Search

Phosphite radicals HPO/sub 3/- and PO/sub 3//sup 2/-, which exist in an acid-base equilibrium with pK = 5.75, are shown to take part in various types of reactions. In the absence of scavengers, they disappear mainly by second-order disproportionation and combination; a first-order contribution to the decay is also indicated. HPO/sub 3/- and PO/sub 3//sup 2/- are good reductants toward electron acceptors such as tetranitromethane. In this reaction phosphate and C(NO/sub 2/)/sub 3/- are formed. Phosphite radicals can, however, also act as good oxidants, e.g., toward thiols and thiolate ions. These reactions lead to the formation of RS. radicals which were identified either directly, as in the case of penicillamine, through the optical absorption of PenS. or more indirectly through equilibration of RS. with RS- to the optically absorbing RSSR-. disulfide radical anion. A homolytic substitution reaction (S/sub H/2) occurs in the reaction of the phosphite radicals with aliphatic disulfides, yielding RS. radicals and phosphate thioester RSPO/sub 3//sup 2/-. Lipoic acid, as an example of a cyclic disulfide, is reduced to the corresponding RSSR-. radical anion and also undergoes the S/sub H/2 reaction with about equal probability. An addition reaction is observed between phosphite radicals and molecular oxygen. The resultingmore » peroxo phosphate radicals establish an acid-base equilibrium HPO/sub 5//sup -/. reversible PO/sub 5//sup 2 -/. + H+ with a pK = 3.4. Absolute rate constants were determined for all reactions discussed.« less

Tetranitromethane (TNM) reacts by a dissociative electron capture process with solvated electrons in isopropanol (kTNM + e–s= 2.45 × 1010 M–1 s–1) to produce nitroform anions, C(NO2)–3, and NO2. Iso-propanol radicals and iso-propanolperoxy radicals also reduce TNM via an electron transfer reaction with bimolecular rate constants of 7 × 109 M–1 s–1 and 9 × 108 M–1 s–1, respectively. In neutral and acid (HClO4) solutions C(NO2)–3 ions are neutralized to C(NO2)3H by reaction with solvated protons (k= 3.2 × 108 M–1 s–1) and by a proton transfer reaction from isopropanol molecules (k= 4.5 × 102 M–1 s–1). C(NO2)3H dissociates with k= 3.2 × 103 s–1. The equilibrium constant of C(NO2)3H ⇌ C(NO2)–3+ H+sol in isopropanol was determined to be K= 1.0 × 10–5 M. The yield of scavengable reducing species in irradiated isopropanol increases from G= 3.5 at 6.3 × 10–6 M TNM to G= 6.4 at 3.2 × 10–2 M TNM in argon saturated solutions, and from G= 0.75 to G= 4.2 for the same concentrations of TNM in O2 saturated solutions. G(free solvated electrons) was measured to be 1.2. The formation and disappearance of ions have been observed directly by means of pulse radiolysis conductivity measurements. The specific equivalent conductance of C(NO2)–3 ions and solvated protons was determined to be ΛC(NO2)3–+ Hsol+= 51 Ω–1 cm2 equiv.–1.

The absorption spectra of the radicals HC6H5NO2 and OHC6H5NO2 in aqueous solutions have been obtained. These transients have a strong absorption at 4100 A and their molar extinction coefficients are both 3700 M–1 cm–1. The following rate constants have been measured : k(H+C6H5NO2)=(5.6±0.6)× 109 M–1 sec–1; k(OH+C6H5NO2)=(4.7±0.5)× 109 M–1 sec–1; k(O2+OHC6H5NO2)=(2.3±0.3)× 106 M–1 sec–1; k(OHC6H5NO2+OHC6H5NO2)=(6.0±0.4)× 108 M–1 sec–1. About 25% of the reactions between two nitro-hydroxycyclohexadienyl-radicals lead to nitrophenol-isomers by disproportionation. The majority of these reactions lead to other products (probably dimers by combination) which exist in acid and basic forms, the latter having strong absorptions in the visible range. These products are believed to be derivatives of nitro-cyclohexadiene.