Photooxidation von Leukofarbstoffen. III. Sensibilisierte Photooxidation von Leukofluoreszein

Photooxidation of Leuco Dyes. III. Sensitized Photooxidation of Leuco Fluorescein Quantum yields of the sensitized photooxidation of leuco fluorescein are reported. Fluorescein and benzophenone were found to be efficient sensitizers of photooxidation of leuco fluorescein. There is a characteristic dependence of quantum yields on concentration of leuco fluorescein and oxygen in the solution. The results are discussed on the basis of reaction scheme proposed for the sensitized formation of fluorescein.     

Massenspektroskopie von Naturstoffen. XIII. Massenspektroskopische Untersuchungen von A-nor-Allobetulanen

Mass Spectroscopy of Natural Products. XIII. Mass Spectroscopic Investigations of A-nor-Allobetulanes The mass spectroscopic fragmentation behaviour of A-nor-allobetulanes with several substituents at C-2 is discussed. The skeleton fragmentation is comparable to that of C-3-substituted allobetulanes. The nature of the substituent at C-2 influences both the abundance of typical skeleton fragments and the formation of specific ions.     

Massenspectroskopie von Naturstoffen. XV. Vergleichende Kationen-Anionen-Massenspektroskopie von Azidogibberellinen

Mass Spectrometry of Natural Products. XV. Comparative Positive-Negative Ion Mass Spectrometry of Azidogibberellins The fragmentation behaviour of 1-azido-3-hydroxy-gibberellin derivatives has been studied by means of positive and negative ion mass spectrometry, high resolution and metastable transitions. The results obtained allow a mass spectrometric distinction to be made between epimers with different stereochemistry of the ring A substituents.     

Thermofraktographie zur Schnellanalyse von Kunststoffen. 2. Mitt. Identifizierung von Phenolharzen

Thermofractography is suitable for the rapid identification of phenolic resins. 3–4 mg of the material to be investigated are heated in the temperature gradient of 150–450°C. The thermofractogram shows the free phenols of the resin in the range of 150–250°C. The phenols developing through thermolysis from the condensation products appear, depending on the corresponding initial phenol, in the range of 300–450°C. The efficiency of the method is demonstrated on several novolaks and phenolresol.     

Anionen-Massenspektroskopie von Naturstoffen. VII. Vergleichende Anionen-kationenmassenspektroskopische Untersuchungen von Cumarin-Derivaten

Anion Mass Spectroscopy of Natural Products. VII. Comparative Anion-cation Mass Spectroscopic Investigations of Coumarin Derivatives Electron attachment mass spectra (2–4eV) of some simple coumarins and furanocoumarins have been studied in comparison with their respective cation mass spectra. The possibility of distinguishing of some isomeric pairs is discussed.     

Dreikomponentenreaktionen. XI. Bromchlorierung von Cyclopenten in Gegenwart von Alkoholen

Three Component Reactions XI. Bromochlorination of Cyclopentene in the Presence of Alcohols The product composition of reaction mixtures after the addition of bromochlorine to cyclopentene in the presence of several alcohols was determined by GLC in dependence of the molar relations, the temperature and the order of addition. A comparison with the chlorination and bromination is given. The yields of three component products increase in the order bromination-bromochlorination-chlorination and decrease from primary to tertiary alcohols.     

Ozonolyse von Enolethern. 9. Synthese und Ozonolyse von 5,6,7,8-Tetrahydrochroman

Ozonolysis of Enol Ethers. 9. Synthesis and Ozonolysis of 5,6,7,8-Tetrahydrochroman The regioselectivity of the transfer of three oxygens of ozone to the olefinic carbons of the rigid substituted enol ether 5,6,7,8-tetrahydrochroman ( 3 ) is proved by isolation of ω-caprinolactone 5 instead of an earlier claimed oxacyclodecanone 4 .     

Photochemie von Bis-2H-tetrazolen. V. Kurzzeitspektroskopischer Nachweis von Bisnitriliminen

Photochemistry of Bis-2H-tetrazoles. V. Flash Spectroscopic Indication of Bisnitrile Imines The flash photolysis of bis-2H-tetrazoles 3--hyphen;6 was investigated. Nitrile imines were detected spectroscopically as short living intermediates. The absorption maxima of the bis(nitrile imines) 9--hyphen;12 are between 360 and 450 nm. The values are in agreement with those obtained by low temperature photolysis of bis-2H-tetrazoles. For some bis(nitrile imines) a strong influence of the temperature on the absorption maxima was found. The reaction kinetics of bis(nitrile imines) in ethanol and cyclohexane in the presence of acetic acid and acrylonitrile are described.     

Die Polymerisation von Lactamen. VII. Die Autopolymerisation von 8-Capryllactam

By heating of anhydrous 8-capryllactam to 240–280°C in the absence of catalysts polymerization takes place. The polymerization is characterized by a short induction period which decreases with increasing temperature. The degree of polymerization remains almost constant in the region of 40 to 90 percent of polymer content, in the region of high content of polymer the degree of polymerization increases rapidly. At higher temperatures insoluble, crosslinked products are formed. The possible mechanism of autopolymerization of lactames is discussed.     

Photochemie von Aminoketonen. VII. Eine diastereoselektive Synthese von 3-Hydroxy-prolinen

Photochemistry of Aminoketones. VIII. Diastereoselective Synthesis of 3-Hydroxy-prolines Glycine esters react in two steps (aminoalkylation and N-acylation) to N-acyl-N-(β-benzoylethyl)-glycine ester 3 . In less polar solvents these ketonic compounds are n,π^*-excited by 300 nm irradiation. In ether 3 ^* yield mixtures of aminocyclopropanoles 4 , hydroxyprolines 5 and products of additions and cleavages. In benzene and cyclohexane/benzene, respectively, the regioselective photocyclization to 5 is favoured. Furthermore this hydroxyproline synthesis has the advantages of high diastereoselectivity yielding the ( 2,3) E–5 and of high overall-yields in connection with the one pot method. The influence of solvents and substituents on the regio- and diastereoselectivity are explained using a model with stabilization of special conformations of intermediates by dipol-dipol interactions.     

Zur Elektrochemie von Pyryliumverbindungen. I. Kathodische Dimerisierung von 2,6-Diphenylpyryliumperchlorat

Electrochemistry of Pyrylium Compounds. I. Cathodic Dimerization of 2,6-Diphenylpyrylium Perchlorate In the cathodic reduction of 2,6-diphenylpyryliumperchlorate 1 in acetonitrile the corresponding pyranyl radicals 2 are formed, which dimerize to 2,2′,6,6′-tetraphenyl-4,4′-bi-4H-pyrane 3 . This product 3 is converted into 2,2′,6,6′-tetraphenyl-4,4′-bipyrylene 4 by transfer of a hydrid anion to a further pyrylium cation. The electrochemical reduction of 1 is shown to be an advantageous method for preparation of 4 .     

Photooxidation von Leukofarbstoffen. X. Untersuchungen zur Photooxidation von Di-kalium-anthracen-9,10-ylen-bis-sulfat

Photooxidation of Leuco Dyes. X. Investigation of the Photooxidation of Di-potassiumanthracene 9,10-ylene-di-sulfate Photolysis of the title compound (DHAE) in water or ethanol produces anthraquinone and anthrone. In deoxygenated solutions 9,10-dihydroxyanthracene is detected as a long lived intermediate. Laser and conventional flash photolysis reveals three short-lived transients with lifetimes of 200 ns, 2 and 410 ms. Different temperature dependencies are observed for the fluorescence and the photolysis quantum yields. This is interpreted by two successive thermally activated processes: photohomolysis of O S bond and escape of the radical pair from the solvent cage. The results are discussed with the help of a reaction scheme proposed for the photolysis of DHAE.     

Desaktivierungsverhalten von Arenen und Heteroarenen. XII. Kinetik der Photodimerisierung von Akridiziniumsalzen

Deactivation Behaviour of Arenes and Heteroarenes. XII. Kinetics of Photodimerization of Akridizinium Salts Resulting from the photo-kinetic parameters of the deactivation of the akridizinium ion the photodimerization and -monomerization of the dimers obtained are investigated, and the rate constants of partial processes are determined. The values of the quantum yield of the dimerization (c∞) in methanol and the monomerization are 0,23 and 0,49, respectively. The presence of compounds with heavy atoms, electron donors and anions of high polarisibility results in a decrease of the quantum yields. In the case of the dimerization process this effect is more intense than in the case of monomerization. From the comparison of these results with those of fluorescence quenching it can be concluded, that non-luminescent excimers with a life-time of about 1 ns are formed intermediately.     

Photooxidation von Leukofarbstoffen. XII. Kurzzeitspektroskopische Untersuchungen zur Photooxidation von Bis-schwefelsäuremonoestern der Leukoformen von Thioindigoverbindungen

Photooxidation of Leuco Dyes. XII. Time Resolved Investigations on the Photooxidation of Bis-sulfuric Acid Monoesters of Leucothioindigoid Compounds The photooxidation of 4, 4′-dimethyl-6, 6′-dichlorothioindigosol ( 1 ) was studied by means of laser and conventional flash photolysis. Three transients were detected and assigned to a radical R generated by homolytic splitting of one O S-bond of the parent compound and to two further radicals which are formed from R by hydrolytic cleavage of the second ester group. The latter two radicals are in a protolytic equilibrium with each other and react, depending on the nature of the solvent by H-atom abstraction, or by disproportionation forming the leuco-thioindigoid dye or both dye and leuco dye. A mechanistic scheme is proposed.     

Photoabbau von PVC-Folien. III. Einfluß von Wärmestabilisatoren

PVC-films containing variable concentrations of thermal stabilizer (dioctyltin bis-(iso-octylthioglycolate)) have been irradiated by a high-pressure mercury lamp under air and nitrogen. The dehydrochlorination and discoloration have been recorded. The main function of the stabilizer is the suppression of absorptions in the visible region. There are indications of a participation of the stabilizer in the photoreaction.     

Thermofraktographie zur Schnellanalyse von Kunststoffen. 4. Mitt.: Identifizierung der Basiskomponenten von Epoxidharzen

Thermofractography is suitable for the rapid identification of the basic components of epoxy resins. 2–3 mg of the polymer sample are being heated in the temperature gradient of 200 to 450°C. The thus forming decomposition products are being transferred as a starting line onto the separating thin layer by means of a carrier gas. After development the thermofractogram (TFG) shows in the temperature range of 200 to approx. 350°C the free oligomeres. The resulting phenols and their subsequent products appear on the TFG from 350°C. A cycloaliphatic type does not give phenolic fragments. The degradation mechanisms of epoxy resins are being discussed in regard to the TFG results and are being confirmed by establishing TGA curves. For the rapid evaluation of the thermofractograms of epoxy resins a questioning scheme is given as an evaluation key.