Gas phase reactions induced by OH− ion

The site of proton abstraction by OH^? ion in some 4-substituted-3,5,6-triphenyl-Δ′-cyclohexenes has been established from labelling studies. The further fragmentation mode of (M-H)^? ion depends on its structure and stereochemistry. The $\text{exo}$ and $\text{endo}$ nitro isomers exhibit stereochemical differences in the elimination of HNO₂ while the amino and cyano analogues show stereochemically controlled RDA fragmentation mode.     

Turing pattern formation in anisotropic medium

Diffusion of reacting species in chemical and biochemical systems in anisotropic medium is markedly different from those occurring in isotropic medium, therefore approximating diffusion coefficients as constants may not be desirable as this has dynamical consequences. This paper is devoted to the analytical and numerical investigation of the development of spatial patterns in such systems. To this end we consider a general reaction–diffusion system with concentration-dependent diffusion and formulate a scheme to derive the general form of envelope equation for such systems. The theory is applied to the chlorite–iodide–malonic acid system, a standard paradigm for activator–inhibitor mechanism, to derive the instability condition in terms of the anisotropy parameters (\(\kappa _{i}, i = u, v\) that impart concentration-dependence to the diffusion coefficients) and identify the supercritical and subcritical Turing regions in the bifurcation diagram. The theoretical predictions are in good agreement with the numerical simulations.     

Intra–intermolecular gel-free cyclopolymerization of nonconjugated diene with peroxodiphosphate/different activators redox pairs

Gel-free cyclopolymerization of N,N′-methylenebisacrylamide has been carried out using potassium peroxodiphosphate (PDP) as initiator in combination with different activators such as mercaptosuccinic acid (MSA) and thioglycollic acid (TGA) in an inert atmosphere at 45 ± 1°C and 40 ± 1°C, respectively. The rate of polymerization was found proportional to the first power of the monomer and activator concentration and the half-power of PDP in both redox systems. A mechanism involving cyclopolymerization in the propagation path has been proposed. © 1993 John Wiley & Sons, Inc.     

Kinetics and mechanism of oxidation of 8-hydroxyquinoline and its derivatives by cerium(IV) through precursor complex formation

Summary In acid (HClO₄) medium Ce^IV is reduced to Ce^III by 8-hydroxyquinoline (1) and its derivatives, the 5-sulphonate (2) and 7-iodo-5-sulphonate (3), through precursor complex formation. The rates of precursor complex formation have been studied by stopped-flow spectrophotometry for both (1) and (2). Formation of the precursor complex occurs in two concurrent paths involving Ce _aq ⁴⁺ and [Ce(OH)] _aq ³⁺ reacting by I_a and I_d processes respectively. The reaction with (3) is, however, too fast for the stopped-flow method. The rates for subsequent intramolecular electron transfer processes in the precursor complexes are sufficiently slow for all the three species(1)–(3) for evaluation by conventional spectrophotometry. For the electron transfer process the rate varies in the sequence:(2)>(1)(3) due to electron-withdrawing character of the substituent SO ₃ ^– and electron-releasing character of I.     

Kinetics and mechanism of reactions of bis(biguanide)copper(II) ion with 2,2′-bipyridyl and 1,10-phenanthroline in aqueous solution

Summary In aqueous solution [Cu(bigH)₂]²⁺ (bigH=biguanide) reacts with 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) through intermediate formation of ternary complexes [Cu(bigH)(L)]²⁺ and [Cu(bipy)(phen)]²⁺ and binary complexes [CuL₂]²⁺ (L=bipy, phen). The rates of the different steps have been followed in borax buffer (pH 8.0±0.1) by stopped-flow spectrophotometry. For each step k_obs=k₀+k_L[L] and the k_L path appears to be associative. H and S values for the k_L path conform to an isokinetic trend.     

Structural effects on the reactivity of substituted arylphosphines as potential oxygen-scavenging additives for future jet fuels

Efforts to develop oxygen-scavenging additives for future jet fuels (JP-900) are presented. Results from radiolytic experiments are used to develop structure-reactivity relationships for electron-transfer-initiated oxygenation (ETIO) of variously substituted arylphosphines. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:133–138, 1998     

Determination of cadmium by electrothermal atomic absorption spectrometry after microwave-assisted digestion of animal tissues and sewage sludges

The determination of cadmium in different sample types has been carried out by electrothermal atomization atomic absorption spectrometry with D(2)-background correction using a unpyrocoated graphite tube, after pressurized microwave-assisted digestion. Five chemical modifiers [(NH(4))(2)HPO(4), Pd(NO)(3))(2), Ni(NO(3))(2), thiourea and Triton X-100] have been assayed and nickel nitrate has been found to be most effective for an accurate determination of cadmium in mussel tissue, pig kidney and sewage sludge. The characteristic mass of the method is of the order of 1 pg and the limit of detection is lower than 0.1 ng/ml.