Major Primary Products Research Articles

Time-resolved pulsed FTIR emission studies of atom-radical reactions: Product chemiluminescence from the O( 3P)+CF 2(X̃ 1A 1) reaction

A time-resolved interferometer has been used to study the product vibrational infrared chemiluminescence from atom-radical reactions. The entire temporal evolution of the emission spectrum is obtained from a single interferometric scan. Results are given for the O( 3P) + CF 2(X̃ 1A 1) reaction, which exhibits strong emission from highly vibrationally excited CO 2, formed by reaction of O atoms with FCO, the major primary product of the title reaction.

Étude chimique et cinétique de l'oxydation homogène en phase gazeuse d'alcanes légers. I. Isobutane

A literature survey on the homogeneous gas-phase oxidation of light alkanes shows that despite a rather high number of papers there are still, even in the case of isobutane, an important number of unresolved questions, which makes the writing of a reaction scheme rather difficult. To obtain more reliable experimental data, we have studied the homogeneous gas-phase oxidation of isobutane in a conventional static system, at 310 and 340 °C and subatmospheric pressure. This investigation is chiefly aimed at identifying and measuring the major primary products of the reaction. A chain radical scheme based on the primary products and on estimation of the rate constants of the elementary steps by the methods of Thermochemical Kinetics is put forward to interpret our experimental results. Two major reaction routes appear, one corresponding to the formation of isobutene and the other to the formation of isobutene oxide. The conclusions of the present investigation and suggestions for further developments are also mentioned. Keywords: oxidation, chemical kinetics, reaction mechanism, isobutane.

Palaeo-oceanography and biogeography in the Tremadoc (Ordovician) Iapetus Ocean and the origin of the chemostratigraphy of Dictyonema flabelliforme black shales

AbstractHigh concentrations of vanadium, molybdenum, uranium, arsenic, antimony with low concentrations of manganese, iron and cobalt heretofore restricted to Dictyonema flabelliforme-bearing Tremadoc black shales in Balto-Scandia, have been found in coeval black shales in the Saint John, New Brunswick area. Prior palaeogeographic reconstructions place these areas about 400 km. apart in high southern latitudes in the Iapetus Ocean, with New Brunswick in proximity to Avalonia (southeastern Newfoundland). These geochemical similarities are not found in coeval Tremadoc black shales of Bolivia, New York, Quebec, Wales, and Belgium. Palaeo-oceanographic reconstructions of Iapetus support the proximity of Balto-Scandia and the Saint John area during the early Tremadoc and Gee'sx (1981) suggestion that the signature is a feature of eastern Iapetus. Furthermore, first-order modelling of the major surface currents and related primary productivity in the Tremadoc Iapetus Ocean explain the apparent wide latitudinal range of D. flabelliforme (Fortey, 1984) and the anomalous trace metal content of certain black shales of that time. Variations in the elemental content of these black shales is produced by oceanographic and geologic conditions unique to the geographic site. The distinctive Balto-Scandic geochemical signature resulted from the coincidence of anoxic waters transgressing the shelf at latitudes of high organic productivity at the polar Ekman planetary divergence. This produces the conditions for concentrations of V, U, and Mo in the shales. Metal enriched anoxic bottom waters produced by leaching of volcanics or through hydrothermal activity may be the source of the other enhanced signature elements such as As and Sb. The absence of this geochemical signature in younger non-D. flabelliforme Tremadoc and later black shales in Balto-Scandia and other areas suggests that the closing of Iapetus moved the depositional sites into less productive oceanic areas.

Major primary cytotoxic product of 4-hydroxyanisole oxidation by mushroom tyrosinase is 4-methoxy ortho benzoquinone.

It has been shown previously that the initial product of mushroom tyrosinase-catalysed oxidation of the monophenol 4-hydroxyanisole (4HA) is 4-methoxy ortho benzoquinone (4-MOB). This study presents evidence that 4-MOB is primarily responsible for the cytotoxicity of 4HA oxidation products in vitro. Equivalent toxicity in a model system was produced by products of tyrosinase catalysed oxidation of 4HA and by synthetic 4-MOB. Cytotoxicity was estimated both by a blebbing assay and by plating efficiency of exposed cells. HPLC analysis of the reaction mixture revealed a positive correlation between cytotoxicity and 4-MOB concentration.

Oxidation of (CD3)2\dotCX Radicals. III. Reaction of 2-Propanol and (CD3)2\dotC(OH) Radicals with Atomic Oxygen

Abstract The reaction of oxygen atoms with 2-propanol was studied in a fast flow system coupled with a photoionization mass spectrometer. Radicals formed in the primary attack of O(3P) atoms on 2-propanol were photoionized by the Xe lamp and identified as the (CH3)2\dotC(OH) radical from (CH3)2CH(OH) and (CH3)2CD(OH) and the (CD3)2\dotC(OH) radical from (CD3)2CH(OH). The major primary product in the subsequent reaction of O+(CD3)2\dotC(OH) was found to be acetone, (CD3)2CO, (62±4%). Formation of 1-propen-2-ol, CD3C(OH)=CD2, by deuterium abstraction and acetic acid, CD3COOH, by oxygen addition were observed in the reaction of O+(CD3)2\dotC(OH). In the reaction of 18O+(CD3)2\dotC(OH), the acetone produced was mostly (CD3)2CO. This fact shows that acetone is produced predominantly by the hydrogen abstraction by O(3P) from the O–H in the (CD3)2\dotC(OH) radical. A part of the acetone is produced also by the addition of O(3P) to the (CD3)2\dotC(OH) radical; i.e., a small but significant signal of (CD3)2C18O was observed in the reaction of 18O+(CD3)2\dotC(OH). The competition experiment between O(3P) and O2 for the (CD3)2\dotC(OH) radical shows that (CD3)2\dotC(OH) react (0.16±0.02) times as fast with O2 as with O(3P). This result suggests that the reaction of (CD3)2\dotC(OH) with O2 is very rapid. It is proposed that the rapid reaction is hydrogen abstraction by O2 from the O–H in the (CD3)2\dotC(OH) radical to form acetone and HO2.

The photo-oxidations of propyl acetates in synthetic air-HONO-NO x mixtures: Product formation studies and proposed kinetic mechanisms

The formation of products following the hydroxyl radical initiated photo-oxidations of n-and isopropyl acetates has been studied. Mixtures of synthetic air containing a few ppm of nitrous acid, nitric oxide, nitrogen dioxide and one of the propyl acetates were irradiated with sunlamps in a Teflon bag smog chamber. The decay of reactants and the formation of products was monitored by chemiluminescent analysis or by gas chromatography. The major primary products from the photo-oxidation of n-propyl acetate are acetaldehyde and propionaldehyde while from isopropyl acetate they are acetone and methyl nitrate. It was not possible to analyse for formaldehyde, an expected primary product in these systems. The nature and distribution of products indicate that a significant fraction of primary products arise from decomposition reactions of the alkoxy-type radicals generated following the initial attack of hydroxyl radicals on the esters. The derived reaction stoichiometries (molecules of NO oxidised per molecule of ester reacted) are also consistent with the proposed mechanisms.

The photodissociation of phenylsilane at 193 nm

Molecular hydrogen is observed to be one of the major primary products in the 193 nm photodissociation of phenylsilane. A two-channel dissociation mechanism is proposed, yielding PhSiH+H 2 and SiH 2 +PhH with the former predominant. The implications of this observation for experiments which utilise phenylsilane as a precursor for SiH 2 radicals are discussed.

Factors affecting product formation in the photolysis of α-spirocyclopropyl ketones

Photolysis of spiro[2.5]oct-7-en-4-ones results in exclusive β-cleavage in methanol to give 2-ethenylcyclohex-2-en-1-ones and in hydrocarbon solvents to give (E)- and (Z)-2-ethylidenecyclohex-3-en-1-ones. The solvent effect is ascribed to the role of methanol in stabilizing trienol intermediates and engendering their intermolecular ketonization. Photolysis of 8-methylenespiro[2.5]octan-4-ones in methanol gives 2-ethenylcyclohex-2-en-1-ones and bicyclo[4.3.0]non-1(6)-en-2-ones; irradiation in methanol-O-d indicates that the former type of product is formed mainly via a trienol intermediate. Photolysis of 8-methylenespiro[2.5]octan-4-ones in benzene gives 2-ethenylcyclohex-2-en-1-ones together with (E)- and (Z)-2-ethylidene-3-methylenecyclohexan-1-ones; the latter undergo photoconversion to the former during the irradiation. 6,6-Dimethylspiro[2.4]-heptan-4-one on photolysis in methanol undergoes ct-cleavage to give 4-methoxy-7,7-dimethyl-5-oxaspiro[2.5]octane as the major product, whereas under the same conditions 6,6-dimethylspiro[2.5]octan-4-one is reduced to the corresponding alcohol and 6,6,8-trimethylspiro[2.5]octan-4-one undergoes β-cleavage to give 2-ethyl-3,5,5-trimethylcyclohexan-1-one as the major primary product; this trichotomy is interpreted in terms of ring-size and steric factors.

Electronic effects of polar substituents in the gas phase unimolecular elimination of 4-substituted isobornyl acetates

The rates of gas-phase elimination of a series of 4-substituted isobornyl acetates have been measured in the presence of propene between 209–370 °C and within a pressure range 37–153 Torr; a static system with seasoned vessels was used. The reactions are unimolecular, homogeneous, and obey a first-order rate law; electron-withdrawing substituents at C(4) cause a diminution in the elimination rate, such that ρ1–0.69 in a Hammett treatment. The temperature dependence of the rate coefficients is illustrated for the Arrhenius equation for isobornyl acetate: log k/ s–1=(12.82 ± 0.13)–(189.2 ± 1.5) kj mol–1/2.303 RT. The results are consistent with a cyclic transition state in which C(2)–O cleavage is more advanced than that of C(3)–H. The major primary product of elimination of isobornyl acetate is bornylene, which partially isomerises to camphene and tricyclene under the reaction conditions. Bornylene also undergoes a retro-Diels–Alder reaction to yield the trimethylcyclopentadiene and ethylene.

Metabolism of oxybutynin: Establishment of desethyloxybutynin and oxybutyninN-oxide formation in rat liver preparations using deuterium substitution and gas chromatographic mass spectrometric analysis

Oxybutynin is rapidly metabolized in rat liver microsomes. Two major primary oxidation products were identified as N-desethyl oxybutynin and oxybutynin N-oxide. Deuterium substituted substrate was used to aid the identification. N-Desethyl oxybutynin was characterized by gas chromatography electron impact mass spectrometry as its trifluoroacetamide derivative and oxybutynin N-oxide was indicated by the presence of a decomposition product, 2-oxo-3-butenyl-2 cyclohexyl-2-phenylglycolate, as elucidated from the gas chromatographic mas spectrometric analysis. The formation of this product from synthetic oxybutynin N-oxide was verified and occurs by two consecutive rearrangements upon thermolysis of the unstable N-oxide. Attempted titanous chloride reduction of oxybutynin N-oxide resulted in the formation of the hydrolytic products 2-cyclohexyl-2-phenylglycolic acid and 4-diethylamino-2-butynol.

Glycollate Metabolism in the Obligate Chemolithotroph Thiobacillus neapolitanus Grown in Continuous Culture

CO2-limited chemostat cultures of Thiobacillus neapolitanusexcreted 13·5; nmol glycollate min−1 (mg protein)−1. This confirmed the earlier finding that glycollate excretion by T. neapolitanusis dependent on the CO2/O2 ratio applied in the chemostat and thus is probably due to the oxygenase activity of d-ribulose-1,5-bisphosphate (RuBP) carboxylase. RuBP-dependent oxygen uptake and activity of phosphoglycollate phosphatase were demonstrated in cell-free extracts of T. neapolitanus. Thiobacillus neapolitanuswas able to metabolize exogenous glycollate only to a limited extent. The proportion of dry weight that was derived from [1-14C]glycollate by both CO2- and thiosulphate-limited chemostat cultures was only 0·7 % of the total. Short-term labelling experiments with [1-14C]glycollate and enzyme studies indicated that T. neapolitanuscan metabolize glycollate via two pathways. The enzymes of the glycine-serine pathway were demonstrated in cell-free extracts, but on the basis of kinetic experiments it was concluded that this pathway does not play a major role in glycollate metabolism. Malate was the major primary labelling product. Glyoxylate, formed from glycollate, may be incorporated into malate via malate synthase, which was detected in cell-free extracts of T. neapolitanus. The activities of the enzymes needed for the metabolism of glycollate were independent of growth conditions applied in the chemostat. The results are discussed in relation to the possible causes of obligate chemolithotrophy.

Reaction of ethanol and CH3CH(OH) radicals with atomic and molecular oxygen

The reaction of oxygen atoms with ethanol in a fast flow system was studied with a photoionization mass spectrometer. A radical formed from O+C2H5OH was photoionized by the Xe lamp and identified as the alpha-ethanol radical, CH3CH(OH), i.e., CH3CD(OH) (m/e = 46) and CD3CD(OH) (m/e = 49) were observed in reactions of O+CH3CD2OH and C2D5OH, respectively. The major primary product in the subsequent reaction of alpha-ethanol radicals with atomic oxygen was found to be acetaldehyde (79%±8%) and no formation of vinyl alcohol was observed, i.e., CH3CDO (m/e = 45) and CD3CDO (m/e = 48) were observed in reactions of O+CH3CD2OH and C2D5OH, respectively: O(3P)+CH3CH(OH)→CH3CHO+OH (4a). The reaction of 18O(3P)+C2D5OH produced only CD3CDO (m/e = 48). This fact shows that acetaldehyde is produced by the hydrogen abstraction reaction by O(3P) from the O–H in the alpha-ethanol radical. The competition experiment among O(3P) and O2 for the alpha-ethanol radical shows that alpha-ethanol radicals react (0.14±0.04) times more slowly with molecular oxygen than with atomic oxygen. This result suggests that the reaction of alpha-ethanol radicals with molecular oxygen is very rapid, and that the reaction probably proceeds by a two body reaction to form acetaldehyde and HO2.

Spin trap evidence for production of superoxide radical anions by purified NADPH-cytochrome P-450 reductase

Previous evidence for superoxide radicals as initial reduction products of oxygen by NADPH cytochrome P-450 reductase has been indirect. In this paper a technique is described to spin trap radicals produced in incubations of oxygen and reductase. Reference spin trap adducts were synthesized by adding phenyl- t -butyl nitrone (PBN) to superoxide radicals (PBN-OOH) or to hydroxyl radicals (PBN-OH). Both PBN adducts are stable in water or ethyl acetate for hours. Electron Paramagnetic Resonance (EPR) spectra measured in N 2-saturated ethyl acetate allow clear resolution of the hyperfine extrema of PBN-OH and PBN-OOH (2.1 and 4.5 G splitting, respectively). Comparison of EPR spectra from reductase and oxygen incubations with those of synthetic PBN-OOH suggest that superoxide radicals are the major primary reduction product of oxygen.

ChemInform Abstract: REACTION OF ALLYL BROMIDES WITH BROMOFORM AND BASE UNDER PHASE TRANSFER CONDITIONS

AbstractDas Methallylbromid (I) reagiert mit überschüssigem Bromoform in Gegenwart von Cetrimide (Cetyltrimethylammoniumbromid) unter Phasentransferbedingungen zum Tribromid (II) als einzigem Reaktionsprodukt.

Reaction of allyl bromides with bromoform and base under phase transfer conditions

The reaction of allylic bromides with bromoform and aqueous base under phase transfer conditions is strongly dependent on the catalyst; when benzyltriethylammonium chloride is used, the major primary product is a 4,4,4-tribromobut-1-ene.

The mechanism of the pyrolysis of 2, 2, 3, 3-tetramethylbutane

The pyrolysis of 2, 2, 3, 3-tetramethylbutane (TMB) was investigated in the ranges 699-735 K and 3-19 Torr (0.4-2.5 kPa) at up to 4% decomposition. The reaction is strongly self-inhibited and sensitive to the surface/volume ratio of the reaction vessel. A simple Rice-Herzfeld chain terminated by the heterogeneous removal of hydrogen atoms is proposed for the initial, uninhibited reaction generating isobutene and hydrogen in a 2:1 ratio. Self-inhibition is due to abstraction by hydrogen atoms of hydrogen atoms from product isobutene giving resonance-stabilized 2-methylallyl radicals which participate in homogeneous termination reactions. The kinetic characteristics of the major primary products (> 95% on a mole basis), isobutene and hydrogen, are accounted for when reasonable values are assumed for the rate constants for hydrogen atom abstraction by hydrogen atoms from TMB and from isobutene and for initiation and heterogeneous termination of the chain reaction. The kinetic characteristics of the formation of methane and propene (2-4% of total product) are accounted for by the secondary reaction scheme H + i-C 4 H 8 → i-C 4 H 9 , i-C 4 H 9 → CH 3 + C 3 H 6 , CH 3 + TMB → CH 4 + C 8 H 17 , when a reasonable value for the rate constant for the hydrogen atom addition to isobutene is assumed. The kinetic characteristics of the formation of ethene ( ca . 0.1% of total product) are accounted for by the tertiary reaction scheme H + C 3 H 6 → n -C 3 H 7 n -C 3 H 7 → CH 3 + C 2 H 4 , when a reasonable value for the rate constant for the hydrogen atom addition to propene is assumed. The kinetic characteristics of the formation of isobutane ( ca . 1% of total product) are much less affected by an increase in surface/volume ratio of the reactor than are those of the other products. A heterogeneous, secondary source is suggested, viz. 1/2H 2 ( g ) ⇌ H (wall), H (wall) + t-C 4 H 9 ( g ) ⇌ i-C 4 H 10 ( g ), which can generate the observed dependence of the isobutane yield on the reaction conditions but the reasonableness or otherwise of the values of the equilibrium and rate constants it is necessary to postulate is impossible to assess without further work designed specifically to investigate this problem.

Non quasi-stationary state pyrolysis. Kinetic parameters of neopentane pyrolysis mechanism

The study of neopentane pyrolysis during its induction period has allowed to determine, from the quantitative measurement of major primary products only, the rate constant of the limiting chain propagation step, as well as the kinetic parameters of initiation and termination steps.

Thermal Decomposition of Tobacco Cell-wall Polysaccharides

AbstractIn order to clarify the thermal decomposition mechanism of tobacco cell-wall polysaccharides, some of the primary pyrolysis products were investigated using a Curie-point pyrolysis technique. The major primary products of tobacco cellulose prepared from midribs of Nicotiana tabacum, heated at 460°C for 5 seconds in helium or in vacuum, were such 1,6-anhydrosugars as levoglucosan, 1,6-anhydrob-D-glucofuranose, 1,4,3,6-dianhydro-a-D-glucopyranose and levoglucosenone, and such furan compounds as 5-hydroxymethyl-2-furaldehyde and 2-furaldehyde. The major primary pyrolysis products of tobacco xylan prepared from stalks of Nicotiana tabacum were 3-hydroxy-2-penteno-1,5-lactone and 2-furaldehyde. Some discussions of the thermal reaction mechanism were presented, based on these results.

Photo-oxidation of vapour-phase benzene; possible role of the oxygen 1Σ −u state

Optic-acoustic measurements of heat energy yields for vapour-phase benzene, excited at 248 nm, as a function of high oxygen pressure have been used to determine parameters associated with the photo-oxidation of benzene. The results suggest that interaction between the highly vibrationally excited 3B 1u state of benzene and ground state oxygen results in transfer of energy to the 1Σ − u state of oxygen. This state dissociates to give oxygen ( 3P) atoms which react with ground state benzene to give phenol as the major primary product.

Radiation mechanisms—XI: Electron spin resonance studies of irradiated aqueous carbonate and formate solutions using temperature resolved spectroscopy

Exposure of aqueous glasses containing carbonate enriched in 13CO 3 2− gave .OH and e t − as major primary products at 77 K, but .CO 2 − and CȮ 3 − features together with 13C satellite lines grew strongly on annealing above 77 K. Alkaline solutions gave mainly .O − and e t −, but on annealing a new radical, tentatively identified as CȮ 4 3−, was detected. This had E.S.R. parameters comparable with those for 13CȮ 3 −, but with a smaller anisotropy in both A( 13C) and g. This species is thought to result from addition of .O − to CO 3 2− Solutions is methanol (CD 3OD) gave mainly D 2ĊOD, e t −, and .CO 2 3− radicals, but CȮ 3 − grew in strongly on annealing. Neutral aqueous glasses containing formate ions gave HĊO and ĊO 2 − in addition to .OH radicals, together with a broad feature tentatively assigned to HĊO 2 2− or HĊO(OH) − radical. These features were better defined in alkali glasses (HĊO 2 2−) and in 6 mol dm −3 sulphuric acid glasses [HĊO(OH) −]. Features for 13CO 2 − were clearly resolved in the former, but in the acidic glasses a larger 13C hyperfine coupling suggested 13ĊO(OH). The formly radical was also detected in the scidic glasses but not in the alkaline media. The mechanisms of the reactions leading to these intermediates are discussed and compared with those for aqueous nitrite solutions.