Pentazoles: proton and carbon-13 NMR spectra of some 1-arylpentazoles: kinetics and mechanism of degradation of the arylpentazole system

Butler, R. N.; Collier, Seamus; Fleming, Adrienne

doi:10.1039/p29960000801

Cited by 33 publications

(46 citation statements)

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“…It was not possible, however, to answer conclusively, whether 23 decomposed via 21 or directly into phenyl azide (22) and N 2 . The planar pentazole structure was established somewhat later by several crystal-structure analyses [37], and 15 N-, 1 H-, and 13 C-NMR spectra were published [38].…”

Section: Scheme 11 Scheme 12mentioning

confidence: 99%

“…Accordingly, the thermal stability of arylpentazoles, as measured by kinetics [33] [38], is increased by electron-donating substituents and decreased by electronattracting groups in the Ph ring. DH = for the decomposition of the p-Cl-substituted 23 3 22 is 86.3 kJ mol À1 and DS = is 19.9 J mol À1 K À1 [38]. These data are believed to support the decomposition of 23 via 21 to 22, as it was also suggested by Huisgen earlier, by analogy to the ring opening of tetrazoles [33].…”

Section: Scheme 11 Scheme 12mentioning

confidence: 99%

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Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

Rüchardt¹,

Sauer

Sustmann

2005

Helvetica Chimica Acta

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Section: Scheme 11 Scheme 12mentioning

confidence: 99%

Section: Scheme 11 Scheme 12mentioning

confidence: 99%

Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

Rüchardt¹,

Sauer

Sustmann

2005

Helvetica Chimica Acta

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“…15 Solutions of 6 in CD 3 OD:D 2 O containing excess Zn(NO 3 ) 2 were treated with CAN at 240°C and followed by 15 N NMR spectra. † Only 15 N labelled nitrogen atoms are detected.…”

Section: T H I S J O U R N a L I S © T H E R O Y A L S O C I E T Y O mentioning

confidence: 99%

“…13 Recently it has been suggested the N 5 + .N 5 2 is a viable entity. 14 Following our recent establishment of the mechanism of formation of aryl pentazoles from aryldiazonium ions and azide ion, 15 we have been endeavouring to generate HN 5 and its anion N 5 2 . Recently N 5 2 has been detected for the first time from high voltage collisions of 4-pentazolylphenolate ion, N 5 -C 6 H 4 O 2 , in the mass spectrometer.…”

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confidence: 99%

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First Generation of Pentazole (HN₅, Pentazolic Acid), the Final Azole, and a Zinc Pentazolate Salt in Solution: A New N‐Dearylation of 1‐(p‐Methoxyphenyl) Pyrazoles, a 2‐(p‐Methoxyphenyl) Tetrazole and Application of the Methodology to 1‐(p‐Methoxyphenyl) Pentazole.

2003

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Ceric ammonium nitrate (CAN) in methanol-water gave a new N-dearylation of a series of substituted 1-(p-methoxyphenyl) pyrazoles and a 2-(p-methoxyphenyl)tetrazole producing p-benzoquinone and the parent azole in a mole for mole ratio. Application of this reaction to 1-(p-methoxyphenyl) pentazole at 240 °C produced p-benzoquinone. 15 N NMR spectra suggest that pentazole, HN 5 , was also produced and held in solution as N 5 2 with Zn 2+ ion. The 15 N signal from N 5 2 was 210.0 ± 2.0 ppm in agreement with calculated values.The existence of an all-nitrogen aromatic azole ring, R-N 5 , the pentazoles, was proved by Clusius and Hurzeler 1 in Zurich and Huisgen and Ugi 2 in Munich. 3 Since then a significant goal of heterocyclic chemistry has been to prepare the parent pentazole, HN 5 . Ozonolytic degradation of the aryl ring was attempted 4 and recently revisited with controlled limited amounts of ozone, 5 but HN 5 or its anion N 5 2 was not found. Following the recent discovery of N 5 + as a reasonably stable cation in inorganic salts 6,7 there has been renewed experimental interest in allotropes of nitrogen and in N 5 2 in particular. There has also been much theoretical interest in these types of species. [8][9][10][11][12] Metallocene pentazole derivatives have been predicted as viable forms of N 5 2 , but bidentate forms MN 5 (M = Na, K, MgCl + , CaCl + ) and M(N 5 ) 2 (M = Na, K, Mg, Ca) and unidentate Zn(N 5 )Cl and Zn(N 5 ) 2 are calculated to have lower energy. 13 Recently it has been suggested the N 5 + .N 5 2 is a viable entity. 14 Following our recent establishment of the mechanism of formation of aryl pentazoles from aryldiazonium ions and azide ion, 15 we have been endeavouring to generate HN 5 and its anion N 5 2 . Recently N 5 2 has been detected for the first time from high voltage collisions of 4-pentazolylphenolate ion, N 5 -C 6 H 4 O 2 , in the mass spectrometer. 16 We are therefore prompted to make a preliminary report of our work.To remove an aryl group from an arylpentazole without destruction of the pentazole ring a mild oxidizing agent and the appropriate aryl pentazole must be chosen. Ceric (IV) ammonium nitrate (CAN) has been used to remove p-MeOC 6 H 5 -groups from p-methoxyphenyl ethers 17,18 and N-p-methoxyphenyl azetidines. [19][20] The methoxyphenyl ring is removed as p-benzoquinone and the use of H 2 18 O has proved that the two quinone oxygens arise from water in the solvent. 18 Successive one-electron oxidations are considered to produce a quinoneimine dication which is hydrolysed. 20 We tested this reaction for the first time with an azole substrate using the 1-N-pmethoxyphenyl pyrazole series shown in Fig. 1. It proved successful and was optimised at low temperatures. The pbenzoquinone is easily detected and estimated. Its presence indicates a mole for mole presence of the azole. High temperatures are not appropriate for this reaction because the azole generated may undergo addition reactions with pbenzoquinone. 21 We also attempted the reaction with the nonmetallic one-electron ...

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Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na₂₀N₆₀ and Na₂₄N₆₀ Nanocages

Zhang

Wang

et al. 2018

Angewandte Chemie

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The experimental detection and synthesis of pentazole (HN 5 )a nd its anion (cyclo-N 5 À )h ave been actively pursued for the past hundred years.T he synthesis of an aesthetic three-dimensional metal-pentazolate framework (denoted as MPF-1) is presented. It consists of sodium ions and cyclo-N 5 À anions in whicht he isolated cyclo-N 5 À anions are preternaturally stabilized in this inorganic open framework featuring two types of nanocages (Na 20 N 60 and Na 24 N 60 ) through strong metal coordination bonds.T he compound MPF-1 is indefinitely stable at room temperature and exhibits high thermal stability relative to the reported cyclo-N 5 À salts. This finding offers anew approach to create metal-pentazolate frameworks (MPFs) and enables the future exploration of interesting pentazole chemistry and also related functional materials.Pentazole (HN 5 )a st he last member in the azole series has been attracting worldwide interest over the past century because of its intriguing aesthetic structure and potential applications as high-performance explosives or propellants. [1, 2] As triking feature of pentazole is that five nitrogen atoms enter ahighly symmetric ring with aromatic character. However,t he inherent instability of the cyclopentazolate anion (cyclo-N 5 À ), arising from its high calculated electron affinity of 5.06 eV and five sterically active free-valence electron pairs in the equatorial plane, [3] has severely hampered pentazole chemistry.D espite arylpentazoles having existed for more than half ac entury, [4] the experimental synthesis of the isolated cyclo-N 5 À salts as well as its parent HN 5 molecule in condensed phases still remains ag reat challenge.Inthis regard, intensive studies have demonstrated that the stability of pentazole ring in the arylpentazoles largely depends on the conjugation of the attached aryl ring featuring as trong electron-detonating group. [5] Theoretical calculations also indicated that the CÀNb ond that links the aryl and pentazole group has arather high dissociation barrier than either the N À Nsingle bond or N = Ndouble bond in the pentazole ring. [6] As ar esult, the biggest challenge in synthesizing ab ulk material containing the isolated cyclo-N 5 À anion is how to selectively cleave the relatively strong CÀ Nbond in the arylpentazoles while keeping the considerably weaker N À Na nd N = Nb onds of the pentazole ring intact.In view of the great attraction and unprecedented challenges in the experimental synthesis of the isolated cyclo-N 5 À anion or its parent HN 5 molecule,significant efforts have been devoted to theoretical studies and experimental detection of the cyclo-N 5 À anion in the solution at the start of this study. [7,8] Several pioneering studies in the experimental detection of cyclo-N 5 À anion were achieved through the negative ion electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation (CID) as the analytical tool. [9][10][11] Very recently,the direct formation of cyclo-N 5 À in THF solution was successful through the redu...

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Pentazoles: proton and carbon-13 NMR spectra of some 1-arylpentazoles: kinetics and mechanism of degradation of the arylpentazole system

Cited by 33 publications

References 11 publications

Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

First Generation of Pentazole (HN₅, Pentazolic Acid), the Final Azole, and a Zinc Pentazolate Salt in Solution: A New N‐Dearylation of 1‐(p‐Methoxyphenyl) Pyrazoles, a 2‐(p‐Methoxyphenyl) Tetrazole and Application of the Methodology to 1‐(p‐Methoxyphenyl) Pentazole.

Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na₂₀N₆₀ and Na₂₄N₆₀ Nanocages

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Pentazoles: proton and carbon-13 NMR spectra of some 1-arylpentazoles: kinetics and mechanism of degradation of the arylpentazole system

Cited by 33 publications

References 11 publications

Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

First Generation of Pentazole (HN5, Pentazolic Acid), the Final Azole, and a Zinc Pentazolate Salt in Solution: A New N‐Dearylation of 1‐(p‐Methoxyphenyl) Pyrazoles, a 2‐(p‐Methoxyphenyl) Tetrazole and Application of the Methodology to 1‐(p‐Methoxyphenyl) Pentazole.

Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na20N60 and Na24N60 Nanocages

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First Generation of Pentazole (HN₅, Pentazolic Acid), the Final Azole, and a Zinc Pentazolate Salt in Solution: A New N‐Dearylation of 1‐(p‐Methoxyphenyl) Pyrazoles, a 2‐(p‐Methoxyphenyl) Tetrazole and Application of the Methodology to 1‐(p‐Methoxyphenyl) Pentazole.

Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na₂₀N₆₀ and Na₂₄N₆₀ Nanocages