Multisite catalysis: a mechanistic study of beta-lactone synthesis from epoxides and CO--insights into a difficult case of homogeneous catalysis

Carbonylation of epoxides with a combination of Lewis acids and cobalt carbonyls was studied by both theoretical and experimental methods. Only multisite catalysis opens a low-energy pathway for trans opening of oxirane rings. This ring-opening reaction is not easily achieved with a single-site metal catalyst due to structural and thermodynamic constraints. The overall reaction pathway includes epoxide ring opening, which requires both a Lewis acid and a tetracarbonylcobaltate nucleophile, yielding a cobalt alkyl-alkoxy-Lewis acid moiety. After CO insertion into the Co-C(alkyl) bond, lactone formation results from a nucleophilic attack of the alkoxy Lewis acid entity on the acylium carbon atom. A theoretical study indicates a marked influence of the Lewis acid on both ring-opening and lactone-formation steps, but not on carbonylation. Strong Lewis acids induce fast ring opening, but slow lactone formation, and visa versa: a good balance of Lewis acidity would give the fastest catalytic cycle as all steps have low barriers. Experimentally, carbonylation of propylene oxide to beta-butyrolactone was monitored by online ATR-IR techniques with a mixture of tetracarbonylcobaltate and Lewis acids, namely BF(3), Me(3)Al, Et(2)Al(+).diglyme, and a combination of Me(3)Al/dicobaltoctacarbonyl. We found that the last two mixtures are extremely active in lactone formation.     

Competitive bromination kinetics of CH3Br and CH2ClBr

The relative-rate method with gas-chromatographic product analysis was applied to study the kinetics of the reactions Br + CH₃Br → CH₂Br + HBr (1) and Br + CH₂ClBr → CHClBr + HBr (2) The rate coefficient ratio of k ₁/ k ₂ = (1.6 ± 0.2) exp[(-15.2 ± 0.3) kJ mol^-1/ RT] was determined in the temperature range of 353 - 410 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anwendung der Ringofentüpfelkolorimetrie mit Hilfe einer Silbersulfid-Standardskala in der anorganischen Papierchromatographie

Zusammenfassung Die bereits früher beschriebene Ringofentüpfelkolorimetrie mit Hilfe einer Silbersulfidstandardskala wird zur halbquantitativen Bestimmung von Metallionen vorgesehlagen, die vorher papierchromatographisch getrennt wurden. Eine einzige Silbersulfidstandardskala reicht zur Bestimmung einer Reihe verschiedener Ionen aus. Weder das zur Herstellung der Papierchromatogramme, noch das zum Waschen der Ringe verwendete Tropfenvolumen muß genau bekannt sein. Am Beispiel der Trennung und Bestimmung von Kupfer, Cadmium, Blei sowie Eisen, Kobalt und Zink wird die Methodik erläutert. Die angeführte Tabelle der Analysenergebnisse zeigt, daß eine ausreichende Genauigkeit (±0 bis ±5% relativ) erzielt werden kann.

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Summary The ring oven-spot colorimetry with the aid of a silver sulfide standard scale as previously described is suggested for the semi-quantitative determination of metal ions, which have previously undergone a paper chromatographic separation. A single silver sulfide standard scale suffices for the determination of a number of different ions. There is no need to know accurately the drop volume employed in the preparation of the paper chromatogram or the drop volume used in washing the rings. The method is illustrated by the separation and determination of copper, cadmium and lead, and also iron, cobalt and zinc. The table of the analytical findings shows that an adequate accuracy (±0 to ±5% relative) can be attained.

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Résumé La colorimétrie à la touche au four annulaire, déjà décrite auparavant, est préconisée pour le dosage semi-quantitatif des ions métalliques, préalablement séparés par chromatographie sur papier, au moyen d'une gamme d'étalons au sulfure d'argent. Une gamme d'étalons unique au sulfure d'argent suffit pour le dosage d'une série d'ions variés. Ni le volume de la goutte utilisé pour la préparation du chromatogramme sur papier, ni celui utilisé pour le lavage de l'anneau n'ont besoin d'être connus exactement. On explique le mode opératoire en prenant comme exemples la séparation et le dosage du cuivre, du cadmium, du plomb, ainsi que ceux du fer, du cobalt et du zinc. Le tableau contenant les résultats d'analyses montre que l'on peut obtenir une exactitude satisfaisante de ±0 à ±5% en valeurs relatives.

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Gewidmet zur 100. Wiederkehr des Geburtstages vonFriedrich Emich.     

On the tautomerism of 2,4-disubstituted 3,4,5,6-tetrahydrobenzo[h]quinazolines

Summary The tautomerism of the title compounds was investigated by¹H-,¹³C-NMR and UV spectroscopy. Compound5 was compared with respect to its spectra with those of appropriate model compounds1,3,4, and6. This gave evidence that5 predominates in the tautomeric from5A.

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Zur Tautomerie von 2,4-disubstituierten 3,4,5,6-Tetrahydrobenzo[h]chinazolinen

Zusammenfassung Die Tautomerie von 2,4-disubstituierten 3,4,5,6-Tetrahydrobenzo[h]chinazolinen wurde durch¹H-,¹³C-NMR- und UV-Spektroskopie untersucht. Der Vergleich der Spektren von5 und der Modellverbindungen1,3,4 und6 legt nahe, daß für5 das Tautomere5A dominiert.

     

Saturated heterocycles, 248. Synthesis of 2,4-dioxo and 4-oxo-2-thioxo derivatives of octahydrocyclopenta[d]pyrimidines

Unsubstituted and 1-benzyl-substituted cis-cyclopenta[d]pyrirnidine-2,4-diones and cis-2-thioxo-cyclopenta[d]pyrimidin-4-ones 9a,b and 10a,b were prepared from the corresponding cis-2-amino-1-cyclopentanecarboxylates 3 and 5 with potassium cyanate and thiocyanate. It was found that the cis derivatives 7a-h readily underwent ring closure, resulting in 3-substituted cis-2,4-cyclopenta[d]pyrimidinediones and cis-2-thioxocyclopenta[d]pyrimidin-4-ones 11a-d and 12a-d , whereas the trans counterparts 8a-d failed to cyclize, but gave hydrolysed amino acid derivatives 13a,b and 14 . This difference in the reactivities of the cis and trans isomers is a further example of the difficulty of preparing cyclopentane trans-fused six-membered 1,3-heterocycles by ring closure.     

Protonation and solvation of pyrazine

Some properties of neutral, once, and twice-protonated pyrazines and their supermolecules with two water molecules were calculated at CNDO level as functions of solvent polarity. The solvents were assumed to be homogeneous continua in which the solute molecules induce electric charges. Atomic net charges, binding energies, force constants, vibrational frequencies, and potential energy distributions were calculated by applying the CNDO optimized geometries of the isolated molecules as references. Pyrazine force constants were scaled to the pyrazine fundamental frequencies. These scaling factors were transferred to the other molecules. For supermolecules the additional scaling factors were chosen based on the chemical similarity of the coordinates.The symmetries of the monocations are reflected in the charge distribution and in the values of the force constants. With increasing molecular charge and increasing solvent polarity the fundamental shifts become more larger and more negative. The calculated frequencies were assigned to normal modes. The influence of the solvent polarity on the binding energies is very interesting: For isolated species that of the neutral molecules is the lowest and that of the bication is the highest, and with increasing polarity all binding energies increase, but the higher the charge, the quicker the increase and the order reverses.The calculated values for the pyrazine parts of the supermolecules are mostly close to those of the corresponding results of the nonhydrated species with the same charge. The results for the substituents are close to the corresponding free species. The interactions are expressed most frequently in the hydrogen bonds. These are investigated in detail. The NH bond lengths are underestimated as a consequence of the CNDO approximation. For water substitution NH stretching force constants and frequencies are low, and the coupled OH stretching force constants and frequencies are large. For the hydroxoniumion substitutent the situation is opposite: In the case of two hydroxonium ion substituents, the two stretching coordinates are mixed in the corresponding normal modes.     

A facile synthesis of 3-(substituted benzyl)piperidines

A convenient new method has been developed for preparation a series of 3-(substituted benzyl)piperidines by addition of substituted phenylmagnesium bromide to pyridine-3-carboxaldehyde followed by one pot deoxygenation and heteroaromatic ring saturation in the presence of palladium catalyst.     

Hydrogen-shift isomerism: mass spectrometry of isomeric benzenesulfonate and 2-, 3- and 4-dehydrobenzenesulfonic acid anions in the gas phase

The isomeric 3- and 4-dehydrobenzenesulfonic acid anions b and c were prepared by collision induced dissociation (CID) of the [M - H](-) ions of isomeric sulfobenzoic acids obtained by negative electrospray ionization (ESI). The CID spectra (MS(3)) of anions b and c are different from each other, and both are different from that of the isomeric benzenesulfonate anion a, obtained from benzenesulfonic acid. The stability of ions b and c shows that 1,2-proton transfer does not take place in this system under the conditions of the CID experiment. Density functional (DFT) calculations at B3LYP/6-31+G(2d,p) level of theory show that benzenesulfonate anion a is the most stable isomer, and the energies of isomers b and c are higher by more than 65 kcal mol(-1). The calculated energies of the transition states involved in the 1,2-hydrogen migration leading to the interconversion of the isomeric anions are very high (>120 kcal mol(-1)relative to ion a, barrier energies >55 kcal mol(-1)), much higher than those of transition structures leading to fragmentation. This situation does not allow isomerization of ions b and c to a, under the conditions of the CID experiments. The isomeric 2-dehydrobenzenesulfonic acid anion isomerizes to the benzenesulfonate anion a by a facile proton transfer from the SO(3)H group to the adjacent position 2. The results of this work indicate that the gas phase deprotonation of meta- and para-sulfobenzoic acids is a kinetically controlled process.     

Similarities between polyelectrolyte gels and biopolymer solutions

Small angle neutron scattering (SANS) measurements and osmotic swelling pressure measurements are reported for polyelectrolyte gels and solutions under nearly physiological conditions. A synthetic polymer (sodium-polyacrylate) and three biopolymers (DNA, hyaluronic acid, and polyaspartic acid) are studied. The neutron scattering response of these anionic polyelectrolytes is closely similar, indicating that at larger length scales the organization of the polymer molecules is not significantly affected by the fine details of the molecular architecture (e.g., size and chemical structure of the monomer unit, type of polymer backbone). The results suggest that specific interactions between the polyelectrolyte chains and the surrounding monovalent cations are negligible. It is found that the osmotic compression modulus of these biopolymer solutions determined from the analysis of the SANS response decreases with increasing chain persistence length. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3679–3686, 2006     

Saturated heterocycles. 254 . synthesis and stereochemistry of saturated or partially saturated pyridazino-[6,1-b]- and phthalazino[1,2-b]quinazolinones

By the reaction of anthranilic hydrazide 1 with cis-2-(p-methylbenzoyl)-1-cyclohexanecarboxylic acid 2a or diendo-3-(p-methylbenzoyl)bicyclo[2.2.1]heptane-2-carboxylic acid 2b , fused tetra- and pentacyclic ring systems 3a, b were prepared, trans-2-Amino-1-cyclohexanecar-bohydrazide 4b was reacted with 3-(p-chlorobenzoyl)propionic acid 5 to yield the pyridazino[6,1-b]quinazolinone 6 . From the reaction of cis-2-amino-1-cyclohexanecarbohydrazide 4a with 2a , three isomeric partially saturated 8H-phthalazino[1,2-b]quinazolin-8-ones 7a-c were formed. The reaction of diexo-2-aminobicyclo[2.2.1]heptane-3-carbohydrazide 4c and 2a furnished the pentacyclic derivatives 8 and 9 containing a 3-aryl-4,5-dihydropyridazine or 3-arylhexahydropyridazine ring C with cis annelated C/D rings. The formation of 8 and 9 involving different ring systems can be rationalized by two reaction pathways: (i) in the bislactam 9 the carboxyl group acylates the hydrazide, while (ii) in 8 it forms a pyridazine ring with the cyclic amino group by cyclocondensation. The structures of the products were elucidated by ¹H and ¹³C nmr methods, including DEPT, DNOE and 2D-HSC measurements.