Methyl nitrate radicals

Quinolinium 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide dimensions, 2, 110 Quinolinium iodide, 1-alkyl-Ladenburg rearrangement, 2, 300 Quinolinium iodide, 1-methyl-Ladenburg rearrangement, 2, 300, 335 Quinolinium iodide, [l-methyl-4-[3(5)-pyrazolyl]-blood sugar level and, 5, 291 Quinolinium perchlorate, 1-ethoxy-hydroxymethylation, 2, 300 Quinolinium perchlorate, 1-methyl-nitration, 2, 318 Quinolinium salts alkylation, 2, 293 Beyer synthesis, 2, 474 electrophilic substitution, 2, 317 free radical alkylation, 2, 45 nitration, 2, 188 reactions... 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

Reductive scission of the nitrate radical and methylation with the Purdie... 

Proof of Constitution.—Reference to Table XII will show that all of the methods mentioned above as being suitable for the synthesis of 4,6-dimethylglucose have been correlated by means of crystalline derivatives. If the tosyl, benzyl and nitrate radicals can be regarded as being non-migratory (and there is no evidence to the contrary) then the course of the synthesis from 4,6-acetals (the constitution of which has been proved by their conversion into 2,3-dimethyl-D-glucose) leaves no doubt that the methyl groups occupy positions 4 and 6. 

The 5 n2 reactions of the radical anions (CHCr and CHBr ) and the closed-shell anions (CH2CF and CH2Br ) with CH3CI and CHsBr have been studied by using density functional theory. The closed-shell anions were found to be more reactive than the radical anions, in agreement with experiment. Other details of the systems were also elucidated. Ab initio and semiempirical (AMI) methods were used to study the gas-phase S 2 reactions between methyl nitrate and various nucleophiles. ... 

Photolytic. Photolysis of acetone in air yields carbon monoxide and free radicals, but in isopropanol, pinacol is formed (Calvert and Pitts, 1966). Photolysis of acetone vapor with nitrogen dioxide via a mercury lamp gave peroxyacetyl nitrate as the major product with smaller quantities of methyl nitrate (Warneck and Zerbach, 1992). 

Photolytic. Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight (A, = 300-450 nm) photooxidized 2-butanone into peroxyacetyl nitrate and methyl nitrate (Cox et al., 1980). They reported a rate constant of 2.6 x 10 cm /molecule-sec for the reaction of gaseous 2-butane with OH radicals based on a value of 8 x 10 cm /molecule-sec for the reaction of ethylene with OH radicals. 

Photolytic. When synthetic air containing gaseous nitrous acid and 4-methyl-2-pentanone was exposed to artificial sunlight k = 300-450 nm), photooxidation products identified were acetone, peroxyacetal nitrate, and methyl nitrate (Cox et al, 1980). In a subsequent experiment, the OH-initiated photooxidation of 4-methyl-2-pentanone in a smog chamber produced acetone (90% yield) and peroxyacetal nitrate (Cox et al, 1981). Irradiation at 3130 A resulted in the formation of acetone, propyldiene, and free radicals (Calvert and Pitts, 1966). 

Gray and Rogers are of the opinion that free radicals take part in all explosive decomposition reactions of methyl nitrate. 

The products of the thermolysis of 3-phenyl-5-(arylamino)-l,2,4-oxadiazoles and thiazoles have been accounted for by a radical mechanism.266 Flash vacuum pyrolysis of 1,3-dithiolane-1-oxides has led to thiocarbonyl compounds, but the transformation is not general.267 hi an ongoing study of silacyclobutane pyrolysis, CASSF(4,4), MR-CI and CASSCF(4,4)+MP2 calculations using the 3-21G and 6-31G basis sets have modelled the reaction between silenes and ethylene, suggesting a cyclic transition state from which silacyclobutane or a trcins-biradical are formed.268 An AMI study of the thermolysis of 1,3,3-trinitroazacyclobutane and its derivatives has identified gem-dinitro C—N bond homolysis as the initial reaction.269 Similar AMI analysis has determined the activation energy of die formation of NCh from methyl nitrate.270 Thermal decomposition of nitromethane in a shock tube (1050-1400 K, 0.2-40 atm) was studied spectrophotometrically, allowing determination of rate constants.271... 

The first step in the pyrolysis of the alkyl nitrates has been supposed to be O N bond fission to give NO2 and an alkoxy radical. The activation energy is 39-5 kcal for methyl nitrate and 39-9 or 34-6 kcaP <> for ethyl nitrate. If the latter value for ethyl nitrate is taken, and assumed to be i)(EtO -NO2) a value for the heat of formation of the ethoxy radical in good agreement with that given by Rebbert and Laidler is obtained, so apparently we may put D(MeO -NO2) =40 kcal, and i)(EtO -NO2) =34 kcal. In the opinion of the present author, however, the mechanism of the reaction is not sufficiently well established to allow this to be done. The discrepancy between the result of Adams and Bawn and that of Phillips 390 is large and may well be because of the different pressure ranges in which these authors worked. A further examination of the effect of pressure on rate constant is necessary before it can be taken as established that the reaction is of the first order. 

Qualitative work on the photolysis of methyl nitrate suggests free radicals are formed via step (a) . In the photolysis of ethyl nitrate at 2654 A (a) seems to be the exclusive primary step at 3130 A there are some contributions from (b) and (c)... 

Methyl nitrate was found to be present in the products of the decomposition of azomcthanc (Cllj-N- N-nij) when the latter substance was subjected to ultraviolet irradiation II6). This was due to an intermediate formation of CTI3O1 radical which reacted with NO to yield the nitrate ester ... 

Isoprene is a eonjugated diene (2-methyl-buta-1,3-diene), volatile and hardly soluble in water under normal pressure it boils at 34 C (Merck, 1999) and dissolves up to 1.47x10 M at 21.5 C, with a Henry s constant of 0.027 mole kg atm at 25 C (NIST, 2001). Isoprene is a metabolite in plants, microbes, animals and humans, and a major biogenic trace compound emitted to the atmosphere. It is very reactive towards atmospheric gas-phase oxidants such as hydroxyl and nitrate radicals or ozone. At higher concentrations, 220 - 7000 ppm, it is carcinogenic to rodents and possibly carcinogenic to humans (Melnick and Sills, 2001). 

An example in which formation of a carbon radical is not the initial reaction is provided by the atmospheric reactions of organic sulfides and disulfides. They also provide an example in which rates of reaction with nitrate radicals exceed those with hydroxyl radicals. 2-dimethylthiopropionic acid is produced by algae and by the marsh grass Spartina alternifolia, and may then be metabolized in sediment slurries under anoxic conditions to dimethyl sulfide (Kiene and Taylor 1988), and by aerobic bacteria to methyl sulfide (Taylor and Gilchrist 1991). It should be added that methyl sulfide can be produced by biological methylation of sulfide itself (HS ) (Section 6.11.4). Dimethyl sulfide — and possibly also methyl sulfide — is oxidized in the troposphere to sulfur dioxide and methanesulfonic acids. 

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