s-Trioxane
[CAS# 110-88-3]

Identification

• Classification: Organic raw materials >> Aldehyde
• Name: s-Trioxane
• Synonyms: 1,3,5-Trioxacyclohexane; 1,3,5-Trioxane; Trioxymethylene
• Molecular Formula: C₃H₆O₃
• Molecular Weight: 90.08
• CAS Registry Number: 110-88-3
• EC Number: 203-812-5
• SMILES: C1OCOCO1

Properties

• Density: 1.1±0.1 g/cm³, Calc.^*, 1.17 g/mL (Expl.)
• Melting Point: 59-62 °C (Expl.)
• Index of Refraction: 1.385, Calc.^*
• Boiling Point: 114.5 °C (760 mmHg), Calc.^*, 114-116 °C (Expl.)
• Flash Point: 45.0 °C, Calc.^*, 45 °C (Expl.)

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

Safety Data

• Hazard Symbols: GHS02;GHS08;GHS07 Danger
• Risk Statements: H228-H335-H361
• Safety Statements: P203-P210-P240-P241-P261-P271-P280-P304+P340-P318-P319-P370+P378-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Reproductive toxicity	Repr.	2	H361
Flammable solids	Flam. Sol.	1	H228
Specific target organ toxicity - single exposure	STOT SE	3	H335
Reproductive toxicity	Repr.	2	H361d

• Transport Information: UN 1325

Discovery and Applications

s-Trioxane, also known as 1,3,5-trioxane, is a cyclic trimer of formaldehyde with the molecular formula C₃H₆O₃. It consists of a six-membered ring with alternating carbon and oxygen atoms, where each carbon bears two hydrogen atoms. This white crystalline solid has been recognized for its stability, volatility, and ease of polymerization, making it significant in industrial and chemical contexts.

The discovery of s-trioxane is closely associated with the early investigations into the polymerization of formaldehyde in the 19th century. Formaldehyde, first prepared by Alexander Butlerov in 1859 through the oxidation of methanol, was found to undergo trimerization under acidic conditions to form s-trioxane. Its formation is favored under low-temperature and acidic environments, typically catalyzed by mineral acids such as sulfuric acid. The reaction involves the reversible combination of three molecules of formaldehyde into the cyclic trimer. The structure of s-trioxane was confirmed by elemental analysis, chemical reactivity, and later, spectroscopic techniques including nuclear magnetic resonance and X-ray crystallography.

s-Trioxane has been extensively used as a stable source of formaldehyde. Upon heating or under acidic or basic conditions, it decomposes to release formaldehyde gas, allowing it to serve as a convenient and safer alternative to aqueous formaldehyde solutions. This application is particularly important in chemical synthesis, where formaldehyde is used in resin manufacture, polymer chemistry, and various organic transformations. Because of its solid form and reduced volatility compared to aqueous formaldehyde, s-trioxane allows for more precise control over formaldehyde delivery.

In polymer chemistry, s-trioxane is employed as a monomer for the production of polyoxymethylene (POM) plastics, commonly known as acetal resins. These high-performance engineering thermoplastics are valued for their rigidity, dimensional stability, and low friction. The cationic ring-opening polymerization of s-trioxane, often initiated by boron trifluoride or other Lewis acids, leads to the formation of high-molecular-weight polyoxymethylene. The resulting polymer has widespread applications in the automotive, electronics, and consumer goods industries.

s-Trioxane has also been used as a component of solid fuel tablets, especially for military and camping purposes. In combination with hexamine or other solid fuels, s-trioxane serves as a clean-burning fuel with high calorific value. It burns with a smokeless flame and produces minimal residue, making it practical for portable heating and cooking in field conditions. These tablets are compact, stable, and ignitable without complex equipment, offering logistical advantages in environments where liquid or gas fuels are impractical.

In analytical chemistry, s-trioxane has been used in laboratory procedures requiring a controllable source of formaldehyde. It serves as a reagent in qualitative and quantitative analysis involving the reactivity of aldehydes. Due to its relatively low toxicity and ease of handling, it is sometimes preferred over aqueous formaldehyde in controlled settings.

The compound’s structure has made it a model system for studying cyclic acetals and their thermodynamic and kinetic behavior. Investigations into the ring-opening and depolymerization reactions of s-trioxane have contributed to the understanding of acetal stability, polymerization dynamics, and mechanistic pathways in organic chemistry.

Though s-trioxane is considered to be of low acute toxicity, safety guidelines recommend avoiding excessive inhalation or ingestion. Its decomposition products, primarily formaldehyde, are classified as hazardous and should be handled with care. In industrial use, proper containment and ventilation are required to mitigate risks associated with formaldehyde exposure.

s-Trioxane remains an important compound in the synthesis of formaldehyde-based materials and in applications requiring compact, high-energy solid fuels. Its stability, reactivity, and versatility continue to support its utility in both laboratory and industrial settings.

References

2023. Synthesis of diallyl acetals from allyl alcohol and paraformaldehyde or 1,3,5-trioxanes. Russian Chemical Bulletin, 72(12).
DOI: 10.1007/s11172-023-4100-y

2019. Synthesis and structure of 2,4,6-tricyclobutyl-1,3,5-trioxane. Acta Crystallographica Section E, 75(11).
DOI: 10.1107/S205698901900896X

2023. 1,3-Dioxacyclanes: synthesis based on petrochemicals, chemical transformations, and applications. Russian Chemical Bulletin, 72(11).
DOI: 10.1007/s11172-023-4027-3