Chloromethane

Chloromethane (Methyl Chloride, CH₃Cl, CAS 74-87-3) is a colorless, flammable gas at ambient temperature and pressure, with a faint ethereal odor. It boils at -24.2 °C and has an explosive limit of 8.1%–17.4% in air. Slightly soluble in water but readily miscible with most organic solvents, chloromethane is primarily used as a key feedstock for producing methylchlorosilanes—the building blocks for silicone oils, rubbers, and resins. It also serves as a methylating agent in pharmaceutical and agrochemical synthesis. Due to its flammability and toxicity, strict safety controls including leak-proof pressurized cylinders, explosion-proof ventilation, and separation from oxidizers are mandatory during storage and handling.

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Product Introduction

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Physicochemical properties

Physical state: Gaseous (25℃), liquefaction point -24.2℃, boiling point -24.1℃, melting point -97.7℃
Density: Gas 2.15 g/L (air ≈ 1.29), Liquid 0.916 g/cm³ (20℃)
Solubility: Slightly soluble in water (approx. 0.48 g/100 mL, 20℃), readily soluble in ethanol, ether, chloroform, and acetone
Flammability: Flammable, explosion limits 8.1%–17.4% (volume, air); burns with a blue-green flame, producing HCl, CO₂, and H₂O
Chemical behavior: Typical primary haloalkane, highly SN2 reactive; can be eliminated to form ethylene under strong alkali/high temperature, or undergo ammonolysis, cyanolysis, or Grignardization; further chlorination with Cl₂ under light yields CH₂Cl₂, etc.
Stability: Chloromethane is stable under dry conditions; it decomposes and explodes when exposed to open flames or high temperatures.

Core Uses

Organosilicon monomer raw material (largest consumer): Reacts with silicon powder at 250–300℃ under copper catalysis to produce a mixture of methylchlorosilanes, which is then fractionated to obtain dimethyldichlorosilane (DMDCS): 2CH₃Cl + Si → (CH₃)₂SiCl₂ (main) + CH₃SiCl₃ + (CH₃)₃SiCl. This is the source of silicone rubber, silicone oil, and silicone resin, consuming the majority of global chloromethane.

Methylating agent: Used as a mild methylating agent in pharmaceutical and pesticide synthesis (cheaper than iodomethane and less toxic than dimethyl sulfate), for the O/N-methylation of phenols, carboxylic acids, and amines.

Historical uses in refrigeration and foaming: Initially used as a low-temperature refrigerant (R-40) and polyurethane foaming agent. Due to the greenhouse effect (GWP≈13) and flammability, it has been gradually replaced by HFCs and HFOs, with only a small repair market remaining in China. Other niche areas include tetramethyllead synthesis (obsolete), solvent extraction, and acrylate modification.

Safety and Storage

Toxicity: Narcotic; high concentrations depressant to the central nervous system; IDLH 2000 ppm; chronic exposure damages the liver, kidneys, and thyroid.

GHS: Flammable gas (F+), Acute Toxic (Acute Tox 4), Specific Target Organ Toxicity (STOT SE 3)

Storage: Chloromethane must be stored in pressure-resistant steel cylinders in a cool, well-ventilated area, away from sources of ignition, oxidizing agents, and alkali metals. In the event of a leak, use explosion-proof fans to dilute the gas; do not discharge it into underground drains (as it is heavier than air and will accumulate in low-lying areas).

Fire Extinguishing: After shutting off the gas supply, use dry powder, CO₂, or water mist; if water is scarce, shut off the gas supply first, then inerte.

Exposure: If inhaled, move to fresh air; if breathing stops, administer artificial respiration and seek medical attention; for liquid contact with skin, prevent frostbite.

FAQ

Q: Toxicity and Occupational Health

A:Acute toxicity: Rat inhalation LC₅₀ (4h) 5300 ppm; mouse inhalation LC₅₀ 10,000 ppm; moderately toxic, but high concentrations can be fatal;

Primary hazards: Neurotoxicity + liver and kidney damage:

Inhalation irritates the respiratory tract; high concentrations cause headache, dizziness, nausea, drowsiness, and ataxia; severe cases may lead to coma and respiratory failure;

Long-term low-level exposure can cause neurasthenia syndrome, hepatomegaly, and renal dysfunction;

Skin contact with the liquid causes frostbite (due to rapid vaporization and heat absorption);

Carcinogenicity: Classified by IARC as Group 3 (not classifiable as to its carcinogenicity to humans), though long-term occupational exposure is clearly linked to nervous system damage;

Occupational exposure limits:

China GBZ 2.1: PC-TWA 60 mg/m³ (≈28 ppm), PC-STEL 120 mg/m³

ACGIH TLV-TWA: 50 ppm (103 mg/m³), STEL 100 ppm

OSHA PEL: 100 ppm (TWA)

⚠️ Major hazard: Colorless and odorless; leaks are difficult to detect; relies on instrument monitoring rather than the sense of smell.

Q: Key Points for Handling and Storage

A: Fully enclosed system with leak alarms (detecting both toxic and combustible gases); open-system operations are strictly prohibited.

PPE: Wear a half-face respirator with an organic vapor cartridge for routine inspections; use a Self-Contained Breathing Apparatus (SCBA) for high-concentration leaks; wear cold-resistant gloves and safety goggles when handling the liquid.

Storage: Store in a dedicated, cool, and well-ventilated gas cylinder room (≤30°C); keep cylinders upright and secured; store away from heat sources, ignition sources, and strong oxidizers (e.g., chlorine, oxygen); maintain a residual pressure of ≥0.05 MPa in the cylinders.

Leak Response: Quickly evacuate personnel to an upwind location and eliminate ignition sources; use water spray to dilute and dissolve the substance (noting its low solubility); transfer the material to a tanker truck or dedicated collection vessel using an explosion-proof pump; do not use a direct water jet on the leak (as this may cause the substance to spread).

Firefighting: Shut off the gas supply, then extinguish the fire using dry chemical powder, CO₂, or water spray; if the gas supply cannot be shut off, allow the fire to burn itself out to prevent a flashback explosion.

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