Propene
[CAS 115-07-1]

Identification

• Classification: Organic raw materials >> Hydrocarbon compounds and their derivatives >> Acyclic hydrocarbon
• Name: Propene
• Synonyms: 1-Propylene; HC 1270; Methylethylene; Propylene; R 1270
• Molecular Formula: C₃H₆
• Molecular Weight: 42.08
• CAS Registry Number: 115-07-1
• EC Number: 204-062-1
• SMILES: CC=C

Properties

• Density: 0.6±0.1 g/cm³ Calc.^*, 1.49 g/mL (Expl.)
• Melting point: -185 °C (Expl.)
• Boiling point: -47.7 °C 760 mmHg (Calc.)^*, -47.7 °C (Expl.)
• Flash point: -69.5±9.0 °C (Calc.)^*, -108 °C (Expl.)
• Index of refraction: 1.348 (Calc.)^*, 1.357 (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
Specific target organ toxicity - single exposure	STOT SE	3	H336

chemBlink Chemical Story

A three-carbon gas helped change the way chemists think about building large molecules. Propene, also called propylene, is registered as CAS 115-07-1. Its formula is C₃H₆, and its defining feature is a carbon-carbon double bond beside a methyl group. That small asymmetry becomes important when many propene molecules join to form polypropylene.

The double bond distinguishes propene from propane, the saturated three-carbon alkane. It also distinguishes its connectivity from cyclopropane, which shares the formula C₃H₆ but places the carbon atoms in a ring. These examples show why a formula does not identify a structure by itself. For propene's polymer chemistry, the location and geometry of the double bond provide the starting opportunity.

In addition polymerization, the monomer's double-bond framework is converted into connections along a growing saturated chain. The methyl groups remain as side groups on the polypropylene backbone. No small molecule has to be eliminated from every monomer during this chain-building step. This is a different construction principle from polymerizations that connect monomers while releasing substances such as water.

Connecting the atoms is only part of the challenge. The spatial arrangement of the methyl-bearing units also matters. Regular arrangements can support different packing behavior from an irregular sequence, affecting how polymer chains organize into a solid. The term tacticity describes this stereochemical pattern along a polymer chain; it is not simply another word for molecular weight or monomer purity.

Giulio Natta's research brought stereospecific polymerization into this story. In his 1963 Nobel Lecture, he described the preparation of new polymers from propylene and other monomers beginning in 1954, together with investigation of their ordered structures. The achievement was not the first recognition that small molecules could form chains, but control over aspects of the spatial arrangement within those chains.

The history connects naturally with catalyst design. A catalyst does more than provide an alternative route for bond formation: its environment can influence how successive monomer units are incorporated. The resulting structure depends on the actual catalytic system and reaction conditions. Saying that a material was made from propene therefore does not, by itself, specify the stereochemical organization or properties of the polymer obtained.

Nor are the monomer and the polymer interchangeable substances. Propene is a small, volatile molecule, whereas polypropylene is a distribution of macromolecular chains. Chain length, stereochemical sequence, and the organization of chains in the solid all help determine the behavior of a particular grade. The original feed supplies the repeating structural motif, but it does not uniquely define every finished material made from it.

This change can be viewed locally as well as along an entire chain. The original double bond has a planar arrangement, whereas incorporation into a saturated backbone creates a different spatial setting around the methyl-bearing carbon. Repeating an oriented local event many times produces a chain-level pattern. It is this connection between a small bond-forming decision and a repeated macromolecular arrangement that makes stereospecific polymerization a particularly revealing example of molecular control over materials.

This makes propene a useful bridge between molecular and materials chemistry. The double bond supplies a point for chain growth, the methyl group creates a stereochemical distinction, and catalysis helps determine how that distinction is repeated. A familiar plastic can thus be traced back to decisions about how a small molecule approaches a reaction site. The story shows that making a polymer involves not only joining many units, but also controlling the architecture that emerges from their sequence.

References:
1. NIST Chemistry WebBook. Propene, CAS 115-07-1: molecular identity. https://webbook.nist.gov/cgi/cbook.cgi?ID=C115071
2. Natta G. From the stereospecific polymerization to the asymmetric autocatalytic synthesis of macromolecules. Nobel Lecture, 12 December 1963. https://www.nobelprize.org/uploads/2018/06/natta-lecture.pdf
3. Max Planck Society. Patent solution in a canning jar: Ziegler-Natta catalysts and stereoregular polypropylene. https://www.mpg.de/8361429/flashback-ziegler

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