Tetrapropylammonium tetraoxoruthenate
[CAS# 114615-82-6]

Identification

• Classification: Chemical reagent >> Organic reagent >> Amine salt (ammonium salt)
• Name: Tetrapropylammonium tetraoxoruthenate
• Synonyms: Tetrapropylammonium perruthenate
• Molecular Formula: C₁₂H₂₈N.RuO₄
• Molecular Weight: 351.43
• CAS Registry Number: 114615-82-6
• EC Number: 628-415-8
• SMILES: CCC[N+](CCC)(CCC)CCC.O.O.O.[OH-].[Ru]

Properties

• Melting point: 160 °C (Decomposes) (Expl.)

Safety Data

• Hazard Symbols: GHS03;GHS07 Danger
• Risk Statements: H272-H315-H319-H335
• Safety Statements: P210-P220-P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P370+P378-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Oxidising solids	Ox. Sol.	2	H272
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Oxidising solids	Ox. Sol.	3	H272

Discovery and Applications

Tetrapropylammonium tetraoxoruthenate is an inorganic-organic hybrid compound composed of the tetrapropylammonium cation ([(C₃H₇)₄N]⁺) and the tetraoxoruthenate(VIII) anion ([RuO₄]⁻). Its chemical formula is typically written as [(C₃H₇)₄N][RuO₄], and it appears as a deep red or purple crystalline solid. The compound is notable for being a stable, isolable form of the highly reactive and powerful oxidizing agent, ruthenium tetroxide (RuO₄), in the form of its monovalent anionic salt.

The discovery of this compound is rooted in research conducted during the 20th century on the stabilization of high-valent transition metal oxides. Ruthenium tetroxide is a volatile and strongly oxidizing molecule with a tetrahedral geometry, isoelectronic with osmium tetroxide. It is typically unstable in its neutral form under ambient conditions. However, by forming a salt with a bulky, lipophilic cation such as tetrapropylammonium, chemists were able to isolate the tetraoxoruthenate(VIII) anion in a solid-state, stable form.

Tetrapropylammonium tetraoxoruthenate is prepared by reacting ruthenium dioxide (RuO₂) or another ruthenium source with strong oxidants like hypochlorite (ClO⁻) or peroxides in an aqueous basic medium, in the presence of tetrapropylammonium hydroxide or bromide. Under these conditions, Ru(VIII) is stabilized as the [RuO₄]⁻ anion, and the large organic cation facilitates its crystallization.

Structurally, the [RuO₄]⁻ anion retains a nearly perfect tetrahedral geometry similar to that of the neutral RuO₄ molecule. The Ru–O bond distances are short, consistent with the high oxidation state of ruthenium and the multiple bond character. The lipophilic nature of the tetrapropylammonium cation contributes to the solubility of the salt in organic solvents such as chloroform and dichloromethane, enabling its use in organic phase oxidations.

This compound is primarily employed as a reagent in organic synthesis. It acts as a powerful and selective oxidizing agent, capable of converting alkenes to ketones or carboxylic acids, alcohols to aldehydes or ketones, and in some cases cleaving carbon-carbon double bonds completely to generate smaller oxidized fragments. Compared to neutral RuO₄, the [RuO₄]⁻ anion provides more controlled reactivity, and its salts are easier to handle due to reduced volatility and greater thermal stability.

The compound has been investigated for its potential in catalytic oxidation systems. In some reactions, [RuO₄]⁻ serves as a precursor or intermediate in catalytic cycles involving ruthenium-based oxidants. Although its use is limited due to cost and handling considerations, it offers a powerful tool in situations requiring high selectivity and strong oxidation capacity.

In terms of safety, tetrapropylammonium tetraoxoruthenate must be handled with great care. Like RuO₄, the compound is highly oxidizing and can react violently with reducing agents or combustible materials. It is toxic by inhalation, ingestion, and skin contact, and strict protective measures must be used during handling, including gloves, protective eyewear, and a fume hood. The compound should be stored under inert conditions and away from heat or organic materials.

In summary, tetrapropylammonium tetraoxoruthenate is a stable, isolable salt of the powerful oxidizer [RuO₄]⁻, useful in selective organic oxidations and studies involving high-valent ruthenium species. It is valued for its solubility in organic solvents and the ability to deliver Ru(VIII) reactivity in a manageable solid form. Its applications are primarily found in research and specialized synthetic chemistry.

References

2014. Ruthenium Tetroxide and Perruthenate Chemistry. Recent Advances and Related Transformations Mediated by Other Transition Metal Oxo-species. Molecules (Basel, Switzerland), 19(5).
DOI: 10.3390/molecules19056534

2010. A Double Donor‐Activated Ruthenium(VII) Catalyst: Synthesis of Enantiomerically Pure THF‐Diols. Angewandte Chemie (International ed. in English), 49(8).
DOI: 10.1002/anie.200903090

2008. The grounds for the activity of TPAP in oxidation catalysis in supercritical carbon dioxide when confined in hybrid fluorinated silica matrices. Physical chemistry chemical physics : PCCP, 10(20).
DOI: 10.1039/b716405j