Reactivity of poly-alcohols towards OH, NO3 and SO4− in aqueous solution

Abstract

Radicals and radical anions such as OH, NO(3) and SO(4)(-) can act as important oxidants in aqueous solutions, e.g. as a part of the tropospheric multiphase system. In the present study the aqueous phase kinetics of OH, NO(3) and SO(4)(-) radical reactions with the following ten aliphatic poly-alcohols 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol, 1,2-butanediol, 1,4-butanediol, 1,5-pentanediol, (2R,3S)-butane-1,2,3,4-tetraol (meso-erythritol), (2R,4R)-pentane-1,2,3,4,5-pentol (arabitol) and (2R,3R,4R,5R)-hexane-1,2,3,4,5,6-hexol (mannitol) were investigated. These alcohols are both of anthropogenic and of biogenic origin and all are highly water soluble. All rate constants throughout this study were determined as a function of the temperature between 278 < or = T [K] < or = 328. OH radical reactions with poly-alcohols (k(2nd) = 1.6-4.7 x 10(9) L mol(-1) s(-1)) are the fastest among the three investigated radicals. The corresponding NO(3) radical (k(2nd) = 0.66-1.5 x 10(7) L mol(-1) s(-1)) and SO(4)(-) radical (k(2nd) = 2.7-5.3 x 10(7) L mol(-1) s(-1)) reactions are on average two orders of magnitude slower. All three radicals react by an H-abstraction mechanism preferably at the alpha-carbon atom of the investigated alcohols. Kinetic measurements were performed using laser flash photolysis-long path absorption (LFP-LPA). Rate constants were measured either directly following the NO(3) and SO(4)(-) concentration-time profile or by a competition kinetics method using a well characterized reference reaction (SCN(-)) for OH radicals. Furthermore, obtained kinetic data are used to extend existing reactivity correlations for H-abstraction reactions with bond dissociation energies in aqueous solution and to calculate the tropospheric lifetimes of the alcohols.