Nitroform anions

The pulse radiolysis technique gives a direct way for measuring the hydrated electron yield. To get the stationary yield, one can simply follow the electron absorption signal as a function of time and, from the known value of the extinction coefficient (Table 6.2), evaluate g(eh). Alternatively, the electron can be converted into a stable anion with a known extinction coefficient. An example of such an ion is the nitroform anion produced by reaction of eh with tetrani-tromethane (TNM) in aqueous solution ... 

The intensity of absorption gives the product G , where G is the observed yield and is the molar extinction coefficient. The absolute value of was determined by Fielden and Hart (1967) using an H2-saturated alkaline solution and an alkaline permanganate-formate solution, where all radicals are converted into Mn042. They thus obtained = 1.09 x 104 M- cm1 at 578 nm, which is almost identical with that obtained by Rabani et al. (1965), who converted the hydrated electron into the nitroform anion in a neutral solution of tetrani-tromethane. From the shape of the absorption spectrum and the absolute value of at 578 nm, one can then find the absolute extinction coefficient at all wavelengths. In particular, at the peak of absorption, (720)/ (578) = 1.7 gives at 720 nm as 1.85 X 104 M 1cm 1. 

Using basic pH leads to higher plateau rate constants, indicating that the ratedetermining step is reaction 18. Reaction 17 must be at least as fast as the rate of 02 addition in the highest 02 concentration used, kn 8 x 105 s 1, which is the limit of the instrument measurement. The G of benzene in pulse radiolysis was found to be equal to that of the nitroform anion (1.6 x 10-7 molJ-1) as can be expected from reactions 17-19. Since the yield of the cyclohexadienylperoxyl radical is 2.9 x 10-7 mol. 1 1 it means that only a fraction (ca 60%) of the cyclohexadienylperoxyl radicals eliminates HO2. The H02 elimination occurs by H-transfer of the allylic hydrogen to the oxygen... 

Nitronate salts can react with alkyl halides to yield polynitroaliphatic compounds with varying degrees of success. The main by-products of these reactions arise for competitive 0-alkylation. Alkyl nitrates are formed as by-products when the nitroform anion is used in these reactions. ... 

The protein 2-i mg/ml) is dissolved in 0.1 M potassium phosphate buffer, pH 7.5, containing 10 M EDTA. A 0.15 M solution of TNM is prepared in 95 % ethanol, and 20 pi is added per ml of protein solution (final TNM concentration 0.003 M). After 60 min at room temperature the reaction is terminated by the addition of 50 pi of 1 M mercapto-ethanol, followed immediately by exhaustive dialysis against 1 % NH4HCO3 at 4°C. The dialysis removes excess TNM and the colored nitroformate anion, which is a product both of the nitration reaction and of decomposition of the reagent. The dialyzed protein derivative is lyophilized. 

Or From Tetrabutyl-Ammonium Superoxide. Tetrabutyl-ammonium superoxide was found convenient for the superoxide dismutase assay since it dissolved readily without decomposition in N,N-dimethyl form-amide (70). Infusions of this solution into a cuvette containing aqueous oxidized cytochrome c reduced the available cytochrome c. In the presence of different erythrocuprein concentrations the reduction rate was progressively diminished. According to McCord and Fridovich (70) an enzyme unit was defined as 50% inhibition of the rate of reduction of cytochrome c. Alternatively tetranitromethane was found appropriate for monitoring Or (70, 136—148) where the stable nitroform anion C(N02)3 is being formed (Equ. (a)) ... 

Two distinct primary transients have been observed by optical spectroscopy in its pulse radiolysis [54]. One of these is not affected by O2 and has been attributed to an A-centered radical cation, A/ N-EDTA , directly bridged to the second EDTA nitrogen. Using strong reductants as probes, e.%. N,N,N N -tetramethylphenylenediamine, G(A/ A/ -EDTA) = 1.6 x 10 mol J has been obtained. Besides generating iV iV-EDTA, the OH radicals produce C-centered radicals by H-abstraction. These have reducing properties and are rapidly oxidized by tetranitromethane, giving rise to nitroform anion, G(NF ) = 4.2 x 10 mol J . The C-centered radicals react rapidly k = 7.6 x 10 dm mol s ) with O2, and subsequent fast 02 elimination. The Schiff bases thus formed hydrolyze to the final products. 

Slettenhaar et al., 2003). 44 wt.-% HNF in water (maximum solubility is about 50 wt.-% at 20 °C) was catalytically decomposed with the catalyst Pt/Al2Q3Si previously described for HAN (Farhat et al., 2008). The gaseous products formed during the catalytic decomposition are major N2, medium NO, N2O and CO2, minor CO and traces of NO2. Raman analysis of the trapped solution evidenced the complete disappearance of hydrazinium cation, the formation of nitric acid and ammonium, whereas nitroformate anion remains in the solution. Pt, Rh and Pd catalysts supported on doped alumina were used for HNF decomposition (Courtheoux et al., 2004b). 

Table 11.1. Second-Order Rate Constant k[) for Nitroform Anion Formation, and the Association Parameter (Ki/n) and the Roughly Estimated Association Constant (J i) of Tetranitromethane with Micelles from Micelle Aggregation Number n...

The quasidiffusion character of the first wave observed both at hydrogen ion concentrations lower and higher than equivalent results, in accordance with Eqs. (71) or (125) in [9], with the shift of the wave to more positive potentials both with increase in c 304 (with constant concentration of the nitroform salt) and with increase in the content of nitroform anions in the solution at Ch o4 = constant. Here, when the current is quasidiffusion in nature with respect to hydrogen ions (i. e., under conditions with a relative excess of anions), the ratio of the concentration of the electrochemically inactive to the active form takes the form a = [H+]/[HAJ, whereas with an excess of hydrc n ions it takes the form a = [A"]/[HA]. 

---