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Hexamethylene diisocyanate (HDI) is an organic compound in the class known as
isocyanateIsocyanate is the functional group of elements –N=C=O , not to be confused with the cyanate functional group which is arranged as –O–C≡N or with isocyanide, R-N≡C. Any organic compound which contains an isocyanate group may also be referred to in brief as an isocyanate. An isocyanate may have more...
s. More specifically, it is an
aliphaticIn organic chemistry, aliphatic compounds are acyclic or cyclic, non-aromatic carbon compounds.Thus, aliphatic compounds are opposite to aromatic compounds.- Structure :...
diisocyanate. It is produced in relatively small quantities, accounting for (with
isophorone diisocyanateIsophorone diisocyanate is an organic compound in the class known as isocyanates. More specifically, it is an aliphatic diisocyanate. It is produced in relatively small quantities, accounting for only 3.4% of the global diisocyanate market in the year 2000...
) only 3.4% of the global diisocyanate market in the year 2000. Aliphatic diisocyanates are used in special applications, such as enamel coatings which are resistant to abrasion and degradation from ultraviolet light. These properties are particularly desirable in, for instance, the exterior paint applied to aircraft.
Synthesis
There are two steps to the synthesis of pure HDI:
- Phosgenation: Reaction of hexamethylene diamine with phosgene
Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...
to form crude HDI
- Purification: Distillation of crude HDI to extract pure HDI
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