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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| Names | |
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| Preferred IUPAC name
2,4-Diisocyanato-1-methylbenzene | |
| Other names
Toluene diisocyanate | |
| Identifiers | |
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3D model (JSmol) |
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| 744602 | |
| ChEBI |
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| ChEMBL |
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| ChemSpider |
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| ECHA InfoCard | 100.008.678 
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| EC Number |
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PubChem CID |
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| RTECS number |
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| UNII |
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| UN number | 2078 |
CompTox Dashboard (EPA) |
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| Properties | |
| 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) |
| Reacts | |
| Vapor pressure | 0.01 mmHg (25°C)[1] |
| Hazards | |
| GHS labelling: | |
   
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| Danger | |
| H315, H317, H318, H319, H330, H334, H335, H351, H412 | |
| 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) | |
| 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). | |
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).
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.
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]
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