Oxyhalogen-sulfur chemistry: kinetics and mechanism of oxidation of N-acetylthiourea by chlorite and chlorine dioxide

The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).     

Theoretical and experimental exploration of rules for combining transport parameters in laminar membranes

Permeabilities, time lags, and mean first passage times were measured in silastic (Sil) and ethylene vinyl acetate copolymer (EVAc) membranes and in the series composites Sil/EVAc and EVAc/Sil. These measurements were used to test phenomenological rules derived previously [R. A. Siegel, J. Phys. Chem. 95, 2556 (1991)] relating the parameters of the constituent membranes to the same parameters for the membrane composites. Reasonable agreement was found between experimental results and these rules. As predicted, permeability and time lag are the same in either direction of transport through the series composite, while mean first passage time is direction dependent. In addition to the experimental results, the combination rules are rederived using the partition/diffusion model of membrane transport, and certain new theoretical connections are noted.     

Dodecamethoxy- and hexaoxotricyclobutabenzene: synthesis and characterization

We report herein the syntheses of dodecamethoxytricyclobutabenzene (TCBB) 1 and hexaoxo-TCBB 2, a class of molecules with structural and theoretical interest. The preparation is based on the 3-fold [2 + 2] cycloadditions of benzyne and ketene silyl acetals (KSAs), where the selectively protected 2-iodophloroglucinol derivative served as a synthetic equivalent of benztriyne I, allowing rapid and regioselective annulation of fully functionalized four-membered rings. Structural study on the former compound showed that the C-C bond lengths in the central benzene ring were essentially the same.     

Ionization of noble gases with pulses directly from a laser oscillator

A Ti:sapphire oscillator with an extended cavity generates pulses with 0.5 microJ energy at a repetition rate of 6 MHz and pulse durations of 50 fs. Tight focusing creates peak intensities exceeding 10(14) W/cm2, which is sufficient for ionizing helium, a nonlinear process where at least 17 photons are absorbed simultaneously.     

Properties of operator stable distributions in infinite-dimensional Banach spaces

The results of this paper concern the connections between different characterizations of operator stable distributions in infinite-dimensional separable Banach spaces. Such assertions are closely related with the strong and uniform operator topology. In particular, the new motions of strongly and uniformlyG-stable distributions are discussed.     

Memory of Chirality in Electron Transfer Mediated Benzylic Umpolung Reactions of Arene–Cr(CO)3 Complexes

As density functional calculations suggest , Cr(CO)₃-complexed benzylic radicals (such as 2 ) exhibit a significant degree of configurational stablility. This was exploited in an efficient method for the electron transfer mediated transformations of readily available 1-arylalkanol–Cr(CO)₃ derivatives 1 to afford alkylated products 3 in good yields and with a high degree of stereochemical retention.     

Au nanolayers deposited on polyethyleneterephtalate and polytetrafluorethylene degraded by plasma discharge

Polyethyleneterephtalate (PET) and polytetrafluorethylene (PTFE) foils were modified by plasma discharge. The effect of plasma modification on polymer surface wettability and on properties of gold coatings were studied as a function of time from plasma exposure (aging time) and polymer substrate temperature. Thickness, sheet resistance, and surface topology of gold layers were studied. Aging of the plasma‐exposed samples is accompanied by increase in contact angle, which is explained by rearrangement of the polymer segments in the polymer surface monolayer, and a decrease in the concentration of polar groups. The aging also leads to a decline in surface roughness R_a measured by atomic force microscopy (AFM). Under deposition conditions, comparable thicknesses of deposited Au layers were prepared on pristine PET and plasma‐treated PET and PTFE samples. The thinnest Au layers were evaporated onto pristine PTFE. The sheet resistance decreases with increasing thickness of Au layer. Plasma treatment leads to an increase of PTFE surface roughness, which becomes even more pronounced after Au deposition. A higher roughness shows that the PET samples are deposited with the Au layer at temperatures above the glassy transition temperature T_g. Copyright © 2006 John Wiley & Sons, Ltd.