Low-temperature radiolysis of aqueous solutions of alkali

Russian Chemical Bulletin -     

Dissolution of cellobiose in the aqueous solutions of chloride salts: Hofmeister series consideration

The effects of chloride salts on the dissolution of cellobiose in aqueous solution were investigated using calorimetry and ¹H NMR. The dissolution of cellobiose in salt solutions is a typical entropy-driven process. The activity of ZnCl₂ and LiCl hydrated ions is enhanced as the hydration number decreases with increasing temperature. Zn²⁺ and Li⁺ hydrates can interact with the oxygen atoms at the O5 and O6 positions of cellobiose and associate with the Cl^? anions, leading to the breakage of cellobiose hydrogen bonds. We found that the solubility of cellobiose in aqueous solutions is on the order of ZnCl₂ > LiCl > NaCl > H₂O > KCl > NH₄Cl, which is consistent with the Hofmeister series. For the first time, we recognized the specific ionic effects of the Hofmeister series on the dissolution of cellobiose in salt aqueous solutions. This finding is helpful for understanding the dissolving mechanism of cellulose in aqueous solvents with salts and providing fundamental knowledge for finding and designing new cellulose solvents.     

Pulse radiolysis of adrenaline in acid aqueous solutions

Pulse radiolysis of adrenaline in acid aqueous solutions (pH 1–3) was carried out. The rate constants for the reactions of adrenaline with H and OH were determined: k(H + adr.) = (0·9±0·1) × 10⁹ dm³ mol⁻¹ s⁻¹; k(OH + adr.) = (1·65±0·15) × 10¹⁰ dm³ mol⁻¹ s⁻¹. The H-adduct of adrenaline has two λ_max, at 280 and 355 nm, with ϵ₂₈₀ = 420 m² mol⁻¹ and ϵ₃₅₅ = 390 m² mol⁻¹, which disappears according to a first order reaction, k₁ = 1·4 × 10³ s⁻¹. The spectra formed by OH attack was assigned to the corresponding benzoxy radical with absorption maxima at 285 and 365 nm and ϵ₂₈₅ = 620 m² mol⁻¹ and ϵ₃₆₅ = 105 m² mol⁻¹. Due to the overlapping of the intermediates, no decay kinetics could be obtained.     

The radiolysis of bromophenol blue in aqueous solutions

The effect of gamma radiation on the color intensity of aerated and oxygenated aqueous solution of bromophenol blue (BPB) was investigated. Ionizing radiation at increasing absorbed doses (D) brought about gradual bleaching (i.e. decrease in optical absorbance, -ΔA) of bromophenol blue solutions. The molar extinction coefficients of acidic, neutral, and alkaline solutions were measured and found to be independent of temperature during spectrophotometry between 20 and 40°C. Aerated and oxygen-saturated acidic solutions showed a linear response -ΔA vs D) up to doses of 2.4 and 2.1 kGy, respectively. Aerated alkaline solutions on the other hand showed a linear response up to 4.8 kGy. The decoloration yields for 5 × 10^-5 M bromophenol blue aqueous solutions, G(-BPB), obtained from the decrease in absorbance at 591 nm wavelength for acidic, neutral, and alkaline solutions, were 0.244, 0.113, and 0.098 (100 eV)^-1, respectively. The first-order rate constant for the reaction of OH radical with bromophenol, obtained from competition reactions with ethanol at pH 4, was found to be 9.1 +- 1.2 × 10⁹ M^-1 s^-1. The degree of decoloration of bromophenol blue in acidic solutions was found to decrease upon the addition of ethanol, G(-BPB) decreasing from 0.24 to 0.088 upon the addition of ethanol at a concentration of 10^-2M. Suggestions are made for possible radiation dosimetry in the dose range (0.1–5 kGy) by means of spectrophotometric analysis of absorption spectra.     

Pulse radiolysis of aqueous solutions of tetraphenylphosphonium ions

The reactions of tetraphenylphosphonium ion (Ar₄P⁺) with e_aq⁻, H atoms and OH radicals have been investigated. The absorption spectra of three transient species were obtained. Ar₄P· radicals formed by the reaction: Ar₄P⁺ + e_aq⁻ → Ar₄P· have a maximum absorption at 305 nm [ε₃₀₅ = (9400 ± 300) dm³ mol⁻¹ cm⁻¹] and decays by second-order kinetics with the rate constant 2k = (2·7 ±0·4) × 10⁹ dm³ mol⁻¹ s⁻¹. H atoms and OH radicals form transient adducts to the phenyl groups of the Ar₄P⁺ ion with the rate constants of (1·5 ± 0·3) × 10⁹ dm³ mol⁻¹ s⁻¹ and (3·0±0·3) × 10⁹ dm³ mol⁻¹ s⁻¹, respectively. Both adducts have broad absorption spectra at 300≈380 nm (λ_max = 340 nm) with the molar extinction coefficients ε₃₄₀ = 5400±300 dm³ mol⁻¹ cm⁻¹ for the H adduct and ε₃₄₀ = 3500±200 dm³ mol⁻¹ cm⁻¹ for the OH adduct.     

Pulse radiolysis study of dithio-oxamide in aqueous solutions

The reactions of e⁻ _aq, H-atoms, OH radicals and some one electron oxidants and reductants were studied with dithio-oxamide (DTO) in aqueous solutions using pulse radiolysis technique. The transient species formed by the reaction of e⁻ _aq with DTO at pH 6.8 has an absorption band with λ _max at 380 nm and is reducing in nature. H-atom reaction with DTO at pH 6.8 also produced the same transient species. The semi-reduced species was found to be neutral indicating that the electron adduct gets protonated quickly. However at pH 1, the species produced by H-atom reaction had a different spectrum with λ _max at 360 and 520 nm. Reaction of acetone ketyl radicals and CO₂ ⁻ radicals with DTO at pH 6.8 gave transient spectra which were identical to that obtained by e⁻ _aq reaction. However at pH 1, the spectrum obtained by the reaction of acetone ketyl radicals with DTO was similar to that obtained by H-atom reaction at that pH. The transient species formed by OH radical reaction with DTO in the pH range 1–9.2 also has two absorption maxima at 360 and 520 nm. This spectrum was identical with the spectrum obtained by H-atom reaction at pH 1. This means that all these radicals viz. OH, H-atom and (CH₃)₂COH radicals react with DTO at pH 1 by H-abstraction mechanism. The transient species produced was found to be sensitive to the presence of oxygen. One-electron oxidizing radicals such as Br₂ ^−· and SO₄ ^−· radicals reacted with DTO at neutral pH to give the same species as produced by OH radical reaction having absorption maxima at 360 to 520 nm. At acidic pHs, only Br₂ ^−· and Cl₂ ^−· radicals were able to oxidize DTO to give the same species as produced by OH radical reaction. The semioxidized species is a resonance stabilized species with the electron delocalized over the-N-C-S bond. This species was found to be neutral and non-oxidizing in nature.     

Pulse radiolysis of pyridine and methylpyridines in aqueous solutions

The radicals formed from pyridine, 3-methylpyridine, 3,5-dimethylpyridine, 2,6-dimethylpyridine and 2,4,6-trimethylpyridine by attack of H, e^-_aq, OH and O^•- in acqueous solutions were investigated by pulse radiolysisin the pH-range 1–13.8. The UV-vis. absorption spectra as well as the formation and decay kinetics for the protonated and unprotonated forms of the methylpyridine radicals studied are presented. The pK_a-values for the OH-adducts were determined.     

Pulse radiolysis of pyridinecarboxylic acids in aqueous solution

The reactivity of OH, e^-_aq and H radicals towards aqueous carboxypyridines: picolinic acid (2-pyridinecarboxylic acid), PA; isonicotinic acid (4-pyridinecarboxylic acid), i-NA; 2,6-pyridinedicarboxylic acid, 2,6-PDCA; and 3,5-pyridinedicarboxylic acid, 3,5-PDCA was investigated in the pH-range 1–13.8. The absorption spectra of the OH-adducts, H-adducts and pyridinyl radicals are given as well as the formation and decay kinetics. In acid (but not in alkaline) solution, the reaction of H-atoms leads to the formation of two distinct products, namely H-adduct and pyridinyl radicals. The yields of pyridinyl radical are: 20% for PA, 75% for i-NA, 60% for 2,6-PDCA and 25% for 3,5-PDCA (a yield of 50% has been found earlier for nicotinic acid, NA).     

Gamma radiolysis of erythrosine dye in aqueous solutions

Beryllium-7, mainly measured via γ-spectrometry, is used as a (natural) radiotracer for education and science. For activities?<?0.1 Bq and samples containing also longer-lived ¹⁰Be, accelerator mass spectrometry (AMS) is the method-of-choice. We demonstrate that ⁷Be and ¹⁰Be can be quantified at the Dresden AMS facility on the same prepared BeO. Detection limits (⁷Be) are?~?0.6 mBq. Samples as small as tens of millilitres of rainwater can be chemically processed (after acidification) within a few hours without expensive and slow ion exchange. Isobar (⁷Li) suppression by chemistry and AMS is sufficient to guarantee for an ultrasensitive, cheap, and fast detection method for ⁷Be allowing high sample throughput.

     

The gamma radiolysis of aqueous solutions of ferriciminodiacetate and ferricglycinate

Radiolytic G-values were determined for [−Fe(III)IDA], Fe(II), (−IDA) and CHO-COOH in deoxygenated aqueous solutions of Fe(III)IDA and Fe(III)gly, and in the presence of scavengers, t-butanol, 2-propanol, methanol, sodium formate and O₂. The metal ion was reduced by e^-_aq, H or secondary radicals HO₂, CO⁻₂, CH₂-OH and (CH₃)₂C-OH, while the OH radical did so indirectly through α-hydrogen abstraction from the ligand followed by intramolecular electron transfer. The rate constant k[OH + Fe(III)IDA], determined by the competition kinetics method at pH 2.0, was 1.7 × 10⁸ M^-1 s^-1.     

Nitrite formation in the radiolysis of aerated aqueous solutions of ammonia

Gamma irradiation of aerated aqueous solutions of ammonia leads to the formation of nitrite as a radiolytic product. Its yield increases with increasing concentration of NH₃ as well as O₂. OH radicals react with NH₃ to give NH₂ radicals, which in the presence of O₂ form NH₂O₂ radicals. These radicals finally lead to the formation of nitrite. G(NO₂⁻) decreases with increasing radiation dose due to secondary reactions. Its initial yield, however, is more than 1/2G_OH, while hydrogen peroxide yield is less than the expected value viz. G(H₂O₂) + 1/2G(e_aq⁻), indicating its participation in reactions with radiation produced free radicals. G(H₂) is 0.35 in aerated aqueous solutions of 10⁻³ mol dm⁻³ NH₃ and 0.23 in the absence of oxygen. Implications of these results to the use of NH₃ in primary coolant water of pressurized water nuclear power reactors of the VVER type are discussed.     

Effect of iso-propanol on the radiolysis of aqueous solutions of periodate

The -radiolysis of IO ₄ ^– in aqueous solution and binary solutions containing iso-propanol has been studied as a function of reactant concentration and absorbed dose. The disappearance of periodate ion in the presence of alcohol is found to be higher as compared to that observed in the pure system. The trend in the G-values determined at various combinations of the reactant concentrations suggests the occurrence of a chain reaction in the radiolytic process.     

Behavior of aluminum in its anodic oxidation in aqueous solutions of acids and their salts

Influence exerted by the nature and concentration of an electrolyte and by the electrolysis temperature on the process of anodic oxidation of aluminum in aqueous solutions was studied. It was shown that two modifications of aluminum hydroxide are formed as electrolysis products. Making higher the electrolyte concentration and raising the process temperature results in that the fraction of boehmite aluminum hydroxide in the product increases and that of bayerite aluminum hydroxide decreases. A scheme by which aluminum is anodically oxidized in aqueous solutions is suggested.