Nitrous oxide, free radical

Titov claims that the free radical mechanism applies for nitration of aliphatic hydrocarbons, of aromatic side chains, of olefins, and of aromatic ring carbons, if irf the latter case the nitrating agent is ca 60—70% nitric acid that is free of nitrous acid, or even more dil acid if oxides of nitrogen are present... 

The stratosphere contains, however, only small amounts--a few tenths of a ppb-of chlorine free radicals of natural origin. They are produced by the decomposition of methyl chloride, CH3Q. The nitrogen oxides (NO and NO2) are more abundant and are produced in the stratosphere by the decomposition of nitrous oxide, N2O. Both CH3CI and N2O are of biological origin these compounds, released at the Earth s surface, are sufficiently stable to reach the stratosphere in significant amounts. 

Hart and Henglein [14] also reported the sonolytic decomposition of nitrous oxide in aqueous solutions under pure argon, pure N2O and the mixture of the two gases and reported the formation of species such as N2, O2, N02 and N03 with the maximum yield being in the Ar/N20 mixture in the vol% ratio of 85 15. Although H20 is thermodynamically much more stable than N2O but they postulated that all H20 and N2O molecules in an argon bubble were converted into free radicals in the short time of adiabatic compression phase of the bubble. They proposed a series of free radical reactions for the formation of all these species in aqueous solutions. 

Nitric oxide is a free radical that quickly reacts in air to produce nitrogen dioxide. It is also an important biological messenger and transmitter. Nitrous oxide is a colorless, nonflammable, nontoxic gas with a slightly sweet odor and taste. Nitrous oxide is called laughing gas and has been used as a recreational inhalant, anesthetic, oxidizer, and propellant. 

Much experimental evidence established that the reaction occurs by a free-radical mechanism164 173 similar to that suggested above [Eqs. (10.26)—(10.28)] for liquid-phase nitration. The nitrous acid produced during the transformation is unstable under the reaction conditions and decomposes to yield nitric oxide, which also participates in nitration, although less effectively. It was found that nitric acid and nitrogen dioxide yield identical products but that the former gives better yields and higher rates.172... 

Another effect of high oxygen concentrations was increased oxidative attack on the solvent. This is shown in Figure 2. Methane and methyl acetate were detected in most of the runs, and it is likely that these materials were formed by free-radical attack on acetic acid. Loss of nitric acid to the nonregenerable species nitrous oxide and nitrogen was reduced in the presence of high oxygen concentrations. 

To generate carbohydrate radicals by radiation is in many respects superior to other radical-generating techniques, as no additive is needed, and, except for the small yield of H2Os (from reaction 1 compare Sect. II,3e), no material that could interfere with the free-radical reactions is introduced. Nitrous oxide itself is largely inert towards free-radical attack (compare, Sect. II,3f). 

Flart EJ, Flenglein A (1985) Free radical and free atom reactions in the sonolysis of aqueous iodide and formate solutions. J Phys Chem 89 4342-4347 Flart EJ, Flenglein A (1986) Sonolytic decomposition of nitrous oxide in aqueous solution. J Phys Chem 90 5992-5995... 

Probable mechanism of nitrous-oxide- and nitrogen-containing acid formation. Hydrogen peroxide ability to induce free-radical oxidation reactions. 

When oxides of nitrogen come in contact with water, both nitrous and nitric acids are formed (18) (Table IV). Toxic reactions may result from pH decrease. Other toxic reactions may be a consequence of deamination reactions with amino acids and nucleic acid bases. Another consideration is the reactions of oxides of nitrogen with double bonds (Table IV). The cis-trans isomerization of oleic acid exposed to nitrous acid has been reported (19). Furthermore, the reaction of nitrogen dioxide with unsaturated compounds has resulted in the formation of both transient and stable free radical products (20, 21) (Table V). A further possibility has been raised in that nitrite can react with secondary amines to form nitrosamines which have carcinogenic properties (22). Thus, the possible modes of toxicity for oxides of nitrogen are numerous and are not exhausted by this short list. 

Newaz MA, Yousefipour Z, Nawa NN (2005) Modulation of nitric oxide synthase activity in brain, liver, and blood vessels of spontaneously hypertensive rats by ascorbic acid protection from free radical injury. Qin Exp Hypertens 27(6) 497-508 Nunn JF, Chanarin I, Taimer AG, Owen ER (1986) Megaloblastic bone marrow changes after repeated nitrous oxide anaesthesia. Reversal with fofinicacid. Br J Anaesth 58(12) 1469-1470 Parker WD Jr, Hass R, Stumpf DA, Parks J, Eguren LA, Jackson C (1984) Brain mitochondrial metabolism in experimental thiamine deficiency. Neurology 34(11) 1477-1481... 

One of the few cases in which hydrogenated surface complexes have been suggested to be active involves the decomposition of nitrous oxide.The reaction was suggested to involve hydrogen in the carbon, although the reaction mechanism was written in terms of gas phase hydrogen involved in a free radical chain reaction. As a result, the importance of hydrogenated complexes is open to question. 

There are a variety of photochemical reactions involving free nitrous oxide (NO) as persistent radical. Often there is an initial fragmentation, as presented in Scheme 6 for TV, 7V-dimethyl-/V-nitro-samine. One example is the Barton reaction of nitrite esters (Scheme 15). It allows the functionalization of methyl groups in steroids and utilizes an intermediate 1,5-hydrogen atom migration, which converts the initially formed oxygen-centered radical to a carbon-centered species.69... 

An alternative mechanism was suggested by Oxley and coworkers. [59] They concluded that above 160°C the decomposition occurs by a free-radical mechanisms while an ionic mechanism is important below this temperature. The decomposition of ADN leads to nitrous oxide, nitric acid or nitrate and nitrogen gas. It was assumed that the first step in ADN decomposition is hydrogen transfer to form ammonia and dinitramic acid. Several proposed decomposition pathways for ADN decomposition that involve conversion of the dinitramide ion to N2O have been proposed but they await confirmation.[59]... 

Effects of Added Scavengers. Several additives were used to obtain more information about the reaction mechanism. Adding 5% nitrous oxide had no measurable effect on product yields. However, with 5% added oxygen or ethylene, all products listed in Table II except CoF4 were eliminated, and new but unidentified products were formed. These results strongly suggest that the final products from pure F-cyclobutane arise from a free radical sequence. 

A general review of pulse radiolysis studies on electron transfer in solution is presented together with some recent unpublished data. Electron transfer processes occurring in irradiated solutions of metal ions, inorganic anions, and various aliphatic and aromatic organic compounds are discussed with respect to general redox phenomena in radiation and free radical chemistry. Specific topics include the measurement of peroxy radical formation, the use of nitrous oxide in alkaline radiation chemistry, and cascade electron transfer processes. Some implications of the kinetics of electron transfer are discussed briefly. 

In addition to the reactions of these two free radicals, the ionic species formed during the irradiation may also take part in the radiation-induced crosslinking of PS [Heusinger and Rosenberg, 1969]. Radiation-induced crosslinking of PS is accelerated by the presence of nitrous oxide [Amemiya et al, 1963], which supports the participation of cationic reactions e.g., reaction R-33) in its crosslinking. 

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