Propylene oxide

Description

Propylene oxide is an allergic and irritant agent, used as a solvent and raw material in the chemical industry as starting material and intermediate for a broad spectrum of polymers.

Description

Propylene oxide (PO), formally 2-methyloxirane, is low-boiling liquid that is useful for making many commercial materials. It was known as long ago as 1866, when Eduard Linnemann at the University of Lemberg (Germany) described the conversion of PO to acetone.
The initial method for producing PO was the chlorination of propylene in water to give a mixture of chlorohydrins, followed by dehydrochlorinaton with potassium hydroxide. A process developed subsequently was the direct oxidation of propylene with an organic hydroperoxide. Both processes are in use today.
About two-thirds of worldwide PO production (≈13 million t/year) is used to make polyether polyols, which play an important role in the manufacture of the versatile polyurethane foam. Another ≈20% is hydrolyzed to propylene glycol. As an industrial epoxide, PO is second in importance only to ethylene oxide. PO is a chiral molecule, but almost all of it is produced as the racemic mixture.
As shown in the hazard information table, exposure to PO can cause a wide range of health and environmental problems, some severe. It must be handled with extreme care.

Chemical properties

Propylene oxide is soluble in water and miscible with most organic solvents. It is found to be an excellent low-boiling solvent for cellulose acetate, nitrocellulose, adhesive compositions and vinyl chloride-acetate resins. It is also a solvent for hydrocarbons, gums and shellac. Some of its uses are as a solvent and stabilizer in DDT aerosol-type insecticides, and as a fumigant and food preservative. Since it is an acid acceptor, it is also used as a stabilizer for vinyl chloride resins and other chlorinated systems.

Physical properties

Propylene oxide is a colorless liquid with an agreeable, ether-like odor. Experimentally determined detection and recognition odor threshold concentrations were 24 mg/m³ (10 ppm_v) and 84 μg/m³ (35 ppm_v), respectively (Hellman and Small, 1974).

The Uses of Propylene oxide

Propylene oxide is used as a fumigant forfoodstuffs; as a stabilizer for fuels, heat-ing oils, and chlorinated hydrocarbons; asa fuel–air explosive in munitions; and toenhance the decay resistance of wood andparticleboard (Mallari et al. 1989). Recentstudies indicate that the fumigant potentialof propylene oxide enhances at a low pres-sure of 100 mm Hg which could render it asan alternative to methyl bromide for rapiddisinfection of commodities (Isikber et al.2004).

The Uses of Propylene oxide

Chemical intermediate in preparation of polyethers to form polyurethanes; in preparation of urethane polyols and propylene and dipropylene glycols; in preparation of lubricants, surfactants, oil demulsifiers. As solvent; fumigant; soil sterilant.

The Uses of Propylene oxide

It can be used as a dehydrating agent for the preparation of slides in electron microscopy. Occupational dermatitis was also reported while using a skin disinfectant swab.

Definition

ChEBI: An epoxide that is oxirane substituted by a methyl group at position 2.

Production Methods

Propylene oxide is synthesized commercially from propylene through the intermediate propylene chlorohydrin. It also can be made by peroxidation of propylene using alkylhydroperoxides, but this method produces coproducts as well, often styrene or cumene. Propylene oxide is also synthesized via oxidation of propylene with hydrogen peroxide, which produceswater as the only coproduct.

General Description

A clear colorless volatile liquid with an ethereal odor. Flash point -35°F. Boiling point 95°F. Density 6.9 lb./gal. Flammable over a wide range of vapor-air concentrations. If contaminated, may polymerize with evolution of heat and possible rupture of container. Vapors irritate eyes, skin, and respiratory system. Prolonged contact with skin may result in delayed burns. Vapors heavier than air. Used as a fumigant, in making detergents and lubricants, and to make other chemicals.

Air & Water Reactions

Highly flammable. Soluble in water.

Reactivity Profile

1,3-Propylene oxide react with oxidizing agents and strong acids . Reacts with Grignard reagents and organolithium compounds. An explosion occurred when Propylene oxide was added to an epoxy resin. Propylene oxide was concluded that polymerization was catalyzed by an amine accelerator in the resin [Bretherick, 5th Ed., 1995]. Underwent polymerization when mixed with sodium hydroxide causing ignition and explosion of a drum of the crude product. [Combust Sci. Technol., 1983].

Hazard

Highly flammable, dangerous fire risk, explosive limits in air 2–22%. An irritant. TLV: 20 ppm; animal carcinogen.

Health Hazard

Exposure to propylene oxide vapors cancause moderate to severe irritation of the eyes, mucous membranes, and skin. Inhala-tion can also produce weakness and drowsi-ness. Symptoms of acute exposure in testanimals were lachrymation, salivation, gasp-ing, and labored breathing and dischargefrom nose. Harris et al. (1989) in a studyon Fischer-344 female rats found no adverseeffect below a 300-ppm exposure level.However, at the chronic inhalation levelof 500 ppm the gain in the maternal bodyweight and food consumption were reducedsignificantly. In a similar chronic inhalationstudy on Wistar rats, Kuper et al. (1988)observed a decrease in the body weight anddegenerative and hyperplastic change in thenasal mucosa when rats were exposed to300 ppm of propylene oxide. The investiga-tors have reported an increase in the inci-dence of malignant tumors in the mammaryglands and other sites in female rats.
Contact with its dilute aqueous solutionscan produce edema, blistering, and burns onthe skin. It is mutagenic in the Ames test anda suspected animal carcinogen. Its carcino-genicity in humans is not established. Omuraet al. (1994) reported dose-dependent testicu-lar toxicity of this compound in rats inducedfrom repeated intraperitoneal injections. Itsodor threshold is 200 ppm.

Fire Hazard

Vapor is heavier than air and may travel considerable distance to source of ignition and flash back. Vapors form explosive mixture with air. If polymerization takes place in container, there may be a violent rupture of container. Explosion hazard is severe when exposed to flame. Violently reacts with acetylide- forming metals such as copper or copper alloys, ammonium hydroxide; chlorosulfonic acid; hydrochloric acid; hydrofluoric acid; nitric acid; oleum and sulfuric acid. Hazardous polymerization may occur. Avoid active catalytic surfaces such as anhydrous chlorides of iron, tin, and aluminum; peroxides of iron and aluminum; and alkali metal hydroxides, high temperatures; alkalies; aqueous acids; amines and acidic alcohols.

Chemical Reactivity

Reactivity with Water No reaction; Reactivity with Common Materials: No reactions; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Not pertinent; Polymerization: Polymerization can occur when this product is exposed to high temperatures or is contaminated with alkalies, aqueous acids, amines, and acidic alcohols; Inhibitor of Polymerization: Not pertinent.

Industrial uses

Propylene oxide finds its largest use as chemical intermediates. It reacts readily with dilute amounts of mineral acids (e.g., hydrochloric acid) to form the chlorohydrin addition product. This reactivity with acid makes this epoxy solvent valuable acid acceptor-type stabilizers for several chlorinated solvents. Trace amounts of hydrogen chloride from chlorinated solvent degradation are immediately neutralized by reaction with the propylene oxide stabilizer. Reaction of propylene oxide with an alcohol or phenol in the presence of an acid catalyst yields the monoether of propylene glycol.

Contact allergens

Propylene oxide is an allergic and irritant agent, used as a solvent and raw material in the chemical industry, as the starting material and intermediate for a broad spectrum of polymers. It can be used as a dehydrating agent for the preparation of slides in electron microscopy. Occupational dermatitis was also reported following the use of a skin disinfectant swab.

Safety Profile

Confirmed carcinogen with experimental carcinogenic, neoplastigenic, and tumorigenic data. Poison by intraperitoneal route. Moderately toxic by ingestion, inhalation, and skin contact. An experimental teratogen. Experimental reproductive effects. Human mutation data reported. A severe skin and eye irritant. Flammable liquid. A very dangerous fire and explosion hazard when exposed to heat or flame. Explosive reaction with epoxy resin and sodium hydroxide. Forms explosive mixtures with oxygen. Reacts with ethylene oxide + polyhydric alcohol to form the thermally unstable polyether alcohol. Incompatible with NH4OH, chlorosulfonic acid, HCl, HF, HNO3, oleum, H2SO4. Dangerous; can react vigorously with oxidizing materials. Keep away from heat and open flame. To fight fire, use alcohol foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and fumes.

Potential Exposure

Propylene oxide is used as an interme- diate in the production of polyether polyols and propylene glycol; as a fumigant; in the production of adducts as ure- thane foam ingredients; in detergent manufacture; as a component in brake fluids.

Carcinogenicity

Propylene oxide is reasonably anticipated to be a human carcinogenbased on sufficient evidence of carcinogenicity from studies in experimental animals.

Environmental Fate

Biological. Bridié et al. (1979) reported BOD and COD values of 0.17 and 1.77 g/g using filtered effluent from a biological sanitary waste treatment plant. These values were determined using a standard dilution method at 20 °C for a 5 d period. When a sewage seed was used in a separate screening test, a BOD value of 0.20 g/g was obtained. The ThOD for propylene oxide is 2.21 g/g.
Photolytic. Anticipated products from the reaction of propylene oxide with ozone or OH radicals in the atmosphere are formaldehyde, pyruvic acid, CH3C(O)OCHO, and HC(O)OCHO (Cupitt, 1980). An experimentally determined reaction rate constant of 5.2 x 10^-13 cm³/molecule?sec was reported for the gas phase reaction of propylene oxide with OH radicals (Güsten et al., 1981).
Chemical/Physical. The reported hydrolysis half-life for the conversion of propylene oxide to 1,2-propanediol in water at 25 °C and pH 7 is 14.6 d (Mabey and Mill, 1978). The second-order hydrolysis rate constant of propylene oxide in 3.98 mM perchloric acid and 36.3 °C is 0.124/M?sec (Kirkovsky et al., 1998).
May polymerize at high temperatures or on contact with alkalies, aqueous acids, amines, and acid alcohols (NIOSH, 1997).
At an influent concentration of 1.0 g/L, treatment with GAC resulted in an effluent concentration of 739 mg/L. The adsorbability of the GAC used was 52 mg/g carbon (Guisti et al., 1974).

storage

Propylene oxide is stored in a flammableliquid cabinet isolated from combustible andoxidizable materials. It is shipped in glassbottles and metal containers under a nitrogenatmosphere.

Shipping

UN1280 Propylene oxide, Hazard Class: 3; Labels: 3-Flammable liquid

Purification Methods

Dry the oxide with Na2SO4 or CaH2 and fractionally distil it through a packed column (glass helices), after refluxing with Na, CaH2, or KOH pellets. [Beilstein 17 I 4, 17 II 131, 17 III/IV 17, 17/1 V 17.] The R(+)enantiomer [15448-47-2] and the S(-)enantiomer [16088-62-3] have b 33-34o/atm and [] 20 ±14.6o (neat). [Beilstein 17/1 V 17.]

Toxicity evaluation

The toxic effects of propylene oxide are related to its ability to react directly, without metabolic activation, with cellular macromolecules, nucleophilic sites, and nonprotein sulfhydryls. Therefore, it reacts with various components of cells, including DNA, RNA, and proteins.

Incompatibilities

Vapors may form explosive mixture with air. Reacts with strong oxidizers, anhydrous metal chlor- ides; chlorine, iron, strong acids; caustics and peroxides. Polymerization may occur due to high temperatures or con- tamination with alkalis, aqueous acids; amines, metal chlor- ides; and acidic alcohols. Attacks some plastics, coatings and rubber.

Waste Disposal

Concentrated waste contain- ing no peroxides-discharge liquid at a controlled rate near a pilot flame. Concentrated waste containing peroxides- perforation of a container of the waste from a safe distance followed by open burning