Propylene oxide
Encyclopedia
Propylene oxide is an organic compound
with the molecular formula CH3CHCH2O. This colourless volatile
liquid is produced on a large scale industrially, its major application being its use for the production of polyether polyols for use in making polyurethane
plastics. It is chiral
epoxide
, although it commonly used as a racemic mixture.
This compound is sometimes called 1,2-propylene oxide to distinguish it from its isomer
1,3-propylene oxide, better known as oxetane
.
. Two general approaches are employed, one involving hydrochlorination and the other involving oxidation. In 2005, about half of the world production was through chlorohydrin technology and one half via oxidation routes. The latter approach is growing in importance.
The reaction produces a mixture of 1-chloro-2-propanol and 2-chloro-1-propanol, which is then dehydrochlorinated. For example:
Lime
is often used as a chlorine absorber.
. In the present of catalyst, air oxidation occurs as follows:
The coproducts of these reactions, t-butyl alcohol
or styrene, are useful feedstock for other products. For example, t-butyl alcohol reacts with methanol
to give MTBE, an additive for gasoline. Before the current ban of MTBE, propylene
/isobutene was one of the most important production process.
without significant production of other products. This method is a variant of the POSM process (co-oxidation) that uses cumene hydroperoxide instead of ethylbenzene hydroperoxide and recycles the coproduct (alpha-hydroxycumene) via dehydration
and hydrogenation
back to cumene.
In March 2009, BASF
and Dow Chemical started up their new HPPO plant in Antwerp. In the HPPO-Process, propylene is oxidized with hydrogen peroxide
:
In this process no side products other than water are generated.
plastics. About 20% of propylene oxide is hydrolyzed into propylene glycol
, via a process which is accelerated by acid or base catalysis
. Other major products are polypropylene glycol
, propylene glycol ethers, and propylene carbonate
.
NHRA
rules for safety reasons. It has also been used in glow fuel
for model aircraft and surface vehicles, typically combined in small percentages of around 2% as an additive to the typical methanol
, nitromethane
, and oil mix. It is also used in thermobaric weapon
s, and microbial fumigation
.
in commercial orchards, one incident occurring in Canada, and one incident in the United States.
Pistachio nuts can also be subjected to propylene oxide to control Salmonella. It is a method approved by the FDA.
previously used for dehydration. In a typical procedure, the sample is first immersed in a mixture of equal volumes of ethanol and propylene oxide for 5 minutes, and then four times in pure oxide, 10 minutes each.
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...
with the molecular formula CH3CHCH2O. This colourless volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
liquid is produced on a large scale industrially, its major application being its use for the production of polyether polyols for use in making 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...
plastics. It is chiral
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
epoxide
Epoxide
An epoxide is a cyclic ether with three ring atoms. This ring approximately defines an equilateral triangle, which makes it highly strained. The strained ring makes epoxides more reactive than other ethers. Simple epoxides are named from the parent compound ethylene oxide or oxirane, such as in...
, although it commonly used as a racemic mixture.
This compound is sometimes called 1,2-propylene oxide to distinguish it from its isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
1,3-propylene oxide, better known as oxetane
Oxetane
Oxetane, or 1,3-propylene oxide, is an heterocyclic organic compound with the molecular formula C3H6O, having a four-membered ring with three carbon atoms and one oxygen atom....
.
Production
Industrial production of propylene oxide starts from propylenePropylene
Propene, also known as propylene or methylethylene, is an unsaturated organic compound having the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons, and it is also second in natural abundance.-Properties:At room temperature and...
. Two general approaches are employed, one involving hydrochlorination and the other involving oxidation. In 2005, about half of the world production was through chlorohydrin technology and one half via oxidation routes. The latter approach is growing in importance.
Hydrochlorination route
The traditional route proceeds via the conversion of propylene to chloropropanols:The reaction produces a mixture of 1-chloro-2-propanol and 2-chloro-1-propanol, which is then dehydrochlorinated. For example:
Lime
Lime (mineral)
Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...
is often used as a chlorine absorber.
Co-oxidation of propylene
The other general route to propylene oxide involves co-oxidation of the organic chemicals isobutene or ethylbenzeneEthylbenzene
Ethylbenzene is an organic compound with the formula C6H5CH2CH3. This aromatic hydrocarbon is important in the petrochemical industry as an intermediate in the production of styrene, which in turn is used for making polystyrene, a common plastic material....
. In the present of catalyst, air oxidation occurs as follows:
- CH3CH=CH2 + Ph-CH2CH3 + O2 → CH3CHCH2O + Ph-CH=CH2 + H2O
The coproducts of these reactions, t-butyl alcohol
Tert-Butanol
tert-Butanol, or 2-methyl-2-propanol, is the simplest tertiary alcohol. It is one of the four isomers of butanol. tert-Butanol is a clear liquid with a camphor-like odor. It is very soluble in water and miscible with ethanol and diethyl ether...
or styrene, are useful feedstock for other products. For example, t-butyl alcohol reacts with methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
to give MTBE, an additive for gasoline. Before the current ban of MTBE, propylene
Propylene
Propene, also known as propylene or methylethylene, is an unsaturated organic compound having the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons, and it is also second in natural abundance.-Properties:At room temperature and...
/isobutene was one of the most important production process.
Oxidation of propylene
In April 2003, Sumitomo Chemical commercialized the first PO-only plant in Japan, which produces propylene oxide from oxidation of cumeneCumene
Cumene is the common name for isopropylbenzene, an organic compound that is an aromatic hydrocarbon. It is a constituent of crude oil and refined fuels. It is a flammable colorless liquid that has a boiling point of 152 °C...
without significant production of other products. This method is a variant of the POSM process (co-oxidation) that uses cumene hydroperoxide instead of ethylbenzene hydroperoxide and recycles the coproduct (alpha-hydroxycumene) via dehydration
Dehydration reaction
In chemistry and the biological sciences, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...
and hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
back to cumene.
In March 2009, BASF
BASF
BASF SE is the largest chemical company in the world and is headquartered in Germany. BASF originally stood for Badische Anilin- und Soda-Fabrik . Today, the four letters are a registered trademark and the company is listed on the Frankfurt Stock Exchange, London Stock Exchange, and Zurich Stock...
and Dow Chemical started up their new HPPO plant in Antwerp. In the HPPO-Process, propylene is oxidized with hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
:
- CH3CH=CH2 + H2O2 → CH3CHCH2O + H2O
In this process no side products other than water are generated.
Uses
Between 60 and 70% of all propylene oxide is converted to polyether polyols for the production of polyurethanePolyurethane
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...
plastics. About 20% of propylene oxide is hydrolyzed into propylene glycol
Propylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
, via a process which is accelerated by acid or base catalysis
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
. Other major products are polypropylene glycol
Polypropylene glycol
Polypropylene glycol or polypropylene oxide is the polymer of propylene glycol. Chemically it is a polyether. The term polypropylene glycol or PPG is reserved for low to medium range molar mass polymer when the nature of the end-group, which is usually a hydroxyl group, still matters...
, propylene glycol ethers, and propylene carbonate
Propylene carbonate
Propylene carbonate is an organic compound, a cyclic carbonate of propylene glycol. This colorless and odorless liquid is useful as a polar, aprotic solvent...
.
Historic and niche uses
Propylene oxide was once used as a racing fuel, but that usage is now prohibited under the USUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
NHRA
National Hot Rod Association
The National Hot Rod Association is a drag racing governing body, which sets rules in drag racing and host events all over the United States and Canada...
rules for safety reasons. It has also been used in glow fuel
Glow fuel
Glow fuel is a generic term used to describe a fuel source used in model engines -- generally the same or similar fuels can be used in model airplanes, helicopters, cars and boats. Glow fuel can be burned by very simple two stroke engines or by more complicated four stroke engines and these...
for model aircraft and surface vehicles, typically combined in small percentages of around 2% as an additive to the typical methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, nitromethane
Nitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
, and oil mix. It is also used in thermobaric weapon
Thermobaric weapon
A thermobaric weapon, which includes the type known as a "fuel-air bomb", is an explosive weapon that produces a blast wave of a significantly longer duration than those produced by condensed explosives. This is useful in military applications where its longer duration increases the numbers of...
s, and microbial fumigation
Fumigation
Fumigation is a method of pest control that completely fills an area with gaseous pesticides—or fumigants—to suffocate or poison the pests within. It is utilized for control of pests in buildings , soil, grain, and produce, and is also used during processing of goods to be imported or...
.
Fumigant
The United States Food and Drug Administration has approved the use of propylene oxide to pasteurize raw almonds beginning on September 1, 2007 in response to two incidents of contamination by SalmonellaSalmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
in commercial orchards, one incident occurring in Canada, and one incident in the United States.
Pistachio nuts can also be subjected to propylene oxide to control Salmonella. It is a method approved by the FDA.
Microscopy
Propylene oxide is commonly used in the preparation of biological samples for electron microscopy, to remove residual ethanolEthanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
previously used for dehydration. In a typical procedure, the sample is first immersed in a mixture of equal volumes of ethanol and propylene oxide for 5 minutes, and then four times in pure oxide, 10 minutes each.
Safety
Propylene oxide is a probable human carcinogen, and listed as an IARC Group 2B carcinogen.External links
- WebBook page for C3H6O
- Propylene oxide at the United States Environmental Protection AgencyUnited States Environmental Protection AgencyThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
- Propylene oxide - chemical product info: properties, production, applications.
- Propylene oxide at the Technology Transfer Network Air Toxics Web Site