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Dichlorine heptoxide
Dichlorine heptoxide
Dichlorine heptoxide
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Dichlorine heptoxide
Names
IUPAC name
Dichlorine heptoxide
Other names
Chlorine(VII) oxide; Perchloric anhydride; (Perchloryloxy)chlorane trioxide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
UNII
  • InChI=1S/Cl2O7/c3-1(4,5)9-2(6,7)8 checkY
    Key: SCDFUIZLRPEIIH-UHFFFAOYSA-N checkY
  • InChI=1.001/Cl2O7/c3-1(4,5)9-2(6,7)8
    Key: SCDFUIZLRPEIIH-UHFFFAOYAG
  • O=Cl(=O)(=O)OCl(=O)(=O)=O
Properties
Cl2O7
Molar mass 182.901 g/mol
Appearance colorless liquid, colorless gas
Density 1.9 g/cm3
Melting point −91.57 °C (−132.83 °F; 181.58 K)
Boiling point 82.07 °C (179.73 °F; 355.22 K)
hydrolyzes to form perchloric acid
Thermochemistry
275.7 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 oxidizer, contact explosive[1]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
3
OX
Related compounds
Related compounds
 Manganese heptoxide
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 ?)

Dichlorine heptoxide is the chemical compound with the formula Cl2O7. This chlorine oxide is the anhydride of perchloric acid. It is produced by the careful distillation of perchloric acid in the presence of the dehydrating agent phosphorus pentoxide:[1]

2 HClO4 + P4O10 → Cl2O7 + H2P4O11

Cl2O7 can be distilled off from the mixture.

It may also be formed by illumination of mixtures of chlorine and ozone with blue light.[2] It slowly hydrolyzes back to perchloric acid.

Structure

[edit]

Cl2O7 is an endergonic molecule, meaning it is intrinsically unstable, decomposing to its constituent elements with release of energy:[3]

2 Cl2O7 → 2 Cl2 + 7 O2 (ΔH° = −132 kcal/mol)

Dichlorine heptoxide is a covalent compound consisting of two ClO3 groups linked by an oxygen atom. It has an overall bent molecular geometry (C2 symmetry), with a Cl−O−Cl angle of 118.6°. The chlorine–oxygen bond lengths are 1.709 Å in the central region and 1.405 Å within each ClO3 cluster.[1] In this compound, chlorine exists in its highest formal oxidation state of +7.

Chemistry

[edit]

Dichlorine heptoxide reacts with primary and secondary amines in carbon tetrachloride solution to yield perchloric amides:[4]

2 RNH2 + Cl2O7 → 2 RNH−ClO3 + H2O
2 R2NH + Cl2O7 → 2 R2N−ClO3 + H2O

It also reacts with alkenes to give alkyl perchlorates. For example, it reacts with propene in carbon tetrachloride solution to yield isopropyl perchlorate and 1-chloro-2-propyl perchlorate.[5]

Dichlorine heptoxide reacts with alcohols to form alkyl perchlorates.[6]

R−OH + O3Cl−O−ClO3 → R−O−ClO3 + HO−ClO3

Dichlorine heptoxide is a strongly acidic oxide, and in solution it forms an equilibrium with perchloric acid.

Safety

[edit]

Although it is the most stable chlorine oxide, Cl2O7 is a strong oxidizer as well as an explosive that can be set off with flame or mechanical shock, or by contact with iodine.[7] Nevertheless, it is less strongly oxidising than the other chlorine oxides, and does not attack sulfur, phosphorus, or paper when cold.[1] It has the same effects on the human body as elemental chlorine, and requires the same precautions.[8]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Dichlorine heptoxide

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from Grokipedia
Dichlorine heptoxide is a with the formula Cl₂O₇, representing the highest oxide of where the element exhibits a +7 . It functions as the anhydride of and appears as a colorless, oily, volatile that is a potent . The molecular structure of dichlorine heptoxide consists of two ClO₃ groups bridged by a central oxygen atom, resulting in a bent Cl–O–Cl arrangement with C₂ symmetry and a bond angle of 118.6°. Key physical properties include a of -91.5 °C, a of 82 °C, and a of 1.9 g/cm³ at standard conditions. Chemically, it is relatively stable among chlorine oxides but reacts exothermically with to regenerate and is highly reactive toward organic materials, posing significant explosion risks upon shock or heating. Dichlorine heptoxide is synthesized primarily through the dehydration of with , often conducted in a like at low temperatures to yield the product via . In and specialized applications, it serves as a versatile perchlorylating , enabling the formation of alkyl perchlorates from alcohols, N-perchlorylamines from amines, and other derivatives useful in and synthesis, though its handling demands stringent safety protocols due to its instability.

Properties

Physical properties

Dichlorine heptoxide has the Cl2_2O7_7 and a of 182.901 g/mol. It appears as a colorless oily at and can be readily vaporized to form a gas. The phase has a of 1.9 g/cm3^3. It exhibits a of -91.5 °C and a of 82 °C under standard conditions. Dichlorine heptoxide is miscible with nonpolar solvents such as and but tends to hydrolyze upon contact with , forming . Early observations of its physical state as a volatile were reported in the late during initial preparations involving dehydration of .

Thermochemical properties

Dichlorine heptoxide exhibits thermodynamic instability arising from its endergonic formation, characterized by a positive . For the gaseous phase at 298 , Δ_f H° = 65.9 ± 2 kcal/mol (276 ± 8 kJ/mol). This positive value indicates that the molecule is less stable than its constituent elements, contributing to its propensity for despite being the most stable among chlorine oxides. The primary thermal decomposition pathway is highly exothermic:
2\ceCl2O7(g)→2\ceCl2(g)+7\ceO2(g)2 \ce{Cl2O7(g)} \rightarrow 2 \ce{Cl2(g)} + 7 \ce{O2(g)}
with ΔH° ≈ -132 kcal/mol at standard conditions, derived from the of Cl₂O₇. This reaction underscores the molecule's energetic favorability toward dissociation into elemental and oxygen, limiting its stability at elevated temperatures. As the anhydride of , dichlorine heptoxide participates in a temperature-dependent equilibrium:
2\ceHClO4(l)⇌\ceCl2O7(g)+\ceH2O(g)2 \ce{HClO4(l)} \rightleftharpoons \ce{Cl2O7(g)} + \ce{H2O(g)}
The position of this equilibrium shifts toward Cl₂O₇ at higher temperatures and reduced water content, as dehydration of requires heating to favor anhydride formation. The of gaseous Cl₂O₇ shows strong temperature sensitivity, governed by the parameters A = 5.314, B = 1880.127, C = 1.731 (P in bar, T in ) over 228–352 K, reflecting rapid changes in volatility that influence phase behavior.

Synthesis

Dehydration method

The primary laboratory synthesis of dichlorine heptoxide employs the dehydration of using as the dehydrating agent. The reaction proceeds according to the equation 2HClO4+P4O10→Cl2O7+H2P4O112 \mathrm{HClO_4} + \mathrm{P_4O_{10}} \rightarrow \mathrm{Cl_2O_7} + \mathrm{H_2P_4O_{11}}. This method originated from early 20th-century investigations into chemistry, with the first reported preparation achieved by A. Michaelis and R.E. Conn in 1900 through the reaction of anhydrous with . In a typical procedure, is mixed with excess in a suitable reaction vessel, often in a ratio of approximately 1:1.5 by weight to ensure complete removal of . The mixture is gradually heated while maintaining temperatures below 0°C to minimize , followed by under reduced pressure (around 2 mm Hg) to collect the volatile dichlorine heptoxide as a colorless in a cooled receiver, such as one maintained at -78°C with a dry ice-acetone bath. The is continued until no further product distills over, typically requiring careful monitoring to avoid explosive . Yields from this method are modest, often around 10-20%, limited by the compound's instability and competing or reactions. Common impurities include residual , which can carry over if dehydration is incomplete, and traces of lower chlorine oxides like ClO₂ formed during handling; purity is enhanced by redistillation or passing the product vapor over heated, reduced to remove reducible impurities. The resulting product is verified for purity by its colorless appearance and near 82°C under reduced . The process demands specialized equipment, including borosilicate or glassware to withstand the strong oxidizing and corrosive conditions, along with pumps, fractionating columns for precise temperature control, and traps filled with to dry incoming gases and prevent moisture ingress.

Photochemical method

Dichlorine heptoxide can be synthesized through the photochemical reaction of gas with , where light facilitates the decomposition and oxygen transfer processes. The overall reaction is represented by the equation: \ceCl2+7/3O3−>Cl2O7\ce{Cl2 + 7/3 O3 -> Cl2O7} This method involves the photosensitized decomposition of ozone by chlorine under illumination. In the procedure, gaseous mixtures of Cl₂ and O₃ are prepared and exposed to ultraviolet light at a wavelength of 366 nm, typically within a temperature range of 254–296 K, to initiate the reaction and promote the formation of the product. The illumination generates chlorine atoms that interact with ozone, leading to the buildup of dichlorine heptoxide as the final chlorine-containing species. Quantum yields for ozone removal under these conditions range from 1.9 ± 0.2 at −21 °C to 5.8 ± 0.5 at 24 °C, while the quantum yield for Cl₂ removal is lower at 0.11 ± 0.02 at 24 °C, indicating relatively inefficient conversion overall. At a high level, the mechanism begins with the photodissociation of Cl₂ into chlorine atoms by the incident light, which then react with O₃ to produce ClO radicals. Subsequent steps involve ClO reacting with additional O₃ to form intermediates like OClO (chlorine dioxide radical), which further participate in oxygen atom transfer reactions, ultimately yielding Cl₂O₇ through combination of chlorine oxide species. The initial quantum yield for OClO formation follows an Arrhenius expression, Φᵢ[OClO] = 2.5 × 10³ exp[−(3025 ± 625)/T], highlighting the temperature dependence of the activation process. This light-driven pathway avoids thermal inputs but requires specialized equipment for ozone generation and controlled photolysis setups. This photochemical approach was investigated in key 20th-century studies, such as the examination of Cl₂-O₃ photolysis kinetics, which confirmed Cl₂O₇ as the end product and provided quantitative data on reaction efficiencies, contributing to understanding gas-phase chemistry.

Structure

Molecular structure

Dichlorine heptoxide, Cl₂O₇, features a molecular structure composed of two ClO₃ groups bridged by a single oxygen atom, forming a symmetric O(ClO₃)₂ unit. This arrangement results in an overall bent geometry with C₂ symmetry, where the bridging oxygen lies on the C₂ axis. Electron diffraction studies in the gas phase have determined the Cl–O–Cl bond angle at the bridging oxygen to be 118.6 ± 0.6°. This angular configuration distinguishes Cl₂O₇ from simpler chlorine oxides, such as the bent C_{2v} (Cl₂O) or the angular (ClO₂), by incorporating two near-tetrahedral ClO₃ moieties linked via the bridge. In the solid phase, the of Cl₂O₇ exhibits a cubic close-packed lattice of oxygen atoms, with chlorine atoms occupying tetrahedral interstitial sites. This packing arrangement, determined by , reflects an ionic character in the condensed state, with molecules best described as (ClO)₂O₂⁻ units, while maintaining the molecular integrity observed in the gas phase.

Bonding

Dichlorine heptoxide exhibits chlorine atoms in the +7 , the highest formal for the element, while each oxygen atom carries a -2 . This assignment follows from the molecular formula Cl₂O₇, where the total charge balance requires 2(+7) + 7(-2) = 0. The compound's bonding is predominantly covalent, consistent with its molecular nature as a volatile liquid, rather than ionic like lower chlorine oxides. The central bridging Cl–O–Cl linkage features two equivalent Cl–O bonds with a length of 1.709 , typical of single covalent bonds between and oxygen. In contrast, the terminal Cl–O bonds within each ClO₃ group measure 1.405 , significantly shorter than the bridging bonds and indicative of partial character. This shortening arises from in the ClO₃ units, where multiple Lewis structures distribute the bonding electrons, involving overlap between oxygen p-orbitals and chlorine d-orbitals to form pπ–dπ interactions that strengthen the terminal bonds.

Chemistry

Dichlorine heptoxide serves as the anhydride of and participates in a equilibrium with : \ceCl2O7+H2O⇌2HClO4\ce{Cl2O7 + H2O ⇌ 2 HClO4} This process is exothermic and occurs slowly at ambient temperatures, with a reported rate constant of approximately 10−410^{-4} s−1^{-1} at 25 °C. As a potent , dichlorine heptoxide generates upon dissolution in , yielding solutions with values near 0 due to the strong acidity of HClO₄ (pKₐ ≈ -10). The equilibrium predominantly favors the dissociated acid form in aqueous environments with sufficient , whereas the intact anhydride is preferred in anhydrous media, reflecting the reversible dehydration of . The mechanism centers on the cleavage of the central oxygen bridge in the Cl–O–Cl moiety, an exothermic step releasing 23–30 kJ/mol, facilitated by nucleophilic attack from on the electron-deficient chlorine centers. Dichlorine heptoxide exhibits acid-base reactivity by forming salts with bases. For instance, its reaction with produces : \ceCl2O7+2NaOH−>2NaClO4+H2O\ce{Cl2O7 + 2 NaOH -> 2 NaClO4 + H2O} It also interacts with primary and secondary amines in non-aqueous solvents like carbon tetrachloride to yield perchloric amides; with ammonia, this leads to ammonium perchlorate under conditions involving trace moisture.

Oxidation reactions

Dichlorine heptoxide acts as a strong in oxidation reactions with alkenes, typically leading to the formation of chloroperchlorates via across the . For instance, the reaction with propene in solution proceeds to give isopropyl in 32% yield and 1-chloro-2-propyl in 17% yield after 24 hours at . Similar electrophilic s occur with other alkenes; 2-butene yields 3-chloro-2-butyl (26–30%) through stereospecific trans , alongside minor products like 3-keto-2-butyl (2%) and 2,3-butanediperchlorate. With , the products include 1-chloro-2-hexyl and 2-chloro-1-hexyl in a combined 29% yield (3:1 ratio), demonstrating favoring the more stable intermediate. In reactions with alcohols, dichlorine heptoxide serves as a perchlorylating agent to produce alkyl perchlorates, which are covalent esters useful in synthesis. Primary alcohols such as 1-pentanol react to form pentyl perchlorate in 63% yield, while ethyl alcohol gives ethyl perchlorate in 56% yield. Secondary alcohols often yield ketones as byproducts due to oxidation, for example, 2-pentanol producing 2-pentanone alongside the ester. The mechanism involves nucleophilic attack by the alcohol's oxygen atom on one of the chlorine atoms in Cl₂O₇, followed by cleavage to form the perchlorate ester (ROClO₃) and release of HClO₄ or related species; this O-attack retains stereochemical configuration at the carbon bearing the hydroxyl group. Dichlorine heptoxide also oxidizes inorganic substrates like and , with reactivity depending on . When cold, it does not attack elemental , , or even , indicating relatively mild oxidizing behavior under ambient conditions. At elevated temperatures, however, it promotes oxidation to higher oxides, such as converting to SO₃ or to P₄O₁₀, though specific yields vary with conditions. In , dichlorine heptoxide facilitates generation for structural elucidation of organic compounds; the resulting alkyl perchlorates undergo characteristic displacement reactions with nucleophiles like amines or azides, providing diagnostic products for identification via or . This approach has been applied to confirm the structures of haloalkyl derivatives and energetic materials. Compared to other chlorine oxides, dichlorine heptoxide is a less aggressive oxidant; while ClO₂ rapidly ignites and Cl₂O₆ decomposes violently, Cl₂O₇ requires heating for similar reactivity with non-reactive substrates like or . Its formal chlorine of +7 contributes to high electrophilicity, but the molecular structure stabilizes it against spontaneous .

Safety

Hazards

Dichlorine heptoxide is a strong that can initiate fires or explosions upon contact with combustible materials due to its high reactivity and tendency to support vigorous . As a , it detonates readily when exposed to , mechanical shock, or even contact with iodine, posing significant risks during handling or storage. Its explosive nature stems from a positive (ΔH_f = +276 kJ/mol), making decomposition energetically favorable and amplifying sensitivity to initiation. When maintained at low temperatures, dichlorine heptoxide exhibits reduced reactivity toward certain materials such as , , or paper, oxidizing them without immediate ignition; however, heating significantly increases its aggressiveness, leading to rapid . Its and shock sensitivity is directly linked to exothermic pathways that release and oxygen. Dichlorine heptoxide engages in violent reactions with reducing agents and organic substances, often resulting in or .

Handling precautions

Dichlorine heptoxide demands stringent handling protocols owing to its extreme instability and potent oxidizing properties. Operations involving the compound should be restricted to minimal quantities prepared and used at low temperatures, such as below -10°C, to reduce the risk of spontaneous or . Personnel must employ , including chemical-resistant gloves, safety goggles compliant with EN 166 standards, and respiratory protection, while conducting all manipulations in a well-ventilated to prevent formation and exposure. Mechanical shocks, friction, and contact with organic materials or flammables must be strictly avoided, as these can initiate violent explosions. Health effects from exposure are similar to those of , manifesting as severe irritation to the skin, eyes, and , with potential for burns, coughing, throat pain, and upon inhalation. Skin contact may lead to corrosive damage and , while eye exposure can cause immediate pain and vision impairment. Storage of dichlorine heptoxide is strongly discouraged due to its rapid into greenish-yellow products within days; when unavoidable, confine small amounts to sealed ampoules maintained at low temperatures under an inert atmosphere, such as , in a cool, dry, and isolated location away from incompatibles like reducing agents or combustibles. Containers must remain tightly closed to exclude moisture, which triggers . In case of spills, evacuate the area immediately, ensure ventilation, and contain the liquid with inert absorbents like , avoiding direct contact. For skin or eye exposures, flush affected areas with copious for at least 15 minutes and seek prompt medical evaluation; inhalation victims should be moved to fresh air and monitored for respiratory distress. Neutralization of spills or residues may involve cautious dilution with followed by treatment with a mild base like , but this must occur under controlled conditions to manage heat evolution and formation—professional hazardous waste disposal is recommended. Dichlorine heptoxide is classified as a hazardous substance under occupational safety regulations, primarily as a strong oxidizer and potential , necessitating compliance with general chemical handling standards such as those outlined by OSHA for reactive materials, though it lacks specific commercial transport designations due to its instability.

References

  1. https://pubchem.ncbi.nlm.nih.gov/compound/123272
  2. https://www.webelements.com/compounds/chlorine/dichlorine_heptaoxide.html
  3. https://www.webqc.org/compound.php?compound=Dichlorine+heptoxide
  4. https://www.chemicalbook.com/article/chemical-reaction-and-synthesis-of-chlorine-heptoxide.htm
  5. https://apps.dtic.mil/sti/tr/pdf/AD0736249.pdf
  6. https://dl.icdst.org/pdfs/files/415f61e9082c7d23df09fb15605aa59d.pdf
  7. https://www.chemister.ru/Databases/Chemdatabase/properties-en.php?dbid=1&id=4184
  8. https://www.webqc.org/compound.php?compound=Dichlorine%2Bheptoxide
  9. https://www.researchgate.net/publication/216247221_Heats_of_formation_of_perchloric_acid_HClO4_and_perchloric_anhydride_Cl2O7_Probing_the_limits_of_W1_and_W2_theory
  10. https://webbook.nist.gov/cgi/cbook.cgi?ID=C12015531&Mask=4
  11. https://www.chemicalaid.com/tools/equationbalancer.php?equation=HClO4%2B%252B%2BP4O10%2B%253D%2BCl2O7%2B%252B%2BH2P4O11
  12. https://www.ic.unicamp.br/~stolfi/EXPORT/projects/wikipedia/00-DOCS/Brauer_HandbookOfPreparativeInorganicChemistry.pdf
  13. https://www.sciencedirect.com/topics/chemistry/dichlorine
  14. https://www.sciencedirect.com/science/article/abs/pii/0047267079800040
  15. https://academic.oup.com/book/6435/chapter/150255719
  16. https://pubs.acs.org/doi/10.1021/ic50088a019
  17. https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.198813391
  18. https://doi.org/10.1039/TF9656101821
  19. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Period/Period_3_Elements/Acid-base_Behavior_of_the_Oxides
  20. https://pubchem.ncbi.nlm.nih.gov/compound/Chlorine-oxide-_Cl2O7
  21. https://www.researchgate.net/publication/244426030_Hydrolysis_solvation_and_reduction_of_SO3_S2O6_ClO3OH_Cl2O7_and_ArO4_-_Relating_chemical_properties_to_the_instability_of_SO_ClO_and_ArO_groups
  22. https://apps.dtic.mil/sti/tr/pdf/AD0754778.pdf
  23. https://pubs.acs.org/doi/10.1021/ja00817a033
  24. https://cheman.chemnet.com/dict/dict--10294-48-1--1.html
  25. https://webbook.nist.gov/cgi/cbook.cgi?ID=C12015531
  26. https://chemcraft.su/sites/chemcraft.su/files/field/file/bretherick_s_handbook_of_reactive_chemical_hazards_7th_ed.pdf
  27. https://library.sciencemadness.org/library/books/perchloric_acid_and_perchlorates.pdf
  28. https://www.guidechem.com/msds/12015-53-1.html
  29. https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=198&toxid=36
  30. https://pubchem.ncbi.nlm.nih.gov/compound/Perchloric-Acid#section=Safety-and-Hazards
  31. https://pubchem.ncbi.nlm.nih.gov/compound/Perchloric-Acid#section=Handling-and-Storage
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