- REACTION OF PHENOXY RADICAL WITH NITRIC OXIDE
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The association of C6H5O with NO was studied with the cavity-ring-down method by directly monitoring the decay of C6H5O in the presence of varying, excess amounts of NO.The bimolecular rate constant determined in the temperature range 297-373 K can be effectively represented by k1=10-12.12+/-0.24e(194+/-185)/T cm3 molecule-1 with a negative activation energy of 0.8 kcal mol-1 (1 kcal=4.184 kJ).In order to understand better the mechanism of the reaction, ab initio molecular orbital calculations were also carried out at the MP4(SDQ)/6-31G* level of theory using the HF optimized geometries.The molecular structures and energetics of five C6H5N1O2 isomers were calculated.Among them, the most likely and stable association product, phenyl nitrite (C6H5ONO), was found to be 17 kcal mol-1 below the reactants, C6H5O+NO.Combining the measured rate constant and the calculated equilibrium constant for the association reaction, C6H5O+NO=C6H5ONO the rate constant for the unimolecular decomposition of C6H5ONO was obtained as k-1=4.6*1015E-8580/T s-1.The relatively large frequency factor suggests that a loose transition state was involved in the reaction, akin to those of its alkyl analogs (RONO, R=CH3, C2H5, etc.).
- Yu, T.,Mebel, A. M.,Lin, M. C.
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- Kinetics and thermochemistry of the reversible combination reaction of the phenoxy radical with NO
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The kinetics of association reaction of the phenoxy radical with NO were studied by flash photolysis coupled with UV absorption spectrometry. The influence of resonance stabilization energy of radicals on R-NO bond dissociation energy was also analyzed. B
- Berho,Caralp,Rayez,Lesclaux,Ratajczak
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- Atmospheric chemistry of the phenoxy radical, C6H5O(?): UV spectrum and kinetics of its reaction with NO, NO2, and O2
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Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C6H5O(?) radicals. Pulse radiolysis experiments gave σ(C6H5O(?))235 nm = (3.82 ± 0.48) × 10-17 cm2 molecule-1, k(C6H5O(?) + NO) = (1.88 ± 0.16) × 10-12, and k(C6H5O(?) + NO2) = (2.08 ± 0.15) × 10-12 cm3 molecule-1 s-1 at 296 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(?) radicals with O2 was observed in smog chamber experiments, and we derive an upper limit of k(C6H5O(?) + O2) -21 cm3 molecule-1 s-1 at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NOx. Density functional calculations and gas chromatography-mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C6H5O(?) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C6H5OH) = (1.93 ± 0.36) × 10-10], several chlorophenols [k(Cl + 2-chlorophenol) = (7.32 ± 1.30) × 10-12, k(Cl + 3-chlorophenol) = (1.56 ± 0.21) × 10-10, and k(Cl + 4-chlorophenol) = (2.37 ± 0.30) × 10-10], and benzoquinone [k(Cl + benzoquinone) = (1.94 ± 0.35) × 10-10], all in units of cm3 molecule-1 s-1. A reaction between molecular chlorine and C6H5OH to produce 2- and 4-chlorophenol in yields of (28 ± 3)% and (75 ± 4)% was observed. This reaction is probably heterogeneous in nature, and an upper limit of k(Cl2 + C6H5OH) ≤ 1.9 × 10-20 cm3 molecule-1 s-1 was established for the homogeneous component. These results are discussed with respect to the previous literature data and to the atmospheric chemistry of aromatic compounds.
- Platz,Nielsen,Wallington,Ball,Hurley,Straccia,Schneider,Sehested
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p. 7964 - 7974
(2007/10/03)
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- Cyclodextrin catalysis in the basic hydrolysis of alkyl nitrites
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The influence of β-cyclodextrin (β-CD) on the hydrolysis reaction of a variety of structural types of alkyl nitrites (RONO) is studied in acid and in basic aqueous solutions.Acid-catalysed hydrolysis of alkyl nitrites is inhibited by the presence of β-cyclodextrin.The results are accounted for by assuming the formation of host-guest complexes between β-cyclodextrin and alkyl nitrite, which are unreactive or much less reactive than the uncomplexed RONO.We propose that the result is a concenquence of the orientation of alkyl nitrite in the cavity of CD.The degree of inhibition increases with the greater inclusion of the alkyl nitrite in the CD cavity.The kinetic data are quantitatively analyzed to afford the stability constants of the host-guest complexes.On the contrary, the presence of β-cyclodextrin strongly increases the rate of hydrolysis of alkyl nitrites in a basic medium, that is at a pH value higher than the pKa of β-cyclodextrin.This feature suggests the formation of a reactive complex between the alkyl nitrite and β-cyclodextrin, whose ionized CD hydroxy group promotes a nucleophilic attack in the rate-limiting step.This behaviour is consistent with a higher reactivity towards alkyl nitrites of an ionized CD hydroxy groups as compared with the OH-; the contrary occurs in the case of esters, whose cleavage by cyclodextrin in basic aqueous media has been studied extensively over the last several years.
- Iglesias, Emilia,Fernandez, Aurora
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p. 1691 - 1700
(2007/10/03)
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- Cw laser absorption study of the reactions of phenyl radicals with NO, NO2, O2 and selected organics between 298-404 K
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The applied aspect concerning the reactivity of phenyl relates to its suggested participation in the formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) and of soot. In the present paper we report the first application of a direct detection method of phenyl in the gas phase. It will be shown that by using the 488 nm laser line absorption in the $UNK2A1 - $UNK2B1 transition phenyl can be detected with sufficient sensitivity to enable kinetic investigations of its reactions. To our knowledge this has not been achieved before. Rate constant for the reactions of phenyl (C6H5) radicals with NO, NO2, O2, C2H4, 2-butene, benzene, toluene and CCl4 have been determined using a combined laser photolysis laser absorption technique. Phenyl radicals were generated by 248 nm excimer laser photolysis of C6H5X, where X = Cl, Br and NO. Their temporal behaviour was monitored using cw-laser line absorption in the $UNK2A1 - $UNK2B1 transition at 488 nm. The magnitude of the rate coefficients k1 and k2 and their negative temperature dependence suggest that the reactions between phenyl and NO/NO2 occur as radical recombination and/or (in the case of NO2) as O-atom metathesis reaction. The apparent low reactivity of phenyl with O2 is likely to be caused by insufficient thermal stability of the phenylperoxi radical.
- Preidel,Zellner
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p. 1417 - 1423
(2007/10/02)
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- The Synthesis and Application of Novel Nitrating And Nitrosating Agents
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Alcohols and phenols are efficiently nitrated with thionyl chloride nitrate or thionyl nitrate, even in the presence of an aromatic moiety.While thionyl chloride nitrate is suitable for nitration of primary OH-groups in carbohydrates, thionyl nitrate is reactive enough to react with secondary OH-groups as well.These reagents permit the highly selective nitration of the 5'-, 2',5'- and 3',5'-OH-groups of ribonucleosides to produce either mono- or diprotected nitro derivatives in high yields.Carbon acids and the enol form of some ketones are efficiently nitrated with trifluoromethanesulfonyl nitrate/potassium tert-butoxide.Lutidine N-oxide(2,6-(CH3)2C5H3N->O) was found to have marked effect on nitration reactions.Similarly, thionyl chloride nitrite and thionyl nitrite exhibit an excellent capacity for nitrosation of the aforementioned substrates
- Hakimelahi, Gholam H.,Sharghi, Hashem,Zarrinmayeh, Hamide,Khalafi-Nezhad, Ali
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p. 906 - 915
(2007/10/02)
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