Ammonia hydroxyl radical reaction

In the atmosphere, ammonia is estimated to have a half-life of several days. The primary fate process is reaction of ammonia with acid air pollutants and removal of the resulting ammonium compounds by dry or wet deposition. Rain washout and reaction with photochemically produced hydroxyl radicals are also expected to contribute to the atmospheric fate of vapor-phase ammonia. In water and soil, ammonia will volatilize to the atmosphere and be removed by microbial processes, by adsorption to sediment and soil matrices as well as by plant uptake. 

In the atmosphere, ammonia can be removed by rain or snow washout. Reactions with acidic substances, such as H2SO4, HCl, or HNO3 (all produced in high concentrations from anthropogenic activities) produce ammonium aerosols, which can undergo dry or wet deposition. The gas phase reaction of ammonia with photochemically produced hydroxyl radicals is thought to contribute about 10% to the overall atmospheric removal process. The best estimate of the half-life of atmospheric ammonia is a few days. 

The vapor-phase reaction of ammonia with photochemically produced hydroxyl radicals is known to occur. The rate constants for this reaction have been determined to be 1.6x10 cm molecule-sec, which translates to a calculated half-life of 100 days at a hydroxyl radical concentration of 5x10 molecules/cm (Graedel 1978). This process reportedly removes 10% of atmospheric ammonia (Crutzen 1983). Since ammonia is very soluble in water, rain washout is expected to be a dominant fate process. The half-life for ammonia in the atmosphere was estimated to be a few days (Brimblecombe and Dawson 1984 ... 

Rate constants for the reaction of hydrogen, methane," or ammonia with hydroxyl radicals generated by flash photolysis of water in the gas phase have been determined. 

Also characteristic ate the particulate secondary pollutants sulfate and nitrate, the latter being especially associated with photochemical smog processes. Nitrate formation during daytime occurs through reaction of nitrogen dioxide with the hydroxyl radical, with subsequent neutralization of nitric acid vapor by ammonia to form ammonium nitrate (NH4NO3) particles, which equilibrate with their gas-phase precursors and are termed semivolatile ... 

Inorganic nitrates or nitric acid are formed by several reactions in smog. Among the important reactions forming HNO3 are the reaction of N2O5 with water and the addition of hydroxyl radical to NO2. The oxidation of NO or NO2 to nitrate species may occur after absorption of gas by an aerosol droplet. Nitric acid formed by these reactions reacts with ammonia in the atmosphere to form ammonium nitrate ... 

Smith, I.W., and R. Zellner (1975), Rate measurements of OH by resonance absorption. IV. Reaction of hydroxyl radical OH with ammonia and nitric acid, Int. J. Chem. Kinet., Symp. 1, 341-351. 

Reduction of Ketones and Enones. Although the method has been supplanted for synthetic purposes by hydride donors, the reduction of ketones to alcohols in ammonia or alcohols provides mechanistic insight into dissolving-metal reductions. The outcome of the reaction of ketones with metal reductants is determined by the fate of the initial ketyl radical formed by a single-electron transfer. The radical intermediate, depending on its structure and the reaction medium, may be protonated, disproportionate, or dimerize.209 In hydroxylic solvents such as liquid ammonia or in the presence of an alcohol, the protonation process dominates over dimerization. Net reduction can also occur by a disproportionation process. As is discussed in Section 5.6.3, dimerization can become the dominant process under conditions in which protonation does not occur rapidly. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

There has been a short review of the oxidative nucleophilic substitution of hydrogen in nitroarenes in which recent results with carbon, nitrogen, and oxygen nucleophiles are summarized and the preferred oxidants are discussed.11 The oxidative substitution of nitroarenes with carbanions of isopropyl phenylacetate in liquid ammonia-KMn04 initially yields products (4) which may suffer hydroxylation at the o -position, and dimeric and trimeric products may be formed by couplings of nitrobenzylic radicals formed during the reaction.12... 

This shows that the reaction depends upon the two remaining ammonia hydrogens which unite with the non-hydroxyl oxygen of the nitrous acid forming water, leaving the hydroxyl group of the nitrous acid for the alkyl radical. We shall find when we study the primary amines... 

It will be noted that in all of the reactions of the anhydrides the tendency is to reform the acid by removing one hydrogen from the other compound present. The remaining acyl group then unites with the residue of the reagent and a new compound is formed. The character of the new compound depends upon the residue of the reagent. With water H—OH we obtain the hydroxyl compound of the acyl radical, that is, the acid itself, while with alcohols we obtain the alkyl-oxy compound of the radical, i.e.y an ester, and with ammonia the amino, (—NH2), compound of the acyl radical, i.e., an amide. 

Reactions with Nitrous Acid.—With nitrous acid (HO—NO) primary amines, due to the presence of two remaining ammonia hydrogen atoms, react with the oxygen of nitrous acid which is linked directly to the nitrogen alone. In the case of the alkyl amines the reaction does not stop here, but the hydroxyl group of the nitrous acid unites with the alkyl radical forming an alcohol and the nitrogen is set free. 

Formation of hydroxyl quinoline must have been initiated by ionic reactions that involved and OH ions. Hydrogenation by Ha enables the heterocyclic ring to be saturated, and this can be followed by hydrogenolysis of C-N bonds that first open the hetero-ring and then convert the resultant aliphatic and aromatic amine intermediates to hydrocarbons and ammonia (24). Also direct attack of OH on quinoline may have led to formation of hydroxyl quinoline. It has been suggested that both ionic reaction and free radical capping are possible under supercritical conditions (25). 

The reported measured rate constant for reaction of hydrazine with atmospheric hydroxyl (OH) radicals producing ammonia and nitrogen gas was 6.lx 10 cm molecule s (Harris et al. 1979). The rate constant for 1,1-dimethylhydrazine was not measured since the chemical decomposed rapidly in the test system, but the value was estimated at 5 /10 cm molecule s . Assuming an average OH radical concentration of about 10 molecLile/cm . the tropospheric half-lives ofboth chemicals due to reaction with OH were estimated to be about 3 hours. The half-lives are expected to range from less than 1 hour in polluted urban air to 3-6 hours in less polluted atmospheres (Tuazon et al. 1981). 

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