The Thermochemistry And Reactivity Of Alkoxyl Radicals

Gray, Peter; Williams, Alan L.

doi:10.1021/cr50026a002

Cited by 257 publications

(103 citation statements)

References 105 publications

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“…For the first-order decoinpositioil of the isohexide nitrates in the non-hydrosylic solvents the activation energy of 37 ltcal/mole and log frequency factor of 15 calculated from the data of Table I11 were in good agreement with the values quoted for gaseous and condensed nitrate esters (10,11,12). This suggested a free radical mechanisin for this case also.…”

Section: A N D Discussionsupporting

confidence: 76%

“…I t is \\re11 established that the first and rate-deter~ni~ling step in the thermal decomposition of nitrate esters in the gaseous state is the fissioil of the oxygen-nitrogen boncl, generating a free alkoxyl radical (10,11). X similar mechanism for the first-order thermal decomposition of the esters in the conde~lsed state seems probable (12).…”

Section: A N D Discussionmentioning

confidence: 99%

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The Action of Pyridine on the Dinitrate Esters of 1,4;3,6-Dianhydrohexitols

Jackson¹,

Hayward²

1960

Can. J. Chem.

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In contrast to the rapid and selective replacement of a secondary 0-nitro group by hydrogen in the hexitol hexanitrates a t 25-50' C, the dinitrate esters of the 1,4;3,6-dianhydrides of D-n~annitol, D-glLIcitoI, and L-iditol (cis-isohexides) reacted slowly in anhydrous pyridine a t 87-115" C. The chief products were a polymer, nitrogen oxides, and pyridinium nitrate; the yield of mononitrates did not exceed lOyo and none of the parent diols were formed.The relative rates of the first-order decon~position of the nitroxy groups in the isomeric dinitrates were in reverse order to that for S N~ reaction a t carbon in these compounds.Activation energies and frequency factors were determined and water was shown to have a retarding effect.Thermal decomposition of the dinitrates in solution in nitrobenzene, nl-xylene, or syintetrachloroethane was much slower than the pyridine reaction a t the same temperature and was independent of the polarity of the solvent and the conformation of the ester. INTRODUCTIONDulcitol and D-inannitol hexanitrates have been shown to react selectively with pyridine to yield the corresponding 1,2,4,5,6-pentanitrates (1, 2). The rate of reaction was different for the two hexitol derivatives and the resulting pentanitrates were essentially stable to pyridine under the same conditions. Sorbitol hexanitrate reacted similarly with pyridine but the pentanitrate was not fully characterized (3). The reaction was inconveniently fast for kinetic studies even a t 25" C and the n~ultiplicity of nitroxy groups and inolecular conformations further complicated the problem of sorting out the reaction mechanism.The three known isomeric 1,4;3,6-dianhydrohexitols (the cis-isohexides) and their derivatives have been shown to behave characteristically in certain types of reactions clue to differences in their restricted conformations (4, 5 ) . In an attempt to determine the mechanism of the pyridine -nitrate ester reaction the dinitrates of the isohexides (1-111, Fig. 1) were selected for study since observation of similar steric effects in their reactions with pyridine would aid in diagnosis of the type of mechanism involved. The presence of only two, non-vicinal, secondary, nitroxy groups in these isomers was also expected t o simplify analysis of the results. RESULTS A N D DISCUSSIONThe three isohexide dinitrates (Fig. 1) were prepared in crystalline form and characterized through their nitrogen contents, infrared spectra, and nearly quantitative conversion to the parent diols. The physical constants and nitrogen contents of the isomers are show11 in Table I. The dinitrates dissolved readily in pyridine and the colorless solutions were stable over several weeks a t roorn temperature. No vigorous reaction occurred on heating under reflux; however, slow decomposition, accoinpailied by a red coloration of the solution and evolution of oxides of nitrogen, began a t temperatures above 50" C.At 115" C 0.424 M solutions of the isohexide dinitrates in anhydrous pyridine decoinposed according to an apparent firs...

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Section: A N D Discussionsupporting

confidence: 76%

Section: A N D Discussionmentioning

confidence: 99%

The Action of Pyridine on the Dinitrate Esters of 1,4;3,6-Dianhydrohexitols

Jackson¹,

Hayward²

1960

Can. J. Chem.

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“…Bands attributed to ethoxyl radicals were detected in fluorescence when ethyl nitrate was irradiated in the Schumann region (12). The reactions postulated to account for the photoproducts paralleled those invoked for thermal decomposition where the initial, rate-determining step has been established as homolytic alkoxy-nitro bond fission (1,13,14). Photolysis of polynitrate esters in the condensed state also caused evolution of nitrogen and the oxides of carbon and nitrogen; the thermal stability of the explosive compounds was reduced and, for cellulose nitrate, depolymerization and oxidation occurred (15)(16)(17)(18)(19)(20)(21).…”

Section: Introductionmentioning

confidence: 90%

“…Photolysis of methyl and ethyl nitrates in the gas phase yielded hydrogen, nitromethane, formaldehyde, and acetaldehyde in addition to nitrogen, carbon, and their oxides (1,10,11). Bands attributed to ethoxyl radicals were detected in fluorescence when ethyl nitrate was irradiated in the Schumann region (12).…”

Section: Introductionmentioning

confidence: 99%

Photolysis of Nitrate Esters: Part I. Photonitration of Diphenylamine

Hayward¹,

Kitchen²,

Livingstone³

1962

Can. J. Chem.

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The photolysis of nitrate esters dissolved in benzene or ethanol or absorbed on hlter paper occurred readily under illumination in the 265 mp t o 334 mp spectral region. Equimolar amounts of 1,4;3,6-dianhydro-D-glucitol-2,5-dinitrate and diphenylamine dissolved in absolute ethanol or benzene did not react in the dark a t 25'. Irradiation of the nitrogen-purged solutions for 2 hours a t 15' with a mercury arc followed by chromatographic separation yielded 2-nitro-, 4-nitro-, N-nitroso-, and 4-nitroso-diphenylamine together with about 4% unreacted diphenylamine and an unidentified mixture of more polar compounds. In a partial fractionation of the aromatic photoproducts approximately 80% of the original diphenylamine was recovered in the form of the monosubstituted derivatives which contained about 37% of the original ester nitrogen as C-nitro groups and 2 to 3% as C-and iV-nitroso groups.

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“…In this paper we derive values for the heats of formation of the alkylthio radicals by comparing the few reliable (1) carbon-sulfur bond dissociation energies with the carbon-oxygen values obtained from the relatively well-studied alkoxy radicals (2,3).…”

Section: Introductionmentioning

confidence: 99%