What Is Propylene Oxide?
Propylene oxide is a three-carbon organic compound with a cyclic ether structure.
It is also known as propylene oxide, propylene oxide, methyloxirane, and 1,2-epoxypropane. It is a clear, colorless liquid at room temperature.
Uses of Propylene Oxide
Propylene oxide is rarely used in its raw state. In general, it is often used as a raw material for propylene glycol, polypropylene glycol, pigments, pharmaceutical intermediates, and disinfectants.
Among them, propylene glycol is a substance obtained by hydrolysis of propylene oxide and is mostly used as a raw material for polyester resins. Polypropylene glycol is a polyether obtained by ring-opening polymerization of propylene oxide and is used as a raw material for polyurethane foam.
In addition, it is widely used as a water retention agent in foodstuffs and cosmetics due to its moderate hydrophilic properties.
Characteristics of Propylene Oxide
Propylene oxide has a molecular formula of C3H6O, a molecular weight of 58.08, a colorless volatile liquid with an ether odor, a specific gravity of 0.8304 at 20°C, a flash point of -37°C, a boiling point of 33.9°C, a freezing point of -104.4°C, a viscosity of 0.38 mPa-s (at 20°C), and is soluble in water, alcohol, and ether. It is soluble in water, alcohols, and ethers.
It has a cyclic ether structure, and ring-opening polymerization produces polyethylene oxide, a polyether. It generally reacts readily with active hydrogen compounds.
Other Information on Propylene Oxide
1. Production Method of Propylene Oxide
There are two industrial production methods: chlorohydrin method and direct oxidation method.
Chlorohydrin Method
Chlorohydrin is synthesized from propylene to form chlorohydrin, which is then used to produce propylene oxide.
Chlorohydrin formation reaction (yield is about 90%)
CH3CH=CH2 + Cl2 + H2O → CH3CHOHCH2Cl (α-chlorohydrin) + HCl
CH3CH=CH2 + Cl2 + H2O → CH3CHClCH2OH (β-chlorohydrin) + HCl
Synthesis of propylene oxide from chlorohydrin
CH3CHOHCH2Cl or CH3CHClCH2OH + 1/2Ca(OH)2
→CH3CHCH2O (Propylene Oxide) + 1/2CaCl2 + H2O
Direct Oxidation Method
Propylene oxide is directly formed by oxidizing propylene.
Direct oxidation of propylene
CH3CH=CH2 + 1/2O2 → CH3CHCH2O (Propylene Oxide)
Propylene oxide is oxidized by peroxide, which is an oxidizing agent, and isobutane and ethylbenzene are used as peroxides. The Halcon process is known as an industrially advantageous process.
2. Safety of Propylene Oxide
Handling
Propylene oxide has a wide explosion limit of 2.8~37% and a vapor density of 2.00, twice that of air. It is a highly volatile and flammable liquefied gas with a boiling point near room temperature, and its vapor can explode by itself due to electric sparks.
When mixed with air, it becomes an explosive gas mixture. Fire is strictly prohibited and contact with acids and alkalis must be avoided. Although it is considered relatively stable under normal conditions, high temperatures and direct sunlight should be avoided.
Toxicity
Direct contact with skin will cause burns, and contact with eyes will cause keratitis. Inhalation of concentrated vapor strongly irritates the nose, throat, and bronchial tubes. Since it is also classified as a mutagenic chemical, be sure to wear protective goggles, protective gloves, and a gas mask for organic gases when handling it.