n-Butane
[CAS 106-97-8]

Identification

• Classification: Organic raw materials >> Hydrocarbon compounds and their derivatives >> Acyclic hydrocarbon
• Name: n-Butane
• Synonyms: HC 600; HC 600 (hydrocarbon); LPG; Liquefied petroleum gas; R 600
• Molecular Formula: C₄H₁₀
• Molecular Weight: 58.12
• CAS Registry Number: 106-97-8
• EC Number: 203-448-7
• SMILES: CCCC

Properties

• Density: 0.6±0.1 g/cm³ Calc.^*, 0.579 g/mL (Expl.)
• Melting point: -138 °C (Expl.)
• Boiling point: -1.7±3.0 °C 760 mmHg (Calc.)^*, -0.5 °C (Expl.)
• Flash point: -70.9±6.6 °C (Calc.)^*
• Solubility: Slightly soluble (Expl.)
• Index of refraction: 1.354 (Calc.)^*, 1.345 (Expl.)

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

Safety Data

• Hazard Symbols: GHS02;GHS04 DangerGHS02
• Risk Statements: H220
• Safety Statements: P203-P210-P222-P280-P377-P381-P403

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable gases	Flam. Gas	1	H220
Gases under pressure (liquid)	Press. Gas (Liq.)		H280
Gases under pressure (compressed)	Press. Gas (Comp.)		H280
Germ cell mutagenicity	Muta.	1B	H340
Carcinogenicity	Carc.	1A	H350
Carcinogenicity	Carc.	1B	H350
Specific target organ toxicity - single exposure	STOT SE	3	H336
Gases under pressure (dissolved)	Press. Gas (Diss.)		H280

• Transport Information: UN 2037F 2.1

chemBlink Chemical Story

A molecule familiar as a fuel can also be the starting point for selective chemical manufacturing. n-Butane, CAS 106-97-8, connects these two roles. Its four carbon atoms form an unbranched chain, with the formula C₄H₁₀. Burning it releases energy by extensive oxidation; converting it into a useful chemical intermediate requires a catalyst that directs oxidation along a much more selective path.

The prefix n identifies the normal, unbranched isomer. Isobutane has the same formula but a different carbon skeleton, so the two names do not describe interchangeable pure substances. Even the unbranched chain is not a rigid straight rod: rotation around carbon-carbon bonds gives different conformations without changing connectivity. Distinguishing molecular constitution from molecular shape helps explain why a simple structural formula is only the beginning of its physical chemistry.

At ordinary room temperature and atmospheric pressure, n-butane is a gas, but pressure can maintain it as a liquid. This phase behavior makes compact storage possible and explains the practical significance of liquefied hydrocarbon fuels. When liquid evaporates, it takes up heat from its surroundings. The same connection between pressure, temperature, and phase also underlies its refrigerant designation R-600, which must be distinguished from the isobutane designation R-600a.

An industrially important chemical destination is maleic anhydride. In this transformation, a saturated four-carbon feed becomes an oxygen-containing cyclic product while preserving a four-carbon skeleton. Simply supplying oxygen would not ensure the desired outcome, because further oxidation can produce carbon oxides instead. Catalysis is therefore about choosing among competing reaction pathways, rather than merely making the feed react faster.

Research on vanadium-phosphorus-oxygen catalysts has examined that problem for decades. A 1985 study compared model vanadium phosphate phases for n-butane oxidation. Later, Cheng and Goddard used computational chemistry to investigate how phosphate-containing surface sites could participate in activation of the alkane. The studies address different levels of explanation: measured catalytic behavior and a proposed molecular account of events at a surface.

Conversion and selectivity are separate quantities in this context. Conversion asks how much n-butane reacted; selectivity asks how the reacted material was distributed among products. A catalyst can consume feed efficiently while sending too much of it toward undesired products. Describing a useful chemical process therefore requires following carbon through the reaction network, not just observing that the starting gas disappeared.

This application is distinct from using the compound as a source of heat. In a fuel application, extensive oxidation is the objective. In chemical manufacture, stopping at a valuable intermediate is the challenge. The molecule is the same, but the desired destination changes the meaning of a successful reaction and the design of the surrounding equipment.

It is also useful to separate a physical cycle from a chemical one. Evaporation and condensation change intermolecular spacing and energy without replacing the molecule's carbon framework. Oxidation changes bonds and produces new substances. A pressure-temperature measurement describes the first kind of behavior, while product analysis is needed for the second. Using the same starting material in both settings does not make those measurements or their objectives interchangeable, even when both applications involve heat transfer.

n-Butane thus offers a compact story about phase behavior and reaction control. Liquefaction explains how a small gas becomes a practical stored material. Selective oxidation explains how that familiar material can become a chemical feedstock. Its usefulness comes from understanding both the physical state of the supplied compound and the particular transformation being asked of its carbon framework.

References:
1. NIST Chemistry WebBook. Butane, CAS 106-97-8: identity and phase-change data. https://webbook.nist.gov/cgi/cbook.cgi?ID=C106978&Mask=4
2. Selective oxidation of n-butane to maleic anhydride by model V-P-O catalysts. 1985. https://experts.arizona.edu/en/publications/selective-oxidation-of-n-butane-to-maleic-anhydride-by-model-vpo-/
3. Cheng MJ, Goddard WA III. The critical role of phosphate in vanadium phosphate oxide for the catalytic activation and functionalization of n-butane to maleic anhydride. J Am Chem Soc. 2013;135:4600-4603. https://doi.org/10.1021/ja3115746

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