What Is Isopropyl Alcohol? Grades, CAS 67-63-0 and the Names Buyers Actually Use

2-Propanol, the secondary alcohol registered under CAS 67-63-0 and EINECS 200-661-7, is sold under the IUPAC name propan-2-ol and the industrial synonyms isopropanol, isopropyl alcohol, IPA, dimethyl carbinol, and sec-propyl alcohol. At 101.325 kPa, the neat material boils at 82.6 °C; its closed-cup flash point is 11.7 °C, its density at 20 °C is 0.7855 g/cm³, and its dynamic viscosity at 20 °C is 2.43 mPa·s. The same CAS number can appear on purchase orders for 70% aqueous topical solution, 99.9 wt% anhydrous solvent, ACS reagent-grade material, HPLC mobile-phase diluent, and low-metal electronics-grade IPA. The operational control is never the name alone; it is the specification attached to lot-release data.

CAS 67-63-0 Versus Buyer Nomenclature on an ISO 9001 Certificate of Analysis

ASTM D770 provides the base specification for isopropyl alcohol, while purchaser-specific limits for water by ASTM D1364 and distillation range by ASTM D1078 may be appended to a certificate of analysis. A compliant C of A lists the registry number CAS 67-63-0 alongside one of the following buyer terms: “2-propanol ACS,” “isopropanol USP,” “propan-2-ol HPLC,” “anhydrous IPA 99.5%,” “99.9% low-water IPA,” “electronics-grade IPA,” or “IPA 70% USP.” The term “rubbing alcohol” is not a sufficient industrial procurement descriptor because it denotes a formulated consumer product and may contain water, stabilizers, or denaturants. Under REACH, the registration dossier for propan-2-ol identifies EC 200-661-7; the neat substance is classified under GHS as Flam. Liq. 2, Eye Irrit. 2, and STOT SE 3. A buyer should reject a C of A that omits CAS 67-63-0, lot number, test method, result, and specification limit.

In procurement practice, “isopropyl alcohol” and “IPA” dominate among pharmaceutical and industrial solvent purchasers, while “propan-2-ol” appears most often in analytical certificates and import documentation aligned with IUPAC naming. “Dimethyl carbinol” and “sec-propyl alcohol” are older synonyms still present in legacy product dossiers but are not recommended for new safety data sheets because of ambiguity. Semiconductor fabs abbreviate to “IPA” with suffixes such as “VLSI” or “low-metal”; pharmaceutical buyers append “USP,” “Ph. Eur.,” or “JP” to “isopropyl alcohol.” The distinction is not cosmetic. A tanker of 99.5 wt% ACS reagent IPA may fail a pharmaceutical cleaning route if the buyer required Ph. Eur. water limits and residual solvent documentation.

The Narrow Water Thresholds That Define Anhydrous and 70% 2-Propanol Commerce

Water content is the primary trade parameter. Neat 2-propanol forms a minimum-boiling azeotrope with water at 87.7 wt% isopropanol, boiling at 80.37 °C under 101.325 kPa. This is lower than the anhydrous boiling point of 82.6 °C; therefore atmospheric distillation alone cannot deliver 99.5% anhydrous material from dilute feed. The 70% by volume aqueous isopropyl alcohol used for topical antiseptic and disinfectant applications corresponds to roughly 64–67 wt% isopropanol depending on temperature and alcoholometric conversion; buyers should not treat 70% by volume and 70 wt% as equivalent. Anhydrous-grade 99.9 wt% IPA is specified with a water limit of 0.1 wt% or lower. The difference is an order of magnitude that changes viscosity, solvent power, and corrosion behavior. For water-sensitive applications, the specification should state both assay by GC and water by Karl Fischer: a C3H8O assay of 99.9% by GC without a water limit does not prove low water.

In immersion cleaning tools used for silicon wafer drying, the required control is not merely water but metal and particle content. Wafers exiting an RCA-type clean are often passed through a heated isopropanol vapor zone to reduce water surface tension and promote Marangoni-assisted drying. Process engineers specify 99.5 wt% minimum IPA with cation limits for sodium, potassium, iron, calcium, and zinc, measured by ICP-MS after evaporation. A single 200 L drum from a non-dedicated filling line can exceed an end-user metal limit of 10 ppb for a critical element if the filling line previously handled a metal-bearing product without validated cleaning. There is no universal SEMI standard for isopropyl alcohol; electronics buyers therefore generate site-specific purchase specifications that combine CAS 67-63-0 with internal ICP-MS, particle-count, and non-volatile-residue criteria. Published data for this specific configuration is limited because wafer fabs do not publicly release drum-level acceptance thresholds.

When a HPLC Buyer Rejects a Tanker of 99.5% IPA for Carbonyl Carryover

HPLC/UV-grade 2-propanol is not merely anhydrous. A buyer runs UV absorbance at 205 nm, 210 nm, 230 nm, and 254 nm against water in a 1 cm quartz cell. Low-level acetone, acetaldehyde, and related oxidation products can raise absorbance in the low-UV range and interfere with gradient baselines. Isopropanol stored warm in partially filled containers can show an increase in acetone content; the carbonyl impurity causes UV cutoff drift even when GC purity remains acceptable. Distillation alone may not remove all trace carbonyls if the column head temperature and reflux ratio are not controlled. A dedicated head with high reflux ratio and nitrogen blanketing reduces carbonyl partitioning but requires validated cleaning between campaigns. A common buyer specification for HPLC grade is UV transmittance ≥ 90% at 210 nm, UV transmittance ≥ 98% at 254 nm, water NMT 0.05%, and residue after evaporation NMT 1 ppm. A solvent can pass at 99.8% GC assay and still fail UV-grade because the interfering carbonyl impurities occur in the low ppm range.

Pharmaceutical buyers use “IPA 70%” for disinfectant efficacy and “isopropyl alcohol Ph. Eur.” for granulation or equipment cleaning. The 70% v/v product is not a simple dilution of anhydrous IPA but a formulated antimicrobial product under local pharmacopeial monographs. ICH Q3C classifies isopropanol as a Class 3 residual solvent with a permitted daily exposure of 50 mg/day; excipient and API release testing may use headspace GC with a limit of 5000 ppm or lower if justified. Cosmetic formulators use the INCI name Isopropyl Alcohol in nail lacquers, hair styling resins, and sanitizer formulations. High-purity anhydrous IPA used in topical products still requires stability data for peroxide and carbonyl formation under heat and UV exposure; amber glass or nitrogen-blanketed packaging is used when peroxide values must remain below 1 ppm.

Azeotropic Distillation, 3A Molecular Sieves, and the 87.7 wt% Boundary

Production of anhydrous 2-propanol begins where simple distillation ends. The water–isopropanol azeotrope at 87.7 wt% isopropanol requires a separation train using azeotropic distillation with an entrainer, pressure-swing adsorption, or membrane dehydration. The kinetic diameter of water is approximately 0.26 nm, while isopropanol is larger; 3A zeolites with a nominal pore opening of 0.3 nm selectively adsorb water and can reduce water to 0.1 wt% or lower. Regeneration of 3A molecular sieves is typically conducted at 200–250 °C under dry nitrogen; incomplete regeneration leaves a water heel that raises product moisture. On 25,000 L storage tanks, field failures are mainly due to atmospheric venting without nitrogen blanketing. Moist air drawn during tank breathing is absorbed at the liquid surface, increasing water by 0.05–0.2 wt% per quarter for low-turnover tanks. The exact water ingress depends on local dew point, tank fill level, breather desiccant condition, and transfer frequency.

What Happens to a 200-L Drum of 99.5 wt% IPA Under Humid Storage?

A closed standard 200 L tight-head steel drum with 2-in and 3/4-in closures can maintain anhydrous IPA for months if the gasket is intact and the drum remains sealed. Once opened, water uptake is not linear; it depends on ambient relative humidity, headspace volume, and the number of closure operations. At 25 °C and 60% RH, a partially filled drum can show measurable water increase by Karl Fischer within days. Filling lines that do not purge drums with dry nitrogen after sampling and reclosure generate higher headspace moisture. For flammable-liquid storage, isopropanol is assigned UN 1219, transport class 3, packing group II; storage should be in grounded steel or HDPE containers away from oxidizers, with ventilation designed for a closed-cup flash point of 11.7 °C. API RP 2003 recommends inlet fill velocities below 1 m/s to reduce static charge accumulation. After any opening, the drum is no longer certified to the original water specification unless re-analyzed by Karl Fischer.

On a flexographic printing press using isopropanol as a solvent ink diluent and roller wash, recovered solvent is rarely saleable as original grade without analysis. Solvent recovery systems using packed columns often return IPA at 87–90 wt% from water-bearing waste streams; the distillate requires off-site dehydration or molecular-sieve finishing to reach 99.5 wt%. Coatings formulators that buy “IPA 99%” for viscosity adjustment in polyamide inks should request a water limit because residual water above 0.5 wt% can invert polyamide resin solubility in mixed-solvent systems and increase flocculation. Precision electro-optical assembly cleaning likewise requires a 99.9% low-residue IPA with a non-volatile residue limit below 1 ppm when the final rinse must leave no UV-detectable film after evaporation.