Toluene diisocyanate

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Toluene-2,4-diisocyanate
Toluene diisocyanate
Toluene diisocyanate
Ball and stick model of toluene diisocyanate
Ball and stick model of toluene 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
3D model (JSmol)
744602
ChEBI
ChEMBL
ChemSpider
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EC Number
  • 2,4: 209-544-5
  • 2,6: 202-039-0
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RTECS number
  • 2,4: CZ6300000
  • 2,6: CZ6310000
UNII
UN number 2078
  • InChI=1S/C9H6N2O2/c1-7-2-3-8(10-5-12)4-9(7)11-6-13/h2-4H,1H3 checkY
    Key: DVKJHBMWWAPEIU-UHFFFAOYSA-N checkY
  • 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
  • 2,4: Cc1ccc(cc1\N=C=O)\N=C=O
  • 2,6: CC1=C(C=CC=C1N=C=O)N=C=O
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:
GHS05: CorrosiveGHS06: ToxicGHS07: Exclamation markGHS08: Health hazard
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)

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3
1
1
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]
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).

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.

Synthesis

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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]

File:TDI-Synthese.svg

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).

Description and description of reactivity

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The isocyanate functional groups in TDI react with hydroxyl groups to form carbamate (urethane) links. The two isocyanate groups in Toluene diisocyanate 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]

Applications

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Toluene diisocyanate is used in the production of rigid polyurethane foams with a high temperature stability.

It is also sometimes used in rocket propellants.[5]

Hazards

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TDI is classified as "very toxic" by the European Community.[4] This is due to the high pulmonary risk of prolonged exposure at low doses.

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]

See also

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References

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