Heptane: A Versatile Non-Polar Solvent

CAS Registry Number: 142-82-5

Overview

Heptane is a straight-chain alkane hydrocarbon with the chemical formula C₇H₁₆ and a molecular weight of 100.20 g/mol. It appears as a colorless, volatile liquid with a characteristic gasoline-like odor. Heptane is a major component of gasoline and is widely used as a non-polar solvent in various industrial and laboratory applications. As a solvent, it is considered a greener alternative to hexane.

Key Properties

• Boiling Point: 98.4°C

• Melting Point: -90.7°C

• Density: 0.68 g/mL at 20°C

• Vapor Pressure: 40 mmHg at 20°C

• Flash Point: -7°C (closed cup)

• Explosive Limits: 0.8% – 6.7% in air

• Autoignition Temperature: 220°C

• Solubility: Very poor in water (2.2 mg/L at 25°C); soluble in ethanol, ether, and other organic solvents

• Log Pow: 4.66 (indicates potential for bioaccumulation)

Major Applications

Laboratory and Industrial Solvent

Heptane is extensively used as a non-polar organic solvent for dissolving organic compounds without interacting with them. It serves in chromatographic purification, extraction processes, and as a reaction medium for sensitive chemical syntheses.

Pharmaceutical Industry

Heptane is employed as an inert solvent for the purification, recrystallization, and washing of active pharmaceutical ingredients (APIs). It is also used as a pharmaceutical reference standard for quality control analysis by gas chromatography.

Extraction and Manufacturing

• Extraction and purification of natural substances such as CBD (cannabidiol)

• Manufacturing of inks, paints, varnishes, and adhesives

• Production of synthetic rubbers (e.g., polybutadiene) in solution

• Component of rubber solvent naphtha and paint thinners

Fuel and Octane Rating

Heptane has historical significance as the "zero point" of the octane rating scale, as it causes knocking in engines. A 100% n-heptane fuel serves as the baseline (0 octane) against which isooctane (100 octane) is compared.

Safety Information

Hazards Classification (GHS)

Heptane is classified as a dangerous substance with the following hazard statements:

• H225: Highly flammable liquid and vapor

• H304: May be fatal if swallowed and enters airways (aspiration hazard)

• H315: Causes skin irritation

• H336: May cause drowsiness or dizziness

• H400/H410: Very toxic to aquatic life with long-lasting effects

Health Effects

• Acute Exposure: Inhalation may cause dizziness, stupor, incoordination, nausea, and unconsciousness. The primary mechanism is nonspecific narcosis (anesthesia-like effects on the central nervous system).

• Skin Contact: Causes irritation and defatting of the skin, potentially leading to dryness and cracking.

• Aspiration Hazard: If swallowed and aspirated into the lungs, may cause chemical pneumonitis.

Chronic Toxicity

Heptane is considered less neurotoxic than hexane, as it does not produce the same gamma-diketone metabolites responsible for hexane-induced peripheral neuropathy. Animal studies have not demonstrated significant neurotoxic effects from heptane exposure. Heptane is not considered mutagenic or carcinogenic.

Exposure Limits

• NIOSH REL: TWA 85 ppm (350 mg/m³); Ceiling 440 ppm (1800 mg/m³) [15-minute]

• OSHA PEL: TWA 500 ppm (2000 mg/m³)

• ACGIH TLV: TWA 400 ppm; STEL 500 ppm

• IDLH: 750 ppm

Incompatibilities

Reacts violently with strong oxidizers, creating fire and explosion hazards. Attacks many plastics.

Handling and Storage

• Storage: Store in fireproof conditions, in a cool, well-ventilated area, separated from strong oxidants.

• Fire Prevention: Use explosion-proof electrical equipment, prevent electrostatic discharge (grounding required), and use non-sparking tools.

• Personal Protection: Wear chemical safety goggles, protective gloves, and appropriate respiratory protection if ventilation is inadequate.

• Spill Response: Remove all ignition sources, do not wash into sewer, collect in sealable containers, and absorb remaining liquid with inert material.

• First Aid: In case of ingestion, do NOT induce vomiting (aspiration risk). Move victim to fresh air for inhalation exposure.