Cyclopentane
[CAS 287-92-3]

Identification

• Classification: Organic raw materials >> Hydrocarbon compounds and their derivatives >> Cyclic hydrocarbon
• Name: Cyclopentane
• Molecular Formula: C₅H₁₀
• Molecular Weight: 70.13
• CAS Registry Number: 287-92-3
• EC Number: 206-016-6
• SMILES: C1CCCC1

Properties

• Density: 0.8±0.1 g/cm³ Calc.^*, 0.751 g/mL (Expl.)
• Melting point: -94 °C (Expl.)
• Boiling point: 49.2 °C 760 mmHg (Calc.)^*, 50 °C (Expl.)
• Flash point: -37.2 °C (Calc.)^*, -37.2 °C (Expl.)
• Solubility: Insoluble in H2O (Expl.)
• Index of refraction: 1.433 (Calc.)^*, 1.405 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02 DangerGHS02
• Risk Statements: H225-H412
• Safety Statements: P210-P233-P240-P241-P242-P243-P273-P280-P303+P361+P353-P370+P378-P403+P235-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable liquids	Flam. Liq.	2	H225
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Aspiration hazard	Asp. Tox.	1	H304
Specific target organ toxicity - single exposure	STOT SE	3	H336
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335

• Transport Information: UN 1146

chemBlink Chemical Story

Making a solid from seawater might sound like the opposite of desalination. In hydrate-based separation research, however, forming the right solid can help separate water from dissolved salts. Cyclopentane, CAS 287-92-3, has attracted attention as a guest molecule in that process. Its role illustrates an unusual application of a small hydrocarbon: helping water organize into cages rather than serving as a fuel or becoming part of a new covalent molecule.

Cyclopentane has the formula C₅H₁₀, with five carbon atoms connected in a saturated ring. The formula alone would not distinguish it from some alkenes, but the connectivity does: its carbon-carbon bonds are single bonds. Nor is it pentane, whose open saturated chain has two additional hydrogen atoms. Ring closure changes the hydrogen count without requiring a carbon-carbon double bond.

The familiar pentagon drawing is also a simplification. A five-membered carbon ring can pucker, reducing unfavorable eclipsing interactions between neighboring bonds. These changing conformations preserve the same chemical connectivity. The distinction between the flat drawing and the moving molecule is a reminder that structural formulas encode bonds more directly than they describe a molecule's complete three-dimensional behavior.

In a clathrate hydrate, water molecules form a hydrogen-bonded host framework containing cavities occupied by guest molecules. Cyclopentane can act as one such guest. The resulting material is not ordinary ice with cyclopentane merely smeared over its surface, and the guest does not become covalently bonded into the water framework. Formation depends on suitable temperature, pressure, and composition, rather than occurring whenever the two liquids meet.

The desalination idea follows from how dissolved salts are distributed. Hydrate formation preferentially incorporates water into the solid framework while leaving much of the salt in the remaining liquid. If the solid can be separated and then dissociated, water can be recovered. A 2017 study investigated cyclopentane hydrate formation together with filtration and washing for seawater desalination. The inclusion of washing highlights a practical difficulty: salty liquid can remain between or on the harvested crystals.

This distinction matters when interpreting an experiment. A framework that largely excludes salt does not automatically produce a collected solid free of brine. Crystal formation, liquid entrainment, separation, and subsequent treatment all influence the recovered water. Measuring the salt content of the final water therefore answers a different question from demonstrating that hydrate crystals formed in the first place.

Later research published in 2023 examined theoretical maximum water yield and temperature optimization for cyclopentane hydrate-based desalination. That framing draws attention to the amount of water recovered and the conditions needed to obtain it, alongside salt removal. A process that gives a small quantity of low-salt water still needs evaluation of productivity, energy use, and handling of the other streams before its overall usefulness can be judged.

Cyclopentane recovery is part of that wider picture. Dissociating the hydrate releases the guest as well as water, so a proposed process must account for their separation and reuse. Low salt content alone also does not establish drinking-water suitability; residual organic material and other quality requirements remain separate considerations. Research demonstrations should consequently be described as separation studies, not as proof of a finished potable-water technology.

The attraction of this chemistry is the connection between molecular recognition and process engineering. A small ring-shaped molecule can influence a water framework, but useful desalination requires control over the entire cycle of formation, collection, and recovery.

References:
1. NIST Chemistry WebBook. Cyclopentane, CAS 287-92-3. https://webbook.nist.gov/cgi/cbook.cgi?ID=C287923&Mask=4
2. Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination. Desalination (2017). https://doi.org/10.1016/j.desal.2016.11.016
3. Investigation of theoretical maximum water yield and efficiency-optimized temperature for cyclopentane hydrate-based desalination. Water Research (2023). https://doi.org/10.1016/j.watres.2023.120707

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