HNO Reactions

The interest in HNO reactions with hemeproteins has several origins. Studies of the nitrogen cycle involved enz5unes, with the intermediacy of assimilatory and dissimilatory nitrite... 

N2 or nitrite, was accumulated via the oxidation of aceto-HX and gly-HX by "OH at neutral and alkaline pH and oxidation of SAHA by N3 or Br2 at alkaline pH. Nitrite was not produced even after exposure of the irradiated solutions to oxygen. The lack of nitrite accumulation under anoxia excludes the reaction of NO with HNO (reactions 6—8) ruling out any release of NO along with HNO. The yields of HNO at neutral pH were determined to be 9 1% and 25 5% for gly-HX and aceto-HX, respectively, and 17 4% for SAHA at alkaline pH. 

The transient nitroxide radicals derived from one-electron oxidation of HXs may decompose via several routes as described in Scheme 2 including dis-mutation (reaction 9) and oxidation (reaction 10) forming acyl nitroso, which yields HNO via hydrolysis (reaction 14) or its reaction with nucleophiles (53), homolysis of the C-N bond forming HNO (reaction 11), internal disproportionation forming NO (reaction 12), and hydrolysis forming H2NO (reaction 13), which via dismutation generates N2 (54,55). 

MbFe =0 reacts with HX (reaction 23) forming the respective nitroxide radical and MbFe =0, which can oxidize not only HX (reaction 24) but also the nitroxide radical (reaction 25), HNO (reaction 26), and NO (reaction 27). 

The independence on [O2] of the accumulation rates of N2O and nitrite in the case of SAHA and aceto-HX implies that the contribution of HNO reaction with O2 is negligible under these experimental conditions. Currently, we have no explanation for the decrease of about 50% in the accumulation rates of nitrite and N2O under normoxia in the case of gly-HX. The rate of reaction 24 decreases upon decreasing [HX], and consequently also the rates of HNO formation via the bimolecular decomposition of RC(0)NH0" and its reaction with MbFe =0. Therefore, the ratio between the rates of nitrite and N2O accumulation increase since the contribution of the pseudo-first-order reaction (HNO + MbFe ), which eventually leads to nitrite formation, exceeds that of the second-order one... 

Butkovskaya, N.I., Kukui, A., Le Bras, G. Branching fractions for H2O forming channels of the reaction of OH radicals with acetaldehyde. J. Phys. Chem. A 108, 1160-1168 (2004) Butkovskaya, N.I., Kukui, A., Pouvesle, N., Le Bras, G. Foimatimi of nitric acid in the gas-phase H02-hNO reaction Effects of temperature and water vapor. J. Phys. Chem. A109,6509-6520 (2005)... 

TABLE 5.1 Equilibrium and rate constants for the reaction AcfD+HNO AcONO + AcOH... 

Acetoxybenzene is prepared by the reaction of benzene with Pd(OAc)2[325,342-345], This reaction is regarded as a potentially useful method for phenol production from benzene, if carried out with only a catalytic amount of Pd(OAc)2. Extensive studies have been carried out on this reaction in order to achieve a high catalytic turnover. In addition to oxygen and Cu(II) salts, other oxidants, such as HNOi, nitrate[346,347], potassium peroxodisulfate[348], and heteropoly acids[349,3S0], are used. HNO is said to... 

The reaction can also be carried out with oleum, distilling the chlorosulfuric acid as it forms. Reaction with oxidizing oxyacids such as HNO Hberates chlorine. Anhydrous sulfates of the heavy metals form addition compounds with HCl that can be released by heating the complex to elevated temperatures. The complex CuSO 2HC1 has been used for storage and transport of HCl (23). 

Both vapor-phase and Hquid-phase processes are employed to nitrate paraffins, using either HNO or NO2. The nitrations occur by means of free-radical steps, and sufftciendy high temperatures are required to produce free radicals to initiate the reaction steps. For Hquid-phase nitrations, temperatures of about 150—200°C are usually required, whereas gas-phase nitrations fall in the 200—440°C range. Sufficient pressures are needed for the Hquid-phase processes to maintain the reactants and products as Hquids. Residence times of several minutes are commonly required to obtain acceptable conversions. Gas-phase nitrations occur at atmospheric pressure, but pressures of 0.8—1.2 MPa (8—12 atm) are frequentiy employed in industrial units. The higher pressures expedite the condensation and recovery of the nitroparaffin products when cooling water is employed to cool the product gas stream leaving the reactor (see Nitroparaffins). 

Only 20—40% of the HNO is converted ia the reactor to nitroparaffins. The remaining HNO produces mainly nitrogen oxides (and mainly NO) and acts primarily as an oxidising agent. Conversions of HNO to nitroparaffins are up to about 20% when methane is nitrated. Conversions are, however, often ia the 36—40% range for nitrations of propane and / -butane. These differences ia HNO conversions are explained by the types of C—H bonds ia the paraffins. Only primary C—H bonds exist ia methane and ethane. In propane and / -butane, both primary and secondary C—H bonds exist. Secondary C—H bonds are considerably weaker than primary C—H bonds. The kinetics of reaction 6 (a desired reaction for production of nitroparaffins) are hence considerably higher for both propane and / -butane as compared to methane and ethane. Experimental results also iadicate for propane nitration that more 2-nitropropane [79-46-9] is produced than 1-nitropropane [108-03-2]. Obviously the hydroxyl radical attacks the secondary bonds preferentially even though there are more primary bonds than secondary bonds. 

HNO conversions to nitroparaffins pass through a maximum at paraffiniHNO molar ratios of approximately 4 1 to 6 1 (32). At higher ratios, a high fraction of the HNO reacts to form alkyl free radicals. At lower ratios, a large fraction of HNO decomposes, as ia reaction 5. 

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