Isoprene (CAS 78-79-5)

Isoprene (C₅H₈) is a colorless volatile liquid (CAS 78-79-5) with a melting point of -146°C and boiling point 34°C. As a key monomer for synthetic rubber (e.g., polyisoprene, butyl rubber), it is widely used in tires, seals, and biofuels. Highly flammable (flashpoint -48°C) and toxic (rat LC₅₀ 180 g/m³), it requires storage at 0–6°C away from light. Applications span rubber, pharmaceuticals, fragrances, and energy sectors, with market prices influenced by crude oil trends.异戊二烯（C₅H₈）是一种无色易挥发液体，CAS号78-79-5，熔点-146°C，沸点34°C。作为合成橡胶（如聚异戊二烯、丁基橡胶）的核心单体，广泛用于轮胎、密封件及生物燃料生产。

Keywords: Isoprene, Chemical properties, Synthetic rubber, Fine chemicals, Energy and industry, Safety and environment

Isoprene (Isoprene) Comprehensive Information

1. Basic Chemical Properties

• ​Chemical Formula: C₅H₈
• ​CAS Number: 78-79-5
• ​Molecular Weight: 68.12 g/mol
• ​Physical Properties:
  • ​Appearance: Colorless volatile liquid with a slight petroleum odor.
  • ​Melting Point: -146°C, ​Boiling Point: 34°C (highly volatile).
  • ​Density: 0.681 g/cm³, ​Flash Point: -48°C (extremely low, flammable).
  • ​Solubility: Insoluble in water; soluble in ethanol, ether, acetone, and other organic solvents.

2. Application Fields

1. ​Synthetic Rubber
   • ​Isoprene Rubber (IR): Accounts for 70% of isoprene consumption, used in tires, shoe soles, seals, etc., with performance similar to natural rubber.
   • ​Butyl Rubber (IIR): Copolymerized with isobutylene for inner tubes and medical bottle stoppers, requiring small amounts of isoprene to improve vulcanization.
   • ​Styrene Block Copolymers (SIS/SEPS): Used in pressure-sensitive adhesives and coatings, representing the second-largest application.
2. ​Fine Chemicals
   • ​Fragrances and Pharmaceuticals: Synthesis of vitamin A, K, and fragrance intermediates (e.g., linalool, geraniol).
   • ​Pesticides and Coatings: Precursors for insecticides, fungicides, and coating additives.
3. ​Energy and Industry
   • ​Biofuels: Used in biodiesel and aviation fuel synthesis.
   • ​Petroleum Resins: Applied in inks and adhesives.

3. Production Methods

1. ​C5 Fraction Separation:
   • Extracted from ethylene cracker C5 fractions (main industrial source).
   • Purified via extractive distillation (solvents like acetonitrile, N-methyl-2-pyrrolidone).
2. ​Synthetic Methods:
   • ​Propylene Dimerization: Catalytic dimerization of propylene (higher cost).
   • ​Isobutylene-Formaldehyde Method: Isobutylene reacts with formaldehyde followed by demethylation (suitable for regions with abundant feedstock).

4. Safety and Environmental Impact

• ​Hazards:
  • ​Flammability: Extremely low flash point (-48°C), explosive when mixed with air (explosion limits 1.5%-10%).
  • ​Toxicity: Rat inhalation LC₅₀ = 180 g/m³ (4 hours); potential carcinogenicity (IARC 2B).
• ​Environmental Risks:
  • ​Atmospheric Chemistry: Emitted naturally (plant release) and industrially (cracking, combustion), contributing to ozone and secondary organic aerosol formation.
  • ​Aquatic Toxicity: Harmful to fish (LC₅₀ >1,000 mg/L).
• ​Storage Requirements:
  • Store sealed in dark, away from oxidizers and strong acids, at 0–6°C.

5. Research Progress

1. ​Atmospheric Chemistry Mechanisms:
   • Photooxidation pathways vary with NOₓ concentrations, affecting secondary organic aerosol formation.
2. ​Thermal Runaway Studies:
   • Oxidation may cause thermal runaway, releasing decomposition products like methyl vinyl ketone and 3-methylfuran.
3. ​Biological Synthesis Applications:
   • Core building block for terpenes (e.g., terpenoids, steroids) in drug and natural product development.

6. Market and Supply Chain

• ​Major Producers:
  • ​International: ExxonMobil, BASF, Shell.
  • ​China: Sinopec, Panjin Heyun Group, etc., with capacity concentrated in East and South China.
• ​Price Trends:
  • Influenced by crude oil prices and cracker operating rates; 2023 price range: 8,000–12,000 CNY/ton (China market).

7. Synonyms and Abbreviations

• ​Aliases: 2-Methyl-1,3-butadiene, isoprene
• ​Abbreviations: IP, IPR

具有易燃性（闪点-48°C）和毒性（大鼠LC₅₀ 180 g/m³），需避光储存于0-6°C。应用涵盖橡胶、医药、香料及能源领域，市场价受原油波动影响。

关键词: 异戊二烯, 化学性质, 合成橡胶, 精细化学品, 能源与工业, 安全与环境