O. P. Pestunova

Detoxication of water containing 1,1-dimethylhydrazine by catalytic oxidation with dioxygen and hydrogen peroxide over Cu- and Fe-containing catalysts

Abstract A number of Cu- and Fe-hydroxide containing catalysts, supported on oxide carriers, were prepared to provide the removal of 1,1-dimethylhydrazine from aqueous solutions via its oxidation by hydrogen peroxide and air oxygen. The Cu-containing samples as well as Fe/ZSM-5 are the most active catalysts in this reaction. The reaction products were analyzed by gas chromatography and UV–Vis spectroscopy. The effect of nature of the oxidizer and catalyst, pH and temperature on both the reaction rate and product composition was studied.

The nature of autocatalysis in the Butlerov reaction

The effect of the nature of an initiator on the kinetics of formaldehyde consumption and on product composition in the Butlerov reaction was studied in a stirred flow reactor and a batch reactor. It was found that, under flow conditions, the kinetics and the product composition of this reaction are independent of the nature of the initiator. The reaction schemes proposed previously for an autocatalytic process mechanism based on the formation of glycolaldehyde from two formaldehyde molecules are incorrect. A correlation between the initiating activities of various monosaccharides and the rates of their conversion into an enediol form was found with the use of a batch reactor. Solid enediol complexes with Ca2+ ions were isolated for glucose, fructose, ribose, and sorbose; the initiating activity of these complexes was found to be much higher than the initiating activity of pure monosaccharides. A self-consistent mechanism was proposed for Butlerov reaction initiation. The formation of the enediol forms of monosaccharides followed by degradation to lower carbohydrates plays a key role in this mechanism. In turn, the initiating activity depends on the position of the carbonyl group in the monosaccharide molecule. The condensation reactions of glycolaldehyde, glyceraldehyde, and dihydroxyacetone with each other were studied. Based on data on the condensation products of lower carbohydrates, a scheme was proposed for the Butlerov reaction. According to this reaction scheme, C2 and C3 carbohydrates mainly undergo an aldol condensation reaction with formaldehyde, whereas the formation of higher monosaccharides occurs by the aldol condensation of lower C2–C3 carbohydrates with each other.

Catalytic condensation of glycolaldehyde and glyceraldehyde with formaldehyde in neutral and weakly alkaline aqueous media: Kinetics and mechanism

The kinetics of glycolaldehyde and glyceraldehyde condensation with formaldehyde in a neutral aqueous medium in the presence of homogeneous phosphates and in a weakly alkaline medium in the presence of MgO was studied. The temperature dependences of the observed kinetic constants and the apparent activation energies of the reactions were determined. A reaction scheme for the interaction of lower monosaccharides with formaldehyde was derived from analyses of the reaction products.

Selective synthesis of erythrulose and 3-pentulose from formaldehyde and dihydroxyacetone catalyzed by phosphates in a neutral aqueous medium

The aldol condensation of formaldehyde and the lower carbohydrate dihydroxyacetone in a neutral aqueous medium is effectively catalyzed by solid compounds (hydroxylapatite and calcium phosphate and carbonate), natural minerals (apatite and vivianite), and soluble phosphates. In excess formaldehyde, the decrease in the concentration of the lower carbohydrate is described by a first-order rate law with respect to dihydroxyacetone. The major products of the reaction between formaldehyde and dihydroxyacetone in the presence of the above catalysts are erythrulose (45–50% selectivity) and 3-pentulose (35–40% selectivity). Branched pentulose and hexulose are also identified among the reaction products.

Kinetics and mechanism of water catalytic oxidation by a Ru3+(bpy)3 complex in the presence of colloidal cobalt hydroxide

Kinetics of the catalytic oxidation of water to molecular oxygen by a tris(bipyridyl) Ru(III) complex is studied in the presence of colloidal cobalt hydroxide stabilized by starch. Oxidant consumption follows the first-order rate law with respect to the oxidant concentration. The dependence of the apparent rate constant of this process on the catalyst concentration, initial oxidant concentration, and initial concentration of its reduced form was determined. The dependence of the oxygen yield on H+ at pH 7–11 and a catalyst concentration of 10-7-10-3 mol1 is studied. An intermediate product of the reaction was found, which is probably a bridged peroxo complex of cobalt. The kinetic scheme and mechanism of the reaction is proposed, which agree with experimental observations.

Prebiotic Carbohydrates and Their Derivates

The most significant experimental results on the putative synthesis of various carbohydrates and their derivates from simple substrates in plausible prebiotic conditions are summarized and discussed. The synthesis of monosaccharides from formaldehyde and lower carbohydrates (glycolaldehyde, glyceraldehyde, dihydroxyacetone) can be catalyzed by different compounds such as lead, phosphate and borate ions and several natural minerals. Lower carbohydrates can be directly formed in aqueous formaldehyde solutions under the action ofUV-irradiation. The possible role of carbohydrates and their derivates in the chemical evolution and development of presumable abiogenic metabolism is illustrated as well.