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

Abstract

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...

Photolysis of Nitrate Esters: Part I. Photonitration of Diphenylamine

“…The absence of a "dark reaction1' between isosorbide dinitrate and diphenyla~nine a t 25" and the slow reaction of the stronger base pyridine with the dinitrate a t 115O (14) ruled out nucleophilic attack of unexcited diphenylamine on the ester from consideration in the lllechailis~n of the photonitration. A comparison of the ultraviolet spectra of the reactants (Fig.…”

“…69.2-70.O0), \vhich showed the same elemental analyses, specific rotation, infrared spectrum, and chronlatographic behavior as the labile form (n1.p. 50.5-51.5") (14). The ~~ltraviolet spectrum of a 111 solution of the dinitrate in absolute ethanol showed no absorption above 250 n~p and no inflection in the rapidly increasing absorption curve which commenced a t an indefinite point around 250 mp and continued beyond 210 mp (Fig.…”

“…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).…”

“…Diphenylamine produced yellow-green spots as for R2. illaterials 1,4;3,6-Dianhydro-D-glucitol-2,5-dinitrate (isosorbide dinitrate) was prepared by the method of Jackson and Hayward (14). The stable form of the con~pound was obtained (m.p.…”

Circular Dichroism of Nitrate Esters: A Planar Symmetry Rule for the Nitrato Chromophore

“…The nitrate esters were synthesized from thecorresponding chiral alcohols (Table 3) (7,24,(28)(29)(30)(31)(32) either with anhydrous nitric acid in acetic acid-acetic anhydride at 0" (23,24) or via the corresponding chloroformate and silver nitrate (25) and were purified by distillation (cu. 0.5 Torr) or chromatography on columns of silica gel developed with chloroform (26).…”