Sigrid S. Dehmlow

Bio: Sigrid S. Dehmlow is an academic researcher from Technical University of Berlin. The author has contributed to research in topics: Cyclopropenone & Ion exchange. The author has an hindex of 6, co-authored 10 publications receiving 797 citations.

Phase transfer catalysis

Abstract: Ion Pairs and Ion Pair Extraction Introduction: The Nature of Phase Transfer Catalysis Ion Pairs in Organic Media Extraction of Ion Pairs from Aqueous Solution Crown Ethers, Cryptates, and Other Chelating Agents as Extractants Solid-Liquid Anion Exchange Mechanism of Phase Transfer Catalysis Mechanistic Investigations Empirical Catalyst Evaluations Unusual and Polymer Supported Catalysts Practical Applications of Phase Transfer Catalysis General Experimental Procedures Formation of Halides Preparation of Nitriles Ester Formation Miscellaneous Displacements Thiols and Sulfides Preparation of Ethers N-Alkylations C-Alkylation of Activated CH-Bonds Alkylation of Ambident Anions Isomerizations and H/D Exchange Additions across Multiple CC-Bonds Addition to C=O and C=N Bonds b'-Eliminations Hydrolysis Reactions Generation and Conversion of Phosphonium and Sulfonium Ylides Nucleophilic Aromatic Substitution Miscellaneous Reactions Organometallic PTC Applications a'-Eliminations Reduction Reactions Oxidation Reactions References Subject Index.

Cyclopropenonchemie, IX. Chemische und photoelektronenspektroskopische Eigenschaften von cyclopropylsubstituierten Cyclopropenonen

Abstract: Bis(1-methylcyclopropyl)acetylen (1a) gibt mit verschiedenen Dichlorcarben-Reagenzien Gemische des acetylenischen Ketons 3a und des Cyclopropenons 4a, wahrend Dicyclopropylacetylen (1b) neben den analog strukturierten Verbindungen 3b und 4b zusatzlich das Produkt 10 der Aufnahme von 2CCl2 (Addition und formale Einschiebung in eine CC-Bindung) liefert. Ahnlich gebaute aliphatische Alkine sind weniger reaktiv, nur mit dem CCl2-Reagens der Phasentransfer-Katalyse werden nennenswerte Umsetzungen zu 12a und b sowie 13a und b erreicht. – In seiner thermischen und Hydrolysebestandigkeit liegt das cyclopropylsubstituierte Cyclopropenon 4b zwischen Diphenylcyclopropenon und dem sehr wenig reaktiven Di-tert-butylcyclopropenon. Dipolmomente und Basizitaten der Cyclopropenone werden zusammgefast; die cyclopropyl-tragenden Verbindungen sind die starksten Basen. Die Photoelektronenspektren einiger Cyclopropenone wurden gemessen, der Substituenteneinflus auf die Ionisationspotentiale der n- und π-Elektronen wird diskutiert. Cyclopropenone Chemistry, IX. Chemical and Photoelectron Spectroscopic Properties of Cyclopropyl-substituted Cyclopropenones Bis(1-methylcyclopropyl)acetylene (1a) reacts with various dichlorocarbene reagents to give mixtures of acetylenic ketone 3a and cyclopropenone 4a, while dicyclopropylacetylene (1b) gives 10 in addition to 3b and 4b. 10 is formed by addition plus formal insertion into a CC-bond by 2 moles of CCl2. Aliphatic alkynes of structures similar to 1a are much less reactive, only the dichlorocarbene of phase transfer catalysis leads to conversions to 12a and b, and 13a and b. – Cyclopropyl substituted Cyclopropenone 4b is thermally and hydrolytically more stable than di-phenylcyclopropenone, though less so than di-tert-butylcyclopropenone. Dipol moments and basicities of cyclopropenones are tabulated. The compounds carrying cyclopropyl groups are the most basic ones. Photoelectron spectra of some cyclopropenones were measured. The influence of substituents on the ionization potentials of n- and π-electrons is discussed.

13C-NMR-Spektroskopie von Cyclopropenonen und Cyclopropenyliumionen (Cyclopropenonchemie: VII)†

Abstract: Die 13C-NMR-Spektren von dreizehn Cyclopropenonen, zwei Cyclopropenthionen, funf zugehoriger Cyclopropenyliumsalze und von drei Cyclobutendionen werden tabelliert und diskutiert. The carbon-13 NMR spectra of thirteen cyclopropenones, two cyclopropenethiones, five related cyclopropenylium salts and three cyclobutenediones are tabulated and discussed.

Cyclopropenschemie, VI. Cyclopropenone Chemistry, VI.

Abstract: The synthesis of methyl-phenylcyclopropenone (1 a) is decribed. Bromination of this and of diphenylcyclopropenone yields saltlike complexes 2 which are in equilibrium with their components. Di-n-propylcyclopropenone and bromine give the ring opened product 3d. la and N-bromosuccinimid give 4 and 5, phenyl brominated derivatives, in sulfuric acid. With cupric bromide substituted β-bromoacrylic acids are formed along with cyclopropenone dimers (7).

Atom efficiency and catalysis in organic synthesis

Abstract: The key to waste minimization in fine chemicals manufacture is the widespread substitution of classical organic syntheses employing stoichiometric amounts of inorganic reagents with cleaner, catalytic alternatives. The E factors (by waste per kg product) of chemical processes increase dramatically on going downstream from bulk to fine chemicals and pharmaceuticals, mainly owing to the use of "stoichiometric" methods. The concept of atom efficiency is a useful tool for rapid evaluation of the amount of waste generated by alternative processes. The general theme of atom-efficient, catalytic processes is illustrated with industrially relevant examples. These include catalysis by solid acids and bases, catalytic reductions and oxidations, catalytic C-C bond formation, asymmetric catalysis, biocatalysis, and catalysis in novel media (aqueous and fluorous biphasic systems, supercritical fluids, and ionic liquids).

13C substituent effects in monosubstituted benzenes

Abstract: A brief analysis is presnted of the current understanding of substituent perturbations in monosubstituted benzenes as determined by substituent induced carbon chemical shifts. A critical tabulation of the four substituent chemical shifts is given for c. 700 monosubstituted benzenes.