Propylene, an organic compound with the molecular formula C3H6, is a colorless, odorless gas with a slightly sweet taste. It is highly flammable and produces a bright flame when burning. Its explosive limit in the air is 2.4% to 10.3%. Insoluble in water, but readily soluble in ethanol and ether.
Physical properties
Density: 1.914kg/m ³
Melting point: -185℃
Boiling point: -47.7℃
Flash point: -108℃
Refractive index: 1.3567
Saturated vapor pressure: 1158kPa (at 25℃)
Critical temperature: 91.9℃
Critical pressure: 4.62MPa
Ignition temperature: 460℃
Explosion upper limit (V/V) : 10.3%
Lower explosive limit (V/V) : 2.4%
Appearance: Colorless gas
Solubility: Slightly soluble in water, readily soluble in ethanol and ether
Chemical properties
"Aggregation"
The chemical properties of propylene are determined by its double bond and the hydrogen atom on the allyl group. In the molecular structure of propylene, due to the low symmetry shown only in the projection on the principal plane, it becomes the smallest stable unsaturated hydrocarbon. This asymmetry is also manifested in the fact that the dipole moment of propylene is only 0.35D, making it prone to various types of chemical reactions. The carbon atoms at positions 1 and 2 have the same structure as the ethylene molecule and are on the same triangular plane. Due to the existence of a double bond, they cannot rotate freely. However, the carbon atom at position 3 is in a tetrahedral state like methane and can rotate freely. The hydrogen atom on the allyl group is attracted to this carbon atom. The hydrogen atom on the allyl group is the main reason that makes its chemical properties different from those of ethylene.
Hydrogenation
Like other alkenes with a double bond, propylene releases the same amount of heat per mole in the hydrogenation reaction, approximately 12.56kJ/mol. However, the hydrogenation reaction of propylene has no industrial value
Hydration
Propylene can be indirectly hydrated under the action of acid. In the presence of a solid catalyst, it can be directly hydrated to obtain isopropyl alcohol. When sulfuric acid is used as a catalyst for hydration, propylene first reacts with sulfuric acid to form sulfate esters, and the sulfate esters hydrolyze to obtain isopropyl alcohol.
Catalytic oxidation
Catalytic oxidation of propylene to acrolein.
The Sohio process, which uses bismuth molybdate or phosphomolybdate as catalysts, represents a new economic breakthrough in acrolein production. Many companies have also developed highly selective multi-component catalyst systems, with selectivity reaching 75% to 84% in terms of propylene.
React with halogens
Propylene and halogens can undergo two addition reactions under different conditions.
Propylene reacts with halogens at room temperature, under gas-phase light exposure or in the presence of a catalyst.
React with hydrogen bromide
The addition of asymmetric alkenes to hydrogen halides, although all proceed according to the rule of asymmetric addition. However, during the reaction, if peroxides are present, hydrogen bromide is different from hydrogen chloride and hydrogen iodide. What is produced is 1-bromopropane instead of 2-bromopropane.
Epoxidation reaction
The co-oxidation method utilizes organic peroxides to generate oxygen free radicals. Under the action of a catalyst, the oxygen in the peroxide portion is transferred to propylene to form epoxides, thereby converting hydrogen peroxides into alcohols or ketones and peracids into acids.
