Hexamethylene diisocyanate (HDI) is the
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
with the formula (CH
2)
6(NCO)
2. It is classified as an di
isocyanate
In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...
. It is a colorless liquid.
It has sometimes been called HMDI but this not usually done to avoid confusion with
Hydrogenated MDI.
Synthesis
Compared to other commercial diisocyanates, HDI is produced in relatively small quantities, accounting for (with
isophorone diisocyanate) only 3.4% of the global diisocyanate market in the year 2000.
[
] It is produced by
phosgenation of
hexamethylene diamine
Hexamethylenediamine is the organic compound with the formula H2N(CH2)6NH2. The molecule is a diamine, consisting of a hexamethylene hydrocarbon chain terminated with amine functional groups. The colorless solid (yellowish for some commercial ...
.
Applications
Aliphatic diisocyanates are used in specialty applications, such as enamel coatings which are resistant to abrasion and degradation by ultraviolet light. These properties are particularly desirable in, for instance, the exterior paint applied to aircraft and vessels. HDI is also sold oligomerized as the trimer or biuret which are used in automotive refinish coatings. Although more viscous in these forms, it reduces the volatility and toxicity. At least 3 companies sell material in this form commercially. It is also used as an activator in process of in situ polymerization of caprolactam i.e. cast nylon process. HDI is also used
bisoxazolidine synthesis as the hydroxyl group on the molecule allows for further reaction with hexamethylene diisocyanate.
Toxicity
HDI is considered toxic, and its pulmonary toxicity has been studied as well as its oligomers.
[{{Cite journal , last1=Wisnewski , first1=Adam V. , last2=Liu , first2=Qing , last3=Miller , first3=Jing-Jing , last4=Magoski , first4=Nadine , last5=Redlich , first5=Carrie A. , date=2002-09-01 , title=Effects of hexamethylene diisocyanate exposure on human airway epithelial cells: in vitro cellular and molecular studies. , journal=Environmental Health Perspectives , volume=110 , issue=9 , pages=901–907 , doi=10.1289/ehp.02110901 , pmc=1240990 , pmid=12204825]
See also
*
Methylene diphenyl diisocyanate
Methylene diphenyl diisocyanate (MDI) is an aromatic diisocyanate. Three isomers are common, varying by the positions of the isocyanate groups around the rings: 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. The 4,4′ isomer is most widely used, and i ...
*
Toluene diisocyanate
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 oft ...
*
Isophorone diisocyanate
References
External links
NIOSH Safety and Health Topic: Isocyanates from the website of the National Institute for Occupational Safety and Health (NIOSH)
Isocyanates