(R)-(-)-Propylene glycol goes by other names, like (R)-(-)-1,2-propanediol and (R)-(-)-propylene glycol. This clear, slightly sweet liquid is a chiral, optically active form of propylene glycol. Its chemical formula is C3H8O2 and the compound weighs 76.09 g/mol. Unlike its racemic or S-form, (R)-(-)-propylene glycol isn’t as commonly found in daily products, which makes its physical and chemical quirks an important point of interest for labs, chemical suppliers, and safety officers. You will often spot it in applications ranging from pharmaceuticals to advanced materials science, where optical activity and specific purity matter.
Take a look at (R)-(-)-propylene glycol’s structure: it's a straight-chain, three-carbon diol with two hydroxyl groups (-OH) bonded to the first and second carbons. This layout holds the key to its chirality—the R-configuration bends polarized light in a specific direction, a trademark of optically pure chemicals that factors into pharmaceutical effect and technical formulations. The density of this material typically stands at 1.036 g/cm3 at 20°C. Its boiling point measures 188.2°C, and it freezes at around -59°C. The substance flows as a viscous, colorless liquid, but under particular temperature drops, it turns to a glassy solid rather than a crystalline powder. In practice, most market formulations sell it in liquid form, though some suppliers offer more concentrated flakes or solidified beads for weighing and controlled dosing.
The most trustworthy product specs nail down purity, optical rotation, and water content. You’ll find bottles labeled “≥99% (R)-(-)-enantiomeric excess,” and reliable suppliers tend to list specific optical rotation values—usually around -8.7° to -9.5° (neat, 20°C)—as proof of enantiomeric purity. Water content stays low; too much moisture alters results in pharmaceutical synthesis or specialty formulation. The market rarely sees this compound as a fine powder, since its melting and glassing points make pure crystalline forms tricky to maintain. Laboratory suppliers sometimes produce it as solution in water or organic solvent, ready for dilution or reaction setups.
The world doesn’t use (R)-(-)-propylene glycol in everyday consumer goods the way it does with its sister compound, racemic propylene glycol. Instead, you’ll see (R)-(-)-propylene glycol pop up in asymmetric synthesis, certain chiral drug manufacturing processes, and specialized research applications where having the “right” enantiomer drives results. In these contexts, the demand goes beyond basic solvent roles—researchers care about molecular orientation, purity, and how the material reacts with other chiral substrates. As someone who handled this compound in a graduate synthesis project, I’ve seen how minor contamination—either from water or the “wrong” enantiomer—skews an entire process, leading to wasted time and materials. SAFETY DATA SHEETS mark it as having low acute toxicity and skin irritation compared to other glycols, but proper handling remains a must. Goggles, gloves, good ventilation—these weren’t guidelines in the lab, they were rules shaped by experience learning the hard way.
Despite relatively mild toxicity, (R)-(-)-propylene glycol is still a chemical, not a drinkable sweetener. Inhalation of vapors can cause coughing or respiratory irritation; spills might cause eye or skin discomfort in sensitive folks. Prolonged or repeated exposure to glycols, in general, throws off the body’s metabolic pathways, so sensible handling stays non-negotiable. In my work, I never saw a spill become a crisis, but any cautious chemist treats even modest irritants with a full cleanup protocol—absorb, ventilate, collect, and label for solvent-safe waste. Most worrying would be large-scale exposure, so industrial users set up fume hoods and spill kits. The Safety Data Sheet usually notes that this glycol isn’t listed as a major hazardous air or water pollutant. Fire risk sits low, though extensive heating can make it decompose into irritating fumes. Standard chemical-resistant gloves and eye shields go a long way toward staying safe—long lab coats and fresh air help maintain a comfortable margin.
For regulatory documentation and import-export tracking, (R)-(-)-propylene glycol falls under HS Code 29053200—classifying it alongside other propylene glycols. From a supply side, its preparation calls for asymmetric reduction reactions using expensive catalysts, with propene or allyl alcohol as upstream sources. Prices reflect both the technical complexity and the scarcity of high-purity, enantiomerically pure batches. Those tracking raw material provenance should focus on sourcing from trusted vendor audits and up-to-date, batch-tested specifications, since off-brand raw stocks occasionally test below the expected optical rotation or contain residual catalysts.
Chasing ultra-high purity in (R)-(-)-propylene glycol means dealing with those pesky contaminants—water, racemic isomers, and trace metals from catalysts. I’ve seen teams cut contamination by triple distilling in inert gas and using molecular sieves to dry the product. Routine testing, including NMR and chiral HPLC, gives early warning about drifts away from spec, while close relationships with bulk suppliers make rapid troubleshooting easier when spikes in impurity appear. For safer workspaces, simple steps like updated hazard training and clear spill protocols make a huge difference. Companies can also design systems that allow for closed transfer and minimized vapor exposure: drum pumps with sealed connectors, containment trays, and integrated fume extraction. Saving money on raw materials never balances out against a ruined synthesis—persistence with solid lab habits beats any shortcut.
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