Dieter Lenoir

FeIII–TAML-catalyzed green oxidative degradation of the azo dye Orange II by H2O2 and organic peroxides: products, toxicity, kinetics, and mechanisms

Oxidation of Orange II ([4-[(2-hydroxynaphtyl)azo]benzenesulfonic acid], sodium salt) by hydrogen peroxide catalyzed by iron(III) complexed to tetra amido macrocyclic ligands (FeIII–TAML activators) in aqueous solutions at pH 9–11 leads to CO2, CO, phthalic acid and smaller aliphatic carboxylic acids as major mineralization products. The products are non-toxic according to the Daphnia magna test. Several organic intermediates have been identified by HPLC and GC-MS that allowed the detailed description of Orange II degradation. The catalytic oxidation can also be performed by organic oxidants such as benzoyl peroxide, tert-butyl and cumyl hydroperoxides. Kinetic studies of the catalyzed oxidation indicated that FeIII–TAML activators react first with ROOR′ to form an oxidized catalyst (kI), which then oxidizes Orange II (kII). Neglecting the reversibility of the first step, the rate equation is rate = kIkII[FeIII][ROOR′][Dye]/(kI[ROOR′] + kII[Dye]); here FeIII and ROOR′ represent the catalyst and peroxide, respectively. The rate constant kI equals (74 ± 3) × 103, (1.4 ± 0.1) × 103, 24 ± 2, and 11 ± 1 M−1 s−1 for benzoyl peroxide, H2O2, t-BuOOH, and cumyl hydroperoxide at pH 9 and 25 °C, respectively. An average value of kII equals (3.1 ± 0.9) × 104 M−1 s−1 under the same conditions. The unraveling of the kinetic mechanism allows the comprehension of the robust reactivity, and this is discussed in detail using the representative results of DFT calculations.

Patterns of isomers of chlorinated dibenzo-p-dioxins as tool for elucidation of thermal formation mechanisms

Abstract This study gives a statistically derived proof for the existence of typical patterns for isomers of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) formed as trace byproducts of incomplete combustion. A large number and variety of samples related to combustion was analyzed for the concentrations of the PCDD/F congeners. The resulting data set was subjected to Principal Component Analysis to show similarities in isomeric patterns of either homologue group. The first principal component (PRIN1) gave a good (83–91%) description of the tetra- to heptachlorodibenzo-p-dioxins and -furans for most samples. It provided a tool to compare patterns of isomers of PCDD/F formation from laboratory scale combustion of precursors on annealed fly ash, calculated thermodynamic stability and calculated reactivity. The aim of the combined statistical and experimental studies was to find relevant pathways for thermal PCDD/F formation. Therefore, it was necessary to prove which precursors were relevant and if the observed patterns were controlled either by thermodynamic stability of the compounds or kinetic processes. The investigated precursors led to thermal formation of PCDD/F at 350°C and nearly all resulting isomeric patterns corresponded to the statistically derived combustion patterns of PCDD/F. Relative abundance calculated from thermodynamic stability of the PCDD isomers showed similarities, but also distinct differences with the combustion patterns. So did isomer distributions according to calculated HOMO-LUMO energies, which are quantitative measures for reactivity of congeners. A model, however, which was derived from a superposition of thermodynamic stability and reactivity of PCDD isomers, gave a qualitative description of the typical PCDD combustion patterns.

Electrophilic Bromination of Alkenes: Environmental, Health and Safety Aspects of New Alternative Methods

More than twenty new alternative methods for bromination of alkenes have been evaluated taking into consideration their resource demands, waste production as well as environmental, health and safety aspects. The cost of bromine and the substances designated to circumvent the application of molecular bromine have also been taken into account. As bromine is only one of several problematic substances being used, its avoidance-by applying bromine supported on solid material or by performing the in situ generation of bromine-does not significantly reduce the technological requirements. On the contrary, the resource demands and amount of waste produced by most new methods are significantly higher compared to the standard methods, especially if the recycling of a carrying agent is not efficient. The method using hydrobromic acid and hydrogen peroxide can be regarded as a competitive alternative to the standard method. The application of certain carrying agents could be interesting, because solvents such as carbon tetrachloride or chloroform used during synthesis could be replaced with less problematic ones during work-up. However, problems associated with these alternatives are not resolved as yet.

Thermal formation of polybrominated dibenzodioxins (PBDD) and dibenzofurans (PBDF) from bromine containing flame retardants

Abstract The incineration of bromine containing flame retardants has been studied at different types of ovens (DIN-, BIS- and VCI-apparatus). Polybrominated dibenzofurans have been detected in the combustion products. Brominated diphenyl ethers yield concentrations up to 16% by incineration in a polymer matrix. The temperature profile depends largely on the type of polymer.

Surface-catalyzed formation of chlorinated dibenzodioxins and dibenzofurans during incineration

Abstract Surface-catalyzed reactions occuring on fly ash are the major contributors to the formation of chlorinated dioxins and furans produced during the incineration process. We investigated the relative importance of dioxin and furan formation via de novo synthesis from particulate carbon and via reactions of other precursors on fly ash. The levels of dioxins produced from pentachlorophenol were very much higher than those produced from carbon. Yields from both processes were strongly influenced by flow rate and heating time, however the two processes were affected differently. Carbon also acted to catalyze the formation of dioxins from pentachlorophenol.

PBDF and PBDD from the combustion of bromine containing flame retarded polymers: A survey

Abstract The formation of polybrominated dibenzofurans (PBDF) and dibenzodioxins (PBDD) during the pyrolysis of different polymers containing brominated organic flame retardants was investigated. The pyrolyses were conducted at two different temperatures (600°C and 800°C) using three different oven configurations. Both the pyrolysis gases and the solid residues were analysed for PBDF and PBDD. PBDF were found in almost all samples, but both the concentration and the degree of bromination varied greatly. The largest yields of PBDF in the percent range were measured in the pyrolysis products of polymers containing brominated diphenyl ethers. The other flame retardants generally yielded only a few ppm of PBDF. PBDD are formed only in a few samples and related to the PBDF in very low concentrations.

Isomer-selective ionization of chlorinated aromatics with lasers for analytical time-of-flight mass spectrometry: First results for polychlorinated dibenzo-p-dioxins (PCDD), biphenyls (PCB) and benzenes (PCBz)

Abstract The combination of laser induced Resonance-Enhanced Multi-Photon Ionization (REMPI) and Time-Of-Flight mass spectrometry (TOF) represents a useful tool for detection of trace quantities of organic substances. REMPI spectra (i.e. laser UV spectra) as well as laser induced mass spectra of several aromatic compounds are presented. The possibility of isomer-selective ionization is demonstrated by REMPI ionization spectra of isomeric compounds: Spectra of three dichlorodibenzo-p-dioxin isomers, three tetrachlorobenzene isomers and three dichlorobiphenyl isomers are shown. Finally the potentiality of laser mass spectrometry in the field of environmental analysis is discussed.

Estimating concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in the stack gas of a hazardous waste incinerator from concentrations of chlorinated benzenes and biphenyls

Abstract We investigated the relationships among concentrations of polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF), benzenes (PCBz), phenols (PCPh), and biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH) measured in the stack gas of a hazardous waste incinerator. International toxicity equivalents (I-TE) correlated most significantly with PCBz and PCB concentrations. We therefore propose to utilize these classes of compounds as indicator parameters from which I-TE values can be estimated. The most accurate estimates were made using pentachlorobenzene (Cl5Bz). The proposal to use Cl5Bz as indicator parameter was supported by regression analyses performed for four additional sampling points within the hazardous waste incinerator and by literature data.

Inhibition of Chlorinated Dibenzo-p-dioxin Formation on Municipal Incinerator Fly Ash by Using Catalyst Inhibitors

Abstract Fly ash-catalysed surface reactions are probably the most important mechanism in the formation of chlorinated dibenzo-p-dioxins (PCDD) and related compounds in municipal incinerators. The introduction of a suitable catalyst inhibitor should decrease the yield and change the distribution of PCDD formed on the fly ash. The addition of catalyst inhibitors containing amino- and hydroxy-functional groups to the fly ash surface greatly inhibited the catalytic activity of the fly ash. 2-aminoethanol and triethanolamine were the most effective catalyst inhibitors. The significance of these results to controlling the emissions of PCDD from municipal refuse incinerators is discussed.

Resonance-enhanced multi-photon ionization: a species-selective ion source for analytical time-of-flight mass spectroscopy

Abstract Resonance-Enhanced Multi-Photon Ionization (REMPI) with UV-laser radiation offers the possibility of species selective ionization. The combination of REMPI and time-of-flight mass spectrometry (resonance-enhanced laser mass spectrometry or LAMS) represents a useful tool for selective detection of trace quantities of organic compounds out of complex matrices.