ISOPENTANE: STRUCTURE, PROPERTIES, USES, OBTAINING - CHEMISTRY - 2025

The isopentane is an organic compound which is condensed formula (CH ₃) ₂ CHCH ₂ CH ₃. It is an alkane, specifically a branched isomer of pentane, characterized by being a highly volatile liquid and used as a foaming agent. Currently, its most recommended name by the IUPAC is 2-methylbutane.

In the image below its structural formula can be seen. Note that a CH ₃ group is actually attached to carbon 2 of the butyl chain. From isopentane, the isopentyl or isopentyl substituent or radical is obtained, being one of the most voluminous alkyl substituents that there may be.

Structural formula of isopentane. Source: NEUROtiker / Public domain

Isopentane is a non-polar, hydrophobic, and flammable compound. Its smell is similar to that of gasoline, and is in fact part of its composition, as it increases its octane number or octane number. It is obtained from the isomerization reaction of n-pentane, although it is naturally achieved in small quantities within natural gas reserves.

Its highly flammable character aside, isopentane is considered a non-toxic substance. A person can ingest it and smell it sparingly before undesirable symptoms, such as vomiting and dizziness, develop. Isopentane can be found in shaving creams and hair conditioners.

Structure of isopentane

Molecular structure of isopentane. Source: Benjah-bmm27 via Wikipedia.

In the upper image we have the molecular structure of isopentane, represented by a model of spheres and bars. The black spheres correspond to the carbon atoms, while the white spheres to the hydrogen atoms. Its carbon skeleton can be said to be robust, branched and voluminous.

The ends of the isopentane molecule are comprised of CH ₃ groups, which are inefficient when it comes to enhancing intermolecular interactions. Isopentane molecules depend on London's dispersive forces and their masses in order to remain cohesive, and thus define a liquid under normal conditions of temperature and pressure.

However, its geometry and the CH ₃ groups are responsible for the isopentane liquid being highly volatile and boiling at a temperature of 28.2 ºC. For example, the linear n-pentane isomer boils around 36 ° C, reflecting its better intermolecular interactions.

Despite its apparent robustness, the isopentane molecule is capable of adopting various spatial configurations, a key factor in the establishment of its crystal at a temperature of -160ºC.

Properties

Physical appearance

Colorless liquid or gas, with a watery appearance, and also giving off an odor similar to that of gasoline. It is a highly volatile substance.

Melting point

Isopentane crystallizes at a temperature range between -161 and -159 ° C.

Boiling point

Isopentane boils at a temperature range between 27.8 and 28.2 ºC. Therefore, as soon as it is exposed outside its container, it will begin to boil and give off large volumes of steam.

Vapor pressure

76.9 kPa at 20 ºC (about 0.76 atm)

Density

0.6201 g / mL at 20 ° C. Isopentane vapors are 2.48 denser than air.

Solubility

Isopentane, being an apolar substance, is insoluble and immiscible with water and some alcohols. It is soluble and miscible in paraffinic solvents, ethers, carbon tetrachloride, and also in aromatic liquids such as toluene.

Refractive index

1,354

Surface tension

15 dyn / cm at 20 ºC

Viscosity

0.214 cP at 20 ºC

Flash point

-51 ° C. This temperature makes isopentane dangerously flammable, so your products should be kept as far away as possible from any flame or heat source.

Autoignition temperature

420 ºC

Applications

Shaving creams contain small amounts of isopentane that act as a propellant and add texture to the product. Source: Pixabay.

Isopentane is an organic solvent that serves as a reaction medium for certain organic syntheses, and it also represents the raw material for the production of other compounds.

It is added to gasoline to increase its octane rating, and to various cosmetic products to improve its texture, such as shaving creams, once it evaporates quickly and leaves behind a bubbly mass.

Similarly, polystyrene is moistened in isopentane so that, when it evaporates, it expands the plastic until creating a kind of foam, with which glasses, models, plates, trays, etc. are designed.

On the other hand, in cryogenics isopentane is used, together with dry ice and liquid nitrogen, to freeze tissues and biological samples.

Obtaining

Isopentane can be obtained from natural gas reservoirs, however occupying only 1% of its content.

Another route, the most widely used at an industrial level, is starting with n -pentane distilled from oil refining processes. Then the n -pentane undergoes a special reaction called isomerization.

The purpose of the isomerization of n-pentane is to obtain its more branched isomers. Thus, among the products we not only have isopentane but also neopentane. This reaction is possible through the use of very specific metallic catalysts, which control what temperature and what pressures are required.

Risks

Isopentane is considered a non-toxic substance. This is partly due to its low reactivity, since its CC or CH bonds are not easy to break, so they do not interfere as such in any metabolic process. In fact, a person is capable of inhaling large amounts of its vapors before suffocation, without apparently suffering collateral damage.

Its ingestion causes nausea and vomiting, and its contact with the skin ends up drying it. On the other hand, medical studies have not been able to determine whether isopentane is a carcinogenic substance. However, it is considered a dangerous pollutant for marine ecosystems and their fauna.

The greatest danger around isopentane is not so much its reactivity, but its flammability: it burns with oxygen in the air. And because its liquid is highly volatile, the slightest leak will release many of its vapors into the environment, which will ignite at the slightest proximity to a flame or any other source of heat.

That is why products containing isopentane should be stored in safe and cool environments.

References

1. Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. (10 ^th edition.). Wiley Plus.
2. Carey F. (2008). Organic Chemistry. (Sixth edition). Mc Graw Hill.
3. Morrison and Boyd. (1987). Organic chemistry. (Fifth edition). Addison-Wesley Iberoamericana.
4. Wikipedia. (2020). Isopentane. Recovered from: en.wikipedia.org
5. National Center for Biotechnology Information. (2020). Isopentane. PubChem Database. CID = 6556. Recovered from: pubchem.ncbi.nlm.nih.gov
6. Elsevier BV (2020). Isopentane. ScienceDirect. Recovered from: sciencedirect.com
7. Jennifer B. Galvin & Fred Marashi. (2010). 2-Methylbutane (Isopentane). Journal of Toxicology and Environmental Health, Part A Current Issues. Volume 58, 1999 - Issue 1-2. doi.org/10.1080/009841099157403