REACTIONS OF THE FERRYL ION WITH SOME COMPOUNDS FOUND IN CLOUD-WATER

The lifetime of the ferryl ion FeO2+, (minutes at pH below 1) is reduc ed by a factor of 50 at pH above 3. This is rationalized in terms of a n acid-base equilibrium between two different hydrolytic forms of this species (Fe(OH)(2)(++) and Fe(OH)(3)(+)) with a pK(a) = 2.0. The rate constants for reactions between FeO2+ and selected compounds found in cloud water were measured in acid solutions by stopped-flow technique . For inorganic reactants: k(HNO2) = 1.1 X 10(4) M-1 s(-1), k(NO2-) le ss than or equal to 10(5) M-1 s(-1) k(Cl-) = 10 X 10(2) M-1 s(-1), k(H SO3-) = 2.5 X 10(5) M-1 s(-1), k(SO2) = 4.5 X 10(5) M-1 s(-1), and k(M n(II)) = 1.0 X 10(4) M-1 s(-1) were obtained and for the organic react ants: k(HCOOH) = 160 M-1 s(-1), k(HCOO-) = 3 X 10(5) M-1, k(CH3COOH) = 3.1 M-1 s(-1), k(CH2(OH)2) = 400 M-1 s(-1), k(CH3COCH3) = 16 M-1 s(-1 ), k(CH3CH20H) = 2.5 X 10(3) M-1 s(-1), k(C6H5OH) = 4.0 X 10(3) M-1 s( -1), and k(C6H5COOH) = 80 M-1 s(-1) were obtained. A good correlation between log(k) and the standard one electron reduction potential (E de grees) indicates that the reactions of inorganic compounds proceed by electron transfer. The reaction mechanisms in case of organic compound s are very similar to the reactions of the OH radical, i.e., H-abstrac tion, and a fairly good correlation between log(ii) and the bond disso ciation energy BDE was obtained. Activation parameters were measured f or the reaction of FeO2+ with HNO2 (E-a = 34.5 kJ/mol); Mn2+ (E-a = 21 .3 kJ/mol); HCOOH (E-a = 22.3 kJ/mol); CH2(OH)(2) (E-a = 44.5 kJ/mol); and C6H5OH (E-a = 28.1 kJ/mol). (C) 1998 John Wiley & Sons, Inc.