Reactions of Hydrated Electrons with Pyridinium Salts in Aqueous Solutions

Abstract

Rate coefficients for the reactions of the hydrated electron (e(aq)(-)) with pyridinium salts in aqueous solutions have been determined using pulse radiolysis techniques. The rate coefficients for pyridine, 1-hydropyridinium chloride, and 1-hydropyridinium nitrate were observed to be 1.4 x 10(10), 4.5 x 10(10), and 5.3 x 10(10) M(-1) s(-1), respectively. The e(aq)(-) was found to primarily attack the pyridine ring, the proton coordinated to the nitrogen atom, and the nitrate counterion, but not the chloride. Results for the corresponding dimer structures of 4,4'-dipyridyl, 1,1'-dihydro-4,4'-bipyridinium dichloride, and 1,1'-dihydro-4,4'-bipyridinium dinitrate had similar trends for e(aq)(-) attack sites. The rate coefficients for pyridinium salts were lower when the pyridinium nitrogen atom is coordinated to a methyl group rather than to a proton. This reduction is probably due to the increase in electron density of the pyridine ring due to the electron-donating methyl group. Pyridinium salts are not major contributors to the production of molecular hydrogen in the radiolysis of aqueous solutions and actually decrease molecular hydrogen yield due to scavenging reactions of the e(aq)(-). The yield of molecular hydrogen decreases from 0.45 to approximately 0.2 molecule/(100 eV) over the scavenging capacity range for the e(aq)(-) of 10(5)-10(9) s(-1). Absorption spectra of the transient species produced by the reactions of pyridinium salts with OH radical and H atom formed in water radiolysis were observed, and rate coefficients for these reactions were determined.

Radiation-induced decomposition of anion exchange resins

“…Radiolytic decomposition of resins representing the Reillex™ family has been studied in length before, however, H 2 formation studies at high water content was not performed in that work [11]. The pulse radiolysis study of pyridinium salts in aqueous solutions, which mimic the core functionality of Reillex™ resins, reveal that pyridinium systems rapidly scavenge solvated electrons as well as hydrogen atoms known to be precursors of H 2 [24]. These data provide a satisfactory explanation for the low H 2 production in Reillex™ HPQ chloride/water slurries.…”

Soft X-ray Heterogeneous Radiolysis of Pyridine in the Presence of Hydrated Strontium-Hydroxyhectorite and its Monitoring by Near-Ambient Pressure Photoelectron Spectroscopy

“…The reason for this is a question of dose. In fact while dose rates are huge in both case, ~10 9 Gy/s for a pulsed e-beam experiment 67 and ~10 7 Gy/s for NAP-XPS (see the Supporting Information, section S7 ), the overall doses differ considerably, 6 Gy per pulse in the former case 67 (6 pulses are sufficient to acquire an absorption spectrum) and more than 10 9 Gy in the latter case (considering that the minimum acquisition time is 25 s).…”

“…The radiolysis of pyridine was extensively studied in “bulk” aqueous solutions, using the pulsed e-beam technique, combined with UV-visible absorption spectroscopy 65 – 67 . Solvated electrons, H • and HO • radicals resulting from the dissociation of water react with pyridine to give pyridinyl radicals, H and HO adducts.…”

“…These experiments give unique information on the kinetics of the primary species (e.g. the reaction rates of the solvated electron) 67 . However they do not point to dissociation products, in contrast to the present case.…”

“…To our knowledge, there is no account of the radiolysis of pyridine adsorbed onto a hydrated smectites using the pulsed e-beam technique. However, admitting, as in bulk water 67 , that the primary products of water radiolysis subsequently react with pyridine, e-beam studies of the radiolysis of confined water in hydrated smectites are quite relevant to the present case 35 , 36 . The radiolysis of water in clays presents specific traits with respect to the bulk water case.…”