Isocyanate
Encyclopedia
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
of elements –N=C=O (1 nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, 1 carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, 1 oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
), not to be confused with the cyanate
Cyanate
The cyanate ion is an anion with the chemical formula written as [OCN]− or [NCO]−. In aqueous solution it acts as a base, forming isocyanic acid, HNCO. The cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron-pair...
functional group which is arranged as –O–C≡N or with isocyanide
Isocyanide
An isocyanide is an organic compound with the functional group -N≡C. It is the isomer of the related cyanide , hence the prefix iso....
, R-N≡C. Any organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
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 reactions with polyols in the production of polyurethanes. The largest use of isocyanates in industry involves the production of polymers. Polymers of common isocyanates are used in the manufacture of foams, paints, lacquers and in electrical insulation.
Chemistry
The isocyanate group reacts with the hydroxylHydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
functional group to form a urethane
Carbamate
Carbamates are organic compounds derived from carbamic acid . A carbamate group, carbamate ester, and carbamic acids are functional groups that are inter-related structurally and often are interconverted chemically. Carbamate esters are also called urethanes.-Synthesis:Carbamic acids are derived...
linkage. If a di-isocyanate is reacted with a compound containing two or more hydroxyl groups (a polyol), long polymer chains are formed, known as polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
s.
The isocyanate group also reacts with the amine functional group. Reaction between a di-isocyanate and a compound containing two or more amine groups, produces long polymer chains known as polyurea
Polyurea
Polyurea is a type of elastomer that is derived from the reaction product of an isocyanate component and a synthetic resin blend component through step-growth polymerization. The isocyanate can be aromatic or aliphatic in nature. It can be monomer, polymer, or any variant reaction of isocyanates,...
s.
The isocyanate group can react with itself. Aliphatic
Aliphatic compound
In organic chemistry, aliphatic compounds are acyclic or cyclic, non-aromatic carbon compounds.Thus, aliphatic compounds are opposite to aromatic compounds.- Structure :...
di-isocyanates can form trimer
Trimer (chemistry)
In chemistry, a trimer is a product derived from three identical precursors. Trimers are typically cyclic. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids. Often, trimerization competes with polymerization....
s, known as biuret
Biuret
Biuret is a chemical compound with the chemical formula H2NCNHCNH2. It is the result of condensation of two molecules of urea and is a problematic impurity in urea-based fertilizers. This white solid is soluble in hot water....
s.
The isocyanate group reacts with water to form carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2). Carbon dioxide is used as a blowing agent (in situ) in order to produce polyurethane foams.
Isocyanates are intermediates in the Hofmann rearrangement
Hofmann rearrangement
The Hofmann rearrangement is the organic reaction of a primary amide to a primary amine with one fewer carbon atom.The reaction is named after its discoverer: August Wilhelm von Hofmann...
, in which a primary amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
is reacted with a hypohalite
Hypohalite
A hypohalite is an oxyanion containing a halogen in oxidation state +1.This includes hypoiodite, hypobromite, hypochlorite, and hypofluorite....
such as sodium hypobromite to form an isocyanate intermediate. The isocyanate is then hydrolyzed
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
with water to yield the corresponding primary amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
.
Common compounds
Methyl isocyanate
Methyl isocyanate is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane, methyl carbylamine, and MIC. Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides . It has also been used in the production of rubbers and adhesives...
(MIC), 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
Methylene diphenyl diisocyanate
Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromatic diisocyanate. It exists in three isomers, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI, but the 4,4' isomer is most widely used. This isomer is also known as Pure MDI. MDI reacts with polyols in the manufacture of polyurethane...
(MDI), 34.1% was toluene diisocyanate
Toluene diisocyanate
Toluene diisocyanate is an aromatic diisocyanate. It is produced for reaction with polyols to form polyurethanes. It exists in two isomers, 2,4-TDI and 2,6-TDI . 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...
(TDI), 3.4% was the total for hexamethylene diisocyanate
Hexamethylene diisocyanate
Hexamethylene 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...
(HDI) and isophorone diisocyanate
Isophorone diisocyanate
Isophorone 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...
(IPDI), and 1.2% was the total for various others.
All major producers of MDI and TDI are members of the International Isocyanate Institute, whose aim is the promotion of the safe handling of MDI and TDI in the workplace, community and environment.
Hazards
Isocyanates are potentially dangerous irritants to the eyes and respiratory tract. No matter which chemical is used, all isocyanates must be treated as a highly hazardous chemical. The greatest risk when dealing with these chemicals involves inhalation of the fine vapours or droplets which irritate the nose lungs and thorax. Increased exposure to isocyanates can lead to sensitization causing workers to experience asthmaAsthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
attacks.
Common health effects caused by all isocyanates include eye irritation leading to watering and discomfort. Dryness of the throat and chest is common and difficulty breathing results from constant exposure, especially when in high concentrations. When the chemicals come in contact with the skin, reddening, swelling and blistering will occur and persist until completely washed off. Dermatitis
Dermatitis
-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...
is also linked to excessive exposure of isocyanates as well as liver and kidney dysfunction.
Isocyanates pose a particular threat when burned as carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
and hydrogen cyanide are formed. These gases are highly toxic and could be fatal if the area isn’t well ventilated. Contamination of isocyanates with water can create toxic gases, so they must be stored in airtight and dry containers. If contamination occurs, never seal the chemicals, as doing so will create unwanted pressure and may lead to an explosion.
Several isocyanates pose a greater risk such as Methylisocyanate as it can create tear gas when released. Methyl isocyanate is extremely toxic and can kill a worker even when exposed to only small concentrations. The toxic effect of this isocyanate is evident in the Bhopal Disaster
Bhopal disaster
The Bhopal disaster also known as Bhopal Gas Tragedy was a gas leak incident in India, considered one of the world's worst industrial catastrophes. It occurred on the night of December 2–3, 1984 at the Union Carbide India Limited pesticide plant in Bhopal, Madhya Pradesh, India...
which killed thousands due to high exposure. Another isocyanate which if not handled with care can cause severe harm is toluene diisocyanate
Toluene diisocyanate
Toluene diisocyanate is an aromatic diisocyanate. It is produced for reaction with polyols to form polyurethanes. It exists in two isomers, 2,4-TDI and 2,6-TDI . 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...
.
Information on handling, personal protective equipment, exposure monitoring, transport, storage, sampling and analysis of MDI
MDI
MDI may refer to:In computer science:*Media Delivery Index, a metric used in IPTV networks*Medium dependent interface, a type of Ethernet port connection*Microsoft Document Imaging Format, a proprietary file format...
and TDI
TDI
-Chemistry:*Tolerable Daily Intake ,*Toluene diisocyanate, an organic chemical-Entertainment:*Total Drama Island, an animated reality series that started July 8, 2007...
, dealing with accidents, and health and environmental information has been published.
See also
- IsothiocyanateIsothiocyanateIsothiocyanate is the chemical group –N=C=S, formed by substituting sulfur for oxygen in the isocyanate group. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. These natural isothiocyanates, such as allyl isothiocyanate, are also...
- PolyurethanePolyurethaneA polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
- Methylisocyanate
- Polyols
- Fire classesFire classesIn firefighting, fires are identified according to one or more fire classes. Each class designates the fuel involved in the fire, and thus the most appropriate extinguishing agent. The classifications allow selection of extinguishing agents along lines of effectiveness at putting the type of fire...
External links
- NIOSH Safety and Health Topic: Isocyanates, from the website of the National Institute for Occupational Safety and Health (NIOSH)
- Health and Safety Executive, website of the UK Health and Safety Executive, useful search terms on this site — isocyanates, MVR, asthma
- http://www.diisocyanates.org International Isocyanate Institute
- http://www.actsafe.ca/wp-content/uploads/resources/pdf/Isocyanates.pdf
- Isocyanates – Measurement Methodology, Exposure and Effects Isocyanates in Working Life Workshop Article (1999)
- Health and Safety Executive, Guidance Note (EH16) Isocyanates: Toxic Hazards and Precautions (1984)
- The Society of the Plastics Industry – Technical Bulletin AX119 MDI-Based Polyurethane
- Foam Systems: Guidelines for Safe Handling and Disposal (1993)
- An occupational hygiene assessment of the use and control of isocyanates in the UK by Hilary A Cowie et al. HSE Research Report RR311/2005. Prepared by the Institute of Occupational MedicineInstitute of Occupational MedicineThe Institute of Occupational Medicine was founded in 1969 by the National Coal Board as an independent charity. The IOM is a major independent centre of scientific excellence in the fields of occupational health and environmental health, occupational hygiene and occupational safety...
for the Health and Safety ExecutiveHealth and Safety ExecutiveThe Health and Safety Executive is a non-departmental public body in the United Kingdom. It is the body responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare, and for research into occupational risks in England and Wales and Scotland...