Oxokohlenstoffe und verwandte Verbindungen. 27. Synthese von Dihydrocyclobuta[a]naphthalen-1,2-dionen und Cyclobuta[a]naphthalen-1,2-dionen durch Anellierung von Alkoxy-(1-alkenyl)benzolen mit 3-Chlor-3-cyclobuten-1,2-dion. Anwendungsbereich und Grenzen

Oxocarbons and Related Compounds. 27. Synthesis of Dihydrocyclobuta[a]naphthalene-1,2-diones and Cyclobuta[a]naphthalene-1,2-diones via Annulation of Alkoxy-(1-alkenyl)benzenes with 3-Chloro-3-cyclobutene-1,2-dione. Scope and Limitations The reaction of alkoxy-(1-alkenyl)benzenes with semisquaric chloride ( 3 ) has been investigated systematically. 1,2-Dialkoxy- and 1-alkoxy'-2-alkoxy″-4-(1-alkenyl)benzenes ( 6a–j ) and ( 11a–i ) react with 3 to give the 3,4-dihydrocyclobuta[a]naphthalene-1,2-diones ( 8a–j ) and ( 12a–i ). Treatment of the dihydrocyclobuta[a]naphthalene-1,2-diones with 1.2 equiv. bromine effects dehydrogenation and affords cyclobuta[a]naphthalene-1,2-diones ( 9a–e ) and ( 13b–f ). Any efforts to extend this annulation reaction to dimethoxy-(1-alkenyl)benzenes with the methoxy groups in other than the 1,2-positions, e. g. 14a, b, 16a, b have been unsuccessful. The reaction of 1,2,3-trimethoxy-4-(1-propenyl) [and 4-(1-butenyl)]-benzenes ( 18a ) and ( 18b ) with semisquaric chloride ( 3 ) leads to the elimination of HCl and CH₃OH and gives 5,6-dimethoxy-3-methyl [and 3-ethyl]-cyclobuta[a]naphthalene-1,2-diones ( 20a ) and ( 20b ). The reaction pathway of this novel annulation reaction is discussed.     

2-furyloxirane: II. Reduction,hydrolysis, alcoholsis and the uncatalysed polymerization induced by OH groups

The reduction of furyloxirane (FO) with different reducing agents was conducted under various experimental conditions and occurred essentially by the α-opening of the oxirane ring. It was also shown that the presence of Lewis acids favoured this mode of ring opening. The hydrolysis of furanic oxiranes was accompanied by oligomerization even in the absence of a catalyst. Moreover, very small quantities of water induced the oligomerization of FO giving degrees of polymerization of 40–50. This behaviour is unique since aliphatic and aromatic oxiranes are not activated by water alone. The alcoholysis of FO catalysed by metal alkoxides showed variable extents of α- and β-opening of the oxirane ring, depending on the steric hindrance of the alkoxide used.     

Dilute solution properties of randomly branched poly(methyl methacrylate)

Randomly branched poly(methyl methacrylate) samples were prepared by copolymerization with different amounts of ethylene dimethacrylate. The molecular weight distributions, radius of gyration distributions, and intrinsic viscosity distributions were measured by size exclusion chromatography with refractive index, multiangle light-scattering, and viscosity detectors. The effect of branching on the radius of gyration was compared with the effect on the intrinsic viscosity. It was found that the intrinsic viscosity contraction factor gⁱ scales with the radius of gyration contraction factor g, with the exponent, ϵ, having a value in the range 0.8–1.0. © 1996 John Wiley & Sons, Inc.     

Design and performance of biofilters for the removal of alkylbenzene vapors

Three identical biofilters, run under the same conditions but inoculated with different mixed cultures, were fed a mixture of toluene, ethylbenzene, and o-xylene (TEX) gases. Inert porous perlite was used as support material, in contrast to the more conventional biofiltration systems where natural supports are used. Biodegradation started in all three biofilters a few hours after inoculation, without previous adaptation of the inocula to the toxic mixture. Despite acidification of the systems to pH values below 4·5, the elimination capacities reached were fully satisfactory. The best performing biofilter, in which bacteria were dominant, showed an elimination capacity of 70 g TEX m⁻³ h⁻¹ with a near complete removal of the mixture up to an influent concentration of 1200 mg TEX m⁻³ at a gas residence time of 57 s. Most of the ingoing carbon was recovered as carbon dioxide in the outgoing gas. In the other biofilters fungi dominated and performance was slightly worse. With single substrates, the elimination capacity was higher for toluene and ethylbenzene than for the TEX mixture, whereas o-xylene removal was slowest in all cases. Also when feeding the mixture to the biofilters, o-xylene was removed most slowly.     

Role of fermentative and antioxidant metabolisms in the induction of core browning in controlled‐atmosphere stored pears

Pears (Pyrus communis L cv Blanquilla) were stored at various CO₂ concentrations to induce core browning. The severity of core browning and the products and enzymes associated with fermentative and antioxidant metabolisms were determined immediately after harvest and in healthy and damaged fruits after storage. The incidence and severity of brown core increased with CO₂ concentration. Acetaldehyde and ethanol concentrations and alcohol dehydrogenase (ADH, EC 1.1.1.1) activity increased in all fruits during storage, but more in fruits with brown core than in healthy fruits. Pyruvate decarboxylase (PDC, EC 4.1.1.1) activity decreased slightly during this time. Ascorbate contents decreased whereas glutathione concentrations increased during storage in fruits with brown core compared to the same fruits at harvest. Superoxide dismutase (SOD, EC 1.15.11) activity increased during storage but was not affected by brown core. In contrast, a significant increase in both ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) activities and a significant decrease in catalase (CAT, EC 1.11.1.6) activity were found in damaged fruits. Malonaldehyde (MDA) and 4‐hydroxyalkenal (4‐HNE) contents increased significantly in the damaged fruits as a result of peroxidation. Collectively, our results suggest that brown core in pears is indirectly correlated with fermentation and involves oxidative damage which may be a causal factor in brown core development. © 2001 Society of Chemical Industry     

Curing and Photostabilization of Thermoset and Photoset Acrylate Polymers

The light‐stability of thermosetting acrylate and UV‐cured acrylate polymers has been tested in an accelerated QUV weatherometer. Infrared spectroscopy was used to monitor in situ the chemical changes occurring upon both curing and photoageing of 35 μm thick clearcoats. The curing was shown to proceed more extensively in photoset than in thermoset acrylate polymers which contain 6 and 20% unreacted functional groups, respectively. During photoageing, the loss of the binder structural groups is accompanied by the production of oxidation products (carbonyl and hydroxyl groups). The UV‐cured polyurethane‐acrylate coating was shown to be more resistant to accelerated weathering than the melamine/acrylate thermoset currently used as automotive finishes. The addition of a hydroxyphenyltriazine UV‐absorber and a hindered amine light stabilizer (HALS) radical scavenger was found to increase substantially the light stability of acrylate clearcoats.     

Anlagen‐ und Prozesstechnik für die Mikrobearbeitung mit Vakuum‐UV Excimer‐Laser

With the F₂‐Excimer laser a tool has now become available for the precise structuring of challenging materials like fused silica or PTFE (Teflon®). However, the short wavelength of 157 nm with a characteristic photon energy of 7.9 eV has special requirements regarding beam guiding and the optical components like mirrors lenses or objectives. The process and system technology introduced here is capable to produce micro‐structures with a lateral resolution in the μm‐range with a depth resolution in the sub‐μm range.     

The Activation of O2 at Ruthenium Complexes: Catalytic Chlorination of Unsaturated Organic Substrates within the System O2/HCl/H2O

A solution of RuCl₃ in concentrated hydrochloric acid is capable of chlorinating aromatic compounds catalytically, if O₂is present as the oxidizing agent (brominations can be achieved in hydrobromic acid). When olefins are chosen as substrates, two Cl atoms are added to the double bond in an anti fashion, while hydrochlorination products are formed simultaneously. According to the products observed in both types of reactions for various substrates in this 3‐phase system, the halogenations proceed via electrophilic pathways.