 2,6: CC1=C(C=CC=C1N=C=O)N=C=O
Properties
Chemical formula	C₉H₆N₂O₂
Molar mass	174.2 g/mol
Appearance	Colorless liquid
Odor	sharp, pungent^[1]
Density	1.214 g/cm³, liquid
Melting point	21.8 °C (71.2 °F; 294.9 K)
Boiling point	251 °C (484 °F; 524 K)
Solubility in water	Reacts
Vapor pressure	0.01 mmHg (25°C)^[1]
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H315, H317, H318, H319, H330, H334, H335, H351, H412
Precautionary statements	P201, P202, P260, P261, P264, P271, P272, P273, P280, P281, P284, P285, P302+P352, P304+P340, P304+P341, P305+P351+P338, P308+P313, P310, P312, P320, P321, P332+P313, P333+P313, P337+P313, P342+P311, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 1 1
Flash point	127 °C (261 °F; 400 K)
Explosive limits	0.9–9.5%^[1]
Lethal dose or concentration (LD, LC):
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]
NIOSH (US health exposure limits):
PEL (Permissible)	C 0.02 ppm (0.14 mg/m³)^[1]
REL (Recommended)	Ca^[1]
IDLH (Immediate danger)	Ca [2.5 ppm]^[1]
Related compounds
Related isocyanates	Methylene diphenyl diisocyanate Naphthalene diisocyanate, 1,3-Diisocyanatobenzene
Related compounds	Polyurethane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is ^YN ?) Infobox references

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.

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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]}

References

^ ^a ^b ^c ^d ^e ^f NIOSH Pocket Guide to Chemical Hazards. "#0621". National Institute for Occupational Safety and Health (NIOSH).
^ "Toluene-2,4-diisocyanate". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b Randall, D.; Lee, S. (2003). The Polyurethanes Book. New York: Wiley. ISBN 978-0-470-85041-1.
^ ^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)
^ "Ababil-100/Al Fat'h". GlobalSecurity.org. Archived from the original on 15 April 2019.
^ 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.
^ Ripley, Will; Jiang, Steven; Mullen, Jethro (13 August 2023). "Tianjin explosion: Dozens dead, areas of Chinese port city devastated". CNN. Retrieved 1 October 2023.
^ 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

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

This page was last edited on 9 January 2024, at 02:56

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