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Toluene diisocyanate

IUPAC name 2,4-diisocyanato-1-methyl-benzene
Other names Tolylene diisocyanate
Methyl phenylene diisocyanate
CAS number 86-91-9
RTECS number CZ6300000
SMILES c1(C)c(N=C=O)cc(N=C=O)cc1
Molecular formula C9H6N2O2
Molar mass 174.2 g/mol
Appearance Colorless to pale yellow, liquid
Density 1.214 g/cm3, liquid
Melting point

21.8 °C (295.0 K)

Boiling point

251 °C (524 K)

Solubility in water Reacts
MSDS External MSDS
EU classification Very toxic (T+)
Carc. Cat. 3
NFPA 704
R-phrases R26, R36/37/38, R40,
R42/43, R52/53
S-phrases (S1/2), S23, S36/37, S45, S61
Flash point 127 °C
Related Compounds
Related isocyanates Methylene diphenyl diisocyanate
Naphthalene diisocyanate
Related compounds Polyurethane
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Toluene diisocyanate (TDI) is an aromatic diisocyanate. It is produced for reaction with polyols to form polyurethanes. It exists in two isomers, 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 a highly produced diisocyanate, accounting for 34.1% of the global isocyanate market in 2000, second only to MDI.[1]



There are six steps to the synthesis of pure 2,4-TDI:[1]

  • Nitration: Reaction of toluene with nitric acid and a catalyst to form dinitrotoluene
  • Hydrogenation: Reaction of the dinitrotoluene with hydrogen and a catalyst to form a mixture of isomers of toluene diamine (TDA)
  • Purification: Distillation of the TDA mixture to produce meta-TDA
  • Phosgenation: Reaction of the meta-TDA with phosgene to form a crude TDI mixture
  • Purification: Distillation of the crude TDI mixture to produce an 80:20 mixture of 2,4-TDI and 2,6-TDI, known as TDI (80/20)
  • Differentiation: Separation of the TDI (80/20) to produce pure 2,4-TDI and a 65:35 mixture of 2,4-TDI and 2,6-TDI, known as TDI (65/35)


Each of the isocyanate functional groups in TDI can react with a hydroxyl group to form a urethane linkage.

2,4-TDI is an asymmetrical molecule and thus has two isocyanate groups of different reactivity. 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.[1]


Exposure to TDI and its vapors should be avoided. It is a well-documented causative agent of asthma.

See also


  1. ^ a b c Randall, David; Lee, Steve (2002). The Polyurethanes Book. New York: Wiley. ISBN 0-470-85041-8. 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Toluene_diisocyanate". A list of authors is available in Wikipedia.
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