Toluene diisocyanate

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
CAS Number	584-84-9 Y
ChEBI	CHEBI:53556 Y
ChEMBL	ChEMBL1086446 Y
ChemSpider	13835351 Y
Jmol 3D model	Interactive image
RTECS number	CZ6300000
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 InChI=1/C9H6N2O2/c1-7-2-3-8(10-5-12)4-9(7)11-6-13/h2-4H,1H3 Key: DVKJHBMWWAPEIU-UHFFFAOYAL
SMILES Cc1ccc(cc1\N=C=O)\N=C=O
Properties
Chemical formula	C9H6N2O2
Molar mass	174.2 g/mol
Appearance	Colorless to pale yellow liquid
Odor	sharp, pungent
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)
Vapor pressure	{{{value}}}
Related compounds
Related isocyanates	Methylene diphenyl diisocyanate Naphthalene diisocyanate
Related compounds	Polyurethane
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
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. Approximately 1.4 billion kilograms were produced in 2000.

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.

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

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.

It is used in the production of flexible polyurethane foams

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.

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.

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. All major producers of TDI are members of the International Isocyanate Institute, whose aim is the promotion of the safe handling of TDI in the workplace, community, and environment.

See also

• Methylene diphenyl diisocyanate
• Hexamethylene diisocyanate
• Isophorone diisocyanate

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