Hexane: A Widely Used Solvent with Neurotoxic Concerns

CAS Registry Number: 110-54-3

Overview

Hexane is a straight-chain alkane hydrocarbon with the chemical formula C₆H₁₄ and a molecular weight of 86.18 g/mol. It appears as a colorless, volatile liquid with a faint, gasoline-like odor. Commercial hexane is typically a mixture of isomers, with n-hexane content ranging from 20% to 80%. The compound is highly flammable and practically insoluble in water.

Key Properties

• Boiling Point: 69°C

• Melting Point: -95°C

• Density: 0.66 g/mL (water = 1)

• Vapor Pressure: 124–150 mmHg at 20–25°C

• Vapor Density (air=1): 2.97–3.0

• Flash Point: -22°C to -7°F (closed cup)

• Explosive Limits: 1.1% – 7.5% in air

• Water Solubility: 9.5 mg/L (practically insoluble)

• Log Kow: 3.9–4.0 (indicates potential for bioaccumulation)

Major Applications

Industrial Solvent

Hexane is primarily used as a volatile, non-polar solvent in various industries. Major applications include:

• Oilseed Extraction: Used for extracting vegetable oils from soybeans, cottonseed, flaxseed, and other oil seeds

• Cleaning Agent: Used in the printing, textile, furniture, and shoemaking industries

• Adhesives: Component in special glues and adhesives

• Laboratory Use: Widely used as a non-polar solvent for chromatographic purification, extractions, and as a reaction medium

Other Uses

• Paint diluent and thinner

• Filling for thermometers (as a mercury substitute)

• Denaturant for alcohol

• Preparation of organolithium reagents

Health Hazards

Neurotoxicity (Primary Concern)

The most significant health concern from hexane exposure is neurotoxicity. The mechanism involves metabolism to 2,5-hexanedione, which causes delayed distal polyneuropathy. Key findings include:

• Peripheral Neuropathy: Long-term exposure can result in numbness, paresthesia, and leg weakness, potentially leading to paralysis in severe cases

• Exposure Threshold: Concentrations ≥500 ppm for ≥2 months have been associated with human neurotoxicity

• Nonspecific Narcosis: Acute high-level exposure may cause headache, dizziness, nausea, and unconsciousness (similar to anesthetic compounds)

Other Health Effects

• Respiratory: Mild irritation to eyes, nose, and throat; higher exposures may cause respiratory symptoms

• Developmental: Associations with low birth weight and alterations of the neonatal immune system have been reported

• Reproductive: Longer menstrual cycles, increased time to pregnancy, and higher risks of spontaneous abortion have been observed in some epidemiological studies

• Dermal: Repeated skin contact can cause dermatitis and defatting

Carcinogenicity

There is currently inadequate information to assess the carcinogenic potential of hexane. The EPA has concluded that available data are insufficient for a carcinogenicity assessment.

Safety and Handling

Exposure Limits

• NIOSH REL: TWA 50 ppm (180 mg/m³)

• OSHA PEL: TWA 500 ppm (1800 mg/m³)

• ACGIH TLV: TWA 50 ppm

• IDLH: 1100 ppm (10% of LEL)

Fire and Explosion Hazards

Hexane is highly flammable (Class IB flammable liquid). Its vapor is heavier than air and may travel along the ground, causing ignition at distant sources. The flash point is -22°C, and explosive vapor-air mixtures can form at concentrations of 1.1–7.5%.

Incompatibilities

Reacts violently with strong oxidizing agents, creating fire and explosion hazards. Attacks some plastics, rubber, and coatings.

Storage and Handling Precautions

• Storage: Store in fireproof conditions, in a cool (below 29°C), well-ventilated area, separated from strong oxidants

• Electrical Equipment: Use explosion-proof equipment and prevent electrostatic discharge (grounding required)

• Personal Protection: Chemical safety goggles, protective gloves, and appropriate respiratory protection when ventilation is inadequate

• Fire Extinguishing: Use foam, dry powder, or carbon dioxide. Water is ineffective

• Spill Response: Remove all ignition sources, collect in sealable containers, and absorb residual liquid with inert material

First Aid

• Inhalation: Move to fresh air; administer oxygen if breathing difficulty occurs; perform CPR if breathing stops

• Skin Contact: Remove contaminated clothing; wash with soap and water; seek medical attention

• Eye Contact: Irrigate immediately with water for at least 15 minutes; seek medical attention

• Ingestion: Do NOT induce vomiting (aspiration risk); rinse mouth; seek immediate medical attention