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The sulfite radical anion, SO–3, has been proposed as a chain carrier in the aerobic free-radical chain oxidation of sulfur dioxide in aqueous solution. The absorption spectrum of SO–3 has been obtained following the laser photolysis of argon-saturated sodium dithionate solutions at 193 nm. Using kinetic spectrophotometric and ionchromatographic techniques, it has been shown that the laser photolysis of aqueous dithionate solutions generates both the sulfite anion, SO2–3, and the sulfite radical anion, SO–3. the decay of SO–3 in aqueous solution is second-order with an overall rate coefficient of (4.0 ± 0.3)× 108 dm3 mol–1 s–1 at 293 K in the zero ionic strength limit. The reaction proceeds by two channels; recombination to produce dithionate and electron or O– transfer to produce SIV and SVI. SO–3+ SO–3 [graphic omitted] S2O2–6, SO–3+ SO–3 [graphic omitted] SO2–3+ SO3.Product analysis gives a value of 0.8 ± 0.2 for the ratio ka/kb.

The kinetics of the reaction between NO3 radicals and hex-2-yne has been investigated in discharge-flow experiments. The main motivation for this study was to determine whether secondary reactions enter into the determination of the rate constant. The optical and mass-spectrometric detection methods employed yielded essentially the identical result that the stoicheiometry –Δ[NO3]/–Δ[2-C6H10] departs little from unity under the conditions of the experiments. Optical absorption studies were conducted with prolonged contact times to enhance deliberately potential contributions from secondary reactions. At low concentrations of added 2-C6H10, losses of NO3 are practically equal to the amount of the alkyne added. At higher hex-2-yne concentrations, the consumption of NO3 is virtually complete and the shape of the titration curve is also consistent with unity stoicheiometry.The rate constant obtained in the mass-spectrometric experiments for the reaction of NO3 with 2-C6H10 at room temperature is (2.8 ± 0.1)× 10–14 cm3 molecule–1 s–1.

Rate constants have been determined for the reaction of NO3 with propene from room temperature up to T= 553 K. Allowance was made in analysing experimental data for probable secondary reactions. The Arrhenius plot shows some curvature at the higher temperatures, which we suggest can be explained by the abstraction of an allylic H atom followed by chain reactions involving fast radical–radical processes. The rate constant at T= 298 K was found to be (0.93 ± 0.12)× 10–14 cm3 molecule–1 s–1. We propose the following Arrhenius expression, in units of cm3 molecule–1 s–1, for the addition step in the temperature range T= 298–423 K k=(2.04+0.78–0.55)× 10–13 exp[–(943 ± 108)/T]. For the abstraction reaction of an allylic H atom, we present arguments that suggest Arrhenius parameters of A= 6.8 × 10–13 cm3 molecule–1 s–1 and E= 18 kJ mol–1.

Rate constants have been determined as a function of temperature for the reaction of NO3 with ethane, n-butane, isobutane (2-methylpropane) and isopentane (2-methylbutane), at temperatures up to 553 K. Allowance was was made in analysing experimental data for probable secondary reactions. Abstractions of H atoms at primary, secondary, and tertiary sites possess different temperature coefficients. Arrhenius plots for the alkanes n-butane, isobutane and isopentane are linear at the lower temperatures employed, but show curvature at the higher temperatures, probably because of the participation of a sequence of secondary reactions. The rate constants at 298 K were found to be 0.45 ± 0.06, 1.1 ± 0.2 and 1.6 ± 0.2 (in units of 10–16 cm3 molecule–1 s–1) for n-butane, isobutane and isopentane, respectively. Rate constants for ethane were determined only at elevated temperatures (453 K and above). We propose the following expressions for abstraction per H atom at primary, secondary and tertiary sites (in cm3 molecule–1 s–1); (9.5 ± 6.8)× 10–13 exp –(4400 ± 350/T), (6.3 ± 1.5)× 10–13 exp –(3250 ± 90/T) and (2.3 ± 0.6)× 10–12 exp –(2960 ± 90/T).