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Toluene diisocyanate

 

 
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Toluene diisocyanate
 
 
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Toluene diisocyanate (TDI) is an aromatic
Aromaticity

Aromaticity is a chemical property in which a conjugated system ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone....
 diisocyanate
Isocyanate

Isocyanate is the functional group of atoms ?N=C=O , not to be confused with the cyanate functional group which is arranged as ?O?C=N....
. It is produced for reaction with polyol
Polyol

The name polyols refers to alcohols containing multiple hydroxyl groups. In two technological disciplines polyols have special meaning: food science and polymer chemistry....
s to form polyurethane
Polyurethane

A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic chemistry units joined by carbamate links. Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst....
s. It exists in two isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s, 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
Methylene diphenyl diisocyanate

Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromaticity isocyanate. It exists in three isomers, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI....
.

e are six steps to the synthesis of pure 2,4-TDI:

of the isocyanate
Isocyanate

Isocyanate is the functional group of atoms ?N=C=O , not to be confused with the cyanate functional group which is arranged as ?O?C=N....
 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.






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Toluene diisocyanate (TDI) is an aromatic
Aromaticity

Aromaticity is a chemical property in which a conjugated system ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone....
 diisocyanate
Isocyanate

Isocyanate is the functional group of atoms ?N=C=O , not to be confused with the cyanate functional group which is arranged as ?O?C=N....
. It is produced for reaction with polyol
Polyol

The name polyols refers to alcohols containing multiple hydroxyl groups. In two technological disciplines polyols have special meaning: food science and polymer chemistry....
s to form polyurethane
Polyurethane

A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic chemistry units joined by carbamate links. Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst....
s. It exists in two isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s, 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
Methylene diphenyl diisocyanate

Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromaticity isocyanate. It exists in three isomers, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI....
.

Synthesis

There are six steps to the synthesis of pure 2,4-TDI:
  • Nitration: Reaction of toluene
    Toluene

    Toluene, also known as methylbenzene or phenylmethane, is a clear, Water -insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene....
     with nitric acid
    Nitric acid

    Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosion and toxic strong acid that can cause severe burns....
     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
    Phosgene

    Phosgene is the chemical compound with the chemical formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I, but it is also a valued industrial reagent and building block in organic synthesis....
     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)


Chemistry

Each of the isocyanate
Isocyanate

Isocyanate is the functional group of atoms ?N=C=O , not to be confused with the cyanate functional group which is arranged as ?O?C=N....
 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.

Hazards

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

See also

  • Methylene diphenyl diisocyanate
    Methylene diphenyl diisocyanate

    Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromaticity isocyanate. It exists in three isomers, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI....
  • Hexamethylene diisocyanate
    Hexamethylene diisocyanate

    Hexamethylene diisocyanate is an organic compound in the class known as isocyanates. More specifically, it is an Aliphatic compound diisocyanate....
  • Isophorone diisocyanate
    Isophorone diisocyanate

    Isophorone diisocyanate is an organic compound in the class known as isocyanates. More specifically, it is an Aliphatic compound diisocyanate. It is produced in relatively small quantities, accounting for only 3.4% of the global diisocyanate market in the year 2000....


External links

  • , from the website of the National Institute for Occupational Safety and Health (NIOSH)