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.

Tropospheric Aqueous‐Phase Free‐Radical Chemistry: Radical Sources, Spectra, Reaction Kinetics and Prediction Tools

“…It is not clear if the rate constants of this particular reaction can be affected by such drastic measurement conditions. However, the value from Hoffmann et al [24] perfectly fits in an existing correlation between the bond strength of the weakest H-bond in the molecules and the logarithmic rate constants per abstractable Hatom for NO 3 radical reactions. [24] This could indicate that the reaction is faster than measured by Ito et al [85] and Pikaev et al [86] The different reaction conditions discussed before could also be the reason for the differences observed for the reaction of 1,2,3-propanetriol with NO 3 in aqueous solution.…”

“…However, for the prediction of kinetic data Evans-Polanyi-type reactivity correlations can be used for reactions following an H-abstraction mechanism. The latest version of this reactivity correlation is reported in Hoffmann et al [24] and is discussed in a later section. The same indexing is applied for the NO 3 kinetic data (Table 12) as for the OH reactions in Table 2.…”

“…A recent reactivity comparison can be found in Hoffmann et al [24] NO 3 can undergo direct electron transfer reactions with inorganic anions, carboxylate anions, and electron rich aromatic compounds where it is much more reactive than OH as indicated by its much higher one electron reduction potential of 2.41 V against 1.90 V for OH. [84] …”

“…A number of rate constants have been obtained from our laboratory [24] for reactions of OH with diols, including temperature dependence and a number of sugars of interest for atmospheric particle chemistry. Moreover, Arrhenius parameters are now available for these reactions, often for the first time.…”

The Latest on Sugar Substitutes of the Alditol Type with Special Consideration of Erythritol and Xylitol―Rectifications and Recommendations

“…Addition of D-mannitol improved the setting reaction and mechanical strength of apatite [68], owing to its satisfactory dissolution behaviour and its biocompatibility, and because it did not inhibit the compositional transformation to apatitic material. It should also be mentioned that OH radical reactions with erythritol, D-arabitol, and D-mannitol are much faster than the NO 3 and SO 4 -radical reactions [69].…”