Isopropyl alcohol (IPA), also known as isopropanol, is a widely available chemical often found in homes as rubbing alcohol or as a component in various cleaning agents. Its accessibility and low cost have made it a common choice for individuals attempting do-it-yourself (DIY) extractions of botanical compounds, such as those used for herbal tinctures or essential oils. When considering any solvent-based extraction, the primary concern must be the safety of the final product intended for human use. This article examines the chemical properties that make IPA an effective solvent and the significant health risks associated with its residual presence in consumable extracts.
The Chemistry of IPA as a Solvent
IPA is a polar organic solvent, allowing it to dissolve a broad spectrum of compounds from plant material. Its moderate polarity makes it effective at pulling out both polar substances, such as certain water-soluble compounds, and non-polar compounds, including oils, resins, and alkaloids. This solvent power makes IPA attractive for broad-spectrum extractions.
IPA is a secondary alcohol that contributes to its ability to mix completely with water and other organic solvents. This miscibility is helpful when the solvent needs to be diluted or combined with water-containing plant matter. IPA also has a relatively low boiling point (approximately 80.37 degrees Celsius), which facilitates its removal through evaporation after the extraction is complete.
Residual Toxicity and Purity Concerns
The central safety issue with using IPA for extracts intended for consumption is its inherent toxicity compared to food-grade alternatives. Unlike ethanol, which the human body metabolizes into relatively harmless compounds, IPA is oxidized by alcohol dehydrogenase in the liver to form acetone. Acetone is a central nervous system depressant.
Residual IPA left in the final product, even in trace amounts, can lead to intoxication if ingested, with symptoms including dizziness, nausea, and central nervous system depression. The resulting acetone can prolong these effects, potentially leading to respiratory issues or coma. The primary goal of any extraction for consumption is the complete removal of the solvent, but the consequences of incomplete purging are far more severe with IPA than with food-grade ethanol.
Purity and Contaminants
Beyond the toxicity of the solvent itself, the purity of commercially available IPA presents an additional concern. IPA is commonly sold as “rubbing alcohol” in concentrations like 70% or 91%, meaning the remaining percentage is predominantly water. This water content will co-extract unwanted, water-soluble plant material, such as chlorophyll and sugars, which can degrade the quality and taste of the final extract. Moreover, technical or lower-grade IPA may contain trace amounts of other chemical contaminants, including diisopropyl ether or 1-propanol, which pose further health risks if ingested.
Comparing Extraction Solvents
When evaluating solvents for consumable extracts, food-grade ethanol is generally the preferred alcohol because the human body can metabolize it safely. Ethanol extractions are highly scalable and achieve high yields, though they may co-extract chlorophyll, requiring an additional refinement step like winterization. This contrasts sharply with IPA, where the primary risk is the residual solvent itself, not the co-extracted plant material.
Other methods, such as hydrocarbon extraction using butane or propane, offer greater selectivity for non-polar compounds and are highly effective at preserving delicate aromatic molecules known as terpenes. However, these methods require specialized, closed-loop systems and strict environmental controls due to the high flammability of the gases involved. Supercritical carbon dioxide (CO2) extraction provides a highly tunable and clean process, as CO2 leaves no residual solvent in the final product. The drawback to CO2 is the significant cost and complexity of the high-pressure equipment necessary.
Operational Safety and Handling
Even before considering the safety of the final extract, the process of using IPA presents immediate physical hazards to the operator. Isopropyl alcohol is classified as a highly flammable liquid, possessing a low flash point of approximately 11.7 degrees Celsius (53 degrees Fahrenheit). This means the liquid can easily ignite at or near room temperature in the presence of an ignition source, such as a spark, an open flame, or a hot surface.
The vapors of IPA are denser than air and can travel along floors, accumulating in low areas where they can form explosive mixtures with the surrounding air. Adequate ventilation is non-negotiable when working with IPA to prevent both fire risk and the inhalation of vapors, which can cause symptoms like dizziness and irritation. For storage, IPA must be kept in tightly sealed containers and stored in a cool, well-ventilated area, away from heat and strong oxidizing agents.