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. Any
organic compound which contains an isocyanate group may also be referred to in brief as an isocyanate. An isocyanate may have more than one isocyanate group. An isocyanate that has two isocyanate groups is known as a diisocyanate. Diisocyanates are manufactured for reaction with polyols in the production of
polyurethanes.
Encyclopedia
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. Any
organic compound which contains an isocyanate group may also be referred to in brief as an isocyanate. An isocyanate may have more than one isocyanate group. An isocyanate that has two isocyanate groups is known as a
diisocyanate. Diisocyanates are manufactured for reaction with polyols in the production of
polyurethanes.
Synthesis
The normal industrial route to the manufacture of diisocyanates, is to synthesise the desired molecular structure with
amine functional groups at the positions to be occupied by the isocyanate groups. Reaction with
phosgene replaces the amine groups with isocyanate groups.
Common methods for the synthesis of isocyanates in the laboratory are the
Curtius rearrangement of acyl azides and the
Lossen rearrangement of hydroxamic acids.
Chemistry
The isocyanate group reacts with the hydroxyl functional group to form a
urethane linkage. If a diisocyanate is reacted with a compound containing two or more hydroxyl groups , long polymer chains are formed, known as polyurethanes.
The isocyanate group also reacts with the amine functional group. Reaction between a diisocyanate and a compound containing two or more amine groups, produces long polymer chains known as
polyureas.
The isocyanate group can react with itself. Aliphatic diisocyanates can form trimers, known as
biurets.
Common compounds
A monofunctional isocyanate of industrial significance is
methyl isocyanate , which is used in the manufacture of pesticides.
The global market for diisocyanates in the year 2000 was 4.4 million tonnes, of which 61.3 % was
methylene diphenyl diisocyanate , 34.1 % was
toluene diisocyanate , 3.4 % was the total for
hexamethylene diisocyanate and
isophorone diisocyanate , and 1.2 % was the total for various others.zards
The reactivity of isocyanates makes them harmful to living tissue. They are toxic and are known to cause asthma in humans, both through inhalation exposure and dermal contact. Exposure to isocyanates and their vapors should be avoided.
See also
References
External links
- , from the website of the National Institute for Occupational Safety and Health
