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PubMed2002

An efficient nitration of light alkanes and the alkyl side-chain of aromatic compounds with nitrogen dioxide and nitric acid catalyzed by N-hydroxyphthalimide.

Nitration of light alkanes and the alkyl side-chain of aromatic compounds with NO(2) and HNO(3) was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst under relatively mild conditions. For example, the nitration of propane with NO(2) catalyzed by NHPI at 100 degrees C for 14 h gave 2-nitropropane in good yield without formation of 1-nitropropane and cleaved products such as nitroethane and nitromethane. Various aliphatic nitroalkanes, which are difficult to prepare by conventional methods, could be selectively obtained by means of the present methodology by using NHPI as the key catalyst. In addition, the side-chain nitration of alkylbenzenes such as toluene was selectively carried out to lead to alpha-nitrotoluene without the ring nitration. The present reaction provides an efficient selective method for the nitration of light alkanes and alkylbenzenes, which has been very difficult to carry out so far.

Journal Article↗
PubMed2004

Molecular rearrangement. 36. Selective alpha-CH oxidation of alkylarenes by nitrogen dioxide on thermolysis with nitramines.

Thermolysis of 2,4,6-trichloro-N-nitroaniline 1 and N-methyl-2,4-dinitro-N-nitroaniline 2 each with primaryl alkylbenzenes led to the formation of acylbenzenes. Similar reactions with secondary alkylbenzenes afforded a mixture of acetophenone and aliphatic aldehydes. Use of tert-butylbenzene in this reaction yielded formaldehyde and 2,3-diphenyl-2,3-dimethylbutane. The mechanisms of the studied reactions are discussed.

Journal Article↗
PubMed2005

Theoretical study on reaction mechanism of the ketenylidene radical with nitrogen dioxide.

The complex doublet potential-energy surface for the reaction of CCO with NO2, including 8 minimum isomers and 17 transition states, is explored theoretically using the coupled cluster and density functional theory. The association of CCO with NO2 was found to be a barrierless process forming an energy-rich adduct a (OCCNO2) followed by oxygen shift to give b (O2CCNO). Our results show that the product P1 (CO2 + CNO) is the major product with absolute yield, while the product P4 (2CO + NO) is the minor product with less abundance. The other products may be undetectable. The product P1 (CO2 + CNO) can be obtained through R --> a --> b --> P1 (CO2 + CNO), whereas the product P4 (2CO + NO) can be obtained through two channels R --> a--> b --> c --> (d, g) --> P2 (OCNO + CO) --> P4 (2CO + NO) and R --> a --> b --> f --> P3 (c-OCC-O + NO) --> P4 (2CO + NO). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CCO + NO2 reaction is expected to be rapid, which is consistent with the experimental measurement in quality. The present study may be helpful for further experimental investigation of the title reaction.

Journal Article↗
PubMed2006

Photodissociation dynamics of methyl nitrate at 193 nm: energy disposal in methoxy and nitrogen dioxide products.

The photodissociation dynamics of methyl nitrate, CH(3)ONO(2), has been investigated at 193 nm by examining the products from the primary dissociation channel, namely CH(3)O and NO(2). The CH(3)O (X (2)E) photoproducts were probed by laser-induced fluorescence (LIF) on the A (2)A(1)-X (2)E transition under both nascent and jet-cooled conditions. The 3 and 3 bands originating from the vibrationless and C-O stretch (nu(3)) levels, respectively, were characterized to obtain the internal energy distribution of the CH(3)O products. Only a small fraction of the CH(3)O products (< or =10%) were produced with one quantum of C-O stretch excitation as determined from the relative intensities of the bands in combination with transition probabilities derived from dispersed fluorescence measurements and/or calculated Franck-Condon factors. The CH(3)O products also had minimal rotational excitation: those produced in the ground vibrational state had a rotational temperature of 238 +/- 7 K, corresponding to less than 1% of the available energy. Products with C-O stretch excitation were found to have a higher rotational temperature, but still a small fraction of the total energy. Combining the CH(3)O internal energy findings with previous photofragment translational energy measurements [X. Yang, P. Felder and J. R. Huber, J. Phys. Chem., 1993, 97, 10903] indicates that most of the available energy is deposited in the NO(2) fragment. This is verified through dispersed fluorescence measurements which show that the NO(2) fragment is produced electronically excited with internal energies extending to the NO + O dissociation limit. Ab initio calculations confirm that the dominant initial excitation is strongly localized on the NO(2) moiety. The calculations are also used to reveal the forces that give rise to internal excitation of the CH(3)O fragment upon electronic excitation.

Journal Article↗
PubMed1994

No beneficial effect of N-acetylcysteine treatment on broncho-alveolar lavage fluid variables in acute nitrogen dioxide intoxicated rats.

1. In previous studies a rat inhalation model was developed to investigate the efficacy of treatment in acute NO2 intoxication. 2. N-acetylcysteine (NAC) was administered intravenously to study its effect on biochemical variables in broncho-alveolar lavage fluid in acute NO2 intoxicated rats. It was decided to start the intravenous administration of NAC 24 h before the exposure to NO2 to induce higher intracellular glutathione (GSH) levels in lung cells of NAC-treated rats compared to not NAC-treated rats. Because, on theoretical grounds, the therapeutic effect of NAC may be expected to be especially marked during the first 24 h after exposure, the rats were observed for a period of 24 h and were then killed for investigation. A loading dose of 85 mg kg-1 h-1 or 170 mg kg-1 h-1 was followed by a continuous infusion (until autopsy) with a dose of 225 mg kg-1 24 h-1 or 450 mg kg-1 24 h-1 respectively. 3. Twenty four hours after exposure to 175 ppm NO2 (1 ppm is 1.88 mg m-3) for 10 min, NAC did not reduce the increase of variables in broncho-alveolar lavage fluid which reflect the severity of lung damage. 4. The protein and albumin concentration and the activities of angiotensin converting enzyme and alkaline phosphatase in broncho-alveolar lavage fluid after NO2 exposure were even more increased in the NAC-treated than in the saline-treated rats, but none of the differences was statistically significant. 5. In sham exposed rats no effect of NAC was observed.

Acetylcysteine↗
PubMed2005

Acousto-optic measurements of tropospheric nitrogen dioxide column density by solar spectroscopy.

Measurements of column densities of atmospheric gases can be achieved by a solar spectroscopic method that uses differential optical absorption spectroscopy. Because of the scintillation of sunlight intensity in the atmosphere, the variation in intensity will introduce a low-frequency modification of the measured solar spectrum. A spectral capturing-type CCD spectrometer takes milliseconds to capture a solar spectrum, and the effect of sunlight scintillation is negligible. In contrast, without scintillation correction, a scanning-type spectrometer spending minutes to obtain a complete solar spectrum will introduce some amount of errors. We demonstrate an intensity-compensation technique in a scanning-type spectrometer, based on a solid-state acousto-optic tunable filter, for solar spectroscopic measurements.

Journal Article↗
PubMed1995

Short-term association between air pollution and emergency room visits for asthma in Barcelona.

BACKGROUND: Several studies have assessed the association between urban air pollutants and hospital admissions or emergency room visits for asthma with inconsistent results. The objective of this study was to assess the relation between levels of black smoke, sulphur dioxide, nitrogen dioxide, and ozone and adult emergency room visits for asthma in Barcelona, Spain during the five year period 1985-9. METHODS: The daily number of emergency room visits for asthma was obtained from a register of respiratory emergencies designed to study the asthma outbreaks occurring in Barcelona. The association between asthma visits and levels of pollutants was assessed separately for summers and winters with Poisson regression models controlling for meteorological and time related variables. RESULTS: Black smoke was associated with asthma visits in summer but not in winter. The relative risk (RR) of asthma visits for a 25 micrograms/m3 increase of current day concentrations of black smoke was 1.082 (95% CI 1.011 to 1.157). The mean current and previous three day levels of black smoke led to a stronger association (RR = 1.114 (95% CI 1.010 to 1.160). In addition, nitrogen dioxide was associated with asthma visits in both summer (RR = 1.045, 95% CI 1.009 to 1.081) and winter (RR = 1.056, 95% CI 1.011 to 1.104). These associations were slightly higher for the previous day's level of nitrogen dioxide. No associations were found for sulphur dioxide or for ozone. CONCLUSIONS: This study provides further evidence of the effect of particulate pollution on asthma, and it suggests that nitrogen dioxide may have a role in the exacerbation of bronchial asthma in adults.

Adolescent↗
PubMed1986

The changing prevalence of respiratory symptoms in atopic children in response to air pollution.

Following the promotion of anti-air pollution measures in steam power stations using crude oil, atmospheric concentrations of sulphur dioxide, nitrogen dioxide and suspended particulates have declined. These changes in atmospheric concentrations were accompanied by a decline in the prevalence of respiratory symptoms among schoolchildren living near the power stations. In analysing the correlation between air pollutant concentrations and the prevalence of respiratory symptoms, those with positive skin reactions to house dust extract (the positive group) showed a more significant correlation coefficient compared to those who had never had a positive skin reaction (the negative group). In addition, schoolchildren more heavily exposed to air pollutants showed the higher prevalence of respiratory symptoms than the others. With regard to the kind of air pollutants, both sulphur dioxide and nitrogen dioxide were more closely associated with the prevalence of respiratory symptoms than suspended particulates. This study has therefore demonstrated that the positive group is a useful population for monitoring the health effects associated with low-degree air pollution of gaseous agents.

Adolescent↗
PubMedDate not supplied

Mortality and air pollution in Helsinki.

In Helsinki, Finland, from 1987 to 1993, the authors studied the associations between daily concentrations of sulphur dioxide, nitrogen dioxide, ozone, total suspended particulates, and particulates with aerodynamic diameters less than 10 microm (PM10), and the daily number of deaths from all causes and from cardiovascular causes. Investigators used Poisson regressions to conduct analyses in two age groups, and they controlled for temperature, relative humidity, day of the week, month, year, long-term trend, holidays, and influenza epidemics. The PM10 levels were associated significantly with all-cause and cardiovascular mortality among persons under the age of 65 y of age. In the less-than-65-y age group, sulfur dioxide and ozone were also associated significantly with cardiovascular mortality. The effect of ozone was independent of the PM10 effect, whereas sulfur dioxide became nonsignificant when modeled with PM10. An increase of 10 microg/m3 in PM10 resulted in increases in total mortality and cardiovascular mortality of 3.5% (95% confidence interval=1.0, 5.8) and 4.1% (95% confidence interval=0.4, 10.3), respectively. A 20 microg/m3 increase in ozone was associated with a 9.9% (95% confidence interval=1.1, 19.5) increase in cardiovascular mortality; however, ozone results were inconsistent. Moreover, in addition to their separate effects, high concentrations of PM10, ozone, and nitrogen dioxide had a further harmful additive effect. Typically, PM10 was a better indicator of particulate pollution than total suspended particulates. The authors' findings suggest that (a) even low levels of particulates are related to an increase in cardiovascular mortality; (b) ozone--even in low concentrations--is associated, independently, with cardiovascular mortality; and (c) PM10, ozone, and nitrogen dioxide--the essential components of summertime pollution--have harmful interactions at high concentrations.

Adolescent↗
PubMed1992

Possible mechanism of inhibition of nitrite-induced oxidation of oxyhemoglobin by ergothioneine and uric acid.

The time course of oxyhemoglobin oxidation by nitrite consisted of a kinetic lag followed by a transition phase which progressed into a rapid autocatalytic phase. The imidazolthione and imidazolone derivatives, ergothioneine and uric acid, respectively, caused an increase in the duration of the lag phase in a concentration-dependent manner, without affecting the onset and rate of the autocatalytic phase. Neither compound reacted with H2O2 or nitrite, oxidizing species required in the initiation steps of oxyhemoglobin oxidation. On the other hand, both compounds reduced effectively and at comparable rates the high oxidation state of hemoglobin, i.e., ferrylhemoglobin, which is an intermediate species occurring in the autocatalytic phase. In addition, the rate of ergothioneine oxidation, upon its reaction with ferrylmyoglobin, was accelerated by nitrite, thus suggesting a reaction between the thione and nitrogen dioxide. Nitrogen oxide and ferrylhemoglobin are key species in the free radical chain propagation leading to oxyhemoglobin oxidation by nitrite. These data support the view that ergothioneine and urate delay oxyhemoglobin oxidation by nitrite upon the temporary removal of the propagating species, i.e., nitrogen dioxide and, secondarily, ferrylhemoglobin, and within a mechanism encompassing alterations of the nitrite in equilibrium with nitrogen dioxide and ferrylhemoglobin in equilibrium with methemoglobin redox transitions.

Adult↗
PubMed1989

Investigation of a potential cotumorigenic effect of the dioxides of nitrogen and sulfur, and of diesel-engine exhaust, on the respiratory tract of Syrian golden hamsters.

Syrian golden hamsters (480 males and 480 females) allocated into 24 groups were exposed 19 hours per day and 5 days per week for 6, 10.5, 15, or 18 months to total diesel exhaust, diesel exhaust without particles, a mixture of nitrogen dioxide (5 parts per million [ppm]2) and sulfur dioxide (10 ppm), or clean air. Two exposure groups from each test atmosphere were also treated by a single subcutaneous injection of either 3 mg or 6 mg of diethylnitrosamine/kg of body weight to evaluate an enhancing effect of diethylnitrosamine on exposure-related changes. Morphological evaluation was done by histopathology. Minor changes of the larynx and trachea were investigated by scanning electron microscopy, which showed a loss of ciliated cells in all exhaust-exposed groups. After exposure to diesel exhaust with or without particles, focal metaplasia and dysplasia of the respiratory epithelium were seen in the oldest animals by scanning electron microscopy. In the same specimens, attached mucous droplets indicated changes in mucous cells and mucous viscosity. Only the exposure to total diesel exhaust significantly increased the tumor rate in the upper respiratory tract of male hamsters treated with 6 mg of diethylnitrosamine per kg of body weight. At the lower diethylnitrosamine dose, no exposure-related effects on the tumor rates could be observed. The results from this study and from our other inhalation experiments appear to be insufficiently conclusive to demonstrate that diesel-engine exhaust should be classified as a cocarcinogen or enhancer for the test system used.

Animals↗