G.R. Dey

Thiol radical cations and thiyl radicals as direct products of the free electron transfer from aromatic thiols to n-butyl chloride radical cations

Radical and ionic reactions were observed in the pulse radiolysis of thiophenols (ArSH=thiophenol, o-, m- and p-thiocresol or 2-thionaphthol) in n-butyl chloride solution. The main source of aromatic thiyl radicals is the reaction of butyl radicals with the thiols, which proceeds at 1.0–5.6×108 dm3 mol−1 s−1. This radical generation path is completely quenched in the presence of oxygen. Under these conditions, only the electron transfer reaction between n-butyl chloride parent ions and the thiophenols remains and could be well analyzed. It takes place at a rate constant of about 1.5×1010 dm3 mol−1 s−1 and takes two parallel paths–common electron transfer yielding thiophenol radical cations and a more complex ionic reaction resulting directly in thiyl radicals. The latter is thought to proceed via an encounter complex geometry, ArSH···ClBu•+, in which electron transfer is directly followed by immediate deprotonation. The thiyl radicals and the thiol radical cations are characterized by their optical absorption spectra and their kinetic properties. Quantum chemical calculations underpin our mechanistic interpretation and provide information about the charge distribution and reactivity of the thiol radical cations.

Encounter geometry determines product characteristics of electron transfer from 4-hydroxythiophenol to n-butyl chloride radical cations

Abstract The electron transfer reaction between the n -butyl chloride parent ion and 4-thiophenol was studied using pulse radiolysis in solutions of 4-thiophenol in n -butyl chloride. It was found to have a diffusion-controlled rate constant of 1.5×10 10 dm 3 mol −1 s −1 and to involve contributions from all functional groups, i.e. –SH, –OH and the aromatic ring. Consequently, thiyl and phenoxyl radicals and 4-hydroxythiophenol radical cations were observed as direct products of this ion–molecule reaction. This unexpected reaction behavior could be explained by the hypothesis that the encounter geometry of the reaction partners determines the product characteristics.

Methane from benzene in argon dielectric barrier discharge

A first-time account of direct, on-line, instantaneous and efficient chemical conversion of gas phase benzene to methane in argon Dielectric Barrier Discharge (DBD) is presented. In the absence of another overt hydrogen-donating source, potency of analogous parents toward methane generation is found to follow the order: benzene>toluene>p-xylene. Simultaneous production of trace amounts of phenolic surface deposits suggest (a) prompt decomposition of the parent molecules, including a large fraction yielding atomic transients (H-atom), (b) continuous and appropriate recombination of such parts, and (c) trace moisture in parent contributing OH radicals and additional H-atoms, which suitably react with the unreacted fraction of the parent, and also other intermediates. Results highlight Ar DBD to be a simple and exploitable technology for transforming undesirable hazardous aromatics to usable/useful low molecular weight open-chain products following the principles of green chemistry and engineering.

Ozone Generation from Argon-Oxygen Mixtures in Presence of Different Packing Materials within Dielectric Barrier Discharge Gap

Assessments of ozone yield and concentration in Dielectric Barrier Discharge of argon-oxygen mixtures in presence of various packing materials are discussed. These include zeolite molecular sieve 13X pellets, Pyrex beads, Pyrex wool, and porous TiO2-beads, which presented differential reactive surfaces, nano cavities, photo-catalysis, and dissimilar ionic environments. Their utility was evaluated in conjunction with varied gas composition, flow rate, and electrical inputs. In a mixture of 3–21% O2 in argon, the ozone concentration ranged between 16–980 ppm, simultaneous measurements of in situ energy dissipation revealed its yield, G(O3) to change independently from 0.002 to 2.020 μmol J−1. TiO2 packing emerged as the most versatile material to produce O3 in high concentration and yield.

Septum Bleed during GC–MS Analysis: Utility of Septa of Various Makes

The significant presence of septum-related ghost peaks, causing interference in routine gas chromatography-mass spectrometry analyses at sample injection port temperatures above 100°C, is demonstrated. A comparative study with commonly employed septa of various types and makes under varying analytical conditions, e.g., injection port temperature, carrier flow rate, capillary column type and oven heating rate reveal that long-chain hydrocarbons, substituted phthalate derivatives and silanes (silicon compounds) are responsible for such interferences, which is confirmed from their respective peak fragmentation patterns after comparison with standard mass spectrometry library data. Consequently, prior blank studies at actual analysis conditions may become mandatory for quantification and reduction of such interferences, ignoring septa quality and performance claims.