- Flash Pyrolytic Production of Rotationally Cold Free Radicals in a Supersonic Jet. Resonant Multiphoton Spectrum of the 3p2A2''= X2A2'' Origin Band of CH3
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Methyl radicals with the rotational temperature of 40 K are produced by flash pyrolysis prior to supersonic expansion.A mass-resolved resonant MPI spectrum of the 3p2A2'' = X2A2'' origin band shows clearly resolved rotational structure, in sharp contrast to the spectrum at room temperature.Flash pyrolysis, coupled with ionization by resonant MPI or vacuum-UV, provides a potentially general method for obtaining spectra of gas-phase free radicals and reactive intermediates.
- Chen, Peter,Colson, Stephen D.,Chupka, William A.,Berson, Jerome A.
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- Nitrosation of Organic Hydroperoxides by Nitrogen Dioxide/Dinitrogen Tetraoxide
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Cumyl and tert-butyl hydroperoxides react rapidly with NO2/N2O4 in organic solvents in the presence of a base to form the organic nitrate (RONO2) as the major product, together with smaller amounts of the corresponding nitrite (RONO), alcohol, and carbonyl compound (acetophenone or acetone from cumyl and tert-butyl hydroperoxide, respectively).The products from tert-butyl hydroperoxide are similar whether a base is present or not but those from cumyl hydroperoxide are more complex.We have formulated the initial reaction as a nitrosation of the hydroperoxide by N2O4 to give the pernitrite ester.This latter species is unstable and either rearrenges to give the nitrate or dissociates to form alkoxyl radicals and nitrogen dioxide that ultimately give the other observed products.The kinetics of the reaction were studied by stopped flow and are complex, but we conclude the kinetics are consistent with the nitrosation mechenism.The rate constants at 30 deg C are 2.4*104 and 8.1*103 M-1 s-1 for tert-butyl and cumyl hydroperoxides, respectively.We suggest that this facile reaction of NO2/N2O4 with hydroperoxides may have important consequences respect to the pulmonary toxicity of NO2 in smoggy air.
- Pryor, William A.,Castle, Laurence,Church, Daniel F.
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- S-Nitrosocaptopril formation in aqueous acid and basic medium. A vasodilator and angiotensin converting enzyme inhibitor
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The reaction of S-nitrosocaptopril (NOcap) formation was studied in both aqueous acid and basic medium. Captopril (cap) reacts rapidly with nitrous acid in strong acid medium to give the stable - in the timescale of the experiments - NOcap. The kinetic study of the reaction involving the use of stopped-flow, shows that at low sodium nitrite (nit) concentration, the reaction is first-order in both [nit], [H+], and is strongly catalysed by Cl - or Br- (= X-): rate = (k3 + k 4[X-])[H+][nit][cap]. In aqueous buffered solution of acetic acid-acetate the reaction rate is much slower and the decomposition of NOcap was observed; however, the rate of NOcap decay is more than 30-fold slower than its formation. In aqueous basic medium of carbonate-hydrogen carbonate buffer, as well as in alkaline medium, the kinetics of the nitroso group (NO) transfer from tert-butyl nitrite (tBN) to cap was studied using either conventional or stopped flow methods. In mild basic medium, the NOcap decomposes. The NOcap formation is first-order in both tBN and cap concentrations, and the reaction rate increases with pH until to, approximately, pH 11.5, above which value it becomes pH independent or even invariable with the [OH-]. Kinetic results show that the thiolate ion of cap is the reactive species. In fact, the presence of anionic micelles of sodium dodecyl sulfate (SDS) inhibits the reaction due to the separation of the reagents; whereas, cationic micelles of tetradecyltrimethylammonium bromide (TTABr) catalyse the reaction at low surfactant concentration due to reagents concentration in the small volume of the micelle. The rate equation is: rate = kf KSH[cap][tBN]/(KSH + [H+]). The rate of NOcap decomposition in mild basic medium is first-order in both [cap] and [NOcap], and decreases on increasing pH; but, in alkaline medium the NOcap is stable within the timescale of the experiments. Based on the results, the NOcap decomposition yields the disulfide compound that is formed in the nucleophilic attack of the -SH group of cap to the sulfur electrophilic center of NOcap, -S-NO. The resulting rate equation is: rate = kd[H +][cap][NOcap]/(KSH + [H+]).
- Sexto, Alexia,Iglesias, Emilia
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- Rate-limiting NO+ Formation in Nitrosation Reaction in Acetonitrile
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Acid-catalysed nitrosation of methanol, thioglycolic acid, and water in acetonitrile using alkyl nitrites or nitrous acid (except in the case of water), is kinetically zero order in the substrate, consistent with rate-limiting NO+ formation.
- Crookes, Michael J.,Williams, D. Lyn H.
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- Laser-Induced Fluorescence Excitation Spectra of terf-Butoxy and 2-Butoxy Radicals
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Laser-induced fluorescence (LIF) excitation spectra of t-C4H9O (terf-butoxy) and 2-C4H9O (2-butoxy) radicals were investigated in the wavelength range 335-400 nm. The radicals were formed by laser photolysis of the corresponding butyl nitrites at 355 nm. For tert-butoxy, 16 vibronic bands in two progressions were labeled. The dominant progression corresponds to C-O stretching mode with v′c-o = 521 ± 10 cm-1. The transition origin was tentatively assigned at 25 866 cm-1 (386.6 nm). Numerous bands remain unassigned. The LIF excitation spectrum of 2-butoxy, consisting of 15 vibronic bands in four progressions, was observed for the first time. A C-O stretching frequency v′c-o = 567 ± 10 cm-1 was obtained from the dominant progression. The transition origin was tentatively assigned at 26 185 cm-1 (381.9 nm). Three other progressions are evident, which have different vibrational band intervals: 617 ± 10, 590 ± 10, and 552 ± 10 cm-1. Zero-pressure fluorescence lifetimes for numerous vibronic bands of tert-butoxy and 2-butoxy were determined to be about 150 and 85 ns, respectively. These spectra can be used as a convenient spectroscopic tool for kinetic studies of butoxy radicals and should provide a starting point for investigations of their excited states structure and dynamics.
- Wang, Chuji,Shemesh, Liat G.,Deng, Wei,Lilien, Michael D.,Dibble, Theodore S.
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- Copper-Catalyzed Four-Component Reaction for the Synthesis of N-Difluoroethyl Imides
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A general and efficient method for the synthesis N-difluoroethyl imides has been developed. This copper-catalyzed four-component reaction proceeds via in-situ generated difluorodiazomethane, which does not require prior formation and transferring. The reaction is scalable, tolerant toward a range of functional groups, and also suitable for the late-stage functionalization of drugs and drug-like molecules.
- Gao, Yu,Peng, Shan-Qing,Liu, De-Yong,Rui, Pei-Xin,Hu, Xiang-Guo
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Read Online
- Method for recycling byproducts in synthesis of diphenyl sulfide compound
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The invention provides a method for recycling byproducts in synthesis of a diphenyl sulfide compound. The byproducts comprise alkyl alcohol and dimethyl disulfide. The method comprises the steps of (1) mixing the byproducts in synthesis of the diphenyl sulfide compound with a sodium nitrite aqueous solution, adding concentrated hydrochloric acid for reaction, and obtaining alkyl nitrite and dimethyl disulfide; and (2) mixing the products obtained in the step (1) with copper powder, adding an aniline compound for reaction, carrying out desolvation treatment on the obtained reaction solution toobtain a diphenyl sulfide compound and byproducts, and returning the byproducts to the step (1). According to the recycling method, the byproducts do not need to be separated, the byproducts serve asraw materials to be directly applied to synthesis of the diphenyl sulfide compound, the process steps are simple and safe, cyclic utilization of the materials is achieved, and the raw material cost ofindustrial production of the diphenyl sulfide compound and the treatment cost of industrial three wastes are remarkably reduced.
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Paragraph 0083-0088; 0092-0095; 0099-0102; 0106-0111
(2021/03/30)
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- tert-Butyl Nitrite as a Twofold Hydrogen Abstractor for Dehydrogenative Coupling of Aldehydes with N-Hydroxyimides
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A synthetically practical transition metal/catalyst/halogen-free dehydrogenative coupling of aldehydes with N-hydroxyimides promoted solely by tert-butyl nitrite under mild conditions was developed. tert-Butyl nitrite generates two radicals (tBuO and NO) and thus works as a twofold hydrogen abstractor. A diverse array of N-hydroxyimide esters were prepared from either aliphatic or aromatic aldehydes. Benzoyl-substituted aldehydes such as 2-oxo-2-phenylacetaldehyde are also suitable.
- Dai, Peng-Fei,Wang, Yi-Ping,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 9360 - 9364
(2021/12/09)
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- Method and device for continuously preparing alkyl nitrite through channelization
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The invention discloses a method and device for continuously preparing alkyl nitrite through channelization. The method comprises the following steps: storing alkyl alcohol and concentrated HCl aqueous solution in a first container and storing sodium nitrite aqueous solution in a second container; continuously conveying the solution in the first container and the second container into a static mixer for mixing by a first metering pump and a second metering pump respectively, enabling mixed solution to continuously enter a tubular reactor for reaction at the temperature of -20 DEG C-5 DEG C for1-250s, enabling feed liquid after reaction to enter a liquid separation tank and performing aftertreatment on the feed liquid in the liquid separation tank, so as to obtain alkyl nitrite. The preparation method disclosed by the invention has the advantages of being good in process safety and easy in control of reaction conditions, achieving continuous production, being high in product yield andachieving large-scale production only through less investment in the industry.
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Paragraph 0027-0030
(2019/07/04)
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- Cleavage of C(aryl)?CH3 Bonds in the Absence of Directing Groups under Transition Metal Free Conditions
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Organic chemists now can construct carbon–carbon σ-bonds selectively and sequentially, whereas methods for the selective cleavage of carbon–carbon σ-bonds, especially for unreactive hydrocarbons, remain limited. Activation by ring strain, directing groups, or in the presence of a carbonyl or a cyano group is usually required. In this work, by using a sequential strategy site-selective cleavage and borylation of C(aryl)?CH3 bonds has been developed under directing group free and transition metal free conditions. Methyl groups of various arenes are selectively cleaved and replaced by boryl groups. Mechanistic analysis suggests that it proceeds by a sequential intermolecular oxidation and coupling of a transient aryl radical, generated by radical decarboxylation, involving a pyridine-stabilized persistent boryl radical.
- Dai, Peng-Fei,Ning, Xiao-Shan,Wang, Hua,Cui, Xian-Chao,Liu, Jie,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 5392 - 5395
(2019/03/29)
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- Four-Coordinate Copper Halonitrosyl {CuNO}10 Complexes
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While copper nitrosyl complexes are implicated in numerous biological systems, isolable examples remain limited. In this report, we show that [Cl3CuNO]?, with a {CuNO}10 electron configuration, can be generated by nitrite reduction at a copper(I) dichloride anion or by nitric oxide addition to a copper(II) trichloride precursor. The bromide analogue, [Br3CuNO]? was synthesized analogously, and both copper halonitrosyl complexes were characterized by X-ray diffraction and a variety of spectroscopic methods. Experimental data and multireference (CASSCF/NEVPT2) calculations provide strong evidence for a CuII–NO. ground state. Both [Cl3CuNO]? and [Br3CuNO]? release and recapture NO. reversibly, and exhibit nitrosative reactivities toward a wide range of biological nucleophiles, such as amines, alcohols, and thiols.
- Bower, Jamey K.,Sokolov, Alexander Yu.,Zhang, Shiyu
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supporting information
p. 10225 - 10229
(2019/07/03)
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- Organopromoted Selectivity-Switchable Synthesis of Polyketones
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In this work, an organopromoted metal-free pharmaceutical-oriented selectivity-switchable benzylic oxidation was developed, affording mono-, di-, and trioxygenation products, respectively, using oxygen as the oxidant under mild conditions. This process facilitates dioxygenation of 2,6-benzylic positions of heterocycles, which could be inhibited by heterocycle chelation to the metal cocatalysts. Enantiopure chiral ketones could also be prepared. The noninvolvement of transition metals and toxins avoids metal or hazardous residues, consequently ensuring a final-stage gram-scale synthesis of Lenperone.
- Liu, Jie,Hu, Kang-Fei,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 5593 - 5596
(2017/10/25)
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- Copper(II) activation of nitrite: Nitrosation of nucleophiles and generation of NO by thiols
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Nitrite (NO2-) and nitroso compounds (E-NO, E = RS, RO, and R2N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper(II) nitrito complex [C12NNf6]Cu(κ2-O2N)-THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [CuII](κ2-O2N) that leads to S-nitrosation to give the S-nitrosothiol RSNO and copper(Il) hydroxide [CuII]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph2NH and alcohol tBuOH to give Ph2NNO and tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper(II) thiolate [CuII]-SR intermediate formed upon reaction of an additional equiv thiol with [CuII]-OH.
- Kundu, Subrata,Kim, William Y.,Bertke, Jeffery A.,Warren, Timothy H.
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supporting information
p. 1045 - 1048
(2017/05/15)
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- Rhodium(I)-catalyzed synthesis of aryltriethoxysilanes from arenediazonium tosylate salts with triethoxysilane
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An efficient method for the preparation of aryltriethoxy-silanes from arenediazonium tosylate salts has been developed, which expands the substrates of rhodium-catalyzed silylation from iodides, bromides, and triflates to diazonium salts. A new method for hydrodediazoniation has also been explored.
- Tang, Zhi Yong,Zhang, Yuan,Wang, Tao,Wang, Wei
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supporting information; experimental part
p. 804 - 808
(2010/06/14)
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- Atmospheric chemistry of isopropyl formate and tert-butyl formate
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Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH3)2, and tert-butyl formate, HC(O)OC(CH 3)3. Product distributions are reported from both Cl- and OH-initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the α-ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15-20%). The OH radical initiated oxidation of tert-butyl formate gives acetone, formaldehyde, and CO2 as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10-12, and with Cl (1.75 ± 0.35) × 10-11, and for tert-butyl formate with Cl (1.45 ± 0.30) × 10-11 cm3 molecule-1 s-1. Simple group additivity rules fail to explain the observed distribution of sites of H-atom abstraction for simple formates.
- Pimentel, Andre Silva,Tyndall, Geoffrey S.,Orlando, John J.,Hurley, Michale D.,Wallington, Timothy J.,Andersen, Mads P. Sulbaek,Marshall, Paul,Dibble, Theodore S.
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experimental part
p. 479 - 498
(2011/04/12)
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- Kinetics and products of the reactions of oh radicals with 4,4-dimethyl-1-pentene and 3,3-dimethylbutanal at 296 ± 2 k
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Using a relative rate method, rate constants have been measured for the reactions of OH radicals with 4,4-dimethyl-1-pentene [(CH3) 3CCH2CH=CH2] and its major reaction product, 3,3-dimethylbutanal [(CH3)3CCH2CHO], at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained were 2.41 × 10-11 and 2.73 × 10-11 cm3 molecule-1 s-1, respectively, with estimated uncertainties of ±10%. The products identified and quantified by gas chromatography with mass spectrometry and/or flame ionization detection from the 4,4-dimethyl-1-pentene reaction were acrolein [CH2=CHCHO], 3,3-dimethylbutanal, and a molecular weight 112 carbonyl attributed to 4,4-dimethyl-2-pentenal [(CH3)3CCH=CHCHO], with formation yields of 2.7 ± 0.5%, 59 ± 6%, and 3.4 ± 0.6%, respectively. Using direct air sampling atmospheric pressure ionization mass spectrometry, additional products of molecular weight 146, 177, and 193 were observed, and on the basis of expected reaction schemes these are attributed to the dihydroxycarbonyl HOCH2C(CH3)2CH 2C(O)CH2OH, the hydroxynitrates (CH3) 3CCH2CH(OH)CH2ONO2 and/or (CH 3)3CCH2CH(ONO2)CH2OH, and the dihydroxynitrate O2NOCH2C(CH3) 2CH2CH(OH)CH2OH, respectively. The hydroxynitrates were also tentatively identified by gas chromatography, with a summed yield of ~15%. Acrolein and 4,4-dimethyl-2-pentenal arise from H-atom abstraction from the three equivalent CH3 groups and the 3-position CH2 group, and the sum of their formation yields (6.1 ± 0.8%) is expected to be very close to the fraction of the overall reaction proceeding by H-atom abstraction.
- Aschmann, Sara M.,Arey, Janet,Atkinson, Roger
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experimental part
p. 5810 - 5816
(2010/09/06)
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- Spectrokinetic study of the reaction system of 2NO2?N 2O4 with butanols between 320-358 K in the gas phase
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Spectrokinetic studies of the gas-phase equilibrium between nitrogen tetroxide and butanols in the reaction system 2NO2?N 2O4 (1,2), N2O4+ROH? RONO+HNO3 (3,4) have been undertaken in the temperature range 298-358 K. The products - RONO (n-butyl-ONO, sec-butyl-ONO, iso-butyl-ONO and tert-butyl-ONO) - were identified by their UV spectra and the values of the maxima UV absorption cross sections were determined in the range 320-420 nm at 298 K. The temperature dependences of both the forward and reverse rate constants, k3 and k4, were obtained. The extrapolated values of the forward rate constants are 10-18 k3 av/cm3 molec-1 s-1 3.9±1.0; 1.7±0.3; 4.2±0.8; 5.7±1.1 and the reverse rate constants are 10-20 k4av/cm3 molec -1 s-1 0.3±0.1; 2.3±0.6; 0.4±0.1; 2.3±0.6 at 298 K for the reaction of NO2/N2O 4 with n-butanol, sec-butanol, iso-butanol and tert-butanol, respectively. The activation energy for the forward E3 and for the reverse E4 reaction were derived.
- Wojcik-Pastuszka,Jodkowski
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experimental part
p. 131 - 143
(2009/09/25)
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- An easy access to aryl azides from aryl amines under neutral conditions
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A variety of substituted aryl amines were transformed into aryl azides using t-BuONO and moist NaN3 in t-BuOH in good to excellent yields. Smooth transformation was observed with anilines, having electron withdrawing and donating groups. Both acid- and base-sensitive groups survived the reaction conditions. Georg Thieme Verlag Stuttgart.
- Das, Jagattaran,Patil, Santoshkumar N.,Awasthi, Riti,Narasimhulu, C. Prasad,Trehan, Sanjay
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p. 1801 - 1806
(2007/10/03)
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- Oxidation of benzylic alcohols and ethers to carbonyl derivatives by nitric acid in dichloromethane
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Nitric acid in dichloromethane may be successfully employed for the oxidation of benzylic alcohols and ethers to the corresponding carbonyl compounds. The proposed method proved to be of general applicability, affording very good yields of aldehydes and ketones and showing interesting chemoselectivity in many instances, allowing competitive aromatic nitration to be avoided, as well as - in the case of aldehydes - any further oxidation to carboxylic acids. The reaction probably proceeds by a radical mechanism, the active species in the oxidation process being NO2. Competitive formation of nitro esters was observed in some cases, whereas poor results were obtained with allylic and non-benzylic substrates. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Strazzolini, Paolo,Runcio, Antonio
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p. 526 - 536
(2007/10/03)
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- Fluorescence excitation spectrum of the tert-butoxy radical and kinetics of its reactions with NO and NO2
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The fluorescence excitation spectrum of the tert-C4H9O() (tert-butoxy) radical in the wavelength range 330-440 nm was obtained using a combined laser photolysis/laser-induced fluorescence (LIF) technique. The radicals were generated by excimer laser photolysis of di-tert-butylperoxide at λ = 248 nm. Its fluorescence excitation spectrum shows 16 vibronic bands in two progressions, where the dominant progression corresponds to the CO stretching vibration in the first electronically excited state with = (515+/-10) cm-1. The transition origin was assigned at = (25 836+/-10) cm-1 [λ00 = (387.06+/-0.15) nm]. The kinetics of the reactions of the tert-butoxy radical with NO and NO2 over the temperature range T = 223-305 K and pressure range p = 5-80 Torr were determined. The rate coefficients for both reactions were found to be independent of total pressure with kNO = (2.9+/-0.2) 10-11 cm3 s-1 (5-80 Torr) and k = (2.50+/-0.2) 10-10 cm3 s-1 (5-80 Torr) at T = 295 K. The Arrhenius expressions for the reactions of tert-butoxy with NO and NO2 were determined to be kNO = (7.6+/-1.2)x10-12 exp[(3.2+/-0.8) kJ mol-1/RT] cm3 s-1 and kNO2 = (3.5+/-1.2)x10-12 exp[(4.6+/-0.7) kJ mol-1/RT] cm3 s-1. Additionally, the radiative lifetime of the tert-C4H9O() radical after excitation at λ = 341.576 nm was determined to be τrad[tert-C4H9O()] >= (1.5+/-0.1) μs. The fluorescence spectrum of electronically excited tert-butoxy radicals in the range λ = 375-575 nm was obtained following the photolysis of tert-butylnitrite at 193 nm.
- Lotz, Ch.,Zellner, R.
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p. 2352 - 2360
(2007/10/03)
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- Direct studies on the decomposition of the tert-butoxy radical and its reaction with NO
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The first laser induced fluorescence (LIF) spectrum for the tert-butoxy radical is reported following radical generation by excimer laser photolysis of tert-butyl nitrite. The laser flash photolysis-LIF technique is used to measure the temperature dependence of the rate coefficient for the reaction with NO (T = 200-390 K): (CH3)3CO + NO → (CH3)3CONO (3) which can be represented in either Arrhenius or AT(-n) format: k3 = (7.8 ± 1.8) x 10- 12 exp(2850 ± 290 J mol-1/RT) cm3 molecule-1 s-1 k3 = (4.17 ± 0.12) x 10-11(T/200)(-1.27±0.07) cm3 molecule-1 s-1 and the tert- butoxy decomposition. (CH3)3CO→CH3COCH3 + CH3 (2). Whilst the former reaction shows no pressure dependence (p = 70-500 Torr of helium), the latter reaction is in the fall-off regime over the entire range of experimental conditions (T = 303-393 K, p = 13-600 Tort helium). The fall-off data were fitted using an inverse Laplace transformation/master equation model to give the following Arrhenius parameters: k2/(∞)(T) = (1.4±0.6) x 1013 exp[- (57±2) kJ mol-1/RT]. These Arrhenius parameters are significantly lower than previous indirect measurements or calculations and the atmospheric and mechanistic implications are discussed. Finally, reaction (3) was also studied by monitoring the temporal dependence of the NO LIF signal following the photolysis of tert-butylnitrite with no additional NO. The results are in good agreement with the tert-butoxy monitoring and allow for an estimation of the rate parameters for the tert-butoxy self reaction.
- Blitz,Pilling,Robertson,Seakins
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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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- Thermal Decomposition of Nitrate Esters
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Rates of thermal decomposition and solvent rate effects have been measured for a series of nitrate esters.The alkoxy radicals formed by homolysis together with some of their further degradation products have been stabilized by hydrogen donation.Internal and external return of nitrogen dioxide have been demonstrated by solvent cage effects and isotope exchange.Radical-stabilizing substituents favor β-scission.Dinitrates in a 1,5 relationship behave as isolated mononitrates.Dinitrates in a 1,3 or 1,4 relationship exhibit intramolecular reactions.Tertiary nitrate esters in diethyl ether undergo elimination rather than homolysis.
- Hiskey , Michael A.,Brower, Kay R.,Oxley, Jimmie C.
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p. 3955 - 3960
(2007/10/02)
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- Nitrosation by Alkyl Nitrites. Part 5. Kinetics and Mechanism of Reactions in Acetonitrile
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Simple alcohols and thioglycolic acid react with alkyl nitrites and nitrous acid in acidic acetonitrile solution to give the O- and S-nitrosated products, in reactions which are kinetically zero order in the alcohol or thiol concentration.The results are consistent with rate-liminiting NO+ formation.On addition of the parent alcohol (derived from the alkyl nitrite) reactions are slower and there is a change towards a first order dependence upon the substrate concentration, indicating that under these conditions the reaction of NO+ with the substrate is partly rate limiting.The reactivity order is found to be HNO2 > t-butyl-nitrite > i-propyl nitrite > isopentyl nitrite.Similarly aromatic amines yield nitrosamine or diazonium ion products, but now the kinetics are consistent with rate-limiting attack of NO+ with the unprotonated amine.At higher acidities it is proposed that reaction occurs with the protonated form of the amine.The mechanistic implications of the kinetic results are discussed.
- Crookes, Michael J.,Williams, D. Lyn H.
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p. 1319 - 1322
(2007/10/02)
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- Nitrosation by Alkyl Nitrites. Part 2. Kinetics of Reactions in Aqueous Acid Solution with Isopropyl and t-Butyl Nitrites
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The rates of reaction of isopropyl nitrite with sulphamic acid, hydrazoid acid, thioglycolic acid, cysteine, N-methylaniline, and thiourea are markedly reduced by the addition of propan-2-ol.A detailed kinetic analysis of the results is as expected for a mechanism where hydrolysis of isopropyl nitrite occurs rapidly (and reversibly) and released nitrous acid effects nitrosation.The analysis yields values for the equilibrium constant for isopropyl nitrite hydrolysis and also for the rate constants for nitrous acid nitrosation (for a range of substrates), which are in good agreement with the literature values obtained by direct measurement.For t-butyl nitrite the extent of hydrolysis is so great (and the reaction is so rapid) that the kinetics are identical with those obtained using nitrous acid.Under most of the experimental conditions employed the rate-limiting step is the reaction of H2NO2+ with the substrate, but at high for the more reactive species, the rate-limiting step changes to that of hydrolysis of RONO.This is particularly true for the t-butyl nitrite, where it is easier for the nitrosation of the substrate by nitrous acid to compete with the re-nitrosation of the alcohol, since the rate of the latter reaction is much smaller for a tertiary alcohol than it is for a secondary alcohol.Further experimental measurements on the ROH + HNO2 -> RONO system, for both isopropyl and t-butyl nitrites, confirm these mechanistic ideas.
- Crookes, Michael J.,Williams, D. Lyn H.
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p. 1339 - 1344
(2007/10/02)
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- Reaction of alcohol with NO2 on a Cleaned Glass Surface
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Formation of alkyl nitrite from alcohol and NO2 was very fast on a Pyrex glass surface cleaned with chromic acid mixture.The reaction was practically zero order with respect to NO2.The rate constant was (1.7 +/- 0.08)*10E-18 cm3*molecule-1*s-1 for methyl nitrile formation and the apparent activation energy was -53.5 kJ*mol-1.
- Maeda, Yasuaki,Fujio, Yoshifumi,Munemori, Makoto
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p. 2127 - 2130
(2007/10/02)
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- Hydrolysis, Nitrosyl Exchange, and Synthesis of Alkyl Nitrites
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Alkyl nitrites undergo relatively slow hydrolysis in phosphate-buffered aqueous media under neutral conditions with small but significant dependence of reactivity on structure.However, rapid nitrosyl exchange with alcohols is observed, and equilibrium constants for this transformation exhibit remarkable correlation with equilibrium constants for nitrosyl exchange of alcohols with nitrosyl chloride and with nitrous acid. tert-Butyl nitrite has the greatest driving force for nitrosyl transfer among the 12 alkyl nitrites examined, and this capability is used for the synthesis of alkyl nitrites derived from steroidal alcohols and of alkyl thionitrites.
- Doyle, Michael P.,Terpstra, Jan W.,Pickering, Ruth A.,LePoire, Diane M.
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p. 3379 - 3382
(2007/10/02)
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- Gas-phase Reaction of Hydroxyl Radicals with Alkyl Nitrite Vapors in H2O2+NO2+CO Mixtures
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The yields of CO2 from the chain reaction in H2O2+NO2+CO+alkyl nitrite mixtures, in wich OH is the chain carrier and alkyl nitrites induce a chain termination step, have been used to deduce rate constants (ks) for OH attack on alkyl nitrites (RONO) in the vapour phase at ambient temperatures.Values of ks/E9 dm3 mol-1 s-1 as a function of R were determined as follows: 0.71 +/-0.12 (CH3), 1.15+/-0.23 (C2H5), 1.56+/-0.32 (n-C3H7), 3.41+/-1.48 (n-C4H9), 3.89+/-0.58 (sec-C4H9), 3.47+/-0.52 (i-C4H9), 0.91+/-0.15 (t-C4H9), all based on ks=(1.63+/-0.16)E9 dm3 mol-1 s-1 for OH +n-butane.The small increase in ks from R=CH3 to t-4H9 is considered to support a recent postulate that both H-abstraction and NO-abstraction pathways are operative, at least for R=CH3.Under typical, sunlit urban atmosphere conditions it is deduced that OH attack on alkyl nitrites is a minor removal process compared to their photodissociative destruction.
- Audley, Gary J.,Baulch, Donald L.,Campbell, Ian M.,Waters, Des J.,Watling, Gillian
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p. 611 - 618
(2007/10/02)
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