Toluene diisocyanate

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Toluene-2,4-diisocyanate
Toluene diisocyanate
Toluene diisocyanate
Names
IUPAC name
2,4-diisocyanato-1-methyl-benzene
Other names
Tolylene diisocyanate
Methyl phenylene diisocyanate
Identifiers
584-84-9 YesY
ChEBI CHEBI:53556 YesY
ChEMBL ChEMBL1086446 YesY
ChemSpider 13835351 YesY
Jmol 3D model Interactive image
RTECS number CZ6300000
Properties
C9H6N2O2
Molar mass 174.2 g/mol
Appearance Colorless to pale yellow 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
Safety data sheet See: data page
Very toxic (T+)
Carc. Cat. 3
R-phrases R26, R36/37/38, R40,
R42/43, R52/53
S-phrases (S1/2), S23, S36/37, S45, S61
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 127 °C (261 °F; 400 K)
Explosive limits 0.9%-9.5%[1]
Lethal dose or concentration (LD, LC):
14 ppm (rat, 4 hr)
13.9 ppm (guinea pig, 4 hr)
9.7 ppm (mouse, 4 hr)
11 ppm (rabbit, 4 hr)[2]
US health exposure limits (NIOSH):
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
Related compounds
Polyurethane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
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]

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] This chemical was one of many that caused two massive explosions in a chemical warehouse stationed in Tianjin, China on August 13, 2015.[citation needed][6]

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.[7] 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]

  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 and Health. 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. (2005), "Isocyanates, Organic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a14_611 
  5. ^ 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. ^ CNN [1]
  7. ^ 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]