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Dimethyldioxirane
Dimethyldioxirane
Dimethyldioxirane
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Dimethyldioxirane
  Carbon, C
  Hydrogen, H
  Oxygen, O
Names
IUPAC name
3,3-Dimethyldioxirane
Other names
DMDO
Monoperoxyacetone, Murray's reagent
Identifiers
3D model (JSmol)
ChemSpider
UNII
  • InChI=1S/C3H6O2/c1-3(2)4-5-3/h1-2H3 checkY
    Key: FFHWGQQFANVOHV-UHFFFAOYSA-N checkY
  • InChI=1/C3H6O2/c1-3(2)4-5-3/h1-2H3
    Key: FFHWGQQFANVOHV-UHFFFAOYAF
  • CC1(OO1)C
Properties
C3H6O2
Molar mass 74.08 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Dimethyldioxirane (DMDO) is the organic compound with the formula (CH3)2CO2.[1] It is the dioxirane derived from acetone and can be viewed as the monomer of acetone peroxide. It is a powerful selective oxidizing agent that finds some use in organic synthesis. It is known only in the form of a dilute solution, usually in acetone, and hence the properties of the pure material are largely unknown.[2]

Synthesis

[edit]

DMDO is not commercially available because of chemical instability. DMDO can be prepared as dilute solutions (~0.1 M) by treatment of acetone with potassium peroxymonosulfate KHSO
5, usually in the form of Oxone (2KHSO5·KHSO4·K2SO4).[3]

The preparation of DMDO is rather inefficient (typical yields < 3%) and typically only yields a relatively dilute solution in acetone (only up to approximately 0.1 M). This is tolerable as preparation uses inexpensive substances: acetone, sodium bicarbonate, and oxone. Cold solutions (−10 to −20 °C) of DMDO are stable for days. Decomposition is accelerated by light and by heavy metals. The concentration of DMDO may be assayed immediately prior to its use.[2]

Methyl(trifluoromethyl)dioxirane (H
3C)(F
3C)CO
2 can be similarly prepared from methyl trifluoromethyl ketone. It is a stronger oxidant than DMDO.

Uses

[edit]

DMDO is most commonly used for the oxidation of alkenes to epoxides.[4] One advantage of using DMDO is that the only byproduct of oxidation is acetone, a fairly innocuous and volatile compound. DMDO oxidations are particularly mild, sometimes allowing oxidations which might not otherwise be possible.

Despite its high reactivity, DMDO displays good selectivity for electron-rich olefins. DMDO will also oxidize several other functional groups. For example, DMDO will oxidize primary amines to nitro compounds and sulfides to sulfoxides. In some cases, DMDO will even oxidize unactivated C-H bonds:

DMDO can also be used to convert nitro compounds to carbonyl compounds (Nef reaction).[5]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Dimethyldioxirane

View on Grokipedia
from Grokipedia
Dimethyldioxirane (DMDO), also known as Murray's reagent, is a three-membered cyclic organic peroxide with the molecular formula C₃H₆O₂ and the structure featuring a triangular dioxirane ring consisting of a carbon atom bearing two methyl groups bonded to two oxygen atoms. This volatile, yellow compound exists only as a dilute solution in acetone (typically 0.07–0.1 M) and is renowned as a mild, selective electrophilic oxidant that transfers oxygen under neutral conditions without requiring catalysts or metals. First isolated in 1985 through the oxidation of acetone with potassium caroate (Oxone), DMDO's dioxirane structure was confirmed by ¹⁷O NMR spectroscopy in 1987, marking a breakthrough in non-metal-based oxidation chemistry. DMDO is synthesized by reacting acetone with Oxone in buffered with , followed by low-temperature to isolate the as a stable solution at −25°C; this procedure yields concentrations of 0.07–0.09 M with high purity when unreacted are carefully managed. As a strong yet chemoselective oxidant, it exhibits high reactivity toward electron-rich substrates, enabling stereospecific epoxidation of alkenes (e.g., cis-alkenes to cis-epoxides in near-quantitative yields), Baeyer-Villiger oxidation of ketones to esters, and conversion of sulfides to sulfones, often at and with minimal over-oxidation. Its electrophilic nature allows selective oxidation of secondary alcohols over primary ones and has been applied in the dearomatization of indoles and furans to form epoxides or methides, facilitating downstream transformations in synthesis. Due to its instability, DMDO must be handled in a with safety shields, and it decomposes exothermically if concentrated or heated. Beyond traditional batch processes, recent advances include continuous-flow generation of DMDO for scalable epoxidations, enhancing safety and efficiency in polymer and monomer synthesis, such as epoxidizing imidazolium salts for advanced materials with improved thermal properties.

Properties

Structure and nomenclature

Dimethyldioxirane possesses the molecular formula C₃H₆O₂ and features a strained three-membered ring structure consisting of a central carbon atom bonded to two oxygen atoms, with two methyl groups attached to the carbon atom. This triangular dioxirane ring can be viewed as derived from acetone, where the carbonyl group has been converted to the cyclic peroxide moiety. The IUPAC name for the compound is 3,3-dimethyldioxirane, reflecting the dimethyl substitution at the 3-position of the dioxirane parent scaffold. It is commonly referred to as DMDO (an abbreviation for dimethyldioxirane) or Murray's reagent, in honor of Robert W. Murray, who first isolated it in pure form. Another synonym is monoperoxyacetone, emphasizing its structural relation to . Compared to the parent dioxirane (CH₂OO), which is highly unstable and decomposes rapidly at , the two methyl substituents in dimethyldioxirane significantly enhance kinetic stability by reducing through substitution effects. This stabilization arises from hyperconjugative interactions and steric factors that lower the strain energy by approximately 6-10 kcal/mol relative to the unsubstituted analog. Computational studies indicate that the O-O in dimethyldioxirane is about 1.51 , while the C-O bonds are around 1.40 , values similar to those in the parent dioxirane (O-O ≈ 1.51 , C-O ≈ 1.39 ) but with altered reactivity due to the electron-donating methyl groups that weaken the peroxide bond slightly and facilitate oxygen transfer.

Physical and chemical properties

Dimethyldioxirane (DMDO) is handled exclusively as a dilute solution in acetone, appearing as a pale yellow liquid with typical concentrations ranging from 0.08 to 0.10 M. The pure compound has not been isolated owing to its inherent instability and tendency to decompose. Its molar mass is 74.08 g/mol. The predicted boiling point of pure DMDO is approximately -22 °C, while the of the acetone solution is approximately 0.8 g/mL (similar to acetone). DMDO exhibits good in acetone and other organic solvents such as , but it is immiscible with . As a cyclic , DMDO functions primarily as an electrophilic oxygen transfer agent, facilitating selective oxidations under mild conditions. Its nature precludes typical acidity measures like pKa, as it lacks ionizable protons in the conventional sense. Thermodynamically, DMDO is endothermic, with a energy of about 11 kcal/mol that enhances its reactivity compared to less strained analogs; this strain is moderated relative to the parent dioxirane due to dimethyl substitution.

Stability and reactivity

Dimethyldioxirane (DMDO) exhibits limited thermal stability, particularly in its typical acetone solutions, where it remains viable for practical use only under controlled low-temperature conditions. Solutions are stable for weeks when stored at -20 °C, allowing for extended in refrigerated environments. At higher temperatures, such as around (approximately 22 °C), DMDO persists for about 7 hours before significant occurs. Above 0 °C, accelerates primarily through homolysis of the O-O bond, leading to an of approximately 24.9 kcal/mol for the process. This thermal instability is attributed to the strained three-membered ring structure, which facilitates bond breaking, though the gem-dimethyl substitution provides some kinetic stabilization compared to unsubstituted dioxiranes. Photochemical and catalytic factors further compromise DMDO's stability, making careful storage essential. Exposure to , including visible wavelengths up to 450 nm due to UV tailing upon standing, promotes decomposition. Similarly, trace such as iron or catalyze rapid breakdown, as do basic conditions, where the drops dramatically—less than 30 minutes under neutral and even shorter in alkaline media. In the absence of these accelerators, such as in dark storage at -20 °C, solutions maintain stability for weeks, underscoring the importance of inert, low-, and metal-free conditions for longevity. As a reactive species, DMDO functions as a mild and selective oxidant, primarily through concerted oxygen atom transfer mechanisms that avoid radical intermediates under standard conditions. This electrophilic involves a spiro-like , enabling precise oxidations without the harshness of traditional peracids. Decomposition pathways yield products such as acetone (from ring opening), (via ), and reactive oxygen species including , particularly in nucleophile-catalyzed variants. Radical channels, stemming from O-O homolysis, contribute modestly (about 23% at 56 °C) but are not dominant in typical reactivity scenarios.

Synthesis

Preparation from peroxymonosulfate

Dimethyldioxirane (DMDO) is primarily prepared in the through the reaction of acetone, which serves as both solvent and substrate, with (commercially available as Oxone, 2KHSO₅·KHSO₄·K₂SO₄) in the presence of a buffer. This method was first reported by Robert W. Murray and Ramasubbu Jeyaraman in 1985, representing a significant improvement over earlier approaches using , which suffered from lower yields and poorer control over reaction conditions. The reaction proceeds via nucleophilic attack of the oxygen on the electrophilic peroxo moiety of the peroxymonosulfate anion, forming the three-membered dioxirane ring: (\ceCH3)2\ceC=O+\ceHSO5−→\ce(CH3)2C(O2)+\ceHSO4−(\ce{CH3})_2\ce{C=O} + \ce{HSO5^-} \rightarrow \ce{(CH3)2C(O2)} + \ce{HSO4^-} This process generates DMDO in as a dilute solution in acetone, typically without isolation of the pure compound due to its . Standard conditions involve suspending excess Oxone in a of acetone and water, buffered to 7–8 with to maintain neutrality and prevent decomposition. The is cooled to 0–5 °C and stirred vigorously for 10–15 hours to ensure complete conversion, with the temperature controlled to minimize side reactions such as acetone epoxidation or peroxymonosulfate decomposition. After reaction, the is subjected to to collect the acetone solution, which is dried over to yield a clear, pale yellow solution of DMDO. Yields are typically 0.08–0.1 M in DMDO (corresponding to 2–3% based on available Oxone), limited by the equilibrium nature of the formation and competing pathways. The concentration of the resulting solution is determined by iodometric , which quantifies active oxygen content through reaction with to liberate iodine, or by (GC) analysis, often using phenyl methyl as a substrate to monitor epoxidation efficiency via formation. These assays confirm the solution's potency, with providing a direct measure of peroxo and GC offering structural specificity.

Alternative synthetic routes

A modern adaptation for safer and larger-scale production employs continuous flow generation using Oxone in microreactors. In this , a 0.8 M solution of Oxone and 0.33 M K₃PO₄ in a 70:30 water:acetone mixture is used in a at ambient temperature with residence times of 1-5 minutes, followed by filtration and reaction in a PFA coil, generating DMDO for epoxidation and enabling gram-scale of epoxidized materials at rates of 0.8 g/hour without the need for hazardous storage or . This method addresses safety concerns by minimizing the accumulation of the explosive reagent and facilitates on-demand generation for applications like epoxidation. Other oxidants, such as Caro's acid (H₂SO₅), have been employed in historical syntheses by adding a 50% K₂CO₃ solution dropwise to the acid at 0 °C to form the dioxirane in acetone solution. Attempts with peroxyacids like mCPBA, following the general reaction (CH₃)₂C=O + mCPBA → DMDO + PhCO₂H, suffer from low efficiency due to competing side reactions and poor selectivity. All alternative routes yield dilute solutions of dimethyldioxirane (typically 0.04-0.18 M), and isolation of pure material remains unviable owing to the compound's high explosion risk when concentrated, necessitating use or careful handling in solvent.

Applications

Epoxidation of alkenes

Dimethyldioxirane (DMDO) serves as an effective for the epoxidation of alkenes, converting them to the corresponding epoxides while producing acetone as a . The reaction proceeds under mild, neutral conditions, typically at temperatures between 0 and 25 °C, without the need for catalysts or additional . It involves a stereospecific syn addition of oxygen to the , preserving the alkene's in the product. The mechanism of DMDO-mediated epoxidation is a concerted process involving direct oxygen transfer from the dioxirane ring to the through a spiro . In this , the alkene's π-bond interacts with one of the oxygens, leading to simultaneous formation of the two C-O bonds and cleavage of the O-O bond, without involvement of radical or stepwise intermediates. This pathway ensures no skeletal rearrangement occurs and provides high , particularly favoring electron-rich alkenes due to the electrophilic nature of the oxygen atom being transferred. DMDO exhibits broad scope for epoxidizing terminal, internal, and aryl-substituted alkenes, accommodating a variety of functional groups under conditions that avoid over-oxidation. For instance, is converted to in approximately 90% yield within minutes at . Similarly, cis-3-hexene undergoes epoxidation nearly quantitatively, reacting eight times faster than the trans isomer due to steric accessibility in the spiro . Aryl alkenes like yield the 9,10-epoxide in 93% isolated yield at -20 °C. These examples highlight DMDO's for both aliphatic and aromatic systems. Recent developments include continuous-flow generation of DMDO for scalable epoxidations in and synthesis, such as epoxidizing or imidazolium salts for advanced materials with improved thermal properties, enhancing safety and as of 2022. Compared to peracids such as mCPBA, DMDO offers advantages including higher selectivity for acid-sensitive substrates, operation under neutral pH to prevent side reactions like Baeyer-Villiger oxidation, and a recyclable acetone byproduct that simplifies workup. Unlike peracids, which can lead to over-oxidation or ring-opening of sensitive epoxides, DMDO's mild reactivity minimizes such issues, making it preferable for complex syntheses.

Other oxidation reactions

Dimethyldioxirane (DMDO) selectively oxidizes to the corresponding without further oxidation to sulfones, owing to the reagent's controlled reactivity. For instance, the oxidation of thioanisole (methyl phenyl ) proceeds in high yield, typically 80-95%, under mild conditions at low temperatures in . This transformation is widely used for the preparation of due to its high selectivity and avoidance of over-oxidation, even with one equivalent of DMDO. Recent applications include post-polymerization modification of conjugated polymers containing , achieving selective formation to tune optical properties as of 2019. DMDO also facilitates the oxidation of amines, converting tertiary amines to amine N-oxides in quantitative yields at 0 °C, often within less than one hour. For primary amines, DMDO effects a two-step oxidation to nitro compounds under controlled conditions, such as low temperatures to minimize side reactions like . These reactions highlight DMDO's utility in nitrogen-containing interconversions, providing clean access to oxidized derivatives without metal catalysts. In C-H bond activations, DMDO enables the oxidation of unactivated alkanes to alcohols or ketones, targeting tertiary sites preferentially. A representative example is the conversion of to 1-adamantanol via tertiary C-H oxidation, achieving yields of approximately 20-30% under standard conditions. This method demonstrates DMDO's capability for direct functionalization of saturated hydrocarbons, though selectivity for secondary over tertiary sites can vary with substrate sterics. DMDO mediates a variant of the by oxidizing nitronate anions derived from primary nitroalkanes, leading to the corresponding carbonyl compounds under mild, neutral conditions. This approach offers an efficient alternative to classical Nef protocols, accommodating sensitive substrates and proceeding in good yields without acidic workup. Despite these applications, DMDO's efficacy diminishes for electron-poor substrates, where reaction rates slow and alternative oxidants may be preferred. Additionally, many transformations require excess DMDO to achieve satisfactory conversion due to its dilute solutions and nature.

Safety and handling

Hazards

Dimethyldioxirane (DMDO) is a highly reactive organic that poses significant risks due to its unstable three-membered ring structure containing a weak O-O bond. Neat or concentrated DMDO is shock-sensitive and can detonate upon mechanical impact or heating, with solutions above approximately 0.1 M becoming increasingly hazardous and prone to violent decomposition. As a volatile , DMDO exhibits thermal instability, decomposing exothermically at elevated temperatures and potentially leading to runaway reactions if not properly controlled. Health hazards associated with DMDO primarily stem from its irritant nature. Contact with causes , while exposure to eyes results in serious damage requiring immediate flushing and medical attention. Inhalation of vapors or mist can irritate the . may cause gastrointestinal , though specific data for DMDO are limited. Environmental risks arise from DMDO's products, which include acetone—a flammable —contributing to fire hazards and potential air quality issues in confined spaces. residues from incomplete reactions can form concentrates in waste streams, necessitating careful containment to prevent release into or water systems. Toxicity data for DMDO remain limited, with no established LD50 values; it is classified under GHS as a irritant (Category 2) and causing serious eye (Category 2). Analogous are often rated as oxidizing liquids (Category 1).

Storage and disposal

Dimethyldioxirane (DMDO) is typically generated for use due to its instability, but if stored, it should be as a dilute solution in acetone at concentrations below 0.1 M to minimize risks associated with its reactivity as an organic peroxide. Solutions are maintained at low temperatures such as -20 °C in a freezer to prevent , which is accelerated at higher temperatures, with stability observed for up to several weeks under these conditions (though some commercial guidance suggests 10–25 °C). Storage containers should be made of glass and protected from light, as photodecomposition occurs, and kept away from that catalyze breakdown; periodic monitoring of concentration via iodometric is recommended to ensure integrity. Long-term studies indicate that properly stored solutions can retain significant active content for over a year, though fresh preparations are preferred for optimal performance. Handling of DMDO requires strict precautions due to its volatile and oxidizing nature. All operations, including preparation and use, must be conducted in a well-ventilated to avoid inhalation of vapors. Personnel should wear appropriate , including chemical-resistant gloves, safety goggles, and protective clothing, to prevent skin and . or attempts to concentrate the solution are strictly prohibited, as they can lead to hazardous exothermic reactions; excess reagent should be quenched immediately after use with a such as to decompose residual peroxide. Disposal of DMDO solutions follows established protocols for to ensure safe environmental release. Solutions should first be diluted extensively and neutralized using reducing agents like or , followed by testing for residual s using standard kits; neutralized waste may then be discharged to sewer systems in accordance with local regulations. If tests remain positive, residues must be treated via controlled with scrubbing at a licensed facility to prevent contamination of water sources or ecosystems. DMDO is not available as a commercial product due to its instability and is generated or on-demand in laboratory settings only. Handling and storage practices must comply with OSHA standards for and laboratory chemical hygiene, including those outlined in 29 CFR 1910.1450 for occupational exposure limits and safe work practices.

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